Molecular detection of Leishmania parasites from whole bodies of sandflies collected in Nepal

The ongoing risk of Leishmania donovani transmission in eastern Nepal: an entomological investigation during the elimination era

BACKGROUND

Visceral leishmaniasis (VL), a life-threatening neglected tropical disease, is targeted for elimination from Nepal by the year 2026. The national VL elimination program is still confronted with many challenges including the increasingly widespread distribution of the disease over the country, local resurgence and the questionable efficacy of the key vector control activities. In this study, we assessed the status and risk of Leishmania donovani transmission based on entomological indicators including seasonality, natural Leishmania infection rate and feeding behavior of vector sand flies, Phlebotomus argentipes, in three districts that had received disease control interventions in the past several years in the context of the disease elimination effort.

METHODS

We selected two epidemiologically contrasting settings in each survey district, one village with and one without reported VL cases in recent years. Adult sand flies were collected using CDC light traps and mouth aspirators in each village for 12 consecutive months from July 2017 to June 2018. Leishmania infection was assessed in gravid sand flies targeting the small-subunit ribosomal RNA gene of the parasite (SSU-rRNA) and further sequenced for species identification. A segment (~ 350 bp) of the vertebrate cytochrome b (cytb) gene was amplified from blood-fed P. argentipes from dwellings shared by both humans and cattle and sequenced to identify the preferred host.

RESULTS

Vector abundance varied among districts and village types and peaks were observed in June, July and September to November. The estimated Leishmania infection rate in vector sand flies was 2.2% (1.1%-3.7% at 95% credible interval) and 0.6% (0.2%-1.3% at 95% credible interval) in VL and non-VL villages respectively. The common source of blood meal was humans in both VL (52.7%) and non-VL (74.2%) villages followed by cattle.

CONCLUSIONS

Our findings highlight the risk of ongoing L. donovani transmission not only in villages with VL cases but also in villages not reporting the presence of the disease over the past several years within the districts having disease elimination efforts, emphasize the remaining threats of VL re-emergence and inform the national program for critical evaluation of disease elimination strategies in Nepal.

Forty years (1980-2019) of visceral leishmaniasis in Nepal: trends and elimination challenges

BACKGROUND

Visceral leishmaniasis (VL) is an important re-emerging neglected tropical disease associated with poverty. Despite the elimination initiative started in 2005, VL cases have been expanding into geographic areas in Nepal. The present study aims at exploring the trends of VL from 1980 to 2019.

METHODS

This retrospective analysis covers 40 y of VL cases reported by the Epidemiology Diseases Control Division, Nepal. Subgroup analyses for annual incidence were performed by age, sex, seasons, districts and provinces, and VL cases were visualized on in-country maps.

RESULTS

A total of 34 564 cases and 584 deaths of VL were reported during 1980-2019. VL persistently increased until 2006 and was reported from all seven provinces of the country. The highest number of confirmed cases (n=2229) was reported in 2003 and the lowest (n=60) in 1983. VL cases expanded from 12 to 23 endemic districts. The key components of the VL elimination program are early diagnosis; enhanced surveillance; integrated vector management; social mobilization; research and treatment.

CONCLUSIONS

Expansion of VL towards the hilly and mountain regions of Nepal has posed challenges to the elimination program. Urgent VL control measures are required to achieve the elimination goals.

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.

Stray dogs in Nepal have high prevalence of vector-borne pathogens: a molecular survey

Background

Population of stray dogs is significant in large cities of Nepal, such as Kathmandu. Most of stray dogs suffer a lack of basic health care. Considering the clinical relevance, the broad distribution and the lack of information of canine vector borne diseases (CVBD) in Nepal, the aim of this study was to evaluate the prevalence of different vector-borne pathogens (VBP) in stray dogs living in the metropolitan area of Kathmandu, and to assess different traits as possible risk factors.

Methods

A total of 70 canine blood samples from stray dogs attended at the Kathmandu Animal Treatment Centre during August 2017 were collected on filter paper (Flinders Technology Associates (FTA) cards). Data regarding signalment, clinical signs and epidemiological characteristics were recorded for each animal. Real-time polymerase chain reaction assays were performed for Leishmania spp., Ehrlichia spp./Anaplasma spp., Babesia spp./Theileria spp. and Hepatozoon canis.

