Canine visceral leishmaniasis: relationships between clinical status, humoral immune response, haematology and Lutzomyia (Lutzomyia) longipalpis infectivity

Clinical validation of circulating immune complexes for use as a diagnostic marker of canine leishmaniosis

Introduction

Canine leishmaniosis (CanL) is a systemic disease that affects dogs. When multiplication of the parasite cannot be controlled, dogs consistently show high levels of antigen and IgG antibodies, which lead to the formation of circulating immune complexes (CIC). Timely intervention to reduce the parasite load and CIC levels is crucial for preventing irreversible organ damage. However, a diagnostic test to quantify CIC levels is currently lacking.

Methods

In this real-world study, we aimed to examine the performance of a new ELISA to measure CIC levels in dogs naturally infected with Leishmania infantum. Thirty-four dogs were treated according to their clinical condition and followed for 360 days. Before (day 0) and after treatment (days 30, 90, 180, 270, and 360), all dogs underwent a physical examination, and blood samples were obtained for CBC, biochemical profile, serum protein electrophoresis and IFAT. Serum PEG-precipitated CIC were determined by ELISA.

Results

Our results indicate higher CIC levels in dogs in advanced disease stages showing higher antibody titres (p < 0.0001, r = 0.735), anemia (p < 0.0001), dysproteinemia (p < 0.0001), and proteinuria (p = 0.004). Importantly, dogs responding well to treatment exhibited declining CIC levels (p < 0.0001), while in poor responders and those experiencing relapses, CIC were consistently elevated. CIC emerged as a robust discriminator of relapse, with an area under the curve (AUC) of 0.808. The optimal cut-off to accurately identify relapse was an optical density of 1.539.

Discussion

Our findings suggest that declining CIC levels should be expected in dogs showing a favorable treatment response. Conversely, in dogs displaying a poor response and recurrent clinical relapses, CIC levels will be high, emphasizing the need for vigilant monitoring. These findings suggest that CIC could serve as a valuable biomarker for disease progression, treatment efficacy, and relapse detection in CanL. Our study contributes to enhancing diagnostic approaches for CanL and underscores the potential of CIC as a complementary tool in veterinary practice. As we move forward, larger studies will be essential to confirm these findings and establish definitive cut-offs for clinical application.

Signalment, Immunological and Parasitological Status and Clinicopathological Findings of Leishmania-Seropositive Apparently Healthy Dogs

Canine leishmaniosis caused by Leishmania infantum is a disease with a wide range of clinical manifestations. Epidemiological serosurveys performed in Europe often lack a thorough assessment of clinical health status of studied dogs. The aim of this study was to evaluate signalment, immunological and parasitological status and clinicopathological findings of L. infantum-seropositive apparently healthy dogs (n = 212) living in endemic areas. Routine laboratory tests, endpoint in-house ELISA to quantify the anti-Leishmania antibodies, blood Leishmania qPCR and IFN-γ ELISA were performed. All dogs enrolled were L. infantum-seropositive and were classified as healthy (n = 105) or sick (n = 107) according to LeishVet guidelines. The sick group presented a higher proportion of medium to high antibody levels and positive qPCR and lower IFN-γ concentration compared to the healthy group. Sick dogs were mostly classified in LeishVet stage IIa. Biochemical alterations (98%) were the most common clinicopathological findings, with fewer urinary tract (46%) and hematological (40%) alterations. Apparently healthy L. infantum-seropositive dogs can be classified between truly healthy dogs and sick dogs with clinicopathological findings. Sick dogs presented medium to high seropositivity and parasitemia and low IFN-γ concentrations, and their most common clinicopathological abnormalities were serum protein alterations followed by proteinuria and lymphopenia.

Immunoproteomics approach for the discovery of antigens applied to the diagnosis of canine visceral leishmaniasis

In the present study, an immunoproteomic approach using Leishmania infantum parasites isolated from naturally infected dogs from an endemic region of the disease, was carried out to identify new antigens to be used in the diagnosis of canine visceral leishmaniasis (CVL). Protein extracts, obtained from parasites isolated from asymptomatic (CanLA) and symptomatic (CanLS) dogs, were used to perform the two-dimensional gels. Western Blotting assays were carried out by employing a pool of sera from dogs with visceral leishmaniasis (CanLA or CanLS), healthy dogs from an endemic area, or dogs with similar diseases associated with cross-reactions (babesiosis and ehrlichiosis). With these results, it was possible to exclude the spots that showed a cross-reactivity of the sera from groups of healthy dogs, and those with babesiosis or ehrlichiosis. Taken together, 20 proteins were identified, 15 of which have already been described in the literature and 5 of which are hypothetical. An immunogenomic screen strategy was applied to identify conserved linear B-cell epitopes in the identified hypothetical proteins. Two peptides were synthesized and tested in ELISA experiments as a proof of concept for the validation of our immunoproteomics findings. The results demonstrated that the antigens presented sensitivity and specificity values ranging from 81.93% to 97.59% and 78.14 to 85.12%, respectively. As a comparative antigen, a preparation of a Leishmania extract showed sensitivity and specificity values of 75.90% and 74.88%, respectively. The present study was able to identify proteins capable of being used for the serodiagnosis of canine visceral leishmaniasis.

Diagnosis and prevalence of canine leishmaniasis in the Atlas shepherd dog

The aim of this study was to determine the prevalence of canine leishmaniasis in the Atlas shepherd dogs from the Tiaret region of Algeria. A total of 161 dogs were included in this study and four diagnostic techniques were used, namely lymph node cytology, PCR, IFAT and ELISA. 110 out of 161 dogs were positive by at least one diagnostic technique, a percentage of 68.32% of the total number, which represent very high prevalence of canine leishmaniasis in this canine breed. 152 dogs underwent the two serological tests namely IFAT and ELISA among which 137 dogs underwent in addition the molecular examination by PCR. IFAT was positive in 9.86% of the dogs, ELISA was positive in 12.5% while 68% of the dogs proved positive by PCR. 47 dogs with lymph node enlargement underwent lymph node cytology, of which 26 dogs showed forms of amastigotes in their smears after microscopic examination, confirming the usefulness of this approach for the diagnosis of canine leishmaniasis. The clinical signs of the disease in this breed are similar to those of other canine breeds The dominant clinical signs in these dogs were onychogryphosis, poor general condition and lymph node hypertrophy. The autopsy was carried out on 7 dogs that died of canine leishmaniasis, all of which showed splenomegaly, while 5 dogs also showed hepatomegaly. Renal damage was found in 1 dog with frank jaundice. The splenic cytology was positive in all 7 dogs with the presence of amastigote forms in the smears after microscopic examination.

Hemogram Findings in Cats from an Area Endemic for Leishmania infantum and Feline Immunodeficiency Virus Infections

Simple Summary

Some cats positive for Leishmania infantum (Li) show clinical signs and clinicopathological changes, including hemogram abnormalities. However, co-infections or co-morbidities are often detected in cats with leishmaniosis, and they can have a role in the clinical abnormalities observed. In feline Leishmania infantum infections and in clinical cases of feline leishmaniosis, a significant association with feline immunodeficiency virus (FIV) has been detected, but the role of this co-infection is controversial. The aims of this study were to retrospectively evaluate hemogram changes in cats from areas endemic for Leishmania infantum and feline immunodeficiency virus infections (Sicily and Calabria regions, Southern Italy) and to analyze the role of both pathogens in the abnormalities detected. A retrospective cross-sectional study was carried out on 496 cats. Hematological changes in cats positive for Leishmania infantum were found, particularly abnormalities compatible with chronic inflammation including moderate anemia, monocytosis, and morphologically activated monocytes. Moreover, some abnormalities, such as thrombocytosis, seem to arise when cats are co-infected with FIV. Feline leishmaniosis should be considered when some hemogram abnormalities compatible with chronic inflammation are detected.

