Temporal distribution of positive results of tests for detecting Leishmania infection in stray dogs of an endemic area of visceral leishmaniasis in the Brazilian tropics: a 13 years survey and association with human disease

Spatial Analysis and Socio-Environmental Determinants of Canine Visceral Leishmaniasis in an Urban Area in Northeastern Brazil

The urbanization process has led to significant changes in the landscape, shifting the epidemiological profile of the visceral leishmaniasis (VL) in Brazil. Dogs are considered the main urban reservoir of VL, whose infections precede cases in humans. In order to understand the socio-environmental determinants associated with canine visceral leishmaniasis (CVL), we conducted a spatial analysis of CVL cases in northeastern Brazil from 2013 to 2015, georeferencing 3288 domiciled dogs. We used linear mixed models to understand the ecoepidemiological determinants of CVL spatial relative risk (CVL SRR). Our findings indicate heterogeneity in CVL distribution, with 1 km diameter clusters potentially connected within an estimated 4.9 km diameter by the Ripley-K statistic. In our best-fit model, the CVL SRR was positively correlated with the proportion of households with literate heads, with trees, and with open sewage, but negatively correlated with vegetation phenology and mean income of the census sector. Here, we discuss the potential maintenance source of urban CVL clusters on a One Health framework. These findings highlight the complex interplay of socioeconomic and environmental factors in shaping the spatial distribution of CVL.

Global Distribution of Canine Visceral Leishmaniasis and the Role of the Dog in the Epidemiology of the Disease

Visceral leishmaniasis is a disease caused by protozoa of the species Leishmania (Leishmania) infantum (syn = Leishmania chagasi) and Leishmania (Leishmania) donovani, which are transmitted by hematophagous insects of the genera Lutzomyia and Phlebotomus. The domestic dog (Canis familiaris) is considered the main urban reservoir of the parasite due to the high parasite load on its skin, serving as a source of infection for sandfly vectors and, consequently, perpetuating the disease in the urban environment. Some factors are considered important in the perpetuation and spread of canine visceral leishmaniasis (CVL) in urban areas, such as stray dogs, with their errant behavior, and houses that have backyards with trees, shade, and organic materials, creating an attractive environment for sandfly vectors. CVL is found in approximately 50 countries, with the number of infected dogs reaching millions. However, due to the difficulty of controlling and diagnosing the disease, the number of infected animals could be even greater. In the four continents endemic for CVL, there are reports of disease expansion in endemic countries such as Brazil, Italy, Morocco, and Tunisia, as well as in areas where CVL is not endemic, for example, Uruguay. Socio-environmental factors, such as migration, drought, deforestation, and global warming, have been pointed out as reasons for the expansion into areas where it had been absent. Thus, the objective of this review is to address (i) the distribution of CVL in endemic areas, (ii) the role of the dog in the visceral leishmaniasis epidemiology and the factors that influence dog infection and the spread of the disease, and (iii) the challenges faced in the control of CVL.

Transmission-Blocking Vaccines for Canine Visceral Leishmaniasis: New Progress and Yet New Challenges

Dogs with visceral leishmaniasis play a key role in the transmission cycle of Leishmania infantum to humans in the urban environment. There is a consensus regarding the importance of developing a vaccine to control this disease. Despite many efforts to develop a protective vaccine against CVL, the ones currently available, Leish-tec® and LetiFend®, have limited effectiveness. This is due, in part, to the complexity of the immune response of the naturally infected dogs against the parasite and the complexity of the parasite transmission cycle. Thus, strategies, such as the development of a transmission-blocking vaccines (TBVs) already being applied to other vector-borne diseases like malaria and dengue, would be an attractive alternative to control leishmaniasis. TBVs induce the production of antibodies in the vertebrate host, which can inhibit parasite development in the vector and/or interfere with aspects of vector biology, leading to an interruption of parasite transmission. To date, there are few TBV studies for CVL and other leishmaniasis forms. However, the few studies that exist show promising results, thus justifying the further development of this approach.

