Asymptomatic dogs are highly competent to transmit Leishmania (Leishmania) infantum chagasi to the natural vector

Serosurvey of canine leishmaniasis in five departments near an identified human clinical case in Marseille (France)

Leishmania infantum is a protozoan parasite of the family Trypanosomatidae, transmitted by the bite of phlebotomine sand flies (Diptera: Psychodidae). It is responsible for human and canine leishmaniasis in countries bordering the Mediterranean basin. Here we describe a clinical case of human cutaneous leishmaniasis in a 76-year-old female patient living in Marseille. Upon interrogation, the patient had no history of recent travel or contact with animals. The study involved clinical, serological, and molecular investigation of the occurrence of Leishmania infection in 718 dogs from five departments within a 130 km radius perimeter around Marseille. Five dogs showed signs of moderate leishmaniasis. Additionally, the serological survey of dogs revealed a global seroprevalence of 5.1%, with a significantly different prevalence in the Vaucluse department. Molecular analysis and phylogenetic studies highlighted the close relatedness of Leishmania strains between human and canine hosts with 99.6% of identity, indicating local transmission. The findings underscore the importance of serological surveillance in dogs and human. In a One Health approach, it is necessary to continue investigating Leishmania infection in all potential reservoirs, especially for zoonotic L. infantum in wildlife (red foxes, leporids, rodents, etc.) but also in dogs, cats, and equids.

Canine vector-borne infections of working dogs of the Sri Lanka Air Force, and free roaming, and privately owned dogs

Canine vector-borne infections (CVBIs) are a global health problem. The military working dogs of Sri Lanka die at an early age, and CVBIs have been a leading speculated cause. We examined CVBIs in the working dogs of the Sri Lanka air force (SLAF) and free-roaming dogs (FRDs) and privately owned dogs (PODs) country-wide. Giemsa-stained smears were prepared and conventional PCR-positive DNA was subjected to sequencing and phylogeny. Of the 668 dogs sampled, 212 (31.7%) had one or more CVBIs. The prevalence of infections among the FRDs (40.0%) was significantly higher than SLAF working dogs (30.0%; χ2 = 10.5216; p = 0.0012) and PODs (26.2%; χ2 = 5.3414, p = 0.0208) but not between SLAF dogs and PODs (χ2 = 1.7655, p = 0.1838). Many infected dogs were asymptomatic (57.4%), which was higher among the FRDs. Seven infectious agents were identified: Babesia gibsoni, B. canis, Ehrlichia canis, Anaplasma platys, Leishmania sp., Hepatozoon canis, and filaria worms. The most common infection was B. gibsoni (13.8%), followed by E. canis (9.9%). Three tick species: Rhipicephalus linneai, Rhipicephalus haemaphysaloides and Haemophysalis bispinosa were found infesting the dogs. The SLAF dogs were thoroughly quarantined upon arrival, but the infection prevalence was similar to PODs.

Efficacy of a combination of nucleotides and lactoferrin in maintaining stable or improving the clinical picture and laboratory findings of leishmaniotic dogs: A randomized controlled study

This prospective, randomized, controlled, therapeutic study aimed to evaluate the efficacy of a product containing nucleotides and lactoferrin in maintaining or improving the clinical picture and laboratory findings of canine leishmaniosis (CanL). The safety and tolerance of this combination were also assessed. Forty Leishmania infantum-seropositive dogs, not requiring leishmanicidal and/or leishmaniostatic treatment, were enrolled in the study and randomized into treatment (TG) and placebo (CG) groups. Products A (containing nucleotides and lactoferrin) and B (placebo) were blindly administered to TG and CG, respectively, as palatable tablets at a rate of 1 tablet per 10 kg of weight once every 24 h for 6 months. Following inclusion (T0), dogs were followed up after 3 (T90) and 6 (T180) months. At each time point, for all animals enrolled physical examination and laboratory tests (complete blood count, biochemical panel including C-reactive protein [CRP] and ferritin, and serum protein electrophoresis) were performed. The immunofluorescence antibody test to detect antibodies for L. infantum (T0, T180), Ehrlichia canis (T0, T90, and T180), and Anaplasma phagocytophilum (T0, T90, and T180) was executed. A CanL-dedicated clinical score, using a validated scale from 0 (i.e., absence of clinical signs) to 19, was assigned. Four dogs (n=2 in TG, n=2 in CG) did not complete the study. No statistically significant differences in CanL clinical score were observed between CG and TG at T0, T90 and T180. Both TG and CG showed significant variations in anti-L. infantum antibody titres (p=0.0001 and p=0.004, respectively). In TG, antibody titres decreased in 77.8 %, increased in 5.5 %, and remained stable in 16.7 % of dogs, while in CG, decreased in 27.8 %, increased in 50 %, and remained stable in 22.2 % of dogs. During the study, CRP and ferritin remained stable in TG and significantly increased in CG. At T180, 9 out of 18 dogs (50 %) enrolled in the CG, and 1 out of 18 (5.6 %) enrolled in the TG, developed an active form of leishmaniosis. No side effects were reported in any patient included. In conclusion, a 6-month oral administration of a supplement containing nucleotides and lactoferrin was effective in maintaining a stable clinical score, improving antibody titres and potentially reducing the progression from non-active to active forms in L. infatum seropositive dogs. Furthermore, the product was well-tolerated, easy to administer, and free of side effects.

Finding Priority Areas in the Evaluation of Strategies for the Prevention of Leishmaniasis in an Endemic Municipality of Brazil

Visceral leishmaniasis is a zoonotic disease that affects humans and dogs. The infection is endemic in the municipality of Araçatuba, São Paulo, Brazil. Given the role of dogs in the epidemiology of leishmaniasis, strategies to enhance surveillance and reduce transmission are focused on dogs. In this study, we retrospectively analyzed records of canine visceral leishmaniasis from 2013 to 2022. According to this database, the prevalence of dogs testing positive for leishmaniasis fluctuated, with an average of 65.04% (6590/10,133). Cases were clustered in 10 statistically significant areas. Environmental analyses identified a significant geographical association between animals testing positive and higher vegetation density rates compared with animals testing negative. The period from sample collection to diagnosis and euthanasia, as recommended by the Brazilian Ministry, correlated with disease prevalence and decreased over time. These findings serve to implement different action plans against leishmaniasis for each geographic region and to understand the impact and efforts of strategies in an endemic area.

Asymptomatic Leishmania infantum infection in dogs and dog owners in an endemic area in southeast France

The prevalence of asymptomatic leishmaniasis in dogs and their owners in the main endemic areas of France has not been studied to date. The objective of this study was to quantify asymptomatic Leishmania infantum infection in southeast France in healthy people and their dogs using molecular and serological screening techniques. We examined the presence of parasitic DNA using specific PCR targeting kinetoplast DNA (kDNA) and specific antibodies by serology (ELISA for dogs and Western blot for humans) among immunocompetent residents and their dogs in the Alpes-Maritimes. Results from 343 humans and 607 dogs were included. 46.9% (n = 161/343) of humans and 18.3% (n = 111/607) of dogs were PCR positive; 40.2% of humans (n = 138/343) and 9.9% of dogs (n = 60/607) were serology positive. Altogether, 66.2% of humans (n = 227) and 25.7% of dogs (n = 156) had positive serologies and/or positive PCR test results. Short-haired dogs were more frequently infected (71.8%, n = 112) than long-haired dogs (12.2%, n = 19) (p = 0.043). Dogs seemed to be more susceptible to asymptomatic infection according to their breed types (higher infection rates in scenthounds, gun dogs and herding dogs) (p = 0.04). The highest proportion of dogs and human asymptomatic infections was found in the Vence Region, corresponding to 28.2% (n = 20/71) of dogs and 70.5% (n = 31/44) of humans (4.5/100,000 people). In conclusion, the percentage of infections in asymptomatic humans is higher than in asymptomatic dogs in the studied endemic area. It is questionable whether asymptomatic infection in humans constitutes a risk factor for dogs.

Therapeutic success and failure in using miltefosine to treat dogs naturally infected with Leishmania infantum

In urban environments, domestic dogs (Canis familiaris) are a major reservoir for the parasite Leishmania infantum. Miltefosine has been used as the standard treatment for canine visceral leishmaniasis in Brazil. However, therapeutic failures have been reported. In the present study, two dogs (CG03 and CG06) with a diagnosis of infection by L. infantum underwent two cycles of treatment with miltefosine (Milteforan™ - Virbac®). Analyses showed increases in the parasite load of both CG03 and CG06, even after treatment. The clinical score of CG03 dropped from 1 to 0 (after one round of treatment), such that this dog became asymptomatic. CG06 showed clinical worsening, such that its score increased from 1 to 2. After the second therapeutic round, the parasite load in CG03 was found to have decreased, but it was still higher than before drug treatment even though this dog was physically asymptomatic. There was no decrease in the parasite load in CG06 and there was clinical worsening. The clinical response of these dogs to the treatment differed, but the parasite load remained high in both cases, which poses a risk to public health, making it essential take measures to prevent the sandfly vector from accessing the dog.