Abstract

In feline Leishmania infantum (Li) infection and in clinical cases of feline leishmaniosis, co-infection with feline immunodeficiency virus (FIV) has been reported. However, the role of the retroviral co-infection in the impairment of feline clinical health is still controversial. The aim of this study was to evaluate hemogram changes in cats from regions endemic for both Li and FIV infection. Four hundred and ninety-six cats tested for Li (EDTA blood polymerase chain reaction and immunofluorescence antibody test) and for FIV infection (enzyme-linked immune assay) were retrospectively evaluated. Hemogram results including blood smear morphological evaluation were statistically compared considering four infection patterns: Li+FIV+, Li+FIV−, Li−FIV+, and Li−FIV−. Significantly lower values of erythrocytes (Li+FIV−: p = 0.0248; Li−FIV+: p = 0.0392) and hemoglobin (Li+FIV: p = 0.0086; Li−FIV+: p = 0.0249) were found in both infections when compared to Li−FIV− cats, and severity of anemia was more frequently moderate in Li-positive cats (p = 0.0206) and severe in FIV infection (p = 0.024). Li infection was associated with monocytosis (p = 0.0013) and morphologically activated monocytes (p = 0.0209). Moreover, FIV infection was associated with the presence of inflammatory leukogram (p = 0.023), and an association between thrombocytosis and the co-infection was found (p = 0.0347). Li infection in cats induces hematological changes compatible with chronic inflammation, some of which are due to co-infection with FIV.

Leishmania V. braziliensis infection in asymptomatic domestic animals within an endemic region in the Northeast of Brazil

Background:

American cutaneous leishmaniasis is a commonly neglected, vector-borne tropical parasitic disease that is a major public health concern in Brazil. Leishmania (Viannia) braziliensis is the main species associated with the disease. Accurate diagnosis is based on epidemiological surveillance, clinical assessment, and laboratory testing. Leishmania (V.) braziliensis has been detected in several wild and synanthropic mammals. Their epidemiological role has not been entirely elucidated. This study aimed to assess potential L. braziliensis infections in asymptomatic domestic animals, by molecular and serological testing in endemic areas, in the metropolitan region of Recife.

Methods:

Blood samples and conjunctival fluids were collected from 232 animals (canids, felids, equines, and caprines) for the detection of L. braziliensis using molecular tests (conventional and real-time polymerase chain reaction [PCR and qPCR]). For immunological detection, blood samples from 115 dogs were assessed using enzyme-linked immunosorbent assay.

Results:

Real-time quantitative PCR showed positive results for blood and conjunctival samples in all investigated species. The results of the blood and conjunctival samples were 68.2% and 26.9% in Canis familiaris, 100% and 41.7% in Felis catus, 77.3% and 30.8% in Equus caballus/Equus asinus, and 50% and 33.3% in Capra hircus samples, respectively.

Conclusions:

Results from this study adds valuable information to our understanding of the role of asymptomatic domestic animals, L. braziliensis life cycle, and American cutaneous leishmaniasis in Northeast Brazil.

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.

Control of Canine Visceral Leishmaniasis: A Success Case Based on Deltamethrin 4% Collars

The effect of employing collars impregnated with deltamethrin 4% (DM4) to control canine visceral leishmaniasis (CVL) was evaluated. as were the individual factors associated with this infection. A cohort study that included household dogs was conducted between 2002 and 2006. The presence of pathognomonic signals, peridomiciliary sleep habits and breed were the main factors associated with the infection. The use of DM4 collars contributed to the reduction of CVL with an effectiveness of 66%, and the dogs' survival rate was greater than 90% at 50 months. In conclusion, the adoption of DM4 collars reduced the number of euthanized canines and in the incidence of CVL, and this reduction was sustained for one year after discontinuing the use of the collar.

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.

Nutritional adjuvants with antioxidant properties in the treatment of canine leishmaniasis

Clinical improvement of dogs treated for canine leishmaniasis (CanL) requires reducing Leishmania infantum loads, which depend on intracellular oxidant compounds to destroy the parasite. However, oxidative species' excess and antioxidants consumption can culminate in oxidative stress, resulting in increased, widespread inflammation. We aimed to evaluate if early or late addition of nutritional adjuvants (NAs) - omega-3 polyunsaturated fatty acids and B vitamins - to anti-Leishmania drugs (ALDs) in the treatment of CanL would be clinically beneficial. For that, serum biomarkers including oxidative stress parameters were analyzed during 12 months in dogs allocated to two treatment groups: (G1) NAs administered from 30 days prior to the beginning of ALDs; and (G2) NAs administered from 61 days after the beginning of ALDs. Both G1 and G2 continued to receive NAs until the 12th month. The ALDs administered were metronidazole associated with ketoconazole (40 days), followed by allopurinol from day 41 until the 12th month. G1 exhibited superior inflammation control, with reduced globulins (p = 0.025), specific anti-Leishmania immunoglobulins (p = 0.016), total protein (p = 0.031), and an increased serum albumin/globulin ratio (p = 0.033), compared to G2. The early use of NAs associated with ALDs is clinically beneficial in treating dogs with CanL.

Enhanced attraction of sand fly vectors of Leishmania infantum to dogs infected with zoonotic visceral leishmaniasis

BACKGROUND

The sand fly Phlebotomus perniciosus is the main vector of Leishmania infantum, etiological agent of zoonotic visceral leishmaniasis in the Western Mediterranean basin. Dogs are the main reservoir host of this disease. The main objective of this study was to determine, under both laboratory and field conditions, if dogs infected with L. infantum, were more attractive to female P. perniciosus than uninfected dogs.

METHODOLOGY/PRINCIPAL FINDINGS

We carried out a series of host choice experiments and found that infected dogs were significantly more attractive to P. perniciosus than uninfected dogs in the laboratory as well as in the field. Significantly more P. perniciosus fed on infected dogs than on uninfected dogs. However, the fecundity of P. perniciosus fed on infected dogs was adversely impacted compared to uninfected dogs by lowering the number of laid eggs. Phlebotomus perfiliewi, the second most abundant sand fly species in the field site and a competent vector of L. infantum had similar trends of attractivity as P. perniciosus toward infected dogs under field conditions.

CONCLUSIONS

The results strongly suggest that L. infantum causes physiological changes in the reservoir host which lead to the host becoming more attractive to both male and female P. perniciosus. These changes are likely to improve the chance of successful transmission because of increased contact with infected hosts and therefore, infected dogs should be particularly targeted in the control of zoonotic visceral leishmaniasis in North Africa.

