Incidence of symptomatic and asymptomatic Leishmania donovani infections in high-endemic foci in India and Nepal: a prospective study

Effect of indoor residual spraying on sandfly abundance and incidence of visceral leishmaniasis in India, 2016-22: an interrupted time-series analysis and modelling study

BACKGROUND

Efforts to eliminate visceral leishmaniasis in India mainly consist of early detection and treatment of cases and indoor residual spraying with insecticides to kill the phlebotomine sandfly Phlebotomus argentipes that transmits the causative Leishmania protozoa. In this modelling study, we aimed to estimate the effect of indoor residual spraying (IRS) on vector abundance and transmission of visceral leishmaniasis in India.

METHODS

In this time-series analysis and modelling study, we assessed the effect of IRS on vector abundance by using indoor vector-abundance data (from 2016 to 2022) and IRS quality-assurance data (from 2017-20) from 50 villages in eight endemic blocks in India where IRS was implemented programmatically. To assess a potential dose-response relation between insecticide concentrations and changes in sandfly abundance, we examined the correlation between site-level insecticide concentrations and the site-level data for monthly sandfly abundances. We used mathematical modelling to link vector data to visceral leishmaniasis case numbers from the national Kala-Azar Management Information System registry (2013-21), and to predict the effect of IRS on numbers of averted cases and deaths.

FINDINGS

IRS was estimated to reduce indoor sandfly abundance by 27% (95% CI 20-34). Concentrations of insecticides on walls were significantly-but weakly-associated with the degree of reduction in vector abundance, with a reduction of -0·0023 (95% CI -0·0040 to -0·0007) sandflies per mg/m2 insecticide (p=0·0057). Reported case numbers of visceral leishmaniasis were well explained by trends in vector abundance. Village-wide IRS in response to a newly detected case of visceral leishmaniasis was predicted to reduce disease incidence by 6-40% depending on the presumed reduction in vector abundance modelled.

INTERPRETATION

Indoor residual spraying has substantially reduced sandfly abundance in India, which has contributed to reductions in visceral leishmaniasis and related deaths. To prevent the re-emergence of visceral leishmaniasis as a public health problem, surveillance of transmission and sandfly abundance is warranted.

FUNDING

Bill & Melinda Gates Foundation.

TRANSLATION

For the Hindi translation of the abstract see Supplementary Materials section.

A mathematical model of visceral leishmaniasis transmission and control: Impact of ITNs on VL prevention and elimination in the Indian subcontinent

Visceral Leishmaniasis (VL) is a deadly, vector-borne, parasitic, neglected tropical disease, particularly prevalent on the Indian subcontinent. Sleeping under the long-lasting insecticide-treated nets (ITNs) was considered an effective VL prevention and control measures, until KalaNet, a large trial in Nepal and India, did not show enough supporting evidence. In this paper, we adapt a biologically accurate, yet relatively simple compartmental ordinary differential equations (ODE) model of VL transmission and explicitly model the use of ITNs and their role in VL prevention and elimination. We also include a game-theoretic analysis in order to determine an optimal use of ITNs from the individuals' perspective. In agreement with the previous more detailed and complex model, we show that the ITNs coverage amongst the susceptible population has to be unrealistically high (over 96%) in order for VL to be eliminated. However, we also show that if the whole population, including symptomatic and asymptomatic VL cases adopt about 90% ITN usage, then VL can be eliminated. Our model also suggests that ITN usage should be accompanied with other interventions such as vector control.

Monitoring of Leishmania transmission in the postelimination phase: The potential of serological surveys

OBJECTIVES

Monitoring of Leishmania transmission is considered a strategic priority for sustaining elimination of visceral leishmaniasis as a public health problem in the Indian subcontinent. The objective of this study was to evaluate whether serological surveys can distinguish between communities with and without Leishmania transmission, and to assess which serological marker performs best.

METHODS

Seven villages were selected from Bihar and Uttar Pradesh state, India, and categorized as either currently endemic (CE), previously endemic (PE) or nonendemic (NE). Blood samples were analyzed with the rK39 RDT, direct agglutination test (DAT), and rK39 ELISA.

RESULTS

Contrary to the rK39 RDT and DAT, the rK39 ELISA showed a significant difference between all three categories of endemicity, with a seroprevalence of 5.21% in CE villages, 1.55% in PE villages, and 0.13% in NE villages. Even when only looking at the seroprevalence among children aged <10 years, the rK39 ELISA was still able to differentiate between villages with and without ongoing transmission.

CONCLUSION

Our findings suggest the rK39 ELISA to be the most promising marker for monitoring of Leishmania transmission. Further validation is required, and practical, context-adapted recommendations need to be formulated in order to guide policymakers toward meaningful and sustainable surveillance strategies in the post-elimination phase.

Incidence and persistence of asymptomatic Leishmania infection among HIV-infected patients in Trang province, Southern Thailand: A cohort study

Leishmaniasis poses a significant health burden, particularly among immunocompromised patients. In Thailand, Leishmania infection caused by Leishmania martiniquensis and Leishmania orientalis lacks information about the incidence and risk factors among HIV-infected populations. This longitudinal cohort study aimed to investigate the incidence and persistence of Leishmania infection among HIV-infected individuals in an affected area, Trang Province, Southern Thailand. The study also identified risk factors associated with the incidence of Leishmania infection. The study enrolled 373 participants in the HIV clinic, Trang Hospital, who initially tested negative for Leishmania infection during 2015-2016, and 133 individuals initially tested positive for Leishmania infection. Thus, follow-up visits of 506 participants occurred during 2018-2019. Direct Agglutination Test (DAT) and nested PCR (nPCR) identified incidents and persistent cases of Leishmania infection. Cox proportional-hazards regression analyses were performed to assess risk factors for the incidence of Leishmania infection. Among the initially negative group, 12 incident cases comprised one L. orientalis infection and 11 seropositive cases using DAT, resulting in a cumulative incidence of 3.2% and an incidence density of 10.38 per 1000 person-years. Increasing age was a significant predictor of the incidence of Leishmania infection. Five persistent cases comprised one Leishmania donovani complex and four seropositive cases using DAT in the initially positive group, with a cumulative persistence rate of 3.7% and a persistence density of 12.85 per 1000 person-years. All patients were asymptomatic. This study sheds light on the incidence and persistence of Leishmania infection among HIV-infected individuals in Trang Province, Southern Thailand, underscoring the importance of continued monitoring and tailored interventions to mitigate the impact of this co-infection.

Challenges for maintaining post elimination phase of visceral leishmaniasis control programme in India: A field-based study

BACKGROUND

India is going through the maintenance phase of VL elimination programme which may be threatened by the persistence of hidden parasite pools among asymptomatic leishmanial infection (ALI) and PKDL. The present work was designed to determine the burden of VL, PKDL, and ALI and to assess the role of treatment of ALI in maintaining post-elimination phase.

METHODS AND FINDING

The study was undertaken in Malda district, West Bengal, India during October 2016 to September 2021. Study areas were divided into 'Study' and 'Control' arms. VL and PKDL cases of both the arms were diagnosed by three active mass surveys with an interval of one year and treated as per National guideline. ALI of 'Study' arm was treated like VL. ALI of 'Control' arm was followed up to determine their fate. Fed sand-fly pools were analysed for parasitic DNA. No significant difference was noted between the incidence of VL and PKDL in both the arms. Incidence of ALI declined sharply in 'Study' arm but an increasing trend was observed in 'Control' arm. Significantly higher rate of sero-conversion was noted in 'Control' arm and was found to be associated with untreated ALI burden. Parasitic DNA was detected in 22.8% ALI cases and 2.2% sand-fly pools.

CONCLUSION

Persistence of a significant number of PKDL and ALI and ongoing transmission, as evidenced by new infection and detection of leishmanial DNA in vector sand-flies, may threaten the maintenance of post-elimination phase. Emphasis should be given for elimination of pathogen to prevent resurgence of VL epidemics.

The immune response in canine and human leishmaniasis and how this influences the diagnosis- a review and assessment of recent research

Leishmaniasis is a widespread but still underdiagnosed parasitic disease that affects both humans and animals. There are at least 20 pathogenic species of Leishmania, most of them being zoonotic. The diagnosis of leishmaniasis remains a major challenge, with an important role being played by the species of parasites involved, the genetic background, the immunocompetence of the host. This paper brings to the fore the sensitivity of the balance in canine and human leishmaniasis and addresses the importance of the host's immune response in establishing a correct diagnosis, especially in certain cases of asymptomatic leishmaniasis, or in the situation the host is immunosuppressed or acquired leishmaniasis through vertical transmission. The methods considered as a reference in the diagnosis of leishmaniasis no longer present certainty, the diagnosis being influenced mostly by the immune response of the host, which differs according to the presence of other associated diseases or even according to the breed in dogs. Consequently, the diagnosis and surveillance of leishmaniasis cases remains an open topic, requiring new diagnostic methods adapted to the immunological state of the host.

Wuchereria bancrofti infection is associated with progression to clinical visceral leishmaniasis in VL- endemic areas in Muzaffarpur, Bihar, India

BACKGROUND

Co-endemicity of neglected tropical diseases (NTDs) necessitates that these diseases should be considered concomitantly to understand the relationship between pathology and to support disease management and control programs. The aims of the study were to assess the prevalence of filarial infection in asymptomatic Leishmania donovani infected individuals and the correlation of Wuchereria bancrofti infection with progression to clinical visceral leishmaniasis (VL) in Bihar, India.

METHODOLOGY/PRINCIPAL FINDINGS

Within the Muzaffarpur-TMRC Health and Demographic Surveillance System (HDSS) area, a cohort of Leishmania seropositive (n = 476) or seronegative individuals (n = 1130) were sampled annually for three years for filarial infection and followed for progression to clinical VL. To corroborate the results from the cohort study, we also used a retrospective case-control study of 36 VL cases and 71 controls selected from a subset of the HDSS population to investigate the relationship between progression to clinical VL and the prevalence of filarial infection at baseline. Our findings suggest a higher probability of progression to clinical VL in individuals with a history of filarial infection: in both the cohort and case-control studies, progression to clinical VL was higher among filaria infected individuals (RR = 2.57, p = 0.056, and OR = 2.52, p = 0.046 respectively).