Diagnosis of Canine Visceral Leishmaniasis by Flow Cytometry Serology using the rMELEISH Multiepitope Antigen Coupled in a Functional Bead

BACKGROUND

Visceral leishmaniasis (VL) is a zoonotic disease, with dogs being the main reservoir of the Leishmania infantum parasite.

OBJECTIVE

To develop a new flow cytometry test to diagnosis canine VL (CVL) diagnosis.

METHODS

The current study addresses a new flow cytometry test using beads coupled to the multiepitope antigen rMELEISH.

RESULTS

In the study set of samples a sensitivity (87.1%) and specificity (89.9%) was observed. Considering the dogs' clinical status, 20/20 (100.0%) of the symptomatic sera tested positive, while 19/22 (86.4%) of the oligosymptomatic and 16/20 (80.0%) of asymptomatic were positive. In the non-infected control, all samples (0/30) tested as negative. In the cross-reaction control, the test was more efficient in dogs infected with L. braziliensis (2/10) and Trypanosoma cruzi (0/10), than those with Babesia canis (4/10) and Ehrlichia canis (4/10). Dogs immunized with different vaccines (Leishmune, Leish-Tec®, or LBSap) did not present serological reactivity.

CONCLUSION

The flow cytometry serology through coupling the antigen rMELEISH in functional beads showed high accuracy in diagnosing CVL.

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.

Prevalence and incidence of canine visceral leishmaniasis and its clinical-immunological features in an endemic area of the Brazilian Amazon

BACKGROUND

A cohort study for 2 years period analysed the prevalence, incidence and clinical-immunological features of canine Leishmania (L.) chagasi-infection in 316 mongrel dogs in a visceral leishmaniasis-endemic area in Pará State, Brazil.

OBJECTIVE/METHODS

Diagnosis of infection was performed by the indirect fluorescent antibody test (IFAT-IgG), the leishmanin skin test (LST) and a parasite search (from the popliteal lymph node aspiration) at the beginning of the study and at 6, 12 and 24 months intervals.

RESULTS

IFAT/LST revealed three immune profiles of infection: (I) IFAT(+) /LST(-) (81), (II) IFAT(-) /LST(+) (17) and (III) IFAT(+) /LST(+) (13). Prevalence of profiles I, II and III were 25.6, 5.4 and 4.1%, and an overall prevalence 35.1%. Incidence of profiles I, II and III were 5.4, 0.3 and 0.0%, and an overall incidence 5.7% dogs per month. Incidence at the age ranges <1 year, ≥1 year, <7 years and ≥7 years evidenced a highest rate in the age range <1 year (6.6% dogs per month). Parasitological diagnosis was positive in 19% dogs at the prevalence (85.7% profile I), and in 11% at the incidence (100% profile I). The clinical picture of 179 infected dogs showed 145 (81%) of profile I (82% subclinical); 21 (11.7%) of profile II (100% subclinical); and 13 (7.3%) of profile III (84.6% subclinical). Conversion from subclinical to sick dogs was higher (p < 0.05) in profile I (40.2%) than in profiles II (5.8%) and III (9%). Immunological conversion showed that only 3.2% of profile I dogs (prevalence) converted to LST(+) (two at the end of the first 6 months and 1 after 24 months), while 82.3% of profile II dogs converted to IFAT(+) (11 in the first 6 months, whereas three after 12 months). A 100% death rate was observed in dogs from profile I alone.

CONCLUSION

These results reinforce the need of adopting preventive strategies against CVL as early as in the first semester of the dog's life.

Modulation of Macrophage Redox and Apoptotic Processes to Leishmania infantum during Coinfection with the Tick-Borne Bacteria Borrelia burgdorferi

Canine leishmaniosis (CanL) is a zoonotic disease caused by protozoan Leishmania infantum. Dogs with CanL are often coinfected with tick-borne bacterial pathogens, including Borrelia burgdorferi in the United States. These coinfections have been causally associated with hastened disease progression and mortality. However, the specific cellular mechanisms of how coinfections affect microbicidal responses against L. infantum are unknown. We hypothesized that B. burgdorferi coinfection impacts host macrophage effector functions, prompting L. infantum intracellular survival. In vitro experiments demonstrated that exposure to B. burgdorferi spirochetes significantly increased L. infantum parasite burden and pro-inflammatory responses in DH82 canine macrophage cells. Induction of cell death and generation of mitochondrial ROS were significantly decreased in coinfected DH82 cells compared to uninfected and L. infantum-infected cells. Ex vivo stimulation of PBMCs from L. infantum-seronegative and -seropositive subclinical dogs with spirochetes and/or total Leishmania antigens promoted limited induction of IFNγ. Coexposure significantly induced expression of pro-inflammatory cytokines and chemokines associated with Th17 differentiation and neutrophilic and monocytic recruitment in PBMCs from L. infantum-seropositive dogs. Excessive pro-inflammatory responses have previously been shown to cause CanL pathology. This work supports effective tick prevention and risk management of coinfections as critical strategies to prevent and control L. infantum progression in dogs.

Same parasite, different outcomes: unraveling the epidemiology of Leishmania infantum infection in Brazil and Spain

Human leishmaniosis caused by Leishmania infantum is an important health problem worldwide. One of the main aspects arousing interest is the epidemiological scenario surrounding Le. infantum infection in the New World (NW) and Old World (OW). This parasite was introduced to the Americas during European colonization leading to different epidemiology outcomes, even more enigmatic in the face of global changes. Thus, this review aims to highlight the differences and similarities between Le. infantum epidemiology between Brazil (NW) and Spain (OW), as both countries are leading the total number of leishmaniosis cases in their respective continents. Grounded on a systemic view, this article also draws attention to possible common innovative strategies to rethink ways of controlling infections caused by Le. infantum.

The Program for the Control of Visceral Leishmaniasis in Brazil: The Effect of the Systematic Euthanasia of Seropositive Dogs as a Single Control Action in Porteirinha, a Brazilian City with an Intense Transmission of Visceral Leishmaniasis

BACKGROUND

Porteirinha is endemic for visceral leishmaniasis (VL), with intense disease transmission of the disease. We evaluated the impact of canine euthanasia as a single control measure on the incidence of VL in humans and canines.

METHODS

A prospective observational cohort study was carried out over four years (1998-2002) in 8 of the 12 neighborhoods of the city. The dynamics of canine visceral leishmaniasis (CVL) transmission were evaluated for 2 years, before beginning the screening-culling intervention. The comparative morbidity index (CMI) was used to stratify areas with the greatest risk of CVL, and the spatial distribution of human and canine VL cases was compared using univariate and bivariate K-functions.

RESULTS

Human cases conglomerated in three neighborhoods. Spatial clusters were detected for CVL in 1998, 2000, and 2001, but not in 1999, when greater spatial dispersion occurred. The screening and culling intervention reduced the number of human VL cases and decreased the incidence of CVL, mainly in neighborhoods with a high CMI.

CONCLUSIONS

The systematic euthanasia of seropositive dogs was shown to be an effective control action of the Program for Control of Visceral Leishmaniasis (PCLV) in Brazil. The fundamental role of domestic dogs in the epidemiological chain of VL was reaffirmed.

Immunogenic mapping of rDyn-1 and rKDDR-plus proteins and selection of oligopeptides by immunoblotting for the diagnosis of Leishmania infantum-infected dogs

Endemic in Brazil, visceral leishmaniasis (VL) is a zoonotic infection that is among the most important parasitic diseases transmitted by vectors. Dogs are the main reservoirs of canine leishmaniasis (CanL) and their identification is used in some countries as part of disease prevention and control measures in the canine and human population. In this context, serological tests are necessary, composed of antigens capable of correctly identifying infected dogs, minimizing the number of false-negative cases. This study aimed to identify more immunoreactive peptides derived from two previously described whole proteins (rDyn-1 and rKDDR-plus) and compare their performance to the control antigens rK39 and the crude extract for the detection of dogs infected with L. infantum, especially the asymptomatic ones. The three selected peptides and a mixture of them, along with the rDyn-1, rKDDR-plus, rK39, and crude extract antigens were evaluated using indirect ELISA with sera samples from 186 dogs with CanL, being asymptomatic (n = 50), symptomatic (n = 50), co-infected (n = 19), infected with Babesia sp. (n = 7), Ehrlichia sp. (n = 6), T. cruzi (n = 20) and uninfected (n = 34). The results showed that the rDyn-1 protein and the peptide mixture had the highest sensitivity (100% and 98.32%, respectively) and specificity (97.01 and 98.51, respectively). A high degree of kappa agreement was found for rDyn-1 protein (0.977), mixed peptides (0.965), rKDDR-plus protein (0.953), K-plus peptide 1 (0.930) and Dyn-1 peptide (0.893). The mixture of peptides showed the highest likelihood (65.87). The ELISA using the mixture of peptides and the rDyn-1 protein showed high performance for CanL serodiagnosis. More mix combinations of the peptides and additional extended field tests with a larger sample size are recommended.