Relationships between specific antibody responses and clinical signs of dogs living in Tunisian endemic areas of canine leishmaniasis caused by Leishmania infantum

The first step of the diagnostic process of canine leishmaniasis (CanL) is initiated by veterinarians and relies on their assessment of a high number of clinical signs common to other infectious diseases. We investigated herein the relationship between the clinical profile of 64 domestic dogs living in Tunisian endemic areas and their serological immune status with the aim to identify leishmanial serological markers of diagnosis and disease staging. Seven clinical signs were examined and a total clinical score that describes the number (TCS1) and the number plus the intensity of the clinical signs (TCS2) were determined. Laboratory tests consisted of parasitological examination (PE) of Giemsa-stained popliteal lymph node smears, indirect fluorescent antibody test (IFAT), IgG-, IgG1-, IgG2-Enzyme-Linked-Immunosorbent-Assay (ELISA), and IgG1-, IgG2- Western blotting (WB). Dogs' categorization according to the results of routine diagnostic tests, the TCS1 and TCS2, and the relative IgG1 and IgG2 specific reactivity allowed us to show that active CanL is characterized by an increased reactivity of the IgG2 specific antibodies. Interestingly, the IgG1 levels increased in parallel with the TCS1 and especially with the TCS2, indicating that this isotype is a better marker of dogs' health deterioration. PE & IFAT positive dogs which presented the highest TCS2 and IgG1 reactivity demonstrated significantly more severe weight loss and paleness of the mucosal membranes, suggesting that these signs characterize the latest stages of the disease. WB analysis showed that threeleishmanial polypeptides merit attention and further investigations. The antigens with MWs 32kDa reacting with IgG1 and 37kDa reacting withIgG2 antibodies were found associated with the results of diagnostic tests and late CanL stages, whereas the 24kDa antigen reacting with the IgG2 isotype and associated with low TCS2 seems to be a marker of the early stages.

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.

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.

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

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

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.

Comparative study of the use of miltefosine, miltefosine plus allopurinol, and allopurinol in dogs with visceral leishmaniasis

Visceral leishmaniasis (VL) is an infectious disease caused by the protozoan parasite Leishmania (Leishmania) infantum, an intracytoplasmic parasite that affects humans and other species of domestic and wild mammals. In Brazil, the treatment of canine visceral leishmaniasis (CVL) with miltefosine has been implemented since 2016, and the reports on the clinical and immunological conditions of treated dogs are scarce. Thus, this study aimed to assess and monitor the clinical, laboratory, and immunological condition of dogs with CVL before (D₀) and after (D₂₉) using three pharmacotherapeutic protocols: miltefosine monotherapy (Milteforan™, Virbac) (G1), miltefosine plus allopurinol (G2), and allopurinol monotherapy (G3). Forty-five dogs with CVL were assigned to one of three treatment groups. The dogs were evaluated for clinical signs, was well as haematological, biochemical, serological, and cytokine levels. Significant reduction in clinical scores was observed in all protocols, with no differences between groups. We did not observe a clinical cure in any of the dogs in the groups. Haematological and biochemical parameters showed slow recovery, with better results observed in G2. Anti-Leishmania antibody titre remained increased in all groups. The quantification of serum cytokines demonstrated a mixed Th1/Th2 profile in CVL. The IL-2 levels decreased in all groups after treatment. Evaluation of IFN-y and IL-10 did not show changes in the groups analysed, and it did not contribute to short term therapeutic monitoring. All therapeutic protocols promoted, to varying degrees, an improvement in the general condition (clinical signs, haematological, and biochemical levels) of the animals. Through clinical-pathological exams, we found that the combination of miltefosine plus allopurinol promoted better effects in the short-term, representing the best choice for the treatment of CVL, even when compared to the only therapeutic protocol allowed in Brazil, miltefosine monotherapy. Through the quantification of cytokines, IL-2 proved to be a potential therapeutic marker for the monitoring and follow-up of dogs with CVL.

Plasmonic rK28 ELISA improves the diagnosis of canine Leishmania infection

In this study, we evaluated the performance of a new enzyme-linked immunosorbent assay (ELISA) variant known as indirect "plasmonic ELISA" (pELISA) for the detection of Leishmania spp. infection. Serum samples from 170 dogs from an area where canine leishmaniosis (CanL) is endemic and from 26 healthy dogs from a nonendemic area were tested by indirect pELISA, and the results were compared to those of an indirect ELISA (both with recombinant antigen rK28) and those of an immunochromatographic test (dual-path platform, TR-DPP®) using real-time PCR on blood samples or conjunctival swabs as the gold standard. The pELISA, indirect rK28 ELISA and the TR-DPP® immunochromatographic test presented sensitivities of 94.7%, 89.5% and 79.0% and specificities of 100%, 92.7% and 91.5%, respectively. The analysis of the results revealed that the specificity of the indirect pELISA was greater than that of the method recommended by the Ministry of Health in Brazil and may increase the feasibility of diagnosis in resource-constrained countries because it does not require sophisticated instruments to read. Thus, this method can be used as an additional tool for the detection of Leishmania spp. infection in these areas.

Competence of non-human primates to transmit Leishmania infantum to the invertebrate vector Lutzomyia longipalpis

Leishmaniasis is a zoonotic disease of worldwide relevance. Visceral leishmaniasis is endemic in Brazil, where it is caused by Leishmania infantum with Lutzomyia longipalpis being the most important invertebrate vector. Non-human primates are susceptible to L. infantum infection. However, little is known about the role of these species as reservoirs. The aim of this study was to evaluate the transmissibility potential of visceral leishmaniasis by non-human primates through xenodiagnosis using the phlebotomine Lu. longipalpis as well as to identify phlebotomine species prevalent in the area where the primates were kept in captivity, and assess infection by Leishmania in captured phlebotomine specimens. Fifty two non-human primates kept in captivity in an endemic area for leishmaniasis were subjected to xenodiagnosis. All primates were serologically tested for detection of anti-Leishmania antibodies. Additionally, an anti-Lu. longipalpis saliva ELISA was performed. Sand flies fed on all animals were tested by qPCR to identify and quantify L. infantum promastigotes. Eight of the 52 non-human primates were positive by xenodiagnosis, including three Pan troglodytes, three Leontopithecus rosalia, one Sapajus apella, and one Miopithecus talapoin, with estimated numbers of promastigotes ranging from 5.67 to 1,181.93 per μg of DNA. Positive animals had higher levels of IgG anti-Lu. longipalpis saliva when compared to negative animals, prior to xenodiagnosis. Captive non-human primates are capable of infecting Lu. longipalpis with L. infantum. Our findings also demonstrate the relevance of non-human primates as sentinels to zoonotic diseases. Several phlebotomine species, including Lu. longipalpis, have been identified in the area where the primates were maintained, but only one pool of Lutzomyia lenti was infected with L. infantum. This study has implications for public health strategies and conservation medicine.

Visceral leishmaniasis is a zoonotic disease with worldwide distribution. The disease is endemic in several Brazilian regions, including the city of Belo Horizonte, where visceral leishmaniasis is caused by Leishmania infantum and transmitted by Lutzomyia longipalpis. This study evaluated the competence of non-human primates to infect Lutzomyia longipalpis with Leishmania infantum. Eight of 52 non-human primates were positive to leishmaniasis by xenodiagnosis, i.e. capable of infecting sand flies, with averages of 5.67 to 1,181.93 promastigotes/μg of DNA. Positive animals had higher levels of IgG anti-Lu. longipalpis saliva when compared to negative animals, prior to xenodiagnosis. This study highlights the importance of non-human primates in the leishmaniasis cycle, providing information that is relevant for development of better public health strategies, and to conservation medicine.

Use of miltefosine to treat canine visceral leishmaniasis caused by Leishmania infantum in Brazil

Background

Visceral leishmaniasis (VL) is an infectious disease with a variety of clinical signs. The main form of parasite transmission to humans and other mammalian hosts is through the bite of infected arthropod females with Lutzomyia longipalpis serving as the main vector in the Americas. Dogs are the main urban domestic reservoirs of the parasite and the main source of vector infection due to their high prevalence in endemic areas and the large number of parasites in the skin of infected animals. Although miltefosine has been used in Europe since 2002 for treatment of VL infected dogs, in the Americas the treatment of dogs has not been recommended. Therefore, this study aimed to evaluate efficacy of miltefosine observing a reduction of clinical signs in infected dogs and the infectiveness to the vector by Leishmania (L.) infantum.