CONCLUSION

This study describes that progression to clinical VL disease is associated with serological evidence of prior infection with W. bancrofti. The integration of disease programs for Leishmania and lymphatic filariasis extend beyond the relationship of sequential or co-infection with disease burden. To ensure elimination targets can be reached and sustained, we suggest areas of co-endemicity would benefit from overlapping vector control activities, health system networks and surveillance infrastructure.

A review on new natural and synthetic anti-leishmanial chemotherapeutic agents and current perspective of treatment approaches

Leishmaniases are considered among the most neglected yet dangerous parasitic diseases worldwide. According to the recent WHO report (Weekly Epidemiological Record, Sep, 2021), 200 countries and territories reported leishmanises cases in 2020; of which 89 (45%) for CL, and 79 (40%) for VL were endemic. Indian subcontinent (India, Bangladesh and Nepal), one of the three eco-epidemiological hotspots of VL, currently reported 18% of the total cases of VL worldwide. Eastern Mediterranean region and the Region of the Americas together reported >90% of the new CL cases, of which >80% were from Afghanistan, Algeria, Brazil, Colombia, Iraq, Pakistan and the Syrian Arab Republic. While considering the current therapeutic options, conventional anti-leishmanial drugs have long been proved to be toxic and/or expensive and have resulted in extensive drug resistance in India. Recent searches for novel anti-leishmanial drugs have led to find out the prime cellular targets and metabolic pathways to bridge the gap between the known facts and unexplored data. Cutting edge knowledge based drug designing has simplified the search for novel molecules with leishmanicidal efficacy by identifying ligand-receptor interactions and has accelerated the cost effective primary discovery of molecules through computational validation against Leishmaniases. This review focuses on the limitations of conventional drugs, and discusses the chemotherapeutic potential of many novel natural and synthetic anti-leishmanial agents reported since the last decade. It is also interpreted that some of the reported molecules might be tested singly or as a part of combinatorial therapy on pre-clinical and clinical level.

Asymptomatic Leishmania infection in humans: A systematic review

BACKGROUND

Leishmaniasis is a highly prevalent neglected tropical disease. It mainly presents as two forms: cutaneous and visceral leishmaniasis, the latter being the most severe form. However, asymptomatic cases of Leishmania infection result in an increase in the underreporting and transmission of the protozoan OBJECTIVES: In this study, articles on the incidence of asymptomatic Leishmania infection were systematically reviewed.

METHODS

The publications identified in the Medline/PubMed and Science Direct databases included 4568 articles. Inclusion, exclusion, and eligibility criterion analysis resulted in 83 articles being retained. These studies were mostly performed in Brazil (n = 26) and India (n = 15).

RESULTS

Several detection techniques have been used for diagnosis. Among the species found were L. infantum and L. donovani, which result in visceral leishmaniasis, and L. amazonensis, L. braziliensis, and L. panamensis. The incidence rates varied between the analyzed locations, largely due to sampling and the presence or absence of endemism in the regions. The largest populations analyzed were in two studies performed in India and Nepal. One of these studies evaluated 32,529 people and the incidence rate was 8.3% (n = 2702), while the other study evaluated 21,267 people and the incidence rate was 1.76% (n = 375). Only 14.28% of the studies investigated leishmaniasis in blood donors. Preexisting diseases have also been reported.

CONCLUSION

The findings of this systematic review present the incidence of cases of asymptomatic Leishmania infection worldwide, in addition to detailing the studies and offering information for researchers and health authorities to seek alternatives to reduce the number of leishmaniasis cases.

Detection of asymptomatic Leishmania donovani in healthy voluntary blood donors

OBJECTIVE

To check incidence of Asymptomatic Leishmania donovani reporting to Armed Forces Institute of Transfusion Rawalpindi.

MATERIAL AND METHODS

Two thousand (n = 2000) consecutive healthy voluntary blood donors were tested for 18 s rRNA by Real time Polymerase chain reaction. One thousand (n = 1000) subject's permanent resident of Azad Kashmir along with a thousand (n = 1000) healthy voluntary blood donors from rest of Pakistan were included. The study was carried out over a period of three months Jun - Aug 2020.

RESULTS

Total of 2000 blood donors were enrolled in the study, all were males with age ranging from 16 to 60 years. Stratification based on residence, 1000 (50 %) resided in the Azad kashmir, 349 (17.45 %) were from Islamabad and Rawalpindi, 541 (27.05 %) from Punjab mainly residing in Lahore and Multan, 110 (5.5 %) were from other cities of Pakistan. Grouping on the basis of age, 55.25 % (n = 1105) of the donors were 16-25 years old, 19.45 % (n = 389) were in age range of 26-40 years old, 15.55 % (n = 311) were 41-50 years old and 9.75 % (n = 195) 51-60 years old. No donor was diagnosed as an asymptomatic carrier.

CONCLUSION

Screening of blood donors for Leishmania donovani is not recommended.

Chronic Systemic Infection of Mice with Leishmania infantum Leads to Increased Bone Mass

Vector-borne infections of humans with the protozoan parasite Leishmania (L.) infantum can cause a systemic and potentially lethal disease termed visceral leishmaniasis. In the corresponding mouse model, an intravenous infection with L. infantum leads to the persistence of parasites in various organs, including bone marrow (BM). Considering the anatomical proximity between the BM and the cortical bone, we investigated whether a chronic infection with L. infantum affected bone homeostasis. Unexpectedly, chronic infection with L. infantum caused an increase in bone mass in mice. In vivo, an increased number of osteoblasts and osteocytes and a decreased maturation of osteoclasts characterized the phenotype. Confocal laser scanning fluorescence microscopy confirmed the infection of BM macrophages but also revealed the presence of parasites in osteoclasts. In vitro, mature osteoclasts took up L. infantum parasites. However, infection of osteoclast progenitors abolished their differentiation and function. In addition, secretory products of infected BM-derived macrophages inhibited the maturation of osteoclasts. Both in vitro and in vivo, infected macrophages and osteoclasts showed an enhanced expression of the anti-osteoclastogenic chemokine CCL5 (RANTES). Neutralization of CCL5 prevented the inhibition of osteoclast generation seen in the presence of culture supernatants from L. infantum-infected macrophages. Altogether, our study shows that chronic infection with Leishmania increases bone mass by inducing bone formation and impairing osteoclast differentiation and function. © 2022 American Society for Bone and Mineral Research (ASBMR).

Centrin-deficient Leishmania mexicana confers protection against Old World visceral leishmaniasis

Leishmaniasis is one of the top neglected tropical diseases with significant morbidity and mortality in low and middle-income countries (LMIC). However, this disease is also spreading in the developed world. Currently, there is a lack of effective strategies to control this disease. Vaccination can be an effective measure to control leishmaniasis and has the potential to achieve disease elimination. Recently, we have generated centrin gene-deleted new world L. mexicana (LmexCen−/−) parasites using CRISPR/Cas9 and showed that they protect mice against a homologous L. mexicana infection that causes cutaneous disease. In this study, we tested whether LmexCen−/− parasites can also protect against visceral leishmaniasis caused by L. donovani in a hamster model. We showed that immunization with LmexCen−/− parasites is safe and does not cause lesions. Furthermore, such immunization conferred protection against visceral leishmaniasis caused by a needle-initiated L. donovani challenge, as indicated by a significant reduction in the parasite burdens in the spleen and liver as well as reduced mortality. Similar control of parasite burden was also observed against a sand fly mediated L. donovani challenge. Importantly, immunization with LmexCen−/− down-regulated the disease promoting cytokines IL-10 and IL-4 and increased pro-inflammatory cytokine IFN-γ resulting in higher IFN-γ/IL-10 and IFN-γ/IL4 ratios compared to non-immunized animals. LmexCen−/− immunization also resulted in long-lasting protection against L. donovani infection. Taken together, our study demonstrates that immunization with LmexCen−/− parasites is safe and efficacious against the Old World visceral leishmaniasis.

Laboratory diagnostics for human Leishmania infections: a polymerase chain reaction-focussed review of detection and identification methods

Leishmania infections span a range of clinical syndromes and impact humans from many geographic foci, but primarily the world's poorest regions. Transmitted by the bite of a female sand fly, Leishmania infections are increasing with human movement (due to international travel and war) as well as with shifts in vector habitat (due to climate change). Accurate diagnosis of the 20 or so species of Leishmania that infect humans can lead to the successful treatment of infections and, importantly, their prevention through modelling and intervention programs. A multitude of laboratory techniques for the detection of Leishmania have been developed over the past few decades, and although many have drawbacks, several of them show promise, particularly molecular methods like polymerase chain reaction. This review provides an overview of the methods available to diagnostic laboratories, from traditional techniques to the now-preferred molecular techniques, with an emphasis on polymerase chain reaction-based detection and typing methods.

Prevalence and determinants of asymptomatic Leishmania infection in HIV-infected individuals living within visceral leishmaniasis endemic areas of Bihar, India

People living with HIV (PLHIV) have an increased risk of developing visceral leishmaniasis (VL) and poor outcomes compared to HIV negative individuals. Here, we aim to establish the prevalence and determinants of asymptomatic Leishmania infection (ALI) in a cohort of PLHIV in Bihar, India. We hoped to evaluate optimal diagnostic algorithms to detect ALI in PLHIV. We conducted a cross-sectional survey of PLHIV ≥18 years of age with no history or current diagnosis of VL or post kala-azar dermal leishmaniasis (PKDL) at anti-retroviral therapy centres within VL endemic districts of Bihar. ALI was defined as a positive rK39 enzyme-linked immunosorbent assay (ELISA), rK39 rapid diagnostic test (RDT) and/or quantitative polymerase chain reaction (qPCR). Additionally, the urinary Leishmania antigen ELISA was evaluated. Determinants for ALI were established using logistic regression and agreement between diagnostic tests calculated using Cohen’s Kappa. A total of 1,296 PLHIV enrolled in HIV care, 694 (53.6%) of whom were female and a median age of 39 years (interquartile range 33–46), were included in the analysis. Baseline prevalence of ALI was 7.4% (n = 96). All 96 individuals were positive by rK39 ELISA, while 0.5% (n = 6) and 0.4% (n = 5) were positive by qPCR and rK39 RDT, respectively. Negligible or weak agreement was seen between assays. Independent risk factors for ALI were CD4 counts <100 (OR 3.1; 95% CI 1.2–7.6) and CD4 counts 100–199 (OR = 2.1;95% CI:1.1–4.0) compared to CD4 counts ≥300, and a household size ≥5 (OR = 1.9;95% CI:1.1–3.1). A total of 2.2% (n = 28) participants were positive by Leishmania antigen ELISA, detecting 20 additional participants to the asymptomatic cohort. Prevalence of ALI in PLHIV in VL endemic villages in Bihar was relatively high. Using the Leishmania antigen ELISA, prevalence increased to 9.0%. Patients with low CD4 counts and larger household size were found to have significantly higher risk of ALI.