Temporal relationship between human and canine visceral leishmaniasis in an urban area in southeastern Brazil: An application of the ARIMAX model

Visceral leishmaniasis (VL) is a neglected disease of public and animal health importance. With the urbanization of the disease, there is evidence of a temporal correlation between the occurrence of human (HVL) and canine (CVL) visceral leishmaniasis, usually with cases in dogs preceding those in humans. In this context, the objective of this study was to develop a time series model suitable for canine-human transmission of Leishmania infantum. Monthly cases of HVL and CVL from 2006 to 2018 in Belo Horizonte, Minas Gerais, Brazil, were evaluated, and monthly health indicators were calculated for HVL and CVL, i.e., incidence coefficient (HVL_IC) and proportion of seropositive dogs (PSD), respectively. The temporal relationship was evaluated using an autoregressive integrated moving average with exogenous variable (ARIMAX) model for two different periods (January 2006-August 2013 and September 2013-December 2018). During the 13 years studied, 1115 new cases of HVL and 103,358 dogs seropositive for CVL were recorded. HVL_IC and PSD exhibited decreasing trends throughout the first study period (January 2006-August 2013). According to the ARIMAX model adjusted for this period, there was a temporal relationship between HVL_IC and PSD, with HVL_IC being influenced by HVL_IC for the last two and five months and by PSD for the third previous month. For the second study period (September 2013-December 2018), it was not possible to fit an ARIMAX model. This study highlights the improvements made by VL surveillance since 2006 in Belo Horizonte and contributes to a better understanding of the epidemiology of the disease by public health policy-makers, doctors and veterinarians involved in the prevention and control of zoonoses.

Serodiagnosis of leishmaniasis in asymptomatic and symptomatic dogs by use of the recombinant dynamin-1-like protein from Leishmania infantum: A preliminary study

Visceral leishmaniasis (VL) is a fatal manifestation of an infection caused by intracellular protozoa of the Leishmania genus. In New World countries, VL is classified as a zoonotic disease with domestic dogs acting as its main reservoir. Asymptomatic dogs are as competent to transmit Leishmania to the vectors as symptomatic dogs, however current diagnostic tests are limited and present low sensitivity for this important group. The development of accurate tests is fundamental to the early diagnosis, treatment, and control of canine leishmaniasis. In this study, we investigated the use of a recombinant protein (dynamin-1-like protein, Dyn-1) from L. infantum, as a potential target antigen for leishmaniasis serodiagnosis in both symptomatic and asymptomatic dogs. The antigenic performance of the protein was evaluated by means of ELISA assays using sera from symptomatic (n = 25), asymptomatic (n = 34) and non-infected dogs (n = 36) using ELISA. In addition, sera from dogs experimentally infected with Trypanosoma cruzi (n = 49) and naturally infected with Babesia sp. (n = 8) were tested to evaluate possible cross-reactivity. A crude soluble antigen (CSA) of Leishmania was used as an antigen control and K39 and K26 were used as reference antigens because they are already widely used in commercial tests. rDyn-1-based assay showed the highest sensitivity (97%) compared to the antigens K39 (88%), K26 (86%) and crude extract (95%). The highest specificity among the tests was also obtained with the protein rDyn-1 (94%), compared with the other antigens K39 (81%), K26 (87%), and crude extract (77%). This study showed that the rDyn-1 ELISA assay was able to identify 100% of asymptomatic dogs, establishing its potential as a target for the diagnosis of canine leishmaniasis.

rMELEISH: A Novel Recombinant Multiepitope-Based Protein Applied to the Serodiagnosis of Both Canine and Human Visceral Leishmaniasis

BACKGROUND

visceral leishmaniasis (VL) is a critical public health problem in over ninety countries. The control measures adopted in Brazil have been insufficient when it comes to preventing the spread of this overlooked disease. In this context, a precise diagnosis of VL in dogs and humans could help to reduce the number of cases of this disease. Distinct studies for the diagnosis of VL have used single recombinant proteins in serological assays; however, the results have been variable, mainly in relation to the sensitivity of the antigens. In this context, the development of multiepitope-based proteins could be relevant to solving such problem.

METHODS

a chimeric protein (rMELEISH) was constructed based on amino acid sequences from kinesin 39 (k39), alpha-tubulin, and heat-shock proteins HSP70 and HSP 83.1, and tested in enzyme-linked immunosorbent (ELISA) for the detection of L. infantum infection using canine (n = 140) and human (n = 145) sera samples.

RESULTS

in the trials, rMELEISH was able to discriminate between VL cases and cross-reactive diseases and healthy samples, with sensitivity and specificity values of 100%, as compared to the use of a soluble Leishmania antigenic extract (SLA).

CONCLUSIONS

the preliminary data suggest that rMELEISH has the potential to be tested in future studies against a larger serological panel and in field conditions for the diagnosis of canine and human VL.

Can domestic dogs be considered a good reservoir of Leishmania (L.) infantum chagasi in an endemic area of nonulcerated cutaneous leishmaniasis in Southern Honduras?

Dogs are considered to be the main domestic reservoir associated with the transmission of Leishmania (L.) infantum chagasi to humans in endemic areas of visceral leishmaniasis in America. However, little is known about the role of canines as a source of infection in endemic areas of nonulcerated cutaneous leishmaniasis (NUCL). Therefore, the objective of the present study was to investigate the role of dogs as a possible reservoir of the parasite in Southern Honduras. Dogs (n = 107) living with individuals affected by NUCL were clinically examined and biological material was collected for parasitological and immunological diagnosis. Most animals showed a healthy appearance and a few presented slight weight loss (64%), alopecia (7%), onychogryphosis (5%) and skin lesions (1%). The overall seroprevalence of Leishmania infection based on the DDP ^® quick test and/or in-house ELISA serological test was 41%. The presence of the parasite’s DNA was confirmed in 94% of the dogs; however, the average parasite load in the buffy coat was low at 6.09 parasites/µL, ranging between 0.221 and 50.2. The skin of seropositive dogs examined by histopathology using paraffin sections stained by hematoxylin and immunohistochemistry did not show cutaneous lesions or parasite amastigotes. Based on the absence of parasites in the skin and the low parasite load detected in the buffy coat, it seems that the dog does not represent a good source of infection for the vector in the endemic area of NUCL transmission in Southern Honduras. Other domestic and/or wild animals should be investigated.

Pre-test probability and likelihood ratios for clinical findings in canine leishmaniasis

Canine leishmaniasis is a parasitic zoonosis mainly caused by L. infantum; an obligate intracellular protozoan transmitted by haematophagous insects of the genus Phlebotomus, which affects dogs and wild canids. The clinical implications of this disease are highly variable, since infected animals may remain asymptomatic (absence of observable clinical signs) or present a wide spectrum of clinical alterations and degrees of severity, including the death of the animal. Symptoms such as lymphadenomegaly, alopecia, weight loss, keratoconjunctivitis and onychogryphosis are usually the first diagnostic reference available. The objectives of this study are to evaluate the validity (sensitivity, specificity and likelihood ratios) and diagnostic utility (pre-test probability) of the clinical signs commonly associated with canine leishmaniasis based on the prevalence in the area and to explore the combination of symptoms that best predicts the diagnosis of canine leishmaniasis. It is a matched case-control study in the canine population of southern Spain based on the comparison of the findings collected in the clinical history and the results of the LeisSCAN quantitative ELISA. A total of 39 cases and 78 controls were analysed. Approximately 80% of the infected animals showed signs compatible with the disease. The most frequent alterations were cutaneous (64.1%), systemic (51.3%) and oculo-nasal (30.7%). The most useful signs to support this diagnosis were alopecia and epistaxis (LR+ 6.69 and 6.0, respectively) (pre-test leishmaniasis probability is ≥70% for prevalence ≥28% when alopecia or epistaxis is present), followed by lameness (LR+ 5.0). The combinations of signs that showed greater validity were alopecia with hyperkeratosis of the snout and alopecia with onychogryphosis (LR+ > 10). None of the observed signs or their combinations resulted useful to rule out the diagnosis (LR- 0.55 to 1.15). The results found show notable differences in the diagnostic value of the clinical signs, individually and in combination, so we believe that medical decisions should be based on their diagnostic validity (LR+) and the estimation of the pre-test and post-test probability.