Methods

To our knowledge, this is the first controlled study using qPCR and xenodiagnosis to evaluate the efficacy of miltefosine (Milteforan®, Virbac) as a single treatment in Brazil. Thirty-five adult dogs with canine visceral leishmaniasis (CVL), confirmed by clinical and laboratory tests, were included in this study. They received miltefosine at a dose of 2 mg/kg every 24 h for 28 days. The dogs were observed over a three-month period, during which clinical evaluations based on a scoring system were conducted at pre-established times. Parasite load was assessed by cytology and real-time polymerase chain reaction (qPCR). Transmissibility to the vector was evaluated by xenodiagnosis.

Results

At the end of the period, the following were observed: (i) the remission of clinical signs with a reduction in clinical scores for 94.2% of the animals; (ii) a statistically significant reduction (98.7%) in parasitic load by qPCR; and (iii) a reduction in infectivity to sand flies. After treatment, 74.2% of the animals remained or had become non-infectious.

Conclusions

Our study indicates that the use of miltefosine administered orally for 4 weeks contributes to a clinical improvement and reduction in infectivity of dogs to L. infantum.

Current status and management of canine leishmaniasis in Latin America

Latin America encompasses diverse geographical, cultural and socio-economic conditions, which are reflected in the challenges for infectious disease control in the region. One of the most significant regional infectious diseases for humans and domestic dogs is leishmaniasis, occurring as visceral leishmaniasis (VL) caused by Leishmania infantum (syn. L. chagasi) transmitted by sand flies (Lutzomyia longipalpis) and with a canine reservoir, and the more common cutaneous leishmaniasis (CL) involving multiple Leishmania spp. (particularly L. braziliensis), sand fly vectors and reservoir hosts. VL is spreading within Latin America for reasons related to mass migration of human and canine populations, with incursion into novel environments (e.g. related to deforestation) coupled with a background of poverty and poor public health infrastructure. The challenges for control of VL also include: (1) the accurate identification of infected dogs (particularly subclinically infected dogs) with the current reliance on serological rather than molecular diagnostic methods, (2) controversy surrounding the ethics and efficacy of culling of seropositive dogs, (3) the limited efficacy of currently available canine vaccines and their potential to interfere with interpretation of serological testing, (4) the expense associated with distribution of insecticidal dog collars, which may prove to be the most valuable control method, and (5) the cost and therefore accessibility of licensed medical treatment for canine leishmaniasis by the general population. Resolution of these isssues will necessitate a 'One Health' approach to co-ordination of resources between human and veterinary healthcare.

Use of domperidone in canine visceral leishmaniasis: gaps in veterinary knowledge and epidemiological implications

A pivotal strategy to decrease the risk of visceral leishmaniasis in humans is to control the infection and disease progression in dogs, the domestic reservoir of Leishmania infantum (L. chagasi). Immunotherapy is a viable approach to treat sick dogs because cell-mediated immunity is the principal defense mechanism against L. infantum. Domperidone is an immune-stimulatory drug increasingly used in veterinary medicine as a prophylactic or immunotherapeutic agent. Domperidone treatment has shown to prevent overt disease or improve the clinical condition of infected dogs. However, veterinarians should be aware of the potential cardiotoxicity of domperidone when given together with drugs that inhibit CYP450s liver enzymes or those that prolong the QT interval. On the other hand, learning whether domperidone treatment significantly decreases dog infectivity to sand fly vectors is of capital importance since this result should have a palpable impact on the infection risk of humans living in regions endemic for visceral leishmaniasis.

IgG avidity index and complete blood count as biomarkers of clinical disease in naturally infected dogs with Leishmania infantum

Canine visceral leishmaniosis (CVL), a parasitic disease caused by Leishmania infantum, may evolve to a chronic condition and lead to death. Evaluation of infected dogs is important to establish the clinical and laboratory parameters involved in the evolution of the disease. The objectives of the present study were to discriminate a canine population (n = 52) into sub-clinical and clinically affected dogs based on signs and scores, to evaluate the hematological, biochemical, histopathological and parasitological parameters of the two dog groups, and to analyze the results by multivariate regression analysis with the aim of establishing biomarkers of CVL clinical disease. The most common signs observed in the clinically affected dogs (n = 29) were hyperkeratosis, weight loss, onychogryphosis, pale mucosa and lymphadenomegaly. In the multivariate analysis, animals presenting high IgG avidity index and low red blood, lymphocyte and eosinophil counts, and low serum urea concentration had an increased probability of being classified as clinically affected (p <  0.05). All five parameters were considered to be strong biomarkers for monitoring the clinical disease, while IgG avidity percentage was strongly correlated with the number of clinical signs and could function as an indicator of the duration of infection. This is the first report on the application of IgG avidity and of multivariate regression analysis in establishing associations between the clinical signs of CVL and host biomarkers. Since avidity index (AI) percentages were strongly correlated with the number of clinical signs, it could be useful in clinical practice for auxiliary diagnosis of CVL and monitoring disease progression. A limitation of this study is the lack of information on co-infections by Anaplasma platys, Babesia canis vogeli, Ehrlichia canis and Hepatozoon canis. Therefore future studies should evaluate the influence of such co-infections on the associations studied using multivariate methods with larger samples.

Modeling and comparative study of the spread of zoonotic visceral leishmaniasis from Northern to Central Tunisia

During the last twenty years, zoonotic visceral leishmaniasis (ZVL) spread from the north characterized by humid, sub-humid, and semi-arid bio-climates to the arid areas located in Central Tunisia. In order to understand the eco-epidemiological factors involved in the distribution of ZVL, both a sero-epidemiological and an entomological investigation were performed in two governorates situated in two different bio-geographical areas: Bizerte in the north and Kairouan in the center. A mathematical model for transmission of ZVL was built, describing the disease dynamic in these areas. Among 108 sera collected from clinically healthy owned dogs used for guarding houses in the governorate of Bizerte and tested for anti-L. infantum antibodies by indirect immune-fluorescence antibody test (IFAT), 8.3% were positive. From a total of 191 serum samples collected from clinically healthy owned dogs used for guarding houses in the governorate of Kairouan and tested for anti-L. infantum antibodies by IFAT, 26.7% were sero-positive. The cumulative incidences of ZVL in humans in the governorates of Bizerte and Kairouan were 39.17/100,000 and 0.2/100,000 inhabitants, respectively. The infection rates of sand flies with Leishmania DNA in the governorate of Bizerte and Kairouan were 3.8% and 9.4%, respectively. It is important to point out that ZVL epidemic in humans is preceded or concomitant to a high prevalence of Leishmania infantum in dogs and in sand flies. The model showed also a non-linear relationship between dog infection and ZVL in humans. These results suggest an important force of infection (R0) in emerging foci such as the governorate of Kairouan leading to an increased incidence of ZCL in humans. A high prevalence of L. infantum in dogs will result in high prevalence in the vector and obviously high probability to infect human; that it is a key factor for triggering transmission to humans, and subsequently it is an important parameter in the control of ZVL transmission.

Vaccine effectiveness and use of collar impregnated with insecticide for reducing incidence of Leishmania infection in dogs in an endemic region for visceral leishmaniasis, in Brazil

Although a national programme for control of visceral leishmaniosis (VL) is being run in Brazil, the disease continues to spread. This programme is essentially based on culling infected dogs from endemic regions. Thus, there is an urgent need to develop other control measures against VL to deter its advance. Here, a subunit vaccine, a recombinant vaccine, an insecticide-impregnated collar and the associations between these measures were evaluated for reducing the incidence of Leishmania infection in dogs. This was through a cohort study conducted in an endemic region of Brazil, considering the incidence and time of total exposure over a period of 1 year. The incidence of VL was estimated by means of serological and molecular diagnostic tests, 180 and 360 days after the application of the control measures. The estimates of the effectiveness (EF) were not significant in any cohort. The EF of the subunit vaccine, the recombinant vaccine and the collar were 26.4%, 32.8% and 57.7% and the upper limit of the 95% confidence interval for EF were 63.7%, 67.9% and 82.5%, respectively. In conclusion, under the conditions of this study, none of the immunogens for VL control was sufficiently effective to protect dogs against infection. On the other hand, use of collars impregnated with insecticide seems to constitute a method with better prognosis, corroborating other studies in this field.