Results

The overall prevalence detected was 31.43% for Hepatozoon canis, 31.43% for Anaplasma platys, 27.14% for Ehrlichia canis, 18.57% for Leishmania donovani species complex, 12.86% for isolates corresponding to Theileria spp., 12.86% for Babesia vogeli and 2.86% for B. gibsoni. A total of 81.43% of the dogs were positive to at least one of the VBP tested. Co-infections were detected in 41.43% of the dogs. Dogs positive to any of the VBP tested, and particularly to E. canis, were older than those that were negative.

Conclusions

To our knowledge, this is the first molecular detection of VBP in stray dogs from Kathmandu, Nepal. The high prevalence of VBP detected highlights the need to implement a surveillance programme and control strategies for these CVBD in the population of stray dogs in this area.

Detection of DNA of Leishmania siamensis in Sergentomyia (Neophlebotomus) iyengari (Diptera: Psychodidae) and Molecular Identification of Blood Meals of Sand Flies in an Affected Area, Southern Thailand

In Thailand, leishmaniasis is an emerging vector-borne disease that has become a public health concern. In related epidemiological surveys to identify potential Leishmania vectors in the affected areas, DNA of Leishmania martiniquensis (Kinetoplastida: Trypanosomatidae) was detected in Sergentomyia (Neophebotomus) gemmea (Diptera: Psychodidae) and Sergentomyia (Parrotomyia) barraudi (Diptera: Psychodidae). Recently, a more elaborate study was conducted in the same areas that included sand fly species identification, screening sand flies for the presence of Leishmania DNA and blood meal analysis to identify potential reservoir hosts directed toward assessing the risk of human infection. Twenty-nine archived pools of sand flies collected in Hat Samran District, Trang Province were used in this study. Sand fly species were confirmed using PCR encompassing regions within the mitochondrial DNA. Leishmania DNA was detected using PCR of the heat shock protein 70 region (hsp70-PCR) and blood meal identification was performed using PCR of the cyt b gene of vertebrate mitochondrial DNA (cytb-nd1-PCR) and human-specific AluYb8 repeat (AluYb8-PCR). Four sand fly species were confirmed, i.e., Phlebotomus (Anaphlebotomus) stantoni (Diptera: Psychodidae), S. barraudi, Sergentomyia (Neophlebotomus) iyengari (Diptera: Psychodidae), and S. gemmea. Leishmania siamensis was detected in one female S. iyengari. Only human blood was detected in P. stantoni and S. gemmea, while both sun skink (Mabuya multifasciata) and human blood were detected in S. iyengari. In this study, we showed that S. iyengari could be a potential vector of L. siamensis infection among humans.

Transmission of Leishmania infantum in the Canine Leishmaniasis Focus of Mont-Rolland, Senegal: Ecological, Parasitological and Molecular Evidence for a Possible Role of Sergentomyia Sand Flies

Leishmania (L.) infantum is the causative agent in an endemic focus of canine leishmaniasis in the Mont-Rolland district (Thiès, Senegal). In this area, the transmission cycle is well established and more than 30% of dogs and 20% of humans are seropositive for L. infantum. However, the sand fly species involved in L. infantum transmission cycle are still unknown. Between 2007 and 2010, 3654 sand flies were collected from different environments (indoor, peridomestic, farming and sylvatic areas) to identify the main L. infantum vector(s). Nine sand fly species were identified. The Phlebotomus genus (n = 54 specimens; Phlebotomus (Ph) duboscqi and Phlebotomus (Ph). rodhaini) was markedly under-represented in comparison to the Sergentomyia genus (n = 3600 specimens; Sergentomyia (Se) adleri, Se. clydei, Se. antennata, Se. buxtoni, Se. dubia, Se. schwetzi and Se. magna). Se. dubia and Se. schwetzi were the dominant species indoor and in peridomestic environments, near humans and dogs. Blood-meal analysis indicated their anthropophilic behavior. Some Se. schwetzi specimens fed also on dogs. The dissection of females in the field allowed isolating L. infantum from sand flies of the Sergentomyia genus (0.4% of Se. dubia and 0.79% of Se. schwetzi females). It is worth noting that one Se. dubia female not engorged and not gravid revealed highly motile metacyclic of L. infantum in the anterior part of the midgut. PCR-based diagnosis and sequencing targeting Leishmania kinetoplast DNA (kDNA) highlighted a high rate of L. infantum-positive females (5.38% of Se. dubia, 4.19% of Se. schwetzi and 3.64% of Se. magna). More than 2% of these positive females were unfed, suggesting the parasite survival after blood-meal digestion or egg laying. L. infantum prevalence in Se. schwetzi was associated with its seroprevalence in dogs and humans and L. infantum prevalence in Se. dubia was associated with its seroprevalence in humans. These evidences altogether strongly suggest that species of the Sergentomyia genus are probably the vectors of canine leishmaniasis in the Mont-Rolland area and challenge one more time the dogma that in the Old World, leishmaniasis is exclusively transmitted by species of the Phlebotomus genus.