Trial Registration: Clinical Trial Registration CTRI/2017/03/008120.

People living with HIV (PLHIV) are more likely to develop visceral leishmaniasis (VL) and are more likely to have poor outcomes associated with VL-HIV coinfection than HIV-negative individuals. While an estimated 3–14% of immunocompetent individuals living in endemic areas show serological evidence of asymptomatic infection with VL, such data on Leishmania infection in PLHIV in India are lacking. As such we sought to establish the prevalence and determinants of asymptomatic Leishmania infection (ALI) in PLHIV in VL endemic districts of Bihar, India using a combination of molecular and serological assays. We further expand our definition of ALI to include the urinary Leishmania antigen ELISA. The prevalence of ALI in a population of PLHIV residing in VL endemic districts of Bihar, India was found to be as high as 9.0% (n = 116). The majority of individuals were detected by the rK39 enzyme-linked immunosorbent assay (ELISA) (7.4%, n = 96), and very few individuals were detected by quantitative polymerase chain reaction (qPCR) (0.5%, n = 6) or the rK39 rapid diagnostic test (RDT) (0.4%, n = 5). In total, 2.2% (n = 28) were positive by urinary Leishmania antigen ELISA. Low CD4 counts and larger household size were found to be risk factors for ALI. Here, we add to the evidence base for Leishmania-HIV coinfection on the Indian subcontinent.

Increased amphiregulin expression by CD4+ T cells from individuals with asymptomatic Leishmania donovani infection

Objectives

There is an urgent need to be able to identify individuals with asymptomatic Leishmania donovani infection, so their risk of progressing to VL and transmitting parasites can be managed. This study examined transcriptional markers expressed by CD4+ T cells that could distinguish asymptomatic individuals from endemic controls and visceral leishmaniasis (VL) patients.

Methods

CD4+ T cells were isolated from individuals with asymptomatic L. donovani infection, endemic controls and VL patients. RNA was extracted and RNAseq employed to identify differentially expressed genes. The expression of one gene and its protein product during asymptomatic infection were evaluated.

Results

Amphiregulin (AREG) was identified as a distinguishing gene product in CD4+ T cells from individuals with asymptomatic L. donovani infection, compared to VL patients and healthy endemic control individuals. AREG levels in plasma and antigen-stimulated whole-blood assay cell culture supernatants were significantly elevated in asymptomatic individuals, compared to endemic controls and VL patients. Regulatory T (Treg) cells were identified as an important source of AREG amongst CD4+ T-cell subsets in asymptomatic individuals.

Conclusion

Increased Treg cell AREG expression was identified in individuals with asymptomatic L. donovani infection, suggesting the presence of an ongoing inflammatory response in these individuals required for controlling infection and that AREG may play an important role in preventing inflammation-induced tissue damage and subsequent disease in asymptomatic individuals.

Domestic mammals as reservoirs for Leishmania donovani on the Indian subcontinent: Possibility and consequences on elimination

Leishmania donovani is the causative agent of historically anthroponotic visceral leishmaniasis (VL) on the Indian subcontinent (ISC). L. donovani is transmitted by the sand fly species Phlebotomus argentipes. Our collaborative group and others have shown that sand flies trapped outside in endemic villages have fed on cattle and dogs in addition to people. Domestic animals are reservoirs for L. donovani complex spp., particularly L. infantum, in other endemic areas. Multiple studies using quantitative PCR or serological detection methods have demonstrated that goats, cattle, rats and dogs were diagnostically positive for L. donovani infection or exposure in eastern Africa, Bangladesh, Nepal and India. There is a limited understanding of the extent to which L. donovani infection of domestic animals drives transmission to other animals or humans on the ISC. Evidence from other vector-borne disease elimination strategies indicated that emerging infections in domestic species hindered eradication. The predominant lesson learned from these other situations is that non-human reservoirs must be identified, controlled and/or prevented. Massive efforts are underway for VL elimination on the Indian subcontinent. Despite these herculean efforts, residual VL incidence persists. The spectre of an animal reservoir complicating elimination efforts haunts the final push towards full VL control. Better understanding of L. donovani transmission on the Indian subcontinent and rigorous consideration of how non-human reservoirs alter VL ecology are critical to sustain elimination goals.

Identification of asymptomatic Leishmania infections: a scoping review

BACKGROUND

Asymptomatic Leishmania infection may play an important role in the transmission of the parasite in endemic areas. At present there is no consensus on the definition of asymptomatic Leishmania infection, nor is there a safe and accessible gold standard test for its identification.

METHODS

This paper presents a scoping review to summarize definitions of asymptomatic Leishmania infection found in the literature, as well as to detail the approach (molecular, serological, cellular, and/or parasitological tests) used by researchers to identify this asymptomatic population. A scoping review of published and gray literature related to asymptomatic Leishmania infection was conducted; retrieved citations were screened based on predefined eligibility criteria, and relevant data items were extracted from eligible articles. The analysis is descriptive and is presented using tables, figures, and thematic narrative synthesis.

RESULTS

We conducted a screening of 3008 articles, of which 175 were selected for the full review. Of these articles, we selected 106 that met the inclusion criteria. These articles were published between 1991 and 2021, and in the last 5 years, up to 38 articles were reported. Most of the studies were conducted in Brazil (26%), Spain (14%), India (12%), Bangladesh (10%), and Ethiopia (7%). Of the studies, 84.9% were conducted in the immunocompetent population, while 15.1% were conducted in the immunosuppressed population (HIV, immunosuppressive drugs, and organ transplantation population). We report 14 different techniques and 10 strategies employed by researchers to define asymptomatic Leishmania infection in an endemic area.

CONCLUSIONS

The definition of asymptomatic Leishmania infection is not unified across the literature, but often includes the following criteria: residence (or extended stay) in a Leishmania-endemic area, no reported signs/symptoms compatible with leishmaniasis, and positive on a combination of serological, molecular, cellular, and/or parasitological tests. Caution is recommended when comparing results of different studies on the subject of asymptomatic infections, as the reported prevalence cannot be confidently compared between areas due to the wide variety of tests employed by research groups. More research on the importance of asymptomatic immunosuppressed and immunocompetent Leishmania-positive populations in leishmaniasis epidemiology is required.

Transcriptional Shift and Metabolic Adaptations during Leishmania Quiescence Using Stationary Phase and Drug Pressure as Models

Microorganisms can adopt a quiescent physiological condition which acts as a survival strategy under unfavorable conditions. Quiescent cells are characterized by slow or non-proliferation and a deep downregulation of processes related to biosynthesis. Although quiescence has been described mostly in bacteria, this survival skill is widespread, including in eukaryotic microorganisms. In Leishmania, a digenetic parasitic protozoan that causes a major infectious disease, quiescence has been demonstrated, but the molecular and metabolic features enabling its maintenance are unknown. Here, we quantified the transcriptome and metabolome of Leishmania promastigotes and amastigotes where quiescence was induced in vitro either, through drug pressure or by stationary phase. Quiescent cells have a global and coordinated reduction in overall transcription, with levels dropping to as low as 0.4% of those in proliferating cells. However, a subset of transcripts did not follow this trend and were relatively upregulated in quiescent populations, including those encoding membrane components, such as amastins and GP63, or processes like autophagy. The metabolome followed a similar trend of overall downregulation albeit to a lesser magnitude than the transcriptome. It is noteworthy that among the commonly upregulated metabolites were those involved in carbon sources as an alternative to glucose. This first integrated two omics layers afford novel insight into cell regulation and show commonly modulated features across stimuli and stages.

Leishmania infantum infecting the carnivore Nasua nasua from urban forest fragments in an endemic area of visceral leishmaniasis in Brazilian Midwest

Introduction

The aim of the present study was to investigate the occurrence of Leishmania infantum in South American coatis inhabiting two forest fragments in Campo Grande, Mato Grosso do Sul, Midwest region of Brazil, an endemic area of human and canine visceral leishmaniasis (VL).

Material and methods

A total of 110 South American coatis were sampled in the conservation unit "Parque Estadual do Prosa" (PEP) and in the residential area "Vila da Base Aérea" (VBA) from March 2018 to April 2019. As a longitudinal study that include up to six recaptures of the same individual, a total of 190 capture events were obtained. Blood, bone marrow and skin samples were obtained for parasitological (axenic culture), serological (Enzyme Linked Immunosorbent Assay - ELISA and Dual-path Platform immunoassay - DPP^® CVL) and molecular diagnostic assays (targeting kDNA for Leishmania spp. and L. infantum; and HSP70 followed by sequence analysis).

Results

Seropositivity for L. infantum was found in 33 individuals, six in PEP and 27 in VBA. Furthermore, L. infantum was detected by molecular analysis in 16 individuals, seven from PEP and nine from VBA. We also isolated L. infantum from bone marrow of one individual and detected a single positive skin sample in molecular assay from other individual, both from VBA.

Discussion

An overall infection rate of 36.4% (40/110) was observed, significantly higher in the VBA (49.1%) than in the PEP (21.6%), probably because VBA presents: (i) a large number of resident dogs and chickens that would be attracting sandflies; (ii) a denser population of this wild mammal species; and (iii) physical barriers and a lack of functional connectivity in the surroundings, preventing these animals to disperse out. We conclude that South American coati populations living in urban forest fragments of Campo Grande are affected by the epidemiological scenario of VL, known to involve dogs, vectors and humans. We highlight the importance of investigate the parasitism by L. infantum in this and other potential L. infantum reservoirs that inhabit urbanized regions endemic to VL.

Precision Medicine in Control of Visceral Leishmaniasis Caused by L. donovani

Precision medicine and precision global health in visceral leishmaniasis (VL) have not yet been described and could take into account how all known determinants improve diagnostics and treatment for the individual patient. Precision public health would lead to the right intervention in each VL endemic population for control, based on relevant population-based data, vector exposures, reservoirs, socio-economic factors and other determinants. In anthroponotic VL caused by L. donovani, precision may currently be targeted to the regional level in nosogeographic entities that are defined by the interplay of the circulating parasite, the reservoir and the sand fly vector. From this 5 major priorities arise: diagnosis, treatment, PKDL, asymptomatic infection and transmission. These 5 priorities share the immune responses of infection with L. donovani as an important final common pathway, for which innovative new genomic and non-genomic tools in various disciplines have become available that provide new insights in clinical management and in control. From this, further precision may be defined for groups (e.g. children, women, pregnancy, HIV-VL co-infection), and eventually targeted to the individual level.