Association between mast cells, tissue remodelation and parasite burden in the skin of dogs with visceral leishmaniasis

Canine visceral leishmaniosis (CVL) is a zoonosis of major public health impact caused by organisms of the genus Leishmania which is transmitted to human and animals by phlebotomine sand flies. The skin is the first point of contact with Leishmania parasites for sandy fly vectors and it is considered an important reservoir compartment in infected dogs. The aim of this study was to determine the main histophatologic alterations in ear skin of dogs naturally infected by Leishmania infantum with different clinical status and different degrees of parasitism. Therefore, thirty-four dogs naturally infected with L. infantum were grouped according to their clinical status in asymptomatic (AD, n=11), oligosymptomatic (OD, n=11) and symptomatic dogs (SD, n=12) as well as their degrees of parasite load in the skin as low (LP, n=11), median (MP, n=11) and high (HP, n=12) parasitism. Additionally, ten dogs were used as control (CD, n=10). At necropsy, skin samples were collected for further histological and parasitological analysis. The OD and SD groups presented higher parasite burden than AD group. The inflammation was higher in SD group when compared to OD and AD. The LP, MP and HP groups showed an increasing inflammatory process, indicating that a great parasite load is accompanied by a major inflammatory process in the skin. The number of mast cells was higher in the OD and LP groups than CD group, suggesting that these cells may be involved in tissue remodeling, since that an increase of type III collagen fibers and decrease type I collagen fibers were observed in these groups. Taken together, our results enable a better understanding of the alterations in skin of CVL dogs and consequently new insights about the pathogenesis of CVL.

A Vaccine Therapy for Canine Visceral Leishmaniasis Promoted Significant Improvement of Clinical and Immune Status with Reduction in Parasite Burden

Herein, we evaluated the treatment strategy employing a therapeutic heterologous vaccine composed of antigens of Leishmania braziliensis associated with MPL adjuvant (LBMPL vaccine) for visceral leishmaniasis (VL) in symptomatic dogs naturally infected by Leishmania infantum. Sixteen dogs received immunotherapy with MPL adjuvant (n = 6) or with a vaccine composed of antigens of L. braziliensis associated with MPL (LBMPL vaccine therapy, n = 10). Dogs were submitted to an immunotherapeutic scheme consisting of 3 series composed of 10 subcutaneous doses with 10-day interval between each series. The animals were evaluated before (T0) and 90 days after treatment (T90) for their biochemical/hematological, immunological, clinical, and parasitological variables. Our major results showed that the vaccine therapy with LBMPL was able to restore and normalize main biochemical (urea, AST, ALP, and bilirubin) and hematological (erythrocytes, hemoglobin, hematocrit, and platelets) parameters. In addition, in an ex vivo analysis using flow cytometry, dogs treated with LBMPL vaccine showed increased CD3⁺ T lymphocytes and their subpopulations (TCD4⁺ and TCD8⁺), reduction of CD21⁺ B lymphocytes, increased NK cells (CD5^-CD16⁺) and CD14⁺ monocytes. Under in vitro conditions, the animals developed a strong antigen-specific lymphoproliferation mainly by TCD4⁺ and TCD8⁺ cells; increasing in both TCD4⁺IFN-γ⁺ and TCD8⁺IFN-γ⁺ as well as reduction of TCD4⁺IL-4⁺ and TCD8⁺IL-4⁺ lymphocytes with an increased production of TNF-α and reduced levels of IL-10. Concerning the clinical signs of canine visceral leishmaniasis, the animals showed an important reduction in the number and intensity of the disease signs; increase body weight as well as reduction of splenomegaly. In addition, the LBMPL immunotherapy also promoted a reduction in parasite burden assessed by real-time PCR. In the bone marrow, we observed seven times less parasites in LBMPL animals compared with MPL group. The skin tissue showed a reduction in parasite burden in LBMPL dogs 127.5 times higher than MPL. As expected, with skin parasite reduction promoted by immunotherapy, we observed a blocking transmission to sand flies in LBMPL dogs with only three positive dogs after xenodiagnosis. The results obtained in this study highlighted the strong potential for the use of this heterologous vaccine therapy as an important strategy for VL treatment.

In situ CUTANEOUS CELLULAR IMMUNE RESPONSE IN DOGS NATURALLY AFFECTED BY VISCERAL LEISHMANIASIS

Thirty-eight dogs naturally affected by visceral leishmaniasis were recruited in Araçatuba, São Paulo State, Brazil - an endemic area for visceral leishmaniasis. The animals were distributed into one of two groups, according to their clinical and laboratory features, as either symptomatic or asymptomatic dogs. Correlations between clinical features and inflammatory patterns, cellular immune responses, and parasitism in the macroscopically uninjured skin of the ear were investigated. Histological skin patterns were similar in both groups, and were generally characterized by a mild to intense inflammatory infiltrate in the dermis, mainly consisting of mononuclear cells. There was no difference in the number of parasites in the skin (amastigotes/mm²) between the two groups. Concerning the characterization of the cellular immune response, the number of positive inducible nitric oxide synthase (iNOS⁺⁾ cells was higher in the dermis of symptomatic than in asymptomatic dogs (p = 0.0368). A positive correlation between parasite density and macrophages density (p = 0.031), CD4⁺ T-cells (p = 0.015), and CD8⁺ T-cells (p = 0.023) was observed. Furthermore, a positive correlation between density of iNOS⁺ cells and CD3⁺ T-cells (p = 0.005), CD4⁺ T-cells (p = 0.001), and CD8⁺ T-cells (p = 0.0001) was also found. The results showed the existence of a non-specific chronic inflammatory infiltrate in the dermis of dogs affected by visceral leishmaniasis, characterized by the presence of activated macrophages and T-lymphocytes, associated to cutaneous parasitism, independent of clinical status.

Scoring clinical signs can help diagnose canine visceral leishmaniasis in a highly endemic area in Brazil

Canine visceral leishmaniasis (CVL) diagnosis is still a challenge in endemic areas with limited diagnostic resources. This study proposes a score with the potential to distinguish positive CVL cases from negative ones. We studied 265 dogs that tested positive for CVL on ELISA and parasitological tests. A score ranging between 0 and 19 was recorded on the basis of clinical signs. Dogs with CVL had an overall higher positivity of the majority of clinical signs than did dogs without CVL or with ehrlichiosis. Clinical signs such as enlarged lymph nodes (83.93%), muzzle/ear lesions (55.36%), nutritional status (51.79%), bristle condition (57.14%), pale mucosal colour (48.21%), onychogryphosis (58.93%), skin lesion (39.28%), bleeding (12.50%), muzzle depigmentation (41.07%), alopecia (39.29%), blepharitis (21.43%), and keratoconjunctivitis (42.86%) were more frequent in dogs with CVL than in dogs with ehrlichiosis or without CVL. Moreover, the clinical score increased according to the positivity of all diagnostic tests (ELISA, p < 0.001; parasite culture, p = 0.0021; and smear, p = 0.0003). Onychogryphosis (long nails) [odds ratio (OR): 3.529; 95% confidence interval (CI): 1.832-6.796; p < 0.001], muzzle depigmentation (OR: 4.651; 95% CI: 2.218-9.750; p < 0.001), and keratoconjunctivitis (OR: 5.400; 95% CI: 2.549-11.441; p < 0.001) were highly associated with CVL. Interestingly, a score cut-off value ≥ 6 had an area under the curve of 0.717 (p < 0.0001), sensitivity of 60.71%, and specificity of 73.64% for CVL diagnosis. The clinical sign-based score for CVL diagnosis suggested herein can help veterinarians reliably identify dogs with CVL in endemic areas with limited diagnostic resources.