Use of Antigen Combinations to Address Complex Leishmania-Seropositivity Patterns in Dogs Living in Canine Leishmaniosis Endemic Regions of Portugal

Canine leishmaniosis (CanL) is a vector-borne disease caused by Leishmania infantum. Infection in dogs can result in a disease with non-specific clinical signs or in a subclinical condition. Infection diagnosis is crucial to guide public health measures considering the zoonotic potential of L. infantum. Serological approaches to detect infection with a reduced antigen panel potentially limit the quality of the information obtained. To evaluate the impact of using distinct antigens in a serological survey, a cohort with 390 dogs from endemic regions in Portugal was subjected to a serological evaluation using ELISA and DAT. Using ELISA, six Leishmania-specific antigens in conjunction with a non-related antigen, Escherichia coli soluble antigens, were evaluated. The global seroprevalence was 10.5% for DAT and 15.4 to 23.1% for ELISA, depending on the antigen for the latter. Still, only 8.2% of the animals were seropositive to all Leishmania-specific antigens. Importantly, a further 31.0% presented antigen-dependent seropositivity. Considering this observation, a serological score system was proposed and validated to address the complex serology results. With this system, the overall dog seropositivity was 26.9%. This work highlights the limitations of single-antigen serological surveys and presents an approach that might contribute to the establishment of CanL-specific serological profiles.

First Report of Autochthonous Canine Leishmaniasis in Hong Kong

Canine leishmaniasis is a zoonotic disease caused by Leishmania infantum; transmitted by the bite of phlebotomine sand flies. Leishmania infantum amastigotes were identified by cytology from a locally born Hong Kong dog exhibiting nasal, cutaneous, and systemic disease who was part of a kennel of eight dogs. All eight kennel dogs were subsequently tested serologically by enzyme-linked immunosorbent assay (ELISA) and by polymerase chain reaction (PCR) followed by DNA sequencing for L. infantum infection. The local dog was seropositive and blood and splenic tissue were PCR positive for L. infantum whilst the other kennel dogs were negative on serology and PCR. Autochthonous transmission was suspected for the local dog as Hong Kong lacks known vectors of L. infantum. Either vertical transmission from the deceased dam who had previously died with disease suspicious for leishmaniasis or horizontal transmission from a second non-locally born kennel dog who had been diagnosed previously with leishmaniasis was possible. This is the first recorded autochthonous case of canine leishmaniasis in Hong Kong. Leishmaniasis should be considered as a differential for cutaneous or systemic illness in local untraveled dogs in Hong Kong. In addition, as dogs serve as L. infantum reservoirs for human infection attention should be paid to the possibility of leishmaniasis emerging in Hong Kong.

Humoral and Cellular Immune Response in Asymptomatic Dogs with Visceral Leishmaniasis: A Review

Visceral leishmaniasis is one of the deadliest parasitic diseases in the world and affects both humans and dogs. The host immune response to Leishmania infection plays a critical role in the evolution of canine visceral leishmaniasis (CVL) and consequently in the manifestation of clinical signs. The asymptomatic form of the disease is a major concern in the diagnosis of CVL and in the transmission control of Leishmania infection. Asymptomatic dogs are found in large proportions in endemic areas and are an unquantifiable source of infection. The present review analyzes the possible relationship between the activation of the antigen-specific immune response of the host and resistance or susceptibility to CVL. The review focuses on works that address the characterization of the humoral and cellular immune response profile, at both the functional and phenotypic levels, in infected dogs. Most studies relate the absence of clinical symptomatology to an increased proliferative response and a Th1 cytokine profile. Despite the numerous findings pointing to a differential immune response in asymptomatic dogs, the contradictory results reported in this review highlight the importance of establishing a precise clinical classification of the disease, performing more longitudinal studies, and including a higher number of animals in trials.

Visceral Leishmaniasis and the Skin: Dermal Parasite Transmission to Sand Flies

Visceral leishmaniasis is a parasitic disease with significant dermal tropism. The skin is an important site of infection contributing to parasite transmission to naïve sand flies, but understanding how parasitism of host skin and the related immune microenvironment supports or prevents skin parasite replication is now the focus of major investigation in the field of leishmaniasis research. Here, we review dermatoimmunology during visceral leishmaniasis (VL), dermal Leishmania parasite burden, and the role of skin parasitism in transmissibility to sand fly vectors. First, we discuss the epidemiology of VL amongst dogs, the primary zoonotic reservoir for human infection. We explore the association between spatial distribution and the burden of parasites in the skin in driving outward transmission. Factors associated with parasite persistence in the skin are examined. We discuss systemic immunity during VL and what is known about immunological correlates in the skin microenvironment. Finally, we touch on factors egested into the skin during Leishmania inoculation by sand flies. Throughout, we discuss factors associated with the early and chronic establishment of Leishmania parasites in the skin and the role of the dermal immune response.

Visceral leishmaniasis in a recent transmission region: 27.4% infectivity rate among seronegative dogs

American visceral leishmaniasis (VL) is a parasitic disease whose main domestic reservoir in the urban environment is dog and is considered one of the most important zoonoses in the context of public health. Serological tests are typically used for the diagnostic screening of the disease. This study aimed to analyse the performance of different methodologies used in the diagnosis of VL in dogs sampled from a recent transmission area. The sample consisted of 52 dogs separated into groups based on the absence and presence of clinical signs of VL. The following serological techniques were carried out: the DPP® rapid test (RT), the ALERE® RT and an RT and immunoenzymatic assay with a recently developed protein (rKDDR-plus). In addition, molecular techniques were carried out with conjunctival swabs, and bone marrow aspirate samples and parasitological samples were obtained directly from bone marrow aspirates. It was concluded that 27.4% of seronegative dogs were infected, but the serological tests, used as screening tests, showed unsatisfactory sensitivity results (average: 51.2%) for dogs without clinical signs. It was suggested that polymerase chain reaction with conjunctival swabbing be used as a screening test for dogs without clinical signs, as this is a non-invasive collection technique with high-sensitivity values.

The path of canine visceral leishmaniasis versus the path of Center for Zoonoses Control: contributions of spatial analysis to health

Visceral leishmaniasis (VL) is a public health problem in Brazilian municipalities. As much as there is a planning of public policies regards VL in São Paulo State, new cases have been reported and spread. This paper aims to discuss how the Center for Zoonoses Control conducts its actions spatially in endemic city of Presidente Prudente, São Paulo State. Data are from the Municipal Health Department of Presidente Prudente, Adolfo Lutz Institute, and Brazilian Institute of Geography and Statistics. We spatially estimated the dog population per census tract and used geoprocessing tools to perform choropleth maps, spatial trends, and spatial autocorrelation. We found a spatial pattern of higher prevalence in the city’s outskirt and a positive statistically significant spatial autocorrelation (I = 0.2, p-value < 0.000) with clusters of high-high relationships in the Northwest part of the city. Moreover, we identified a different direction in the path of the conducted serosurveys versus the canine VL trend, which stresses the fragility of the Center for Zoonoses Control actions to control the disease. The Center for Zoonoses Control always seems to chase the disease. The spatial analysis may be useful for rethinking how the service works and helps in public policies.

Spatial Point Pattern Analysis Identifies Mechanisms Shaping the Skin Parasite Landscape in Leishmania donovani Infection

Increasing evidence suggests that in hosts infected with parasites of the Leishmania donovani complex, transmission of infection to the sand fly vector is linked to parasite repositories in the host skin. However, a detailed understanding of the dispersal (the mechanism of spread) and dispersion (the observed state of spread) of these obligatory-intracellular parasites and their host phagocytes in the skin is lacking. Using endogenously fluorescent parasites as a proxy, we apply image analysis combined with spatial point pattern models borrowed from ecology to characterize dispersion of parasitized myeloid cells (including ManR+ and CD11c+ cells) and predict dispersal mechanisms in a previously described immunodeficient model of L. donovani infection. Our results suggest that after initial seeding of infection in the skin, heavily parasite-infected myeloid cells are found in patches that resemble innate granulomas. Spread of parasites from these initial patches subsequently occurs through infection of recruited myeloid cells, ultimately leading to self-propagating networks of patch clusters. This combination of imaging and ecological pattern analysis to identify mechanisms driving the skin parasite landscape offers new perspectives on myeloid cell behavior following parasitism by L. donovani and may also be applicable to elucidating the behavior of other intracellular tissue-resident pathogens and their host cells.