Leishmania tarentolae and Leishmania infantum in humans, dogs and cats in the Pelagie archipelago, southern Italy

Visceral leishmaniasis (VL) caused by Leishmania infantum is endemic in the Mediterranean basin with most of the infected human patients remaining asymptomatic. Recently, the saurian-associated Leishmania tarentolae was detected in human blood donors and in sheltered dogs. The circulation of L. infantum and L. tarentolae was investigated in humans, dogs and cats living in the Pelagie islands (Sicily, Italy) by multiple serological and molecular testing. Human serum samples (n = 346) were tested to assess the exposure to L. infantum by immunofluorescence antibody test (IFAT), enzyme-linked immunosorbent assay (ELISA) and Western blot (WB) and to L. tarentolae by IFAT. Meanwhile, sera from dogs (n = 149) and cats (n = 32) were tested for both Leishmania species by IFAT and all blood samples, including those of humans, by specific sets of real time-PCR for L. infantum and L. tarentolae. The agreement between serological tests performed for human samples, and between serological and molecular diagnostic techniques for both human and animal samples were also assessed.

Overall, 41 human samples (11.8%, 95% CI: 8.9–15.7) were positive to L. infantum (5.2%, 95% CI: 3.3–8.1), L. tarentolae (5.2%, 95% CI: 3.3–8.1) and to both species (1.4%, 95% CI: 0.6–3.3) by serology and/or molecular tests. A good agreement among the serological tests was determined. Both Leishmania spp. were serologically and/or molecularly detected in 39.6% dogs and 43.7% cats. In addition to L. infantum, also L. tarentolae circulates in human and animal populations, raising relevant public health implications. Further studies should investigate the potential beneficial effects of L. tarentolae in the protection against L. infantum infection.

Leishmania infantum is the major agent of canine and human leishmaniasis being endemic throughout the Mediterranean basin, including Italy. The protozoan is transmitted through the bite of infected phlebotomine sand flies mainly represented by the species Phlebotomus perniciosus and Phlebotomus perfiliewi as proven vectors in Italy. The sand fly fauna in this country includes, among others Sergentomyia minuta, considered herpetophilic vectors of Leishmania tarentolae. This species non-pathogenic to mammalians has recently been detected in human blood donors and in sheltered dogs. Our data demonstrate the occurrence of both L. infantum and L. tarentolae in humans and animal population living in leishmaniasis endemic area opening new perspectives into the study of this human disease. Therefore, the ecology of L. tarentolae highlights the need of a more comprehensive study on the spread of this parasite and on its potential beneficial role in public health through a cross-protection that could occur against pathogenic Leishmania spp. when L. tarentolae occurs in sympatry.

Preclinical validation of a live attenuated dermotropic Leishmania vaccine against vector transmitted fatal visceral leishmaniasis

Visceral Leishmaniasis (VL), a potentially fatal disease is caused by Leishmania donovani parasites with no vaccine available. Here we produced a dermotropic live attenuated centrin gene deleted Leishmania major (LmCen^−/−) vaccine under Good Laboratory Practices and demonstrated that a single intradermal injection confers robust and durable protection against lethal VL transmitted naturally via bites of L. donovani-infected sand flies and prevents mortality. Surprisingly, immunogenicity characteristics of LmCen^−/− parasites revealed activation of common immune pathways like L. major wild type parasites. Spleen cells from LmCen^−/− immunized and L. donovani challenged hamsters produced significantly higher Th1-associated cytokines including IFN-γ, TNF-α, and reduced expression of the anti-inflammatory cytokines like IL-10, IL-21, compared to non-immunized challenged animals. PBMCs, isolated from healthy people from non-endemic region, upon LmCen^−/− infection also induced more IFN-γ compared to IL-10, consistent with our immunogenicity data in LmCen^−/− immunized hamsters. This study demonstrates that the LmCen^−/− parasites are safe and efficacious against VL and is a strong candidate vaccine to be tested in a human clinical trial.

Karmakar et al produced a dermotropic, live attenuated centrin gene-deleted Leishmania major (LmCen^−/−) vaccine against Visceral Leishmaniasis (VL). They demonstrated in hamsters that a single intradermal injection confers robust and durable protection against lethal VL that is transmitted naturally via bites of L. donovani-infected sand flies.

Antibody and Antigen Prevalence as Indicators of Ongoing Transmission or Elimination of Visceral Leishmaniasis: A Modeling Study

Background

Control of visceral leishmaniasis (VL) on the Indian subcontinent has been highly successful. Control efforts such as indoor residual spraying and active case detection will be scaled down or even halted over the coming years. We explored how after scale-down, potential recurrence of VL cases may be predicted based on population-based surveys of antibody or antigenemia prevalence.

Methods

Using a stochastic age-structured transmission model of VL, we predicted trends in case incidence and biomarker prevalence over time after scaling down control efforts when the target of 3 successive years without VL cases has been achieved. Next, we correlated biomarker prevalence with the occurrence of new VL cases within 10 years of scale-down.

Results

Occurrence of at least 1 new VL case in a population of 10 000 was highly correlated with the seroprevalence and antigenemia prevalence at the moment of scale-down, or 1 or 2 years afterward. Receiver operating characteristic curves indicated that biomarker prevalence in adults provided the most predictive information, and seroprevalence was a more informative predictor of new VL cases than antigenemia prevalence. Thresholds for biomarker prevalence to predict occurrence of new VL cases with high certainty were robust to variation in precontrol endemicity.

Conclusions

The risk of recrudescence of VL after scaling down control efforts can be monitored and mitigated by means of population-based surveys. Our findings highlight that rapid point-of-care diagnostic tools to assess (preferably) seroprevalence or (otherwise) antigenemia in the general population could be a key ingredient of sustainable VL control.

Mathematical modelling of the use of insecticide-treated nets for elimination of visceral leishmaniasis in Bihar, India

Visceral leishmaniasis (VL) is a deadly neglected tropical disease caused by a parasite Leishmania donovani and spread by female sand flies Phlebotomus argentipes. There is conflicting evidence regarding the role of insecticide-treated nets (ITNs) on the prevention of VL. Numerous studies demonstrated the effectiveness of ITNs. However, KalaNet, a large trial in Nepal and India did not support those findings. The purpose of this paper is to gain insight into the situation by mathematical modelling. We expand a mathematical model of VL transmission based on the KalaNet trial and incorporate the use of ITNs explicitly into the model. One of the major contributions of this work is that we calibrate the model based on the available epidemiological data, generally independent of the KalaNet trial. We validate the model on data collected during the KalaNet trial. We conclude that in order to eliminate VL, the ITN usage would have to stay above 96%. This is higher than the 91% ITNs use at the end of the trial which may explain why the trial did not show a positive effect from ITNs. At the same time, our model indicates that asymptomatic individuals play a crucial role in VL transmission.

Evaluation of molecular techniques to visceral leishmaniasis detection in asymptomatic patients: a systematic review

INTRODUCTION

Visceral leishmaniasis (VL) is a systemic and neglected parasitic disease. Its main symptoms are fever, splenomegaly with or without hepatomegaly, and anemia, however, most individuals remain asymptomatic. Due to the lack of a gold standard and the limitations of current diagnostic techniques, where parasitology is ethically unfeasible for individuals without symptoms and serological tests do not differentiate between past and present disease, molecular methodologies are the most suitable.

AREAS COVERED

We performed a systematic review analyzing the molecular techniques based on PCR used, so far, to detect asymptomatic cases of VL in humans. Structured searches were carried out on PubMed, LILACS, Scopus, and Web of Science databases without time and language restrictions. Two reviewers evaluated the studies, performed data extraction, and quality assessment by assigning scores.

EXPERT OPINION

qPCR using RNA targets can be used in the diagnosis of asymptomatic cases of human VL, due to its characteristics. We recommend further studies to analyze the methodology, mainly observing the use of different rRNA targets. Therefore, we hope that this technique contributed to the construction of public policies that address the diagnosis and handling of asymptomatic patients.

A Multi-Country, Single-Blinded, Phase 2 Study to Evaluate a Point-of-Need System for Rapid Detection of Leishmaniasis and Its Implementation in Endemic Settings

With the advancement of isothermal nucleic acid amplification techniques, detection of the pathogenic DNA in clinical samples at point-of-need is no longer a dream. The newly developed recombinase polymerase amplification (RPA) assay incorporated in a suitcase laboratory has shown promising diagnostic efficacy over real-time PCR in detection of leishmania DNA from clinical samples. For broader application of this point-of-need system, we undertook a current multi-country diagnostic evaluation study towards establishing this technique in different endemic settings which would be beneficial for the ongoing elimination programs for leishmaniasis. For this study purpose, clinical samples from confirmed visceral leishmaniasis (VL) and post-kala-azar dermal leishmaniasis (PKDL) patients were subjected to both real-time PCR and RPA assay in Bangladesh, India, and Nepal. Further skin samples from confirmed cutaneous leishmaniasis (CL) patients were also included from Sri Lanka. A total of 450 clinical samples from VL patients, 429 from PKDL patients, 47 from CL patients, and 322 from endemic healthy/healthy controls were under investigation to determine the diagnostic efficacy of RPA assay in comparison to real-time PCR. A comparative sensitivity of both methods was found where real-time PCR and RPA assay showed 96.86% (95% CI: 94.45–98.42) and 88.85% (95% CI: 85.08–91.96) sensitivity respectively in the diagnosis of VL cases. This new isothermal method also exhibited promising diagnostic sensitivity (93.50%) for PKDL cases, when a skin sample was used. Due to variation in the sequence of target amplicons, RPA assay showed comparatively lower sensitivity (55.32%) than that of real-time PCR in Sri Lanka for the diagnosis of CL cases. Except for India, the assay presented absolute specificity in the rest of the sites. Excellent concordance between the two molecular methods towards detection of leishmania DNA in clinical samples substantiates the application of RPA assay incorporated in a suitcase laboratory for point-of-need diagnosis of VL and PKDL in low resource endemic settings. However, further improvisation of the method is necessary for diagnosis of CL.