Sensitivity comparison for the Leishmania spp. detection in different canine tissues using PCR-HRM

BACKGROUND

Leishmaniasis is a vector-borne disease caused by a parasite protozoon from the genus Leishmania. Among the molecular techniques applied for detecting these parasites, real-time PCR with High Resolution Melting (PCR-HRM) proved advantageous since it simultaneously determines both the presence and species of the pathogen in one step, through amplification and later analysis of curves generated by melting temperature.

METHODS

Based on this molecular technique, the goal of this study was to estimate the PCR-HRM sensitivity for Leishmania spp. detection in different canine tissues by evaluating biological samples obtained from popliteal, submandibular, and pre-scapular lymph nodes, from bone marrow and ear pinnae of 28 stray dogs captured in the metropolitan area of Asunción (Paraguay).

RESULTS

The rk39 immunochromatographic test showed that 25/28 tested dogs (89%) presented antibodies against L. infantum. In 20/25 dogs that tested positive for rk39 (80%), it was possible to detect Leishmania spp. by PCR-HRM and determine that the species corresponded entirely to L. infantum. Regarding the analysis of different tissues, the parasite was detected in all popliteal lymph node samples, followed by high detection in submandibular (at 95%) and pre-scapular lymph nodes (at 90%), bone marrow (at 85%), and ear pinnae (at 85%).

CONCLUSIONS

This study demonstrated that the use of real-time PCR-HRM using the molecular marker hsp70 was a highly sensitive method for simultaneously detecting and identifying Leishmania species in different tissues taken from infected dogs. In addition, the usefulness of ear pinnae as easily accessible tissue for molecular diagnosis was emphasized.

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.

Comparison of serological and molecular tests to investigate Leishmania spp. infections in stray dogs from an area of intense visceral leishmaniasis transmission in Brazil

The aim of this study was to investigate the level of exposure to Leishmania infection in stray dogs in an area of intense visceral leishmaniasis transmission in the state of Pernambuco, Brazil. Blood samples from 178 dogs were analyzed using serological and molecular assays: rapid immunochromatographic test (ICT), enzyme-linked immunosorbent assay (ELISA), immunofluorescence antibody test (IFAT), and conventional and quantitative polymerase chain reaction (cPCR and qPCR). Positivity values obtained with serological tests were 71.4% (127/178), 70.2% (125/178), and 50.6% (90/178) using ICT, ELISA, and IFAT, respectively, with 38.8% (69/178) of the dogs were simultaneously positive for all three tests. The positivity values obtained with cPCR and qPCR were 20.2% (36/178) and 38.8% (69/178), respectively, with 11.8% (21/178) testing positive in both molecular assays. Overall, 87.1% (155/178) were positive for anti-Leishmania spp. antibodies and/or Leishmania spp. DNA. Positivity to one or more tests was statistically associated with lymphadenomegaly, skin lesions, lymphocytosis, anemia and hyperproteinemia. The results of this study revealed a high level of exposure to Leishmania in stray dogs in an area of intense human visceral leishmaniasis transmission, suggesting that dogs play a role as reservoirs in the transmission cycle of this zoonosis.

A Novel Sampling Model to Study the Epidemiology of Canine Leishmaniasis in an Urban Environment

Background: Visceral leishmaniasis (VL) is one of the most important parasitic diseases in the world. The domestic dog is the main reservoir of zoonotic VL and a high prevalence of canine leishmaniasis (CanL) is associated with transmission of infection to humans. Here we describe the methodology used to obtain a rapid and representative sample of domestic dogs in the city of Posadas, Misiones, and compare the prevalence of Leishmania infection with a sample of shelter dogs.

Methodology: We used the city land registry to make a random selection of homes and systematically recruited 349 domestic dogs from the selected properties. We also included all dogs from the main canine shelter within the city. Dogs were examined by two experienced veterinarians who recorded the presence of clinical signs common in CanL using a standardized protocol. We extracted a blood sample from each dog and performed four different serological tests to reveal the presence of anti-Leishmania antibodies.