Association between Leishmania infantum DNA in the hair of dogs and their infectiousness to Lutzomyia longipalpis

Diagnosis of infection with Leishmania infantum by DNA detection in the hair has been recently demonstrated in dogs and wild animals. Our objective was to investigate if polymerase chain reaction (PCR) in hair might be used to identify infectious dogs. Thus, we assessed the infectiousness to Lutzomyia longipalpis by xenodiagnosis in comparison with the detection of L. infantum DNA by PCR in the hair, and with serology for anti-Leishmania IgG by ELISA in 15 positive dogs for L. infantum infection. Eight healthy dogs were included as negative controls. Among the 15 infected dogs, 13 were found positive in the ELISA (87%), 12 were PCR positive in the hair (80%), and 10 were positive in xenodiagnosis (67%). Positivity in the hair was associated with positivity in spleen (p=0.0003), seropositivity for antibodies (p=0.0006) and parasite transmission to L. longipalpis (p=0.0028). Considering the benefits to animal welfare and feasibility of hair sampling method, studies in larger and more diverse populations of naturally infected dogs from endemic areas should be conducted to evaluate the sensitivity, specificity, and predictive values of PCR using hair as a possible biomarker of infectiousness in dogs.

Parasite load in the blood and skin of dogs naturally infected by Leishmania infantum is correlated with their capacity to infect sand fly vectors

The sand fly Lutzomyia longipalpis is primarily responsible for the transmission of visceral leishmaniasis (VL) in the New World, and dogs are considered to be the main urban reservoir of this disease. In order to improve the efficacy of control measures, it is essential to assess the transmission capacity of Leishmania infantum to the sand fly vector by naturally infected dogs. The present study investigated the existence of correlations between canine clinical presentation and the intensity of parasite load in the blood, skin and spleen of naturally infected dogs. In addition, we also attempted to establish correlations between the intensity of parasite load in canine tissue and the parasite load detected in sandflies five days after feeding on naturally infected dogs. A total of 23 dogs were examined and classified according to clinical manifestation of canine VL. Blood samples, splenic aspirate and skin biopsies were collected and parasite DNA was quantified by qPCR. Canine capacity to infect Lu. longipalpis with parasites was evaluated by xenodiagnosis and parasite loads were measured five days after feeding. No significant differences were observed with respect to canine clinical manifestation and the parasite loads detected in the blood, skin and spleen samples obtained from naturally infected dogs. Regardless of clinical canine visceral leishmaniasis (CVL) presentation and the degree of parasite burden, almost half of the dogs successfully infected sandflies with parasites, albeit to a low number of sandflies with correspondingly low parasite loads. Parasite loads in both canine blood and skin were shown to be positively correlated with the canine infectiousness to the sand fly vector, and positive correlations were also observed with respect to these tissues and the sand fly infection rate, as well as the parasite load detected in sandflies following xenodiagnosis. In conclusion, this indicates that parasite loads in both blood and skin can function as potentially reliable markers of canine capacity to infect sand fly vector.

Detection of Leishmania infantum in Lutzomyia longipalpis captured in Campo Grande, MS

Leishmaniasis is a zoonotic disease caused by protozoa of the genus Leishmania (Ross, 1903) and is the focus of considerable attention in human and veterinary medicine. In the city of Campo Grande, MS, the causative agent of visceral leishmaniasis is Leishmania infantum (= L. chagasi) primary vector, comprising approximately 92.9% of the local sandfly population, is Lutzomyia longipalpis. The aim of this work was to compare real-time PCR with PCR as a tool for the detection of the kinetoplast DNA (kDNA) of L. infantum in sandflies. Sandflies of this species were caught, and a total of 38 samples with 1-4 individuals in each sample were obtained; these were distributed across 13 districts and divided between seven urban areas of the city of Campo Grande, MS. Three positive samples were found by PCR and, when using real-time PCR, this was able to detect the presence of this agent in 6 of the 13 districts sampled, which were all located on the outskirts of the city, where indicates the greater enzootic potential of these regions, as they are closer to natural forest reserves. We conclude that real-time PCR can be used for epidemiological studies of L. infantum.

Xenodiagnosis on dogs with visceral leishmaniasis: Canine and sand fly aspects related to the parasite transmission

One of the main limitations for the effective control of canine leishmaniasis in endemic areas is the difficulty in identifying infectious dogs. The objective of this study was to determine factors, related to dogs and to parasite detection in sand flies, which are associated with the positive xenodiagnosis of Leishmania infantum using the vector Lutzomyia longipalpis. The xenodiagnosis was performed in 50 owned dogs residing in endemic areas, which were divided into three different groups: G1-26 dogs proved to be infected and classified by severity of VL clinical signs on physical examination; G2-15 dogs proved to be infected and classified by severity of clinical signs and intensity of laboratory abnormalities; G3-nine dogs that were seropositive for anti-Leishmania IgG in ELISA tests. Parasite search in the sand flies after having fed on dogs in the xenodiagnosis was performed by both methodologies, PCR and dissection followed by microscopy. In G1, 58% (15/26) of dogs were able to transmit Leishmania to the vector, when parasite detection in sand flies were performed by PCR technique, 5 days after blood meal, whereas in G2, 53% (8/15) transmitted the parasite to the vector, however, confirmation was performed by direct observation of parasite through optical miscroscopy held 10 days after blood meal. Rate of infectiousness of dogs to sand flies was positively associated to severity of disease (p=0.042 and p=0.040), regardless the method used for clinical classification or for parasite detection in sand flies after xenodiagnosis. In G1 30% (3/10) of dogs with subclinical infection were infectious to the vector, while 80% (12/16) of dogs with clinical disease were also infectious. Even more, 17% (1/6) of dogs that had moderate disease were infectious to the sand flies, while 78% (7/9) of dogs with severe disease were infectious in G2. Still in G2, the proportion of sand flies infected (grade of infectiousness) was significantly lower (p=0.0098) when they fed on dogs with moderate disease (1%) in comparison with dogs with severe disease (38%). The dogs from G3 presented a rate of infectiousness of 11% (1/9), demonstrating that the indirect ELISA is not a good indicator of infectiousness and, therefore, should not be used as a confirmatory test for the euthanasia of dogs, as it is currently done in Brazil.

Clinical, hematological and biochemical alterations in hamster (Mesocricetus auratus) experimentally infected with Leishmania infantum through different routes of inoculation

Background

Leishmaniasis remains among the most important parasitic diseases in the developing world and visceral leishmaniasis (VL) is the most fatal. The hamster Mesocricetus auratus is a susceptible model for the characterization of the disease, since infection of hamsters with L. infantum reproduces the clinical and pathological features of human VL. In this context, it provides a unique opportunity to study VL in its active form. The main goal of this study was to evaluate the clinical, biochemical, and hematological changes in male hamsters infected through different routes and strains of L. infantum.

Methods

In the current study, hamsters (Mesocricetus auratus) were infected with the L. infantum strains (WHO/MHOM/BR/74/PP75 and MCAN/BR/2008/OP46) by intradermal, intraperitoneal and intracardiac routes. The animals were monitored for a nine  month follow-up period.