Xenodiagnosis to evaluate the infectiousness of humans to sandflies in an area endemic for visceral leishmaniasis in Bihar, India: a transmission-dynamics study

Background

Visceral leishmaniasis, also known on the Indian subcontinent as kala-azar, is a fatal form of leishmaniasis caused by the protozoan parasite Leishmania donovani and transmitted by the bites of the vector sandfly Phlebotomus argentipes. To achieve and sustain elimination of visceral leishmaniasis, the transmission potential of individuals exposed to L donovani from across the infection spectrum needs to be elucidated. The aim of this study was to evaluate the relative infectiousness to the sandfly vector of patients with visceral leishmaniasis or post-kala-azar dermal leishmaniasis, before and after treatment, and individuals with asymptomatic infection.

Methods

In this prospective xenodiagnosis study done in Muzaffarpur district of Bihar, India, we included patients with clinically confirmed active visceral leishmaniasis or post-kala-azar dermal leishmaniasis who presented to the Kala-Azar Medical Research Center. These participants received treatment for L donovani infection. We also included asymptomatic individuals identified through a serosurvey of 17 254 people living in 26 high-transmission clusters. Eligible participants were aged 12–64 years, were HIV negative, and had clinically or serologically confirmed L donovani infection. During xenodiagnosis, the forearms or lower legs of participants were exposed to 30–35 female P argentipes sandflies for 30 min. Blood-engorged flies were held in an environmental cabinet at 28°C and 85% humidity for 60–72 h, after which flies were dissected and evaluated for L donovani infection by microscopy and quantitative PCR (qPCR). The primary endpoint was the proportion of participants with visceral leishmaniasis or post-kala-azar dermal leishmaniasis, before and after treatment, as well as asymptomatic individuals, who were infectious to sandflies, with a participant considered infectious if promastigotes were observed in one or more individual flies by microscopy, or if one or more of the pools of flies tested positive by qPCR.

Findings

Between July 12, 2016, and March 19, 2019, we recruited 287 individuals, including 77 with active visceral leishmaniasis, 26 with post-kala-azar dermal leishmaniasis, and 184 with asymptomatic infection. Of the patients with active visceral leishmaniasis, 42 (55%) were deemed infectious to sandflies by microscopy and 60 (78%) by qPCR before treatment. No patient with visceral leishmaniasis was found to be infectious by microscopy at 30 days after treatment, although six (8%) were still positive by qPCR. Before treatment, 11 (42%) of 26 patients with post-kala-azar dermal leishmaniasis were deemed infectious to sandflies by microscopy and 23 (88%) by qPCR. Of 23 patients who were available for xenodiagnosis after treatment, one remained infectious to flies by qPCR on the pooled flies, but none remained positive by microscopy. None of the 184 asymptomatic participants were infectious to sandflies.

Interpretation

These findings confirm that patients with active visceral leishmaniasis and patients with post-kala-azar dermal leishmaniasis can transmit L donovani to the sandfly vector and suggest that early diagnosis and treatment could effectively remove these individuals as infection reservoirs. An important role for asymptomatic individuals in the maintenance of the transmission cycle is not supported by these data.

Funding

Bill & Melinda Gates Foundation.

Epidemiology of Post-Kala-azar Dermal Leishmaniasis

Post-kala-azar dermal leishmaniasis (PKDL) is a cutaneous sequel of visceral leishmaniasis (VL) or kala-azar and has become an entity of epidemiological significance by virtue of its ability to maintain the disease in circulation during inter-epidemic periods. PKDL has been identified as one of the epidemiological marker of “kala-azar elimination programme.” Data obtained in 2018 showed PKDL distribution primarily concentrated in 6 countries, which includes India, Sudan, south Sudan, Bangladesh, Ethiopia, and Nepal in decreasing order of case-burden. In India, PKDL cases are mainly found in 54 districts, of which 33 are in Bihar, 11 in West Bengal, 4 in Jharkhand, and 6 in Uttar Pradesh. In West Bengal the districts reporting cases of PKDL cases include Darjeeling, Uttar Dinajpur, Dakshin Dinajpur, Malda, and Murshidabad. The vulnerability on the young age is documented in various studies. The studies also highlights a male predominance of the disease but recent active surveillance suggested that macular form of PKDL shows female-predominance. It is recommended that along with passive case detection, active survey helps in early identification of cases, thus reducing disease transmission in the community. The Accelerated plan for Kala-azar elimination in 2017 introduced by Government of India with the goal to eliminate Kala-azar as a public health problem, targets to reduceing annual incidence <1/10,000. Leishmania donovani is the established causative agent, but others like L. tropica or L. infantum may occasionally lead to the disease, especially with HIV-co-infection. Dermal tropism of the parasite has been attributed to overexpression of parasite surface receptors (like gp 63, gp46). Various host factors are also identified to contribute to the development of the disease, including high pretreatment IL 10 and parasite level, inadequate dose and duration of treatment, malnutrition, immuno-suppression, decreased interferon-gamma receptor 1 gene, etc. PKDL is mostly concentrated in the plains below an altitude of 600 mts which is attributed to the environment conducive for the vector sand fly (Phlebotumus). Risk factors are also linked to the habitat of the sand fly. Keeping these things in mind “Integrated vector control” is adopted under National vector borne disease control programme as one of the strategies to bring down the disease burden.

Seropositivity of Visceral leishmaniasis on people of VL endemic three districts of Nepal

Visceral leishmaniasis (VL) is a life-threatening vector borne disease caused by the Leishmania donovani species complex. In Nepal, it is transmitted to humans by L donovani infected Phlebotomus argentipes sand flies [12]. The pathogenesis of VL is complex, and the clinical presentation ranges from asymptomatic infection to severe and fatal disease. Asymptomatic infection may act as potential reservoirs for sustained transmission of VL in endemic areas. We investigated the sero-prevalence of symptomatic and asymptomatic infection of VL in people of three endemic districts of Nepal by serology targeting family members and neighbors of VL patients. Sero-survey was conducted among 189 people of villages endemic to VL from Palpa, Sarlahi and Saptari districts during 2016 to 2018 using the rK39 rapid diagnostic test (InBios International, Seattle, WA) to detect anti-Leishmania antibodies. Sero-positivity was 35.7% (10/28) in people tested from Sarlahi districts, 6% (3/50) in Saptari district and 1.7% (1/59) from the Palpa district. In Sarlahi, sero-positivity was found to be highest among the age group below 15 years (44.5%). All family members of diagnosed VL cases in Saptari and Palpa districts were found to be rK39 test negative. In Sarlahi district, among the ten sero-positive cases, nine were febrile and became symptomatic VL cases after few days and one case remained asymptomatic during the six month follow up. Asymptomatic cases in VL endemic districts of Nepal were found to be sero-positive, screening of people in VL endemic districts would be important for prevention of VL transmission.

Prevalence and associated factors of asymptomatic leishmaniasis: a systematic review and meta-analysis

Asymptomatic leishmaniasis is believed to play important role in maintaining the transmission of Leishmania spp. within endemic communities. Therefore, the efforts to eliminate leishmaniasis are daunting if we cannot manage asymptomatic leishmaniasis well. To clarify the global prevalence and factors associated with the asymptomatic Leishmania infection, we assessed the prevalence of asymptomatic leishmaniasis by a systematic review followed by meta-analyses. In addition, factors associated with the asymptomatic leishmaniasis versus symptomatic were also analyzed. We included all of the original articles alluding to the human asymptomatic leishmaniasis that was confirmed by at least one laboratory diagnosis method regardless of age, sex, race, and ethnicity of the patients, study design, publication date or languages. In total, 111 original articles were chosen for the data extraction. Based on our meta-analyses of the original articles reporting asymptomatic leishmaniasis mostly in endemic areas, the prevalence of asymptomatic leishmaniasis was 11.2% [95% confidence interval (CI) 8.6%-14.4%] in general population, 36.7% [95% CI 27.6%-46.8%] in inhabitants living in the same or neighboring household to the symptomatic patients, and 11.8% [95% CI 7.1%-19%] in HIV infected patients. Among individuals with leishmaniasis, 64.9% [95% CI 54.7%-73.9%] were asymptomatic and males were more susceptible to develop symptoms, with OR=1.88, 95% CI 1.19-2.99, P=0.007. Meta-regression analysis showed no significant change in the prevalence of asymptomatic leishmaniasis during the last 40 years.

Laboratory Diagnosis of Cutaneous and Visceral Leishmaniasis: Current and Future Methods

Leishmaniasis is a neglected tropical disease with two main clinical forms: cutaneous and visceral leishmaniasis. Diagnosis of leishmaniasis is still a challenge, concerning the detection and correct identification of the species of the parasite, mainly in endemic areas where the absence of appropriate resources is still a problem. Most accessible methods for diagnosis, particularly in these areas, do not include the identification of each one of more than 20 species responsible for the disease. Here, we summarize the main methods used for the detection and identification of leishmaniasis that can be performed by demonstration of the parasite in biological samples from the patient through microscopic examination, by in vitro culture or animal inoculation; by molecular methods through the detection of parasite DNA; or by immunological methods through the detection of parasite antigens that may be present in urine or through the detection of specific antibodies against the parasite. Potential new methods that can be applied for laboratory diagnosis of leishmaniasis are also discussed.

Estimation of Leishmania spp. infection in asymptomatic people from Muzaffarpur, Bihar, India by antigen-antibody and skin testing

Asymptomatic VL is a concern, considering the risk of transmission in highly endemic areas due to human-to-human transmission. The aim of this study was to report the sero-epidemiological prevalence in Bihar, India, a highly endemic area of VL, using the leishmanin skin test (LST) and the direct agglutination test (DAT). This was a cross-sectional study performed in Muzaffarpur, Bihar, India. Relatives of patients with VL were tested by LST and DAT. Other epidemiological data were evaluated and correlated with tests results. Forty individuals (either previous or current patients), and 109 household contacts were studied. There were 36% of male visceral leishmaniasis family members versus 17.57% of females visceral leishmaniasis family members, thus showing more males with symptomatic disease than females (p< 0.01). All visceral leishmaniasis cases had positive DAT tests, but only 37% of past cases were positive on the skin testing. Amongst healthy household contacts, 34% were DAT-positive, whilst 21% were LST-positive. The overall positivity for both assays combined was 44.8% and 23.8% were DAT-positive alone. The finding of high infection prevalence amongst asymptomatic individuals, and the estimation of those at greater risk for overt disease (DAT-positive alone) are important in the development of future disease control policies.