Results: After clinical examination, 145 domestic dogs (41.5%) and 63 (90%) shelter dogs had clinical signs compatible with CanL (p < 0.001). The seroprevalence among domestic dogs was 20.1% (95% CI 16.1–24.6) which was significantly lower than among the abandoned dogs (38.6%, 95% CI 27.7–50.6, p < 0.001). The spatial distribution of infected dogs was fairly homogenous throughout the city. Among domestic dogs, we observed a positive association between where the dog slept and presence of anti-Leishmania antibodies (p = 0.034). Of the seropositive domestic dogs 38 (54.4%) were asymptomatic.

Conclusions: Our findings demonstrate how seroprevalence results can be highly influenced by sampling methodology. We demonstrate how the land registry can be used to estimate the prevalence of CanL in representative sample of domestic dogs in an urban setting, allowing decision makers to deepen their understanding the epidemiology of CanL in a timely and efficient manner for the development of plans to address both human and canine disease.

Spatio-temporal modelling of Leishmania infantum infection among domestic dogs: a simulation study and sensitivity analysis applied to rural Brazil

BACKGROUND

The parasite Leishmania infantum causes zoonotic visceral leishmaniasis (VL), a potentially fatal vector-borne disease of canids and humans. Zoonotic VL poses a significant risk to public health, with regions of Latin America being particularly afflicted by the disease. Leishmania infantum parasites are transmitted between hosts during blood-feeding by infected female phlebotomine sand flies. With a principal reservoir host of L. infantum being domestic dogs, limiting prevalence in this reservoir may result in a reduced risk of infection for the human population. To this end, a primary focus of research efforts has been to understand disease transmission dynamics among dogs. One way this can be achieved is through the use of mathematical models.

METHODS

We have developed a stochastic, spatial, individual-based mechanistic model of L. infantum transmission in domestic dogs. The model framework was applied to a rural Brazilian village setting with parameter values informed by fieldwork and laboratory data. To ensure household and sand fly populations were realistic, we statistically fitted distributions for these entities to existing survey data. To identify the model parameters of highest importance, we performed a stochastic parameter sensitivity analysis of the prevalence of infection among dogs to the model parameters.

RESULTS

We computed parametric distributions for the number of humans and animals per household and a non-parametric temporal profile for sand fly abundance. The stochastic parameter sensitivity analysis determined prevalence of L. infantum infection in dogs to be most strongly affected by the sand fly associated parameters and the proportion of immigrant dogs already infected with L. infantum parasites.

CONCLUSIONS

Establishing the model parameters with the highest sensitivity of average L. infantum infection prevalence in dogs to their variation helps motivate future data collection efforts focusing on these elements. Moreover, the proposed mechanistic modelling framework provides a foundation that can be expanded to explore spatial patterns of zoonotic VL in humans and to assess spatially targeted interventions.

Prevalence of visceral leishmaniasis in A population of free-roaming dogs as determined by multiple sampling efforts: A longitudinal study analyzing the effectiveness of euthanasia

Free-roaming dogs affected by visceral leishmaniasis (VL) contribute to the geographical expansion of the disease and require special attention from health authorities. The objectives of the present study were to determine the prevalences of VL in a population of free-roaming dogs in an endemic region of Brazil, to establish the spatial distribution of infected dogs, and to examine the effectiveness of euthanasia of infected dogs in controlling the disease in this particular population. Dogs were captured every two months during seven sampling efforts. Capture locations were georeferenced and captured dogs were assessed for the presence of anti-Leishmania antibodies using an enzyme-linked immunosorbent assay (ELISA) as a screening test and the indirect fluorescent antibody test (IFAT) as the confirmatory procedure. Dogs that were seropositive by both assays were considered infected and were submitted to immediate euthanasia. After the end of the collection period, stored sera were evaluated with the Dual-Path Platform test (DPP). Animals positive by this method and by ELISA were also considered infected as currently recommended by the Brazilian Ministry of Health. Spatial analysis was performed using the Kernel technique. A total of 328 dogs were captured at least once during the sampling period, 25 (7.6%) of them were seropositive by ELISA and IFAT and 27 (8.2%) by DPP and ELISA. The prevalence of VL showed an overall decreasing trend. However, even with periodical euthanasia, it was not possible to eliminate the infection and increased prevalences were observed in the fourth and seventh samplings. There was a high overall agreement between the two criteria for defining infection. None of the dogs that tested negative by IFAT at the first capture seroconverted in the subsequent captures but a number of dogs exhibited changes in serological status over time. From the three dogs initially tested negative by ELISA and IFAT, but tested positive by the protocol currently adopted in Brazil, two became negative in subsequent recaptures. Spatial analysis revealed that infected animals concentrated in areas with a high density of free-roaming dogs. The existence of VL among homeless dogs may contribute significantly in the persistence of the disease among the human population, despite the practice of periodical euthanasia. The operational and ethical implications associated with euthanasia of free-roaming dogs, and the failure to control the transmission of VL among this particular population, led us to conclude that interventions promoting responsible ownership of pets may be a more effective strategy.