Leishmaniases, neglected tropical vector-borne diseases, remain today a problem of public health. Classically, the sand flies involved in Leishmania transmission belong either to the Phlebotomus genus (Old World) or to the Lutzomyia genus (New World). In the rural community of Mont-Rolland (Senegal, West Africa), Leishmania infantum is the causative agent in an endemic focus of canine leishmaniasis. Recent surveys revealed more than 30% of dogs and 20% of humans with a positive serological test for Leishmania in this community. However, the sand fly species involved in L. infantum transmission were still unknown. Between 2007 and 2010, we carried out a study in this community to identify the sand fly species responsible for L. infantum transmission. We collected nine species belonging mainly to Sergentomyia genus and in low proportion to Phlebotomus genus. The abundance around dogs and humans, the detection of live and mature parasites in anterior midgut, the high rate of L. infantum-positive females using molecular analyses and the identification of dog and human blood in the fed females incriminates Se. schwetzi and Se. dubia as possible vectors of L. infantum. This hypothesis is strongly supported by statistical analyses performed to compare the prevalence of infected sand flies with the seroprevalence data in humans and dogs.

Concomitant Immunity Induced by Persistent Leishmania major Does Not Preclude Secondary Re-Infection: Implications for Genetic Exchange, Diversity and Vaccination

BACKGROUND

Many microbes have evolved the ability to co-exist for long periods of time within other species in the absence of overt pathology. Evolutionary biologists have proposed benefits to the microbe from 'asymptomatic persistent infections', most commonly invoking increased likelihood of transmission by longer-lived hosts. Typically asymptomatic persistent infections arise from strong containment by the immune system, accompanied by protective immunity; such 'vaccination' from overt disease in the presence of a non-sterilizing immune response is termed premunition or concomitant immunity. Here we consider another potential benefit of persistence and concomitant immunity to the parasite: the 'exclusion' of competing super-infecting strains, which would favor transmission of the original infecting organism.

METHODOLOGY / PRINCIPLE FINDINGS

To investigate this in the protozoan parasite Leishmania major, a superb model for the study of asymptomatic persistence, we used isogenic lines of comparable virulence bearing independent selectable markers. One was then used to infect genetically resistant mice, yielding infections which healed and progressed to asymptomatic persistent infection; these mice were then super-infected with the second marked line. As anticipated, super-infection yielded minimal pathology, showing that protective immunity against disease pathology had been established. The relative abundance of the primary and super-infecting secondary parasites was then assessed by plating on selective media. The data show clearly that super-infecting parasites were able to colonize the immune host effectively, achieving numbers comparable to and sometimes greater than that of the primary parasite.

CONCLUSIONS / SIGNIFICANCE

We conclude that induction of protective immunity does not guarantee the Leishmania parasite exclusive occupation of the infected host. This finding has important consequences to the maintenance and generation of parasite diversity in the natural Leishmania infectious cycle alternating between mammalian and sand fly hosts.