One Health Approach to Leishmaniases: Understanding the Disease Dynamics through Diagnostic Tools

Leishmaniases are zoonotic vector-borne diseases caused by protozoan parasites of the genus Leishmania that affect millions of people around the globe. There are various clinical manifestations, ranging from self-healing cutaneous lesions to potentially fatal visceral leishmaniasis, all of which are associated with different Leishmania species. Transmission of these parasites is complex due to the varying ecological relationships between human and/or animal reservoir hosts, parasites, and sand fly vectors. Moreover, vector-borne diseases like leishmaniases are intricately linked to environmental changes and socioeconomic risk factors, advocating the importance of the One Health approach to control these diseases. The development of an accurate, fast, and cost-effective diagnostic tool for leishmaniases is a priority, and the implementation of various control measures such as animal sentinel surveillance systems is needed to better detect, prevent, and respond to the (re-)emergence of leishmaniases.

Prevalence of asymptomatic Leishmania infection and associated risk factors, after an outbreak in the south-western Madrid region, Spain, 2015

BackgroundA large outbreak of leishmaniasis with 758 cutaneous and visceral leishmaniasis cases occurred in 2009 in Fuenlabrada, in the south-west of the Madrid region of Spain.AimWe aimed to determine the prevalence of asymptomatic Leishmania infection after this outbreak, and its associated risk factors.MethodsA cross-sectional study of 804 healthy individuals living in Fuenlabrada who had no history of leishmaniasis, was conducted between January and July 2015. Asymptomatic infections were sought by either a combination of PCR, immunofluorescent antibody titre, and direct agglutination tests, or by whole blood stimulation assay (WBA) with interleukin-2 (IL-2) quantification.ResultsUsing the first approach, prevalence of asymptomatic individuals was 1.1% (9/804), while the second returned a value of 20.7% (143/804). Older age, being male, proximity to the park where the focus of infection was identified, and living in a detached house, were all strongly associated with the prevalence of asymptomatic infection.ConclusionsThe true number of infected individuals may be underestimated if only serological methods are used. The combination of WBA with IL-2 quantification may allow to better determine the prevalence of asymptomatic Leishmania infection, which would be useful in establishing control measures and in quantifying their impact. In our study, the use of WBA with IL-2 quantification also helped establish the risk factors that influence exposure to and infection by Leishmania.

Leishmania ITS1 Is Genetically Divergent in Asymptomatic and Symptomatic Visceral Leishmaniasis: Results of a Study in Southern Iran

It has been documented that the genotypic traits in symptomatic and asymptomatic cases of visceral leishmaniasis (VL) may be different. The current study aimed to find out and compare the genotype and intraspecies diversity of Leishmania Internal Transcribed Spacer 1 (ITS1) from asymptomatic and symptomatic VL cases in southern Iran. Methods. Buffy coat samples from seven VL patients, with clinical signs and symptoms, and seven asymptomatic VL cases, were evaluated in this study. Samples of asymptomatic individuals were obtained from children living in a VL endemic area in southern Iran, while the samples of symptomatic subjects were obtained from patients admitted to hospitals with a diagnosis of VL. DNA was extracted from the buffy coats of the samples and PCR-amplified, targeting the ITS1of Leishmania. The PCR products were sequenced, and the consensus sequences were assembled and multiple-aligned with a set of Leishmania strains retrieved from the GenBank, using Clustal W. The phylogenetic tree was rooted, using MEGAX software, and the diversities based on haplotype and nucleotides, as well as the number of polymorphic sites, were measured using DnaSP v5.0 software. The results of ITS1 sequencing in 5 out of 7 asymptomatic VL cases showed 99.25% to 100% similarity with the Leishmania infantum ITS1 sequence (accessed number: MN648746), and one isolate was considered as just Leishmania sp. In one sample, 99.75% similarity was seen with the ITS1 sequence of Crithidia fasciculata. Of the symptomatic VL patients, the PCR product revealed a 340 bp band corresponding to L. infantum in all of the samples. By analyzing the ITS1 sequences, all seven sequences formed a clade somewhat different from other Leishmania species and considered as Leishmania sp. Haplotype and nucleotide diversity were much more prevalent in symptomatic cases where six haplotypes were seen in the ITS1 of Leishmania from symptomatic patients and only two haplotypes were observed in the samples from asymptomatic cases. The findings of the current study showed that the Leishmania ITS1 from symptomatic VL and asymptomatic cases has significant genetic differences. Besides, infection with Crithidia fasciculata was reported, for the first time, in an asymptomatic case, which deserves further study.

Assessing the composition of the plasma membrane of Leishmania (Leishmania) infantum and L. (L.) amazonensis using label-free proteomics

Protozoan parasites of the genus Leishmania are causative agents of leishmaniasis, a wide range of diseases affecting 12 million people worldwide. The species L. infantum and L. amazonensis are etiologic agents of visceral and cutaneous leishmaniasis, respectively. Most proteome analyses of Leishmania have been carried out on whole-cell extracts, but such an approach tends to underrepresent membrane-associated proteins due to their high hydrophobicity and low solubility. Considering the relevance of this category of proteins in virulence, invasiveness and the host-parasite interface, this study applied label-free proteomics to assess the plasma membrane sub-proteome of L. infantum and L. amazonensis. The number of proteins identified in L. infantum and L. amazonensis promastigotes was 1168 and 1455, respectively. After rigorous data processing and mining, 157 proteins were classified as putative plasma membrane-associated proteins, of which 56 proteins were detected in both species, six proteins were detected only in L. infantum and 39 proteins were exclusive to L. amazonensis. The quantitative analysis revealed that two proteins were more abundant in L. infantum, including the glucose transporter 2, and five proteins were more abundant in L. amazonensis. The identified proteins associated with distinct processes and functions. In this regard, proteins of L. infantum were linked to metabolic processes whereas L. amazonensis proteins were involved in signal transduction. Moreover, transmembrane transport was a significant process among the group of proteins detected in both species and members of the superfamily of ABC transporters were highly represented. Interestingly, some proteins of this family were solely detected in L. amazonensis, such as ABCA9. GP63, a well-known virulence factor, was the only GPI-anchored protein identified in the membrane preparations of both species. Finally, we found several proteins with uncharacterized functions, including differentially abundant ones, highlighting a gap in the study of Leishmania proteins. Proteins characterization could provide a better biological understanding of these parasites and deliver new possibilities regarding the discovery of therapeutic targets, drug resistance and vaccine candidates.

Xenodiagnosis to address key questions in visceral leishmaniasis control and elimination

Visceral leishmaniasis (VL) remains an important public health issue worldwide causing substantial morbidity and mortality. The Indian subcontinent accounted for up to 90% of the global VL burden in the past but made significant progress during recent years and is now moving towards elimination. However, to achieve and sustain elimination of VL, knowledge gaps on infection reservoirs and transmission need to be addressed urgently. Xenodiagnosis is the most direct way for testing the infectiousness of hosts to the vectors and can be used to investigate the dynamics and epidemiology of Leishmania donovani transmission. There are, however, several logistic and ethical issues with xenodiagnosis that need to be addressed before its application on human subjects. In the current Review, we discuss the critical knowledge gaps in VL transmission and the role of xenodiagnosis in disease transmission dynamics along with its technical challenges. Establishment of state of the art xenodiagnosis facilities is essential for the generation of much needed evidence in the VL elimination initiative.

Asymptomatic Visceral Leishmania infantum Infection in US Soldiers Deployed to Iraq

BACKGROUND

Visceral leishmaniasis (VL), due to Leishmania infantum, is a persistent intracellular parasitic infection transmitted by the bite of infected sand flies. Symptomatic VL has been reported in U.S. soldiers with Iraq deployment. Untreated symptomatic VL can be fatal; asymptomatic VL (AVL) may establish a lifelong risk of reactivation. We report prevalence and AVL risk factors in Operation Iraqi Freedom (OIF) deployers during 2002-11.

METHODS

Healthy soldiers exposed to VL endemic areas in Iraq and 50 controls who never traveled to endemic regions were recruited through military healthcare facilities (2015-17). Responses to a risk factor survey and blood samples were obtained. Leishmania research diagnostics utilized included enzyme-linked immunosorbent assay (ELISA), rk39 test strips, quantitative polymerase chain reaction (PCR), and interferon gamma release (IGRA) assays. Statistical analyses included Fisher exact test, Pearson χ2 test, Mann-Whitney U test, and logistic regression.

RESULTS

200 deployed subjects were enrolled, mostly males (84.0%), of white ethnicity (79.0%), and median age 41 (range 24-61) years. 64% were seropositive for Phlebotomus alexandri saliva antibodies. Prevalence of AVL (any positive test result) was 39/200 (19.5%, 95% confidence interval 14.4%-25.8%). Two (1.0%) PCR, 10 (5%) ELISA, and 28 (14%) IGRA samples were positive. Travel to Ninewa governorate increased risk for AVL (P = .01).

CONCLUSION

AVL was identified in 19.5% of OIF deployers; travel to northwest Iraq correlated with infection. Further studies are needed to inform risk for reactivation VL in US veterans and to target additional blood safety and surveillance measures.

The potential impact of human visceral leishmaniasis vaccines on population incidence

Human visceral leishmaniasis (VL) vaccines are currently under development and there is a need to understand their potential impact on population wide VL incidence. We implement four characteristics from different human VL vaccine candidates into two published VL transmission model variants to estimate the potential impact of these vaccine characteristics on population-wide anthroponotic VL incidence on the Indian subcontinent (ISC). The vaccines that are simulated in this study 1) reduce the infectiousness of infected individuals towards sand flies, 2) reduce risk of developing symptoms after infection, 3) reduce the risk of developing post-kala-azar dermal leishmaniasis (PKDL), or 4) lead to the development of transient immunity. We also compare and combine a vaccine strategy with current interventions to identify their potential role in elimination of VL as a public health problem. We show that the first two simulated vaccine characteristics can greatly reduce VL incidence. For these vaccines, an approximate 60% vaccine efficacy would lead to achieving the ISC elimination target (<1 VL case per 10,000 population per year) within 10 years’ time in a moderately endemic setting when vaccinating 100% of the population. Vaccinating VL cases to prevent the development of PKDL is a promising tool to sustain the low incidence elimination target after regular interventions are halted. Vaccines triggering the development of transient immunity protecting against infection lead to the biggest reduction in VL incidence, but booster doses are required to achieve perduring impact. Even though vaccines are not yet available for implementation, their development should be pursued as their potential impact on transmission can be substantial, both in decreasing incidence at the population level as well as in sustaining the ISC elimination target when other interventions are halted.