High seroprevalence and peripheral spatial distribution of visceral leishmaniasis among domestic dogs in an emerging urban focus in Central Brazil: a cross-sectional study

The Brazilian municipality of Rondonópolis is an emerging urban focus of intense transmission of visceral leishmaniasis (VL), where few investigations have addressed canine reservoirs. This study assessed the seroprevalence and spatial distribution of canine visceral leishmaniasis (CVL) in the urban area of Rondonópolis. A CVL serosurvey was conducted between October 2016 and February 2017 using an immunochromatographic rapid test and enzyme-linked immunosorbent assay. Domestic dogs were sampled from 25 heterogeneous regions previously defined by the Spatial 'K'luster Analysis by Tree Edge Removal algorithm, which considered the socioeconomic and environmental features from the last demographic census. The CVL spatial distribution was analyzed by kernel density estimation (KDE) and spatial scan statistic. All the  autochthonous human VL cases reported between 2014 and 2016 were georeferenced. Of the 600 dogs tested, 115 were seropositive in both tests. The overall CVL prevalence was 19.2% (95%CI: 16.1-22.3%), which varied widely among the evaluated regions (0.0-35.1%). Almost 25% of the sampled households (n = 405) had at least one infected dog. KDE demonstrated that positive CVL households were concentrated in the peripheral areas of the city. Spatial scan statistics detected a spatial cluster with significantly low CVL prevalence in the central region (relative risk = 0.37; p = 0.04), where only one human VL case was reported. Thus, we demonstrated a high prevalence of CVL in domestic dogs from diverse socioeconomic and environmental urban contexts in Rondonópolis. The CVL cases were peripherally distributed and occurred more frequently in areas that had reported human VL.

Risk profile for Leishmania infection in dogs coming from an area of visceral leishmaniasis reemergence

Until the 1980s, visceral leishmaniasis was concentrated in poor rural areas of Brazil. The Vale do Rio Doce, located in the Southeastern Brazilian state of Minas Gerais, was an endemic area with high numbers of human and canine cases. Prophylactic measures adopted since the 1960s reduced the number of cases and the region became a 'controlled endemic' area. In the early 1990s, however, the program was interrupted, and the human disease reemerged in 2008. This cross-sectional study evaluated the prevalence and the risk profile of infection of dogs with Leishmania spp in this reemergence area of visceral leishmaniasis. Among a population of approximately 280,000 people, a total of 3835 dog owners were interviewed about socioeconomic conditions, housing, peridomicile features, and their dogs' characteristics and behavior. Blood samples were collected from 5822 dogs of an estimated canine population of 20,000 and anti-Leishmaniasis antibodies were identified using Dual-Path Platform and ELISA. We observed that 1282 of the 5822 dogs were seropositive for the protozoan indicating a seroprevalence of 22%. The risk factors associated with Leishmania infection in dogs were: non-paved backyard (OR 1.4; 95%CI 1.2-1.7); the presence of dry leaves and decaying fruit in the backyard (OR 1.3; 95%CI 1.1-1.5); medium-sized (OR 1.3; 95% 1.1-1.5) or big-sized dogs (OR 1.8; 95%CI 1.5-2.3); short-haired dogs (OR 1.8; 95%CI 1.5-2.1); dogs that slept in the backyard (OR 2.6; 95%CI 1.8-3.6) or in the balcony (OR 1.6; 95%CI 1.1-2.3); and history of canine visceral leishmaniasis in the household (OR 1.3; 95%CI 1.1-1.5). Our results suggest a strong reemergence of canine visceral leishmaniasis after the discontinuation of the control programs. Also, the observed risk factors reinforce the role of health education and environmental management measures to the effective control of the disease.