Results

The hamsters showed clinical signs similar to those observed in classical canine and human symptomatic VL, including splenomegaly, severe weight loss, anemia, and leucopenia. Therefore the OP46 strain was more infective, clinical signs were more frequent and more exacerbated in IC group with 80 to 100 % of the animals showing splenomegaly, in the last month infection. Additionally, desquamation, hair loss and external mucocutaneous lesions and ulcers localized in the snout, accompanied by swelling of the paws in all animals, were observed. Consequently, the animals presented severe weight loss/cachexia, hunched posture, an inability to eat or drink, and non-responsiveness to external stimuli. Furthermore, regardless of strain, route of inoculum and time assessed, the animals showed renal and hepatic alterations, with increased serum levels of urea and creatinine as well as elevated serum levels of aspartate aminotransferase and alanine aminotransferase.

Conclusions

These results strongly suggest that the inoculation through the intracardiac route resulted in a higher severity among infections, especially in the sixth and ninth month after infection via intracardiac, exhibited clinical manifestations and biochemical/hematological findings similar to human visceral leishmaniasis. Therefore, we suggest that this route must be preferentially used in experimental infections for pathogenesis studies of VL in the hamster model.

Field randomized trial to evaluate the efficacy of the Leish-Tec® vaccine against canine visceral leishmaniasis in an endemic area of Brazil

BACKGROUND

A canine vaccine remains a promising approach for effective control of visceral leishmaniasis (VL), given its complex epidemiology in areas where zoonotic VL is prevalent. Leish-Tec(®) is a recombinant vaccine, based on the Leishmania A2 antigen, against canine VL (CVL). It is, since 2014, the single commercial vaccine licensed in Brazil. Here, Leish-Tec(®) efficacy was estimated through a randomized field trial (RFT), in a highly VL endemic area.

METHODS

The RFT was conducted from 2008 to 2010 in an endemic area of southeastern Brazil, presenting a CVL seroprevalence of 41.9%. Eight hundred forty-seven seronegative dogs were randomly selected to receive Leish-Tec(®) (n=429) or placebo (n=418). Animals were followed up by clinical, serological, and parasitological exams for 18 months. The CVL incidence in both groups was compared through proportion analysis.

RESULTS

A significant reduction in the number of cases of CVL was observed in the vaccine group, as compared with the placebo group, whether efficacy was estimated according to parasitological results (71.4%; 95% CI: 34.9-87.3%; p=0.001; risk ratio=0.287), by adding results of xenodiagnosis and parasitological exams (58.1%; 95% CI: 26.0-76.3%; p=0.002; risk ratio=0.419). Among the animals that converted to a positive anti-A2 serology, efficacy reached 80.8% (95% CI: 37.6-94.1%, p=0.001; risk ratio=0.192). Xenodiagnosis has detected a reduction of 46.6% (p=0.05) in transmission to sand flies from vaccinated animals presenting anti-A2 positive serology.

CONCLUSION

The Leish-Tec(®) vaccine proved significantly effective for prophylaxis of CVL, after natural challenge assured by transmission of Leishmania parasites, in a highly endemic area. Noteworthy, this report has unveiled the complexity of performing a RFT for anti-CVL vaccines in Brazil, which may be helpful for designing of future studies.

New Insights Into the Transmissibility of Leishmania infantum From Dogs to Sand Flies: Experimental Vector-Transmission Reveals Persistent Parasite Depots at Bite Sites

Canine leishmaniasis (CanL) is a chronic fatal disease of dogs and a major source of human infection through propagation of parasites in vectors. Here, we infected 8 beagles through multiple experimental vector transmissions with Leishmania infantum–infected Lutzomyia longipalpis. CanL clinical signs varied, although live parasites were recovered from all dog spleens. Splenic parasite burdens correlated positively with Leishmania-specific interleukin 10 levels, negatively with Leishmania-specific interferon γ and interleukin 2 levels, and negatively with Leishmania skin test reactivity. A key finding was parasite persistence for 6 months in lesions observed at the bite sites in all dogs. These recrudesced following a second transmission performed at a distal site. Notably, sand flies efficiently acquired parasites after feeding on lesions at the primary bite site. In this study, controlled vector transmissions identify a potentially unappreciated role for skin at infectious bite sites in dogs with CanL, providing a new perspective regarding the mechanism of Leishmania transmissibility to vector sand flies.

Clinical and histopathological features of myocarditis in dogs with visceral leishmaniasis

Visceral leishmaniasis (VL) is a cosmopolitan parasitic zoonosis that can promote myocarditis and heart rate changes in canine and human hosts. Thus, histopathological aspects of the myocardium and clinical, hematological, biochemical, radiological and electrocardiographic data were evaluated in a group of 36 dogs naturally infected with VL (VLG) and compared to data from 15 non-infected dogs (CG=Control Group). A prevalence of asymptomatic dogs was present in the CG (100%) and polysymptomatic dogs in the VLG (66%). In addition, two dogs in the VLG demonstrated systolic murmurs in the mitral valve region: one with a II/VI intensity and the other with a III/VI intensity. The mean values of RBC, hemoglobin and hematocrit were lower in dogs in VLG and were associated with higher values of total protein, total leukocytes, neutrophils, creatine kinase overall (CK) and the CK-MB fraction (CK-MB). The absence of radiographic changes was accompanied by a predominance of respiratory sinus arrhythmia associated with episodes of migratory pacemaker and sinus arrest in dogs in VLG (75%), sinus rhythm in dogs in CG (60%) and decreased P wave amplitude in VLG electrocardiography. Mononuclear cell infiltration was detected in the myocardium of 77,8% of dogs in GVL and classified primarily as mild multifocal lymphohistioplasmacytic. Amastigotes were detected in only one dog, which did not allow the association between myocarditis and parasitism, although the myocardial lesions that were found constitute irrefutable evidence of myocarditis in the VLG dogs, accompanied by lenient electrocardiographic changes compared to CG.

Transmissibility of Leishmania infantum from maned wolves (Chrysocyon brachyurus) and bush dogs (Speothos venaticus) to Lutzomyia longipalpis

Leishmania (Leishmania) infantum is the cause of visceral leishmaniasis in the Americas. The disease is transmitted mostly through the bite of the invertebrate vector, the phlebotomine Lutzomyia longipalpis in the New World. Although the domestic dog is considered the most important reservoir of the disease, other mammalian, including wildlife, are susceptible to infection. The goal of this study was to perform xenodiagnosis to evaluate the capacity of naturally infected maned wolves (Chrysocyon brachyurus) and bush dogs (Speothos venaticus) to transmit Leishmania infantum to female sand flies (L. longipalpis). Xenodiagnoses were performed in February and August, 2013, when 77.7% (three maned wolves and four bush dogs) or 100% of the animals were positive, respectively. However, parasite loads in the engorged sand flies was low (<200 promastigotes and <150.2 parasites/μg of DNA). No statistically significant differences were observed between the two species or the two time points (February and August). In conclusion, this study demonstrated that maned wolves (C. brachyurus) and bush dogs (S. venaticus) asymptomatically infected with L. infantum are capable of transmitting L. infantum to the invertebrate host L. longipalpis, although the parasite loads in engorged phlebotomines exposed to these animals were very low.