Seroepidemiology of visceral leishmaniasis among free-roaming dogs and children in Zahedan city, southeast of Iran, 2018-2020

BACKGROUND

Mediterranean visceral leishmaniasis (VL) or kala-azar is an endemic zoonotic disease in Iran. Domestic dogs are the primary reservoir host and source of VL infection. The high-risk populations are children and immune-deficient adults.

OBJECTIVE

Based on the lack of published reports about the VL in Sistan and Baluchestan province in the southeast of Iran, this study aimed to assess the seroprevalence of diseae in free-roaming dogs and children under 12 years old using indirect fluorescent antibody (IFA) test.

METHODS

This cross-sectional study was performed between 2018 and 2020 in Zahedan city, Sistan, and Baluchestan province. Blood samples were taken from 400 children under 12 years old with a fever history accompanied by at least another specific clinical presentation. In the same period, blood samples were collected from 150 stray dogs. Demographic characteristics and clinical manifestations in both humans and dogs were recorded. The IFA test examined all blood samples for the detection of anti-Leishmania infantum antibodies.

RESULTS

Overall, the IFA test results were positive in 8 dogs (5.33%). Only two seropositive dogs (25%) showed obvious clinical symptoms. There was a significant correlation between the positive cases, clinical signs (P = 0.046), and age (P = 0.037) in infected dogs. None of the collected sera from 400 febrile children were positive.

CONCLUSION

According to the present finding, it seems that VL is not endemic in Zahedan city, Sistan, and Baluchestan province, but the domestic cycle of L. infantum has been established in this area. Further investigations would be needed to estimate the status of VL infection in wild canines as a secondary potential reservoir host. Furthermore, periodic monitoring of disease must not be neglected.

Leishmania infantum xenodiagnosis from vertically infected dogs reveals significant skin tropism

BACKGROUND

Dogs are the primary reservoir for human visceral leishmaniasis due to Leishmania infantum. Phlebotomine sand flies maintain zoonotic transmission of parasites between dogs and humans. A subset of dogs is infected transplacentally during gestation, but at what stage of the clinical spectrum vertically infected dogs contribute to the infected sand fly pool is unknown.

METHODOLOGY/PRINCIPAL FINDINGS

We examined infectiousness of dogs vertically infected with L. infantum from multiple clinical states to the vector Lutzomyia longipalpis using xenodiagnosis and found that vertically infected dogs were infectious to sand flies at differing rates. Dogs with mild to moderate disease showed significantly higher transmission to the vector than dogs with subclinical or severe disease. We documented a substantial parasite burden in the skin of vertically infected dogs by RT-qPCR, despite these dogs not having received intradermal parasites via sand flies. There was a highly significant correlation between skin parasite burden at the feeding site and sand fly parasite uptake. This suggests dogs with high skin parasite burden contribute the most to the infected sand fly pool. Although skin parasite load and parasitemia correlated with one another, the average parasite number detected in skin was significantly higher compared to blood in matched subjects. Thus, dermal resident parasites were infectious to sand flies from dogs without detectable parasitemia.

CONCLUSIONS/SIGNIFICANCE

Together, our data implicate skin parasite burden and earlier clinical status as stronger indicators of outward transmission potential than blood parasite burden. Our studies of a population of dogs without vector transmission highlights the need to consider canine vertical transmission in surveillance and prevention strategies.

Incidence and geographical distribution of canine leishmaniosis in 2016-2017 in Spain and France

Leishmania infantum is transmitted by sand flies and causes visceral leishmaniasis (VL) in humans, as well as canine leishmaniosis (CanL) in dogs, the main reservoir of infection in Europe. The infection spread northwards in the last two decades, but case data are scarce, hindering monitoring and evaluation of incidence as is required by European WHO guidelines. We aim to identify the current geographical distribution of CanL incidence in Spain, which has been endemic for CanL, and France, where CanL is emerging. An online survey was conducted among veterinarians in Spain and France questioning CanL incidence in the years 2016-2017. These data were interpolated to estimate incidence in both countries using the geographical analysis ordinary kriging. Two hundred and seventy-three (273) veterinarians from 81 out of 148 French and Spanish districts completed the survey. The mean incidence in veterinary practices was 21 CanL cases per 1000 dogs during the past year, which was higher in Spain (31/1000 dogs/year) than in France (6/1000 dogs/year). Incidence rates were highest in south-eastern Spain, but sporadic cases were found up to the most northern regions of France. Our study confirms the northward spread of CanL in Spain and France, as the incidence rates were higher than reported in previous studies and cases were found in areas formerly considered non-endemic for L. infantum. Monitoring the reservoir of infection in dogs is essential for implementing timely and geographically-targeted interventions to prevent further spread of CanL and VL in Europe.

Canine Leishmaniosis in Greece: An Updated Countrywide Serological Study and Associated Risk Factors

Canine leishmaniosis (Leishmania infantum) is a zoonotic disease that affects dogs worldwide. Greece is enzootic for this disease, and updated data for its current distribution are of major importance. The aim of this cross-sectional serological study was primarily to update the current knowledge of Leishmania infantum seropositivity status within the asymptomatic Greek canine population and, furthermore, to assess the possible climatological and other risk factors. In total, sera of 1265 asymptomatic dogs were collected from all prefectures of the country. A questionnaire that included all individual dog information was completed for all animals. The Speed Leish K^® canine Leishmania antibody test kit (BVT Groupe Virbac, France) was employed. Potential risk factors were evaluated utilizing logistic regression models. Overall, 13.8% (n = 175) of the sampled dogs were seropositive to Leishmania infantum originating from all geographical departments of the country, whereas most prefectures had at least one seropositive animal. Outdoor living, high mean humidity, low mean wind speed and high total annual rainfall were found to increase the seropositivity status against the parasite. Conclusively, Leishmania infantum remains a common parasite challenge in the asymptomatic canine population of Greece, and therefore, its early diagnosis and effective prevention are significant in the country.

Impact of the dog population and household environment for the maintenance of natural foci of Leishmania infantum transmission to human and animal hosts in endemic areas for visceral leishmaniasis in Sao Paulo state, Brazil

When it comes to visceral leishmaniasis (VL) in Brazil, one of the main targets of public health policies of surveillance is the control of domestic canine reservoirs of Leishmania infantum. This paper aims to evaluate the effect of the dog population and household environment for the maintenance of natural foci in the transmission to human and animal hosts in an endemic city for VL, Bauru, in Brazil. We collected 6,578 blood samples of dogs living in 3,916 households from Nov.2019 to Mar.2020 and applied geospatial models to predict the disease risk based on the canine population. We used Kernel density estimation, cluster analysis, geostatistics, and Generalized Additive Models (GAM). To validate our models, we used cross-validation and created a receiver operating characteristic (ROC) curve. We found an overall canine VL (CVL) seroprevalence of 5.6% for the sampled dogs, while for the households, the positivity rate was 8.7%. Odds ratios (OR) for CVL increased progressively according to the number of canines for >2 dogs (OR 2.70); households that already had CVL in the past increased the chances for CVL currently (OR 2.73); and the cases of CVL increase the chances for human VL cases (OR 1.16). Our models were statistically significant and demonstrated a spatial association between canine and human disease cases, mainly in VL foci that remain endemic. Although the Kernel density ratio map had the best performance (AUC = 82), all the models showed high risk in the city's northwest area. Canine population dynamics must be considered in public policies, and geospatial methods may help target priority areas and planning VL surveillance in low and middle-income countries.

Canine Visceral Leishmaniasis in an Area of Sporadic Transmission in Brazil

Canine visceral leishmaniasis is a zoonotic disease caused by the protozoan Leishmania infantum in Latin America. Visceral leishmaniasis (VL) diagnosis in Brazil includes two serological tests according to the Ministry of Health (MH) protocol. Sensitivity and specificity of diagnostic tests, as well as clinical signs of VL, are usually reported in disease-endemic areas; however, it is known that local epidemiological factors can influence these results. This study aimed to evaluate the clinical features, sensitivity, and specificity of TR-DPP^® and EIE-LVC in naturally infected dogs in a region of sporadic VL transmission to humans in Brazil. A total of 288 dogs were clinically evaluated and serological and parasitological (lymph node aspirates) samples were collected for VL diagnosis. TR-DPP and EIE-LVC showed poor sensitivity (0.62 and 0.44, respectively) to detect infected animals, compared with the direct parasitological examination, which is considered a gold standard method. Thus, the protocol of MH presented low sensitivity (0.42) to estimate prevalence and control measures in this region. TR-DPP presented a high negative predictive value (0.89), resulting in its indication as a confirmatory test in sporadic transmission areas. Classical clinical signs of VL were not frequently observed; therefore, clinical scoring systems might not be useful in this region. Veterinarians of nonendemic areas should be alert for asymptomatic dogs, especially those presenting lymph adenomegaly.