Epidemiological aspects and risk factors for infection by Leishmania infantum chagasi in dogs from municipality of Petrolina, Northeastern Brazil

Visceral leishmaniasis (VL) is a disease of great concern for public health because of its high incidence and lethality. Here, we performed a serologic study of domestic dogs in the municipality of Petrolina in northeastern Brazil to evaluate the possible risk factors associated with canine seropositivity for Leishmania infantum chagasi. Blood samples from 1245 dogs in urban and rural areas were collected and examined by indirect immunofluorescent antibody test (IFAT) and an indirect enzyme-linked immunosorbent assay (ELISA). The dogs were subjected to physical examination and classified according to their clinical manifestations. A questionnaire was administered to the owners to detect potential risk factors for infection with Leishmania spp. using logistic regression models. Of the 1245 dogs evaluated, 11.2% (140/1245) were seropositive in both tests (CI 95%: 9.5% to 13.1%). Approximately 60.7% of the reactive dogs were clinically suspect, with lymphadenomegaly, cutaneous ulcerations, onychogryphosis, pale mucous membranes and alopecia being the most obvious symptoms of infection. The seroprevalences in urban and rural areas were 5.4% (CI 95%: 4% to 7.1%) and 23.6% (CI 95%: 19.5% to 28.1%), respectively. The possible risk factors for the presence of anti L. infantum chagasi antibodies were the presence of a green area close to the home of the animal (OR=3.63; p<0.001), a mongrel breed (OR=2.11; p=0.025) and male gender (OR=1.51, p=0.034). The seroprevalence of L. infantum chagasi in the canine population is distributed in a heterogeneous manner, with a higher prevalence in rural areas.

Immunological profile of resistance and susceptibility in naturally infected dogs by Leishmania infantum

Visceral leishmaniasis has a great impact on public health, and dogs are considered the main domestic reservoir of Leishmania infantum, the causal parasite. In this study, 159 animals naturally infected by L. infantum from an endemic area of Brazil were evaluated through an analysis of cellular responses, using flow cytometry, and of the hematological parameters. The results confirmed that disease progression is associated with anemia and reductions in eosinophils, monocytes and lymphocytes. The investigation of the immune response, based on the immunophenotypic profile of peripheral blood, showed declines in the absolute numbers of T lymphocytes CD5(+) and their subsets (CD4(+) and CD8(+)) and a drop of B lymphocytes in asymptomatic seropositive (AD-II) and symptomatic seropositive (SD) dogs. Neutrophils, when stimulated with soluble antigen of L. infantum, showed higher synthesis of interferon (IFN)-γ(+) in AD-II and SD groups, with decreased production of interleukin (IL)-4(+) in asymptomatic seronegative dogs positive for L. infantum infection based on polymerase chain reaction testing (AD-I group). In the AD-II and SD groups, subpopulations of stimulated lymphocytes (CD4(+) and CD8(+)) also exhibited greater synthesis of IFN-γ(+) and IL-4(+) in culture. These results suggest that the animals of the AD-II and SD groups exhibited a mixed immune response (Type 1 and 2) and the AD-I group presenting an immune profile very similar to normal control animals.

Immunotherapy and Immunochemotherapy in Visceral Leishmaniasis: Promising Treatments for this Neglected Disease