Physiological Age Structure and Leishmania spp. Detection in Phlebotomus (Larroussius) orientalis (Parrot, 1936) (Diptera: Psychodidae) at an Endemic Focus of Visceral Leishmaniasis in Northern Ethiopia

Visceral leishmaniasis (VL) caused by Leishmania donovani is endemic in northern Ethiopia, where P. orientalis is the most important presumed vector. This study was designed to determine the physiological age structure and the occurrence of Leishmania infection in the vector of VL in Tahtay Adiyabo district, northern Ethiopia. Sand flies were collected using CDC light traps from peridomestic and agricultural fields between May 2011 and April 2012 and P. orientalis females were dissected for age determination and detection of Leishmania promastigotes. Sand flies were also analyzed for L. donovani detection using molecular methods. Of 1,282 P. orientalis examined for abdominal stages and age characterization, 66.2%, 28.2%, 4.1%, and 1.6% were unfed, freshly fed, half-gravid, and gravid. Parous rate in unfed females was 34.1% and 35.4% in peridomestic and agricultural fields, respectively. Out of 921 P. orientalis females dissected, one specimen (0.1%) was found naturally infected with promastigotes. Five pools (25 females) of unfed P. orientalis were also found with DNA of Leishmania spp. In particular, a single P. orientalis was positive for L. donovani (0.5%). Based on this and other evidences (abundance, human blood feeding, and xenodiagnostic studies), P. orientalis is the principal vector of VL in this endemic focus.

A new molecular surveillance system for leishmaniasis

Presently, global efforts are being made to control and eradicate the deadliest tropical diseases through the improvement of adequate interventions. A critical point for programs to succeed is the prompt and accurate diagnosis in endemic regions. Rapid diagnostic tests (RDTs) are being massively deployed and used to improve diagnosis in tropical countries. In the present report, we evaluated the hypothesis of, after use for diagnosis, the reuse of the Leishmania RDT kit as a DNA source, which can be used downstream as a molecular surveillance and/or quality control tool. As a proof of principle, a polymerase chain reaction-based method was used to detect Leishmania spp. minicircle kinetoplast DNA from leishmaniasis RDT kits. Our results show that Leishmania spp. DNA can be extracted from used RDTs and may constitute an important, reliable, and affordable tool to assist in future leishmaniasis molecular surveillance methods.

The burden of parasitic zoonoses in Nepal: a systematic review

Background

Parasitic zoonoses (PZs) pose a significant but often neglected threat to public health, especially in developing countries. In order to obtain a better understanding of their health impact, summary measures of population health may be calculated, such as the Disability-Adjusted Life Year (DALY). However, the data required to calculate such measures are often not readily available for these diseases, which may lead to a vicious circle of under-recognition and under-funding.

Methodology

We examined the burden of PZs in Nepal through a systematic review of online and offline data sources. PZs were classified qualitatively according to endemicity, and where possible a quantitative burden assessment was conducted in terms of the annual number of incident cases, deaths and DALYs.

Principal Findings

Between 2000 and 2012, the highest annual burden was imposed by neurocysticercosis and congenital toxoplasmosis (14,268 DALYs [95% Credibility Interval (CrI): 5450–27,694] and 9255 DALYs [95% CrI: 6135–13,292], respectively), followed by cystic echinococcosis (251 DALYs [95% CrI: 105–458]). Nepal is probably endemic for trichinellosis, toxocarosis, diphyllobothriosis, foodborne trematodosis, taeniosis, and zoonotic intestinal helminthic and protozoal infections, but insufficient data were available to quantify their health impact. Sporadic cases of alveolar echinococcosis, angiostrongylosis, capillariosis, dirofilariosis, gnathostomosis, sparganosis and cutaneous leishmaniosis may occur.

Conclusions/Significance

In settings with limited surveillance capacity, it is possible to quantify the health impact of PZs and other neglected diseases, thereby interrupting the vicious circle of neglect. In Nepal, we found that several PZs are endemic and are imposing a significant burden to public health, higher than that of malaria, and comparable to that of HIV/AIDS. However, several critical data gaps remain. Enhanced surveillance for the endemic PZs identified in this study would enable additional burden estimates, and a more complete picture of the impact of these diseases.

Various parasites that infect humans require animals in some stage of their life cycle. Infection with these so-called zoonotic parasites may vary from asymptomatic carriership to long-term morbidity and even death. Although data are still scarce, it is clear that parasitic zoonoses (PZs) present a significant burden for public health, particularly in poor and marginalized communities. So far, however, there has been relatively little attention to this group of diseases, causing various PZs to be labeled neglected tropical diseases. In this study, the authors reviewed a large variety of data sources to study the relevance and importance of PZs in Nepal. It was found that a large number of PZs are present in Nepal and are imposing an impact higher than that of malaria and comparable to that of HIV/AIDS. These results therefore suggest that PZs deserve greater attention and more intensive surveillance. Furthermore, this study has shown that even in settings with limited surveillance capacity, it is possible to quantify the impact of neglected diseases and, consequently, to break the vicious circle of neglect.