An Integrated Approach Using Spatial Analysis to Study the Risk Factors for Leishmaniasis in Area of Recent Transmission

Some epidemiological aspects of leishmaniasis in the municipality of Formiga, Brazil, an important touristic site, were evaluated. Those included phlebotomine sand fly vectors, canine infection, and geoprocessing analysis for determining critical transmission areas. Sand flies (224 insects) belonging to ten different species were captured. The most captured species included Lutzomyia longipalpis (35.3%), Lutzomyia cortelezzii (33.5%), and Lutzomyia whitmani (18.3%). A significant correlation between sand fly densities and climatic conditions was detected. Serological diagnosis (DPP and ELISA) was performed in 570 dogs indicating a prevalence of 5.8%. After sequencing the main species circulating in the area were Leishmania infantum and Leishmania braziliensis. Spatial analysis demonstrated that vegetation and hydrography may be related to sand fly distribution and infected dogs. The municipality of Formiga has proven leishmaniasis vectors and infected dogs indicating the circulation of the parasite in the city. Correlation of those data with environmental and human cases has identified the critical areas for control interventions (south, northeast, and northwest). In conclusion, there is current transmission of visceral and canine human cases and the city is on the risk for the appearance of cutaneous cases.

A case report of typical leishmaniasis in dog

Leishmania spp. are vector-borne flagellates transferred by sand flies. They cause cutaneous, mucocutaneous and visceral infections in mammals, especially in humans and dogs. A mature male boxer with ulcerative nodules around his eyes and snout was referred to Small Animal Hospital, Faculty of Veterinary Medicine, University of Tehran. Multiple cutaneous lesions were seen in physical examination. Mild leukocytosis, neutrophilia, left shift, lymphopenia, and thrombocytopenia were reported by the laboratory. Diagnosis was confirmed by the observation of amastigotes in blood samples and inside tissue macrophages. The infection was treated using pentavalent antimonial drug for four weeks.

Evaluation of parasitological examination, kDNA polymerase chain reaction and rK39-based immunochromatography for the diagnosis of visceral leishmaniasis in seropositive dogs from the screening-culling program in Brazil

INTRODUCTION

Dogs play a primary role in the zoonotic cycle of visceral leishmaniasis (VL). Therefore, the accurate diagnosis of infected dogs, primarily asymptomatic dogs, is crucial to the efficiency of VL control programs.

METHODS

We investigated the agreement of four diagnostic tests for canine visceral leishmaniasis (CVL): parasite detection, either after myeloculture or by direct microscopic examination of tissue imprints; kinetoplast-deoxyribonucleic acid-polymerase chain reaction (kDNA-PCR); and an immunochromatographic test (ICT). An enzyme-linked immunosorbent assay (ELISA) and an indirect immunofluorescence test (IFAT), both of which were adopted as part of the screening-culling program in Brazil, were used as reference tests. Our sample set consisted of 44 seropositive dogs, 25 of which were clinically asymptomatic and 19 were symptomatic for CVL according to ELISA-IFAT.

RESULTS

The highest and lowest test co-positivities were observed for ICT (77.3%) and myeloculture (58.1%), respectively. When analyzed together, the overall percentage of co-positive tests was significantly higher for the symptomatic group compared to the asymptomatic group. However, only ICT was significantly different based on the results of a separate analysis per test for each group of dogs. The majority (93.8%) of animals exhibited at least one positive test result, with an average of 2.66 positive tests per dog. Half of the symptomatic dogs tested positive for all four tests administered.

CONCLUSIONS

The variability between test results reinforces the need for more efficient and reliable methods to accurately diagnose canine VL, particularly in asymptomatic animals.

Pathology of dogs in Campo Grande, MS, Brazil naturally co-infected with Leishmania infantum and Ehrlichia canis

Different parasites that commonly occur concomitantly can influence one another, sometimes with unpredictable effects. We evaluated pathological aspects of dogs naturally co-infected with Leishmania infantum and Ehrlichia canis. The health status of the dogs was investigated based on histopathological, hematological and biochemical analyses of 21 animals infected solely with L. infantum and 22 dogs co- infected with L. infantum and E. canis. The skin of both groups showed chronic, predominantly lymphohistioplasmacytic inflammatory reaction. The plasmacytosis in the lymphoid tissues was likely related with the hypergammaglobulinemia detected in all the dogs. The disorganization of extracellular matrix found in the reticular dermis of the inguinal region and ear, characterized by the substitution of thick collagen fibers for thin fibers, was attributed to the degree of inflammatory reaction, irrespective of the presence of parasites. In addition, the histopathological analysis revealed that twice as many dogs in the co-infected group presented Leishmania amastigotes in the ear skin than those infected solely with Leishmania, increasing the possibility of becoming infected through sand fly vectors. Our findings highlight the fact that the health of dogs infected concomitantly with L. infantum and E. canis is severely compromised due to their high levels of total plasma protein, globulins, alkaline phosphatase and creatine kinase, and severe anemia.

Host modulation by a parasite: how Leishmania infantum modifies the intestinal environment of Lutzomyia longipalpis to favor its development

Some reports have described the interference of Leishmania on sand flies physiology, and such behavior most likely evolved to favor the development and transmission of the parasite. Most of these studies showed that Leishmania could modulate the level of proteases in the midgut after an infective blood meal, and decreased proteolytic activity is indeed beneficial for the development of promastigotes in the gut of sand flies. In the present study, we performed a detailed investigation of the intestinal pH in Lutzomyia longipalpis females naturally infected with Leishmania infantum and investigated the production of trypsin by these insects using different approaches. Our results allowed us to propose a mechanism by which these parasites interfere with the physiology of L. longipalpis to decrease the production of proteolytic enzymes. According to our hypothesis L. infantum promastigotes indirectly interfere with the production of trypsin by modulating the mechanism that controls the intestinal pH via the action of a yet non-identified substance released by promastigote forms inside the midgut. This substance is not an acid, whose action would be restrict on to release H⁺ to the medium, but is a substance that is able to interfere with midgut physiology through a mechanism involving pH control. According to our hypothesis, as the pH decreases, the proteolytic enzymes efficiency is also reduced, leading to a decline in the supply of amino acids to the enterocytes: this decline reduces the stimulus for protease production because it is regulated by the supply of amino acids, thus leading to a delay in digestion.

Interaction between canine and human visceral leishmaniases in a holoendemic focus of Central Tunisia

Canine visceral leishmaniasis (CVL) is endemic in the Mediterranean basin. In Tunisia, CVL is spatially associated with human visceral leishmaniasis (HVL) affecting mostly children younger than 5 years old. In this study, seroprevalence of Leishmania infantum infection in dogs was assessed in highly endemic districts of the governorate of Kairouan where more than 50% of HVL cases in Tunisia were reported. An entomological investigation was also carried out in two endemic districts (Bouhajla and Haffouz) to assess sand fly fauna and infection status of sand flies with Leishmania. A total of 191 serum samples were collected from healthy dogs and tested for anti-L. infantum antibodies by indirect immunofluorescence antibody test (IFAT). Overall seroprevalence for L. infantum was 26.7% being highest among dogs in the district of Bouhajla (52.7%) and the lowest in the district of Chbika (5.2%). In dogs, seroprevalence did not differ significantly based on gender or age, with dogs younger than 1 year showing a higher seroprevalence compared to older dogs. These findings suggest strong force of infection in naïve animals in holoendemic regions leading to emerging high incidence of HVL. Concomitant to the high CVL prevalence observed in the Bouhajla district, a significantly high cumulative HVL incidence also was observed in this district. Phlebotomus perniciosus and Phlebotomus longicuspis were the most abundant sand fly species in Bouhajla and Haffouz districts. The rate of Leishmania-DNA infection in sand flies was 9.4%. This finding points to spatial correlation between the occurrence of disease in humans, a high rate of infection in dogs and a high abundance of P. pernicious and P. longicuspis. Thus, CVL is the main risk factor for transmission to humans and subsequently, it is an important parameter for controlling transmission to humans.