Vaccines for human visceral leishmaniasis (VL) are currently under development. In this study, we simulate VL transmission dynamics using mathematical models to explore the potential impact of vaccines on population-wide incidence. We show that some vaccines have high potential to reduce VL incidence, namely those that reduce the infectiousness of infected individuals to sand flies and those that reduce the chance of developing symptoms once infected. The effect of vaccines that lead to protection from infection is potentially the greatest, but depending on the duration of immunity, individuals would require booster doses to guarantee lifelong impact. Vaccines that prevent the development of post-kala-azar dermal leishmaniasis are a promising tool to sustain low VL incidence and prevent recrudescence of infection when regular interventions are halted. Our results strongly support the continued development of VL vaccines, as their potential impact on population incidence can be substantial.

Global genome diversity of the Leishmania donovani complex

Protozoan parasites of the Leishmania donovani complex - L. donovani and L. infantum - cause the fatal disease visceral leishmaniasis. We present the first comprehensive genome-wide global study, with 151 cultured field isolates representing most of the geographical distribution. L. donovani isolates separated into five groups that largely coincide with geographical origin but vary greatly in diversity. In contrast, the majority of L. infantum samples fell into one globally-distributed group with little diversity. This picture is complicated by several hybrid lineages. Identified genetic groups vary in heterozygosity and levels of linkage, suggesting different recombination histories. We characterise chromosome-specific patterns of aneuploidy and identified extensive structural variation, including known and suspected drug resistance loci. This study reveals greater genetic diversity than suggested by geographically-focused studies, provides a resource of genomic variation for future work and sets the scene for a new understanding of the evolution and genetics of the Leishmania donovani complex.

Noninvasive Biological Samples to Detect and Diagnose Infections due to Trypanosomatidae Parasites: A Systematic Review and Meta-Analysis

Unicellular eukaryotes of the Trypanosomatidae family include human and animal pathogens that belong to the Trypanosoma and Leishmania genera. Diagnosis of the diseases they cause requires the sampling of body fluids (e.g., blood, lymph, peritoneal fluid, cerebrospinal fluid) or organ biopsies (e.g., bone marrow, spleen), which are mostly obtained through invasive methods. Body fluids or appendages can be alternatives to these invasive biopsies but appropriateness remains poorly studied. To further address this question, we perform a systematic review on clues evidencing the presence of parasites, genetic material, antibodies, and antigens in body secretions, appendages, or the organs or proximal tissues that produce these materials. Paper selection was based on searches in PubMed, Web of Science, WorldWideScience, SciELO, Embase, and Google. The information of each selected article (n = 333) was classified into different sections and data were extracted from 77 papers. The presence of Trypanosomatidae parasites has been tracked in most of organs or proximal tissues that produce body secretions or appendages, in naturally or experimentally infected hosts. The meta-analysis highlights the paucity of studies on human African trypanosomiasis and an absence on animal trypanosomiasis. Among the collected data high heterogeneity in terms of the I2 statistic (100%) is recorded. A high positivity is recorded for antibody and genetic material detection in urine of patients and dogs suffering leishmaniasis, and of antigens for leishmaniasis and Chagas disease. Data on conjunctival swabs can be analyzed with molecular methods solely for dogs suffering canine visceral leishmaniasis. Saliva and hair/bristles showed a pretty good positivity that support their potential to be used for leishmaniasis diagnosis. In conclusion, our study pinpoints significant gaps that need to be filled in order to properly address the interest of body secretion and hair or bristles for the diagnosis of infections caused by Leishmania and by other Trypanosomatidae parasites.

Genomes of Leishmania parasites directly sequenced from patients with visceral leishmaniasis in the Indian subcontinent

Whole genome sequencing (WGS) is increasingly used for molecular diagnosis and epidemiology of infectious diseases. Current Leishmania genomic studies rely on DNA extracted from cultured parasites, which might introduce sampling and biological biases into the subsequent analyses. Up to now, direct analysis of Leishmania genome in clinical samples is hampered by high levels of human DNA and large variation in parasite load in clinical samples. Here, we present a method, based on target enrichment of Leishmania donovani DNA with Agilent SureSelect technology, that allows the analysis of Leishmania genomes directly in clinical samples. We validated our protocol with a set of artificially mixed samples, followed by the analysis of 63 clinical samples (bone marrow or spleen aspirates) from visceral leishmaniasis patients in Nepal. We were able to identify genotypes using a set of diagnostic SNPs in almost all of these samples (97%) and access comprehensive genome-wide information in most (83%). This allowed us to perform phylogenomic analysis, assess chromosome copy number and identify large copy number variants (CNVs). Pairwise comparisons between the parasite genomes in clinical samples and derived in vitro cultured promastigotes showed a lower aneuploidy in amastigotes as well as genomic differences, suggesting polyclonal infections in patients. Altogether our results underline the need for sequencing parasite genomes directly in the host samples

Visceral leishmaniasis (VL) is caused by parasitic protozoa of the Leishmania donovani complex and is lethal in the absence of treatment. Whole Genome Sequencing (WGS) of L. donovani clinical isolates revealed hitherto cryptic population structure in the Indian Sub-Continent and provided insights into the epidemiology and potential mechanisms of drug resistance. However, several biases are likely introduced during the culture step. We report here the development of a method that allows determination of parasite genomes directly in clinical samples, and validate it on bone marrow and splenic aspirates of VL patients in Nepal. Our study sheds a new light on the biology of Leishmania in the human host: we found that intracellular parasites of the patients had very low levels of aneuploidy, in sharp contrast to the situation in cultivated isolates. Moreover, the observed differences in genomes between intracellular amastigotes of the patient and the derived cultured parasites suggests polyclonality of infections, with different clones dominating in clinical samples and in culture, likely due to fitness differences. We believe this method is most suitable for clinical studies and for molecular tracking in the context of elimination programs.

Longitudinal evaluation of asymptomatic Leishmania infection in HIV-infected individuals in North-West Ethiopia: A pilot study

Background

In endemic regions, asymptomatic Leishmania infection is common. In HIV patients, detection of asymptomatic Leishmania infection could potentially identify those at risk of visceral leishmaniasis (VL). However, data on the prevalence, incidence, and determinants of asymptomatic infection, and the risk of VL are lacking.

Methods

We conducted a cross-sectional survey at a single ART centre, followed by a prospective cohort study amongst HIV-infected adults in HIV care in a district hospital in a VL-endemic area in North-West Ethiopia (9/2015-8/2016). Asymptomatic Leishmania infection was detected using the direct agglutination test (DAT), rK39-rapid diagnostic test (RDT)), PCR on peripheral blood and the KAtex urine antigen test, and defined as positivity on any Leishmania marker. All individuals were followed longitudinally (irrespective of the Leishmania test results). Risk factors for asymptomatic Leishmania infection were determined using logistic regression.

Results

A total of 534 HIV-infected individuals enrolled in HIV care were included in the study. After excluding 13 patients with a history of VL and an 10 patients with incomplete baseline Leishmania tests, 511 were included in analysis. The median age was 38 years (interquartile range (IQR) 30–45), 62.6% were male. The median follow-up time was 12 months (IQR 9–12). No deaths were reported during the study period. Most (95.5%) were on antiretroviral treatment at enrolment, for a median of 52 months (IQR 27–79). The median CD4 count at enrolment was 377 cells/mm3 (IQR 250–518). The baseline prevalence of Leishmania infection was 12.8% in males and 4.2% in females. Overall, 7.4% tested positive for rK39, 4.3% for DAT, 0.2% for PCR and 0.2% for KAtex. Independent risk factors for a prevalent infection were male sex (odds ratio (OR) 3.2; 95% confidence intervals (CI) 14–7.0) and concurrent malaria infection (OR 6.1; 95% CI 1.9–18.9). Amongst the 49 prevalent (baseline) infections with further follow-up, the cumulative incidence of losing the Leishmania markers by one year was 40.1%. There were 36 incident infections during the course of the study, with a cumulative one-year risk of 9.5%. Only one case of VL was detected during follow-up.

Conclusions

We found a high prevalence of asymptomatic Leishmania infection, persisting in most cases. The incidence was more modest and overt VL was rare. Larger and longer studies with more complete follow-up may help to decide whether a test and treat strategy would be justified in this context.

Trial registration

ClinicalTrials.gov NCT02839603

As visceral leishmaniasis (VL) in HIV patients is difficult to treat and associated with high mortality, strategies to detect and treat asymptomatic Leishmania infection in HIV patients should be explored. However, data on the prevalence, incidence, determinants of asymptomatic infection and risk of VL are lacking. We conducted a longitudinal study, including HIV-infected adult patients in HIV care in a district hospital in a VL-endemic area in North-West Ethiopia. Asymptomatic Leishmania infection was evaluated by Leishmania antibody tests (DAT and rK39), urine antigen tests (KAtex) and PCR, and was defined as positivity on any Leishmania marker. We also looked for independent risk factors for asymptomatic Leishmania infection at study recruitment. A total of 511 patients were included in the analysis. The median age was 38 years, 62.6% were male. The median time of residence in a VL-endemic area was 18 years. Most (95.5%) were on antiretroviral treatment at enrolment, for a median of 52 months. The median CD4 count at enrolment was 377 cells/mm³. The baseline prevalence of Leishmania infection was 12.8% in males and 4.2% in females. Overall, 7.4% tested positive for rK39, 4.3% for DAT, 0.2% for PCR and 0.2% for KAtex. Independent risk factors for a prevalent infection were male sex and concurrent malaria infection. Amongst the 49 prevalent infections that were present upon enrolment in the study, the probability of losing the Leishmania markers by one year was 40.1%. There were 36 new infections during the course of the study, with an overall risk of 9.5% by one year of follow-up. One case of VL was detected during follow-up. In conclusion, we found a high prevalence of asymptomatic Leishmania infection, which persisted in most cases. The incidence was more modest. Larger and longer studies would be needed to decide whether a test and treat strategy would be justified in this context.