Application of molecular techniques in the study of natural infection of Leishmania infantum vectors and utility of sandfly blood meal digestion for epidemiological surveys of leishmaniasis

Epidemiological studies on the distribution of leishmaniasis caused by Leishmania infantum Nicolle, 1908 (Kinetoplastida: Trypanosomatidae) have been based principally on serological surveys of the canine reservoir. This methodology is useful due to the facility of sampling, the rapidity in obtaining results, its consistency and because it allows the detection of heterogeneous foci of canine leishmaniasis (CanL) even in small areas. Other investigations have analysed Leishmania parasitism in sandflies (Diptera: Psychodidae: Phlebotominae) by using classical dissection techniques. These techniques allow the vector species to be incriminated in different foci, although they suffer from being very time consuming. Lately, studies in this field are increasingly using molecular techniques, which are faster and easier to perform. In the present work, we applied a nested-PCR in a study of natural infection of sandflies by Leishmania in three isolated farms where serological data on canine leishmaniasis of local dogs were also obtained. The analysis allowed the detection of 38.7% of females with positive nested-PCR (78%, 18% and 0%, respectively, in the different isolated farms). The positive Leishmania DNA samples were genotyped and identified as L. infantum. The results of this work provide new data for the vectorial capacity of Phlebotomus ariasi in a Pyrenean area, which can be considered at risk of becoming a new focus of CanL. The females with positive nested-PCR displayed blood in the midgut at different degrees of digestion, and/or were gravid. According to the multivariate logistic regression analysis, the risk of nested-PCR-positivity increased significantly with the degree of blood digestion (OR = 1.3; P value = 0.025). The Phlebotomus species and the presence of eggs were not statistically associated with nested-PCR positivity (P value of >0.05). The correlation of positive nested-PCR results with the presence of seropositive dogs in the farm confirms the utility of this technique in the study of the distribution and intensity of leishmaniasis foci. Also, the importance of sandfly blood-meal digestion for epidemiological surveys of leishmaniasis foci has been demonstrated.

Zoophilic feeding behaviour of phlebotomine sand flies in the endemic areas of cutaneous leishmaniasis of Sindh Province, Pakistan

Leishmania (Leishmania) major has been identified as the major causative agent of cutaneous leishmaniasis in Sindh Province of southern Pakistan. To make a rational approach for understanding the pathogen transmission cycles, the sand fly species and their natural blood meals in the endemic areas were examined. Total DNA was individually extracted from sand flies collected in four villages in Sindh Province. PCR-RFLP (restriction fragment length polymorphism) and sequence analysis of the 18S ribosomal RNA gene revealed that female sand flies identified were Sergentomyia clydei/Sergentomyia ghesquierei/Sergentomyia magna (68.6%), Sergentomyia dubia (17.1%), Phlebotomus papatasi (7.4%), Phlebotomus alexandri-like sand flies (3.4%) and Sergentomyia dentata (3.4%). PCR amplification of leishmanial kinetoplast DNA did not result in positive signals, suggesting that all 175 tested female sand flies were not infected with leishmanial parasites or contained undetectable levels of leishmanial DNA. Amplification and sequencing of the vertebrate cytochrome b gene in 28 blood-fed sand flies revealed that P. papatasi fed on cattle and wild rat whereas P. alexandri-like specimens fed on human, cattle, goat and dog. Although Sergentomyia sand flies are generally known to feed on cold-blooded animals, S. clydei, S. dubia and S. ghesquierei preferred humans, cattle, goat, sheep, buffalo, dog, donkey, wild rat and Indian gerbil. The epidemiological significance of the zoophilic feeding on various host species by Phlebotomus and Sergentomyia sand flies in Pakistan is further required to study for better understanding the zoonotic transmission of sand-fly-borne pathogens and for appropriate management of the vectors.