Molecular and serological evaluation of zoonotic visceral leishmaniasis in dogs in a rural area of Fars province, southern Iran, as a source of Leishmania infantum infection

Canine visceral leishmaniasis (CVL) is endemic in the southern parts of Iran. The current study aimed at molecular and serological evaluation of zoonotic visceral leishmaniasis in dogs in Fars province, southern Iran. Blood samples were collected from 60 dogs in the three villages in Fars Province. Serum samples were tested for antibodies against L. infantum by direct agglutination test (DAT). DNA was extracted from each dog's buffy coat and tested by PCR, targeting the Leishmania ITS‐2 region. From a total of 60 studied dogs, 25 (41.7%) were female, and 35 (58.3%) were male. Dogs' age ranged from 1 to 7 years, with a mean age of 2.97 (±1.4) years. Anti‐Leishmania antibodies were detected in sera samples of 28 (46.7%) dogs, (titre ≥ 1:320). Out of 28 seropositive cases, 13 (46.4%) were female, and 15 (53.6%) were male. Association between seropositivity and dogs’ clinical signs was statistically significant (p < .05). Leishmania DNA was detected in the buffy coat of 3 of 60 studied dogs which were all seropositive by DAT. The PCR products were sequenced and molecular analysis showed that two of the isolates were Leishmania infantum, and one was L. tropica. The high proportion of seropositive dogs indicates the important role of these animals in the epidemiology of the disease in the region. Infected dogs with or without signs, especially those that are molecularly positive, can act as an active reservoir of the disease in the area.

Examining the Relationship of Clinical and Laboratory Parameters With Infectiousness to Phlebotomus perniciosus and Its Potential Infectivity in Dogs With Overt Clinical Leishmaniasis

Infected dogs are considered the main domestic animal reservoirs for Leishmania infantum parasite. Infectiousness to competent phlebotomine vectors has been associated with many factors, the main being the severity of the disease exhibited by infected dogs. This study examines the relationship between different clinical parameters and the infectiousness to colonized Phlebotomus perniciosus sand flies having a blood meal on dogs. Data obtained in the present study come from an untreated group of Leishmania sick dogs submitted to xenodiagnosis for the evaluation of a spot on insecticide solution. Seventeen dogs were diagnosed as affected by leishmaniasis through clinical examination, immunofluorescence antibody test (IFAT) serology, and loop-mediated isothermal amplification (LAMP). The disease severity (clinical score) was staged by using a numeric value derived from eight clinical and parasitological parameters. Xenodiagnosis was performed on caged dogs exposed for 1.5 h to sand-fly bites. The following parameters related to sand flies were examined: blood feeding (% of blood engorged females), promastigote detection (% of promastigote-positive sand flies), promastigote burden, and the promastigote stage maturation (potential transmissibility rate). Statistical relationship between the clinical score and entomological parameters was investigated, as well as the possible correlation between each clinical and laboratory parameters and sand fly infection/infectivity. The severity of clinical score may influence the blood feeding by, and the probability of promastigote detection in, sand flies; skin lesions seem to be the main factor that influences the rate of blood feeding. Promastigote burden is related to IFAT titer, skin lesions, and clinical score. All entomological parameters are strongly related among them. This study confirms that both P. perniciosus infection and infectivity are influenced by a dog's clinical condition.

Phase II validation study of the rK39 ELISA prototype for the diagnosis of canine visceral leishmaniasis in Brazil

Dogs are the main reservoirs in the domestic transmission cycle of visceral leishmaniasis, and the diagnosis is essential for the effectiveness of the control measures recommended by the Brazilian Ministry of Health. We assessed the diagnostic performance of the ELISA-Vetlisa/BIOCLIN prototype with serum samples from 200 dogs, in triplicate, including symptomatic, oligosymptomatic, asymptomatic, and healthy dogs, originated by two distinct panels (A and B) characterized by parasitological tests as the reference standard. In this study, the prototype kit showed a 99% sensitivity (95%CI: 94.5-100.0) and a 100% specificity (95%CI: 96.4-100.0). The sensitivity of the prototype kit did not vary significantly with the clinical status of the dogs. Considering the final result classification (positive or negative), agreement between the results of repeated tests was almost perfect (kappa = 0.99; 95%CI: 0.98-1.00). ELISA-Vetlisa/BIOCLIN is a promising option for the serological diagnosis of canine visceral leishmaniasis in Brazil.

Assessing L. donovani Skin Parasite Load: A Proof of Concept Study of a Microbiopsy Device in an Indian Setting

Background

In the endgame of the elimination initiative of visceral leishmaniasis (VL) on the Indian subcontinent, one of the main questions remaining is whether asymptomatically infected individuals also contribute to transmission. We piloted a minimally invasive microbiopsy device that could help answer this question. While the potential of this device has been previously illustrated in Ethiopia, no such information is available for the setting of the Indian subcontinent. In this proof of concept study we aimed to assess 1) to what extent skin parasite load obtained with the new microbiopsy device correlates with disease status, 2) to what extent skin parasite load correlates with blood parasite load in the same subject, and 3) to what extent the skin parasite load obtained from different sampling sites on the body correlates with one another.

Methods

We performed a pilot study in Bihar, India, including 29 VL patients, 28 PKDL patients, 94 asymptomatically infected individuals, 22 endemic controls (EC), and 28 non-endemic controls (NEC). Presence of infection with L. donovani in the blood was assessed using Direct Agglutination Test, rK39 ELISA, Whole Blood Analysis measuring IFN-γ and qPCR. A skin sample was collected with the microbiopsy device on two different locations on the body. PKDL patients provided a third skin sample from the edge of a PKDL lesion. Parasite load in the skin was measured by qPCR.

Findings

We found a clear correlation between the skin parasite load obtained with the microbiopsy device and disease status, with both higher skin parasite loads and higher proportions of positive skin samples in VL and PKDL patients compared to asymptomatics, EC, and NEC. No clear correlation between skin parasite load and blood parasite load was found, but a moderate correlation was present between the skin parasite load in arm and neck samples. In addition, we found four positive skin samples among asymptomatic individuals, and 85% of PKDL lesions tested positive using this microbiopsy device.

Conclusions

In line with previous pilot studies, our results from an Indian setting suggest that the microbiopsy device provides a promising tool to measure skin parasite load, and – if validated by xenodiagnosis studies – could facilitate much needed larger scale studies on infectiousness of human subgroups. In addition, we advocate further evaluation of this device as a diagnostic tool for PKDL.

Cytokine profile and parasite load in lymph nodes of dogs naturally infected with Leishmania infantum from distinct epidemiological scenarios in São Paulo State, Brazil

Visceral leishmaniasis (VL) is an important zoonotic vector-borne disease and domestic dogs are considered the main domiciliary and peri-domiciliary reservoir of Leishmania (Leishmania) infantum in South America. Distinct eco-epidemiological scenarios associated to the prevalence of the disease, clusters of parasite genotypes and chemotypes of vectors population are described in Brazil, especially in the state of São Paulo (SP). In this context, the purpose of the present study is to evaluate the clinical signs, histopathological lesions, parasite load and cytokine profile by immunohistochemistry (IHC) in popliteal lymph nodes of canines naturally infected with L. infantum, from different municipalities of the state of SP. Eighty-three dogs with VL, 61 from northwest SP (NWSP) and 22 from southeast SP (SESP), were clinically classified in stage II, with no babesiosis and ehrlichiosis. Subcapsular inflammatory infiltration and histiocytosis were significantly higher in the SESP group (p = 0.0128; 0.0077, respectively). On the other hand, dogs from NWSP revealed 4.6-fold significantly higher parasite burden (p = 0.0004) and higher IHC scores of IL-1β (p = 0.0275) and IL-4 (p = 0.0327) in the popliteal lymph node tissues, which may be associated with the susceptibility and progression of the disease in these dogs. Differences in immune response profile associated with higher parasite load in dogs can also contribute to explain the distinct eco-epidemiological patterns of VL in specific geographic regions.