Visceral Leishmaniasis in the Muzaffapur Demographic Surveillance Site: A Spatiotemporal Analysis

In the Indian subcontinent, visceral leishmaniasis (VL) has a strongly clustered distribution. The “index case approach” is promoted both for active case finding and indoor residual spraying (IRS). Uncertainty exists about the optimal radius. Buffer zones of 50–75 m around incident cases have been suggested for active case finding, for IRS the recommendation is to cover a radius of 500 m. Our aim was to establish optimal target areas both for IRS and for (re)active case finding. We plotted incident VL cases on a map per 6-month period (January–June or July–December) and drew buffers of 0 (same household), 50, 75, 100, 200, 300, 400, and 500 m around these cases. We then recorded total population and numbers of VL cases diagnosed over the next 6-month period in each of these buffers and beyond. We calculated incidence rate ratios (IRRs) using the population at more than 500 m from any case as reference category. There was a very strong degree of spatial clustering of VL with IRRs ranging from 45.2 (23.8–85.6) for those living in the same households to 14.6 (10.1–21.2) for those living within 75 m of a case diagnosed, during the previous period. Up to 500 m the IRR was still five times higher than that of the reference category. Our findings corroborate the rationale of screening not just household contacts but also those living within a perimeter of 50–75 m from an index case. For IRS, covering a perimeter of 500 m, appears to be a rational choice.

Determinants for progression from asymptomatic infection to symptomatic visceral leishmaniasis: A cohort study

BACKGROUND

Asymptomatic Leishmania donovani infections outnumber clinical presentations, however the predictors for development of active disease are not well known. We aimed to identify serological, immunological and genetic markers for progression from L. donovani infection to clinical Visceral Leishmaniasis (VL).

METHODS

We enrolled all residents >2 years of age in 27 VL endemic villages in Bihar (India). Blood samples collected on filter paper on two occasions 6-12 months apart, were tested for antibodies against L. donovani with rK39-ELISA and DAT. Sero converters, (negative for both tests in the first round but positive on either of the two during the second round) and controls (negative on both tests on both occasions) were followed for three years. At the start of follow-up venous blood was collected for the following tests: DAT, rK39- ELISA, Quantiferon assay, SNP/HLA genotyping and L.donovani specific quantitative PCR.

RESULTS

Among 1,606 subjects enrolled,17 (8/476 seroconverters and 9/1,130 controls) developed VL (OR 3.1; 95% CI 1.1-8.3). High DAT and rK39 ELISA antibody titers as well as positive qPCR were strongly and significantly associated with progression from seroconversion to VL with odds ratios of 19.1, 30.3 and 20.9 respectively. Most VL cases arose early (median 5 months) during follow-up.

CONCLUSION

We confirmed the strong association between high DAT and/or rK39 titers and progression to disease among asymptomatic subjects and identified qPCR as an additional predictor. Low predictive values do not warrant prophylactic treatment but as most progressed to VL early during follow-up, careful oberservation of these subjects for at least 6 months is indicated.

Visceral Leishmaniasis IgG1 Rapid Monitoring of Cure vs. Relapse, and Potential for Diagnosis of Post Kala-Azar Dermal Leishmaniasis

Background: There is a recognized need for an improved diagnostic test to assess post-chemotherapeutic treatment outcome in visceral leishmaniasis (VL) and to diagnose post kala-azar dermal leishmaniasis (PKDL). We previously demonstrated by ELISA and a prototype novel rapid diagnostic test (RDT), that high anti-Leishmania IgG1 is associated with post-treatment relapse versus cure in VL.

Methodology: Here, we further evaluate this novel, low-cost RDT, named VL Sero K-SeT, and ELISA for monitoring IgG1 levels in VL patients after treatment. IgG1 levels against L. donovani lysate were determined. We applied these assays to Indian sera from cured VL at 6 months post treatment as well as to relapse and PKDL patients. Sudanese sera from pre- and post-treatment and relapse were also tested.

Results: Of 104 paired Indian sera taken before and after treatment for VL, when deemed clinically cured, 81 (77.9%) were positive by VL Sero K-SeT before treatment; by 6 months, 68 of these 81 (84.0%) had a negative or reduced RDT test line intensity. ELISAs differed in positivity rate between pre- and post-treatment (p = 0.0162). Twenty eight of 33 (84.8%) Indian samples taken at diagnosis of relapse were RDT positive. A comparison of Indian VL Sero K-SeT data from patients deemed cured and relapsed confirmed that there was a significant difference (p < 0.0001) in positivity rate for the two groups using this RDT. Ten of 17 (58.8%) Sudanese sera went from positive to negative or decreased VL Sero K-SeT at the end of 11–30 days of treatment. Forty nine of 63 (77.8%) PKDL samples from India were positive by VL Sero K-SeT.

Conclusion: We have further shown the relevance of IgG1 in determining clinical status in VL patients. A positive VL Sero K-SeT may also be helpful in supporting diagnosis of PKDL. With further refinement, such as the use of specific antigens, the VL Sero K-SeT and/or IgG1 ELISA may be adjuncts to current VL control programmes.

Age trends in asymptomatic and symptomatic Leishmania donovani infection in the Indian subcontinent: A review and analysis of data from diagnostic and epidemiological studies

BACKGROUND

Age patterns in asymptomatic and symptomatic infection with Leishmania donovani, the causative agent of visceral leishmaniasis (VL) in the Indian subcontinent (ISC), are currently poorly understood. Age-stratified serology and infection incidence have been used to assess transmission levels of other diseases, which suggests that they may also be of use for monitoring and targeting control programmes to achieve elimination of VL and should be included in VL transmission dynamic models. We therefore analysed available age-stratified data on both disease incidence and prevalence of immune markers with the aim of collating the currently available data, estimating rates of infection, and informing modelling and future data collection.

METHODOLOGY/PRINCIPAL FINDINGS

A systematic literature search yielded 13 infection prevalence and 7 VL incidence studies meeting the inclusion criteria. Statistical tests were performed to identify trends by age, and according to diagnostic cut-off. Simple reversible catalytic models with age-independent and age-dependent infection rates were fitted to the prevalence data to estimate infection and reversion rates, and to test different hypotheses about the origin of variation in these rates. Most of the studies showed an increase in infection prevalence with age: from ≲10% seroprevalence (<20% Leishmanin skin test (LST) positivity) for 0-10-year-olds to >10% seroprevalence (>20% LST-positivity) for 30-40-year-olds, but overall prevalence varied considerably between studies. VL incidence was lower amongst 0-5-year-olds than older age groups in most studies; most showing a peak in incidence between ages 5 and 20. The age-independent catalytic model provided the best overall fit to the infection prevalence data, but the estimated rates for the less parsimonious age-dependent model were much closer to estimates from longitudinal studies, suggesting that infection rates may increase with age.

CONCLUSIONS/SIGNIFICANCE

Age patterns in asymptomatic infection prevalence and VL incidence in the ISC vary considerably with geographical location and time period. The increase in infection prevalence with age and peaked age-VL-incidence distribution may be due to lower exposure to infectious sandfly bites in young children, but also suggest that acquired immunity to the parasite increases with age. However, poor standardisation of serological tests makes it difficult to compare data from different studies and draw firm conclusions about drivers of variation in observed age patterns.

Visceral leishmaniasis: Spatiotemporal heterogeneity and drivers underlying the hotspots in Muzaffarpur, Bihar, India

BACKGROUND

Despite the overall decrease in visceral leishmaniasis (VL) incidence on the Indian subcontinent, there remain spatiotemporal clusters or 'hotspots' of new cases. The characteristics of these hotspots, underlying transmission dynamics, and their importance for shaping control strategies are not yet fully understood and are investigated in this study for a VL endemic area of ~100,000 inhabitants in Bihar, India between 2007-2015.

METHODOLOGY/PRINCIPAL FINDINGS

VL incidence (cases/10,000/year) dropped from 12.3 in 2007 to 0.9 in 2015, which is just below the World Health Organizations' threshold for elimination as a public health problem. Clustering of VL was assessed between subvillages (hamlets), using multiple geospatial and (spatio)temporal autocorrelation and hotspot analyses. One to three hotspots were identified each year, often persisting for 1-5 successive years with a modal radius of ~500m. The relative risk of having VL was 5-86 times higher for inhabitants of hotspots, compared to those living outside hotspots. Hotspots harbour significantly more households from the two lowest asset quintiles (as proxy for socio-economic status). Overall, children and young adelescents (5-14 years) have the highest risk for VL, but within hotspots and at the start of outbreaks, older age groups (35+ years) show a comparable high risk.

CONCLUSIONS/SIGNIFICANCE

This study demonstrates significant spatiotemporal heterogeneity in VL incidence at subdistrict level. The association between poverty and hotspots confirms that VL is a disease of 'the poorest of the poor' and age patterns suggest a potential role of waning immunity as underlying driver of hotspots. The recommended insecticide spraying radius of 500m around detected VL cases corresponds to the modal hotspot radius found in this study. Additional data on immunity and asymptomatic infection, and the development of spatiotemporally explicit transmission models that simulate hotspot dynamics and predict the impact of interventions at the smaller geographical scale will be crucial tools in sustaining elimination.

Visceral leishmaniasis elimination targets in India, strategies for preventing resurgence

INTRODUCTION

Visceral leishmaniasis (VL) is a fatal parasitic disease caused by a parasite belonging to the Leishmania donovani complex and transmitted by infected female Phlebotomous argentipes sand flies. The VL elimination strategy in the Indian subcontinent (ISC), which has a current goal of reducing the incidence of VL to below 1/10,000 of population by the year 2020, consists of rapid detection and treatment of VL to reduce the number of human reservoirs as well as vector control using indoor residual spraying (IRS). However, as the incidence of VL declines toward the elimination goal, greater targeting of control methods will be required to ensure appropriate early action to prevent the resurgence of VL. Area covered: We discuss the current progress and challenges in the VL elimination program and strategies to be employed to ensure sustained elimination of VL. Expert commentary: The VL elimination initiative has saved many human lives; however, for VL elimination to become a reality in a sustained way, an intense effort is needed, as substantial numbers of endemic subdistricts (primary health centers (PHCs) blocks level) are yet to reach the elimination target. In addition to effective epidemiological surveillance, appropriate diagnostic and treatment services for VL at PHCs will be needed to ensure long-term sustainability and prevent reemergence of VL.