Visceral leishmaniasis in the Indian subcontinent: modelling epidemiology and control

BACKGROUND

In the Indian subcontinent, about 200 million people are at risk of developing visceral leishmaniasis (VL). In 2005, the governments of India, Nepal and Bangladesh started the first regional VL elimination program with the aim to reduce the annual incidence to less than 1 per 10,000 by 2015. A mathematical model was developed to support this elimination program with basic quantifications of transmission, disease and intervention parameters. This model was used to predict the effects of different intervention strategies.

METHODS AND FINDINGS

Parameters on the natural history of Leishmania infection were estimated based on a literature review and expert opinion or drawn from a community intervention trial (the KALANET project). The transmission dynamic of Leishmania donovani is rather slow, mainly due to its long incubation period and the potentially long persistence of parasites in infected humans. Cellular immunity as measured by the Leishmanin skin test (LST) lasts on average for roughly one year, and re-infection occurs in intervals of about two years, with variation not specified. The model suggests that transmission of L. donovani is predominantly maintained by asymptomatically infected hosts. Only patients with symptomatic disease were eligible for treatment; thus, in contrast to vector control, the treatment of cases had almost no effect on the overall intensity of transmission.

CONCLUSIONS

Treatment of Kala-azar is necessary on the level of the individual patient but may have little effect on transmission of parasites. In contrast, vector control or exposure prophylaxis has the potential to efficiently reduce transmission of parasites. Based on these findings, control of VL should pay more attention to vector-related interventions. Cases of PKDL may appear after years and may initiate a new outbreak of disease; interventions should therefore be long enough, combined with an active case detection and include effective treatment.

Case report: Expansion of visceral leishmaniasis to the western hilly part of Nepal

We report the first case of visceral leishmaniasis (VL) from the non-endemic western hilly region of Nepal. The patient presented with a history of high-grade fever, abdominal distension, anemia, and weight loss. The case was confirmed as VL by microscopical detection of the Leishmania species amastigote in bone marrow aspiration and by a positive result for the rK39 test. The patient was treated with 0.5-1.0 mg/kg of Amphotericin B for 14 days (total of 405 mg), and amastigotes were negative on discharge. Five months later, this patient again developed fever, abdominal distension, and anemia. Clinical and hematological examinations suggested a relapse of VL. The patient was treated with 1 mg/kg of Amphotericin B for 18 days (total of 515 mg) and was clinically improved on discharge.

Development of an enzyme-linked immunosorbent assay to identify host-feeding preferences of Phlebotomus species (Diptera: Psychodidae) in endemic foci of visceral leishmaniasis in Nepal

Anthroponotic visceral leishmaniasis, transmitted by Phlebotomus argentipes Annandale & Brunetti (Diptera: Psychodidae) sand flies, is regarded as a major problem of public health importance in the Indian subcontinent. Understanding the feeding behavior of the vector can be used to investigate changes in human-vector contact during intervention programs. An enzyme-linked immunosorbent assay (ELISA) was modified to make it suitable to identify the origin of P. argentipes and Phlebotomus papatasi Scopoli (Diptera: Psychodidae) blood meals. The sensitivity and specificity of the precipitin ring test and ELISA were compared, as well as the stability of the tests across different stages of blood meal digestion. The ELISA was more sensitive and specific than the precipitin test for identifying the sources of blood meals. When using the ELISA method with a plate reader, it was possible to obtain 100% sensitivity and specificity. When comparing the techniques across digestion stages, it was found that there was a drop in sensitivity, 48 and 72 h postblood meal for precipitin and visually read ELISA, respectively. However, the sensitivity of the ELISA using a plate reader was not altered by the digestion time. The feeding habits of P. argentipes and P. papatasi from the Terai region of Nepal, determined by the ELISA developed, showed P. papatasi to be highly anthropophilic, and P. argentipes appeared to feed both on humans and animals, in particular bovines.