Correlations between tissue parasite load and common clinical signs in dogs naturally infected by Leishmania infantum

qPCR is being used for the quantification of parasite load in different tissues of dogs infected by Leishmania infantum with or without clinical manifestations. It may be employed in the diagnosis, monitoring of the infection during treatment, and clinical studies for validation of vaccines. Aimed at enhancing the molecular diagnosis and the subsequent monitoring of the infection, this study evaluated the parasite load in several tissues from dogs infected by Leishmania infantum, showing different clinical status. Thus, the qPCR was performed on skin, conjunctival swab, popliteal lymph node, and bone marrow puncture samples taken from 65 dogs naturally infected by L. infantum. Dogs were divided into three groups per clinical score: group 1 (n = 12), included animals with zero points and no clinical manifestations of the disease; group 2 (n = 35), included animals with a score ranging from 1 to 5 points and moderate clinical manifestations; and group 3 (n = 18), included dogs with a score ranging from 6 to 11 points and intensive clinical manifestations. Another analysis was performed classifying the animals into two groups, considering the presence of, or lack of clinical signs of the disease. Analyses of these results showed that the skin was the tissue with a higher parasite load, followed by popliteal lymph node and bone marrow punctures, and conjunctival swab samples having the lowest loads. Furthermore, the skin was also the tissue with the highest parasite load when evaluating the groups individually. Animals in group 3, with intensive clinical manifestations, showed a higher parasite load in different tissues when compared to animals from groups 1 and 2. Finally, animals with clinical manifestations of the disease showed a higher parasite load when compared to dogs with no manifestations. The importance of the dog as a reservoir of L. infantum in nature is reinforced by the demonstration of skin having the highest amount of parasites/μL in this study's analysis, as well as the fact that skin is the main point of access to the parasite vector. Also, a strong and positive correlation between the intensity of clinical manifestations and the increase of parasite load in the skin was observed. In conclusion, skin was the tissue that was demonstrated to be the best option for the molecular diagnosis of L. infantum infection in dogs with varying clinical statuses used in this study.

Identification and characterization of the hemoglobin-binding domain of hemoglobin receptor in Leishmania

Leishmania internalize hemoglobin (Hb) via a specific receptor (HbR) for their survival. To identify the Hb-binding domain of HbR, we cloned and expressed several truncated proteins of HbR and determined their ability to bind Hb. Our findings reveal that 90% of Hb-binding activity is retained in HbR^41-80 in comparison with HbR^1-471 . We synthesized a 40 amino acid peptide (SSEKMKQLTMYMIHEMVEGLEGRPSTVRMLPSFVYTSDPA) corresponding to HbR^41-80 and found that it specifically binds Hb. Subsequently, we found that the HbR^41-80 peptide completely blocks Hb uptake in both promastigote and amastigote forms of Leishmania and, thereby, inhibits the growth of the parasite. These results demonstrate that HbR^41-80 is the Hb-binding domain of HbR, which might be used as a potential therapeutic agent to inhibit the growth of Leishmania.

A lateral flow immunoassay based on colored latex particles for detection of canine visceral leishmaniasis

Canine visceral leishmaniasis (CVL) is the major source of human visceral leishmaniasis. To control the spread of this disease, early and accurate detection of infected dogs is critical but challenging. The serological diagnosis of CVL remains problematic because there are no reliable commercially available tests. Most laboratories use enzyme-linked immunosorbent assay or the indirect immunofluorescent antibody test. These tests use Leishmania chagasi recombinant antigens K39 or K26 assembled with either gold-labelled Staphylococcus aureus protein A or protein G from Streptococcus pyogenes. In this work, we propose the development, optimization and standardization of a lateral flow immunoassay (LFIA) based on functionalized colored particles and a specific recombinant antigen, as a visual in situ method for the diagnosis of CVL. The following analysis variables were considered: (i) the concentration of the latex-protein complex; (ii) the dilution of the serum; (iii) the composition of the employed buffers; (iv) the nominal capillary flow time through the nitrocellulose membrane; (v) the concentration of reagents fixed in the test and control lines; (vi) the particle size of the colored latex; and (vii) the conjugation method. Then, the obtained strips were evaluated as a visual diagnostic tool based on a panel of positive and negative sera. It was observed that because of its simplicity and performance the LFIA test is a quick and reliable alternative for the diagnosis of CVL either in conventional laboratories or for remote areas where laboratories are not readily accessible for conventional assays.

In vitro Infectivity of Strains Isolated From Dogs Naturally Infected With Leishmania infantum Present a Distinct Pathogenic Profile in Hamsters

Visceral leishmaniasis (VL) is a severe disease caused by Leishmania infantum. Dogs are the parasite's main reservoir, favoring its transmission in the urban environment. The analysis of L. infantum from infected dogs contributes to the identification of more virulent parasites, thereby supporting basic and applied studies such as vaccinal and therapeutic strategies. We proposed the in vitro and in vivo characterization of L. infantum strains from naturally infected dogs from a VL endemic area based on an infectivity and pathogenicity analysis. DH82 canine macrophages were infected in vitro with different strains for infectivity analysis, showing distinct infectivity profiles. The strains that showed greater and lesser infectivity using in vitro analyses (616 and 614, respectively) were used to infect hamsters for pathogenicity analysis. The group infected with strain 616 showed 100% survival while the group infected with strain 614 showed 50% after seven months of follow up. Furthermore, the 614 strain induced more noticeable clinicopathological changes and biochemical abnormalities in liver function, along with high inflammation and parasite load in the liver and spleen. We confirmed high variability of infectivity and pathogenicity in L. infantum strains from infected dogs. The results support the belief that screening for L. infantum infectivity using in vitro experiments is inadequate when it comes to selecting the most pathogenic strain.

Risk factors associated with Leishmania exposure among dogs in a rural area of Ilha Solteira, SP, Brazil

INTRODUCTION:

We sought to determine risk factors (RFs) associated with the presence of antibodies against Leishmania in dogs from a rural area of Ilha Solteira, SP, Brazil.

METHODS:

Serum samples were collected from 250 dogs and tested using indirect enzyme-linked immunosorbent assay (ELISA) and indirect immunofluorescence antibody tests (IFATs). Data concerning dogs, their environment, and their owners’ knowledge of leishmaniasis were collected using a questionnaire. To determine RFs for contact with the parasite, univariate statistical analysis based on chi-squared and Fisher’s exact tests, followed by logistic regression, was used.

RESULTS:

It was found that 79/250 (31.6%) of the dogs were positive by IFAT, and 72/250 (28.8%) by ELISA. A total of 82/250 dogs (32.8%) were positive in at least one test. The RFs associated with occurrences of Leishmania exposure were large body size (OR = 2.25; 95% CI = 1.26-4.04; p = 0.003), presence of chickens (OR = 1.94; 95% CI = 1.05-3.65; p = 0.023), and lack of knowledge about Leishmania among dog owners (OR = 1.74; 95% CI = 0.96-3.21; p = 0.049). After multivariate analysis, the RFs for occurrence of Leishmania exposure in dogs that remained significantly associated were the dog’s size (large dogs) (OR = 1.2; 95% CI = 1.06-1.35; p = 0.003) and presence of chickens on the properties (small farms) (OR = 1.15; 95% CI = 1.02-1.30; p = 0.023).

CONCLUSIONS:

These results may be useful for improving preventive practices to reduce the incidence of Leishmania exposure among dogs in rural areas.

Canine visceral leishmaniasis in area with recent Leishmania transmission: prevalence, diagnosis, and molecular identification of the infecting species

INTRODUCTION:

Canine visceral leishmaniasis (CVL) is an endemic disease in Brazil, and integrated control actions have been adopted by the Brazilian Ministry of Health to control its spread. However, the transmission profile is unknown in areas with recent CVL cases, including Itaúna, located in the Brazilian state of Minas Gerais, where the present study was carried out.

METHODS:

A total of 2,302 dogs from 12 neighborhoods were serologically tested for canine VL using the current diagnostic protocol adopted by the Brazilian Ministry of Health. Test positivity rate (TPR) and CVL prevalence were determined for each neighborhood. The presence of Leishmania was assessed in 60 seropositive dogs which had been recommended for euthanasia. Twenty-two of them (37%) were asymptomatic, and 38 (63%) were symptomatic for CVL. Parasitological (myeloculture and smear/imprint) and molecular (PCR) methods were employed for Leishmania detection in bone marrow, spleen, mesenteric lymph nodes, and ear skin. The infecting Leishmania species was identified by DNA sequencing.

RESULTS:

CVL prevalence (per 1,000 dogs) varied from 0.0-166.67, depending on the neighborhood, with a mean of 68.96 (SD 51.38). Leishmania DNA was detected in at least one tissue from all seropositive dogs, with comparable TPR among tissues. Leishmania parasites were identified in most (54/60) seropositive dogs, and the infecting parasite was identified as Leishmania infantum in all of these.

CONCLUSIONS:

Prevalence of CVL is a contributor to the spread of visceral leishmaniasis in Itaúna.

Bayesian compartmental models and associated reproductive numbers for an infection with multiple transmission modes

Zoonotic visceral leishmaniasis (ZVL) is a serious neglected tropical disease that is endemic in 98 countries. ZVL is primarily transmitted via a sand fly vector. In the United States, it is enzootic in some canine populations; it is transmitted from infectious mother to pup transplacentally, and vector-borne transmission is absent. This absence affords a unique opportunity to study (1) vertical transmission dynamics in dogs and (2) the importance of vertical transmission in maintaining an infectious reservoir in the presence of a vector. In this paper, we present Bayesian compartmental models and reproductive number formulations to examine (1) and (2), providing a mechanism to plan and evaluate interventions in regions where both transmission modes are present. First, we propose an individual-level susceptible, infectious, removed (SIR) model to study the effect of maternal infection status during pregnancy on pup infection progression. We provide evidence that pups born to diagnostically positive mothers during pregnancy are more likely to become diagnostically positive both earlier in life, and at some point during their lifetime, than those born to diagnostically negative mothers. Second, we propose a population-level SIR model to study the impact of a vertically maintained reservoir on propagating infection in a naive canine population through emergent vector transmission using simulation studies. We also present reproductive numbers to quantify contributions of vertically infected and vector-infected dogs to maintaining infection in the population. We show that a vertically maintained canine reservoir can propagate infection in a theoretical naive population in the presence of a vector.

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.

Reactivity of purified and axenic amastigotes as a source of antigens to be used in serodiagnosis of canine visceral leishmaniasis

Although there is a great diversity of techniques and antigens used in the serodiagnosis of canine visceral leishmaniasis (CVL), total sensitivity and specificity have not yet been found. Since the use of amastigote forms in the indirect immunofluorescence assay has shown an improvement in the specificity of the test for the diagnosis of CVL, the performance of amastigotes forms of L. (L.) infantum chagasi as antigen source were evaluated in automatized ELISA test using crude antigen of axenic amastigote and purified amastigote from spleen of hamster chronically infected comparing with ELISA using total antigen produced with promastigote forms of L. (L.) infantum chagasi. One hundred and fifteen sera from dogs with positive parasitological diagnosis by PCR were used. The animals were classified into 2 groups: symptomatic (n = 67) and asymptomatic (n = 48) animals, in accordance with the clinical signs and laboratory tests were. As control, ninety-four sera from dogs with negative parasitological diagnosis were included. No significant difference was found in sensitivity, specificity, predictive values and accuracy between ELISA using whole antigens produced with both axenic and purified amastigotes in comparison with promastigotes forms. Correlation and concordance between the three total antigens tested in ELISA was observed. According to the similar performance among antigens, data pointed out to use antigen from promastigote forms for diagnosing canine leishmaniasis, especially due the easily in the production, lower cost and the abundance of correlative literature.

Canine leishmaniasis in the semi-arid region of Pernambuco, northeastern Brazil: epidemiology, factors associated with seropositivity and spatial analysis

This study aimed to determine the seroprevalence, factors associated with seropositivity to Leishmania infection in dogs and spatial analysis in six municipalities in the semiarid region of Pernambuco, Brazil. Blood samples were collected from 462 dogs, 77 in each municipality, and used for serological analysis [dual path platform (DPP®) and enzyme-linked immunosorbent assay (ELISA)]. Clinical signs of dogs were evaluated and associated factors for Leishmania infection were analyzed using robust Poisson regression model. A seroprevalence of 42.8% (198/462, IC: 95% = 38.6%-47.6%) was detected in dogs that tested positive in both tests, ranging from 29.8% to 55.8%, with higher prevalence in the municipality of Cabrobó (55.8%; P = 0.006). About 67% (132/198) of the seropositive dogs showed one or more clinical signs suggestive of canine leishmaniasis (CanL), such as lymphadenomegaly, skin lesions and conjunctivitis, which were associated with seropositivity. High seroprevalence levels were identified in urban and rural areas in all the municipalities, and the buffer for sand flies around cases covered almost these entire areas. Spatial analysis revealed a significant cluster, showing a relative risk of 1.88 in the urban area of Cabrobó. The higher density of seropositive dogs in urban areas indicates the need effective control measures against CanL to prevent the emergence of canine and human diseases.

Untapped potential: The utility of drylands for testing eco-evolutionary relationships between hosts and parasites

Drylands comprise over 41% of all terrestrial surface area and are home to approximately 35.5% of the world's population; however, both free-living and parasitic fauna of these regions remain relatively understudied. Yet, the very conditions that make these regions challenging to study – extreme environmental conditions and low population density for various organisms – also make them potentially untapped natural laboratories for examining eco-evolutionary relationships between hosts and parasites. Adaptations and ecological patterns illustrated by desert parasite communities can serve as exemplars within the extremes regarding the evolution of virulence, breadth of host spectra, and lifecycle strategies. This review provides relevant examples for each of these three topics using parasites from dryland regions in order to encourage future empirical tests of hypotheses regarding parasite ecology and evolution within dryland ecosystems and stimulate wider investigation into the parasitofauna of arid regions in general. As global climate changes and anthropogenic disturbance increases, desertification is a growing problem which has been labeled as a threat to global health. Thus, deserts not only provide useful natural laboratories in which to study parasite transmission but understanding parasite transmission within these habitats becomes increasingly important as larger, likely highly resource insecure, populations are projected to live on the margins of desert regions in the future.

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Drylands comprise over 41% of Earth's surface but their parasites are understudied.

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Desert parasite communities are exemplars within the extremes of parasite ecology.

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Can test hypotheses of virulence evolution, host spectra, and lifecycle strategies.

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Drylands can provide increasingly important insight into parasite transmission.

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Larger human populations are projected to live in arid regions as climate changes.

A cross-sectional approach including dog owner characteristics as predictors of visceral leishmaniasis infection in dogs

BACKGROUND

Visceral leishmaniasis (VL) is relevant for human and animal public health. Several factors have been associated with the risk of Leishmania infantum infection in dogs. However, dog owner characteristics have been rarely explored.

OBJECTIVES

To estimate the prevalence and to identify the associated factors for VL infection including dog owners characteristics.

METHODS

A cross-sectional study was conducted including dogs from an endemic canine visceral leishmaniasis (CVL) region in the Federal District, Brazil. The infection was detected using parasitological, serological, and molecular methods. The associated factors were identified through Poisson regression modelling.

FINDINGS

The prevalence of infection was 26.25% [95% confidence interval (CI): 20.05 to 33.57]. The associated factors were: short coat prevalence ratio (PR) = 2.33 (95% CI: 1.02 to 5.22); presence of backyard with predominance of soil and/or vegetation PR = 4.15 (95% CI: 1.35 to 12.77); and highest gross family income score PR = 2.03 (95% CI: 1.16 to 3.54).

MAIN CONCLUSION

This is the first study that relates higher socioeconomic status of dog owners as an independent factor associated with higher prevalence of VL infection, along with other strongly associated factors related to receptive environment for phlebotomines. Our findings strengthen the need for exploration of the biological and behavioural bases linking dog owner characteristics to the risk of canine infection in prospective cohort studies.

Cutaneous parasitism in patients with American visceral leishmaniasis in an endemic area

INTRODUCTION:

Visceral leishmaniasis (VL) represents a public health concern in several areas of the world. In the American continent, VL transmission is typically zoonotic, but humans with active VL caused by Leishmania infantum are able to infect sandflies. Thus, individuals with cutaneous parasitic infections may act as reservoirs and allow interhuman transmission. Additionally, the skin may be responsible for reactivation of the disease after therapy. This study’s objective was to evaluate cutaneous parasitism in humans with VL in an American endemic area.

METHODS:

A cross-sectional hospital-based study was conducted in northeast Brazil from October 2016 to April 2017. Biopsies of healthy skin for histopathology and immunohistochemistry were performed prior to treatment in all study patients.

RESULTS:

Twenty-two patients between the ages of five months to 78 years were included in the study. Seven patients (31.8%) tested positive for HIV. Only one patient had cutaneous parasitism, as confirmed by immunohistochemistry prior to treatment. Parasitism was not detected after treatment.

CONCLUSIONS:

Cutaneous parasitism in the healthy skin of humans with visceral leishmaniasis, although unusual, may be a source of infection for phlebotomine sandflies.