Diagnosis of visceral leishmaniasis by polymerase chain reaction of DNA extracted from Giemsa's solution-stained slides

Visceral leishmaniasis (VL) is caused by the protozoan parasite Leishmania donovani and is a potentially fatal disease in endemic areas of the world. Nepal is an endemic area in which VL causes major public health problems in the lowland areas of the southeast regions. The aim of the present study was to evaluate the sensitivity of polymerase chain reaction (PCR) amplification for the detection of Leishmania DNA from Giemsa's solution-stained bone marrow slides. Bone marrow samples were aspirated from a total of 115 VL suspected patients and used to prepare smears on glass slides and for the initiation of in vitro culture. Bone marrow slides were used for microscopic observation, DNA extraction, and subsequent PCR amplification. PCR analysis showed that all the positive samples were of Leishmania parasites. The PCR assay also showed a higher sensitivity (69%) than microscopic examination (57%) and culture (21%). In addition, PCR was able to detect VL in 12% of samples which were negative by microscopy. PCR of DNA extracted from Giemsa's solution-stained bone marrow slides is a suitable tool for confirming diagnosis in patients with VL and may also be useful in the diagnosis of difficult cases. Bone marrow smears are easily stored and can be easily sent to research centers where PCR is available. This makes PCR a good option for diagnosis in the field.

Spatial analysis of Leishmania donovani exposure in humans and domestic animals in a recent kala azar focus in Nepal

SUMMARY

Visceral leishmaniasis (VL) is a major public health problem in the Indian subcontinent where the Leishmania donovani transmission cycle is described as anthroponotic. However, the role of animals (in particular domestic animals) in the persistence and expansion of VL is still a matter of debate. We combined Direct Agglutination Test (DAT) results in humans and domestic animals with Geographic Information System technology (i.e. extraction maps and scan statistic) to evaluate the exposure to L. donovani on these 2 populations in a recent VL focus in Nepal. A Poisson regression model was used to assess the risk of infection in humans associated with, among other factors, the proportion of DAT-positive animals in the proximities of the household. The serological results showed that both humans and domestic animals were exposed to L. donovani. DAT-positive animals and humans were spatially clustered. The presence of serologically positive goats (IRR=9.71), past VL cases (IRR=2.62) and the proximity to a forest island dividing the study area (IRR=3.67) increased the risk of being DAT-positive in humans. Even if they are not a reservoir, domestic animals, and specially goats, may play a role in the distribution of L. donovani, in particular in this new VL focus.

Molecular epidemiology for vector research on leishmaniasis

Leishmaniasis is a protozoan disease caused by the genus Leishmania transmitted by female phlebotomine sand flies. Surveillance of the prevalence of Leishmania and responsive vector species in endemic and surrounding areas is important for predicting the risk and expansion of the disease. Molecular biological methods are now widely applied to epidemiological studies of infectious diseases including leishmaniasis. These techniques are used to detect natural infections of sand fly vectors with Leishmania protozoa and are becoming powerful tools due to their sensitivity and specificity. Recently, genetic analyses have been performed on sand fly species and genotyping using PCR-RFLP has been applied to the sand fly taxonomy. In addition, a molecular mass screening method has been established that enables both sand fly species and natural leishmanial infections to be identified simultaneously in hundreds of sand flies with limited effort. This paper reviews recent advances in the study of sand flies, vectors of leishmaniasis, using molecular biological approaches.

Molecular epidemiology of leishmaniasis in Asia (focus on cutaneous infections)

PURPOSE OF REVIEW

Leishmaniasis has a wider geographical distribution than before. This review focuses on molecular epidemiological studies of new foci of cutaneous leishmaniasis in South and Southeast Asia.

RECENT FINDINGS

In Pakistan, the main causative agent in southern dry areas was determined as Leishmania major followed by Leishmania tropica. There was no correlation between the skin lesion types and the causative species. In the western Indian Himalayas, L. tropica and Leishmania donovani have been reported as the causative pathogens. In Nepal, molecular methods revealed the first case of L. major cutaneous leishmaniasis. Microsatellite analysis of Sri Lankan strains isolated from cutaneous leishmaniasis patients identified L. donovani strains that were closely related to a group of visceral L. donovani isolates from India, Bangladesh, and Nepal. In Taiwan, a third case of indigenous cutaneous leishmaniasis was reported, and the parasite was L. tropica.

SUMMARY

The distribution of cutaneous leishmaniasis has expanded definitively in South and Southeast Asia. Because the possible sandfly vector species are distributed widely over the disease endemic areas, further epidemiological studies are required. Microsatellite analysis of the parasites will be a powerful tool for population genetic and epidemiological studies of Leishmania species in Asia.