Leishmaniasis has several clinical forms: self-healing or chronic cutaneous leishmaniasis or post-kala-azar dermal leishmaniasis; mucosal leishmaniasis; visceral leishmaniasis (VL), which is fatal if left untreated. The epidemiology and clinical features of VL vary greatly due to the interaction of multiple factors including parasite strains, vectors, host genetics, and the environment. Human immunodeficiency virus infection augments the severity of VL increasing the risk of developing active disease by 100–2320 times. An effective vaccine for humans is not yet available. Resistance to chemotherapy is a growing problem in many regions, and the costs associated with drug identification and development, make commercial production for leishmaniasis, unattractive. The toxicity of currently drugs, their long treatment course, and limited efficacy are significant concerns. For cutaneous disease, many studies have shown promising results with immunotherapy/immunochemotherapy, aimed to modulate and activate the immune response to obtain a therapeutic cure. Nowadays, the focus of many groups centers on treating canine VL by using vaccines and immunomodulators with or without chemotherapy. In human disease, the use of cytokines like interferon-γ associated with pentavalent antimonials demonstrated promising results in patients that did not respond to conventional treatment. In mice, immunomodulation based on monoclonal antibodies to remove endogenous immunosuppressive cytokines (interleukin-10) or block their receptors, antigen-pulsed syngeneic dendritic cells, or biological products like Pam3Cys (TLR ligand) has already been shown as a prospective treatment of the disease. This review addresses VL treatment, particularly immunotherapy and/or immunochemotherapy as an alternative to conventional drug treatment in experimental models, canine VL, and human disease.

Evaluation of change in canine diagnosis protocol adopted by the visceral leishmaniasis control program in Brazil and a new proposal for diagnosis

The techniques used for diagnosis of canine visceral leishmaniasis (CVL) in Brazil ELISA and IFAT have been extensively questioned because of the accuracy of these tests. A recent change in the diagnosis protocol excluded IFAT and included the Dual-Path Platform (DPP). We evaluated the prevalence and incidence rates of Leishmania spp. before and after the change in the protocol. In addition, based on our results, we propose a new alternative that is less expensive for the screening and confirmation of CVL. Plasma samples were obtained from a serobank from dogs evaluated in a cross-sectional study (1,226 dogs) and in a cohort study of susceptible animals (n = 447), followed for 26 months. Serology testing was performed using ELISA, IFAT, and DPP. The incidence and prevalence of CVL were determined by using the protocol of the Visceral Leishmaniasis Control and Surveillance Program until 2012 (ELISA and IFAT using filter paper) and the protocol used after 2012 (DPP and ELISA using plasma). The prevalence was 6.2% and the incidence was 2.8 per 1,000 dog-months for the protocol used until 2012. For the new diagnosis protocol for CVL resulted in an incidence of 5.4 per 1,000 dog-months and a prevalence of 8.1%. Our results showed that the prevalence and incidence of infection were far greater than suggested by the previously used protocol and that the magnitude of infection in endemic areas has been underestimated. As tests are performed sequentially and euthanasia of dogs is carried out when the serological results are positive in both tests, the sequence does not affect the number of animals to be eliminated by the Control Program. Then we suggest to municipalities with a large demand of exams to use ELISA for screening and DPP for confirmation, since this allows easier performance and reduced cost.

Severe clinical presentation of visceral leishmaniasis in naturally infected dogs with disruption of the splenic white pulp

In this work, we investigated the association between the disruption of splenic lymphoid tissue and the severity of visceral leishmaniasis in dogs. Clinical and laboratory data from 206 dogs were reviewed. Spleen sections collected during the euthanasia of these animals were analyzed, and the splenic lymphoid tissue samples were classified as well organized (spleen type 1), slightly disorganized (spleen type 2), or moderately to extensively disorganized (spleen type 3). Of 199 dogs with evidence of Leishmania infection, 54 (27%) had spleen type 1, 99 (50%) had spleen type 2, and 46 (23%) had spleen type 3. The number of clinical signs associated with visceral leishmaniasis was significantly higher in the animals with evidence of Leishmania infection and spleen type 2 or 3 than in the animals with spleen type 1. Alopecia, anemia, dehydration, dermatitis, lymphadenopathy, and onychogryphosis were all more frequent among animals with evidence of Leishmania infection and spleen type 3 than among the dogs with evidence of Leishmania infection and spleen type 1. The association between the severity of canine visceral leishmaniasis and the disorganization of the splenic lymphoid tissue was even more evident in the group of animals with positive spleen culture. Conjunctivitis and ulceration were also more common in the animals with spleen type 3 than in the animals with spleen type 1. The serum levels (median, interquartile range) of albumin (1.8, 1.4–2.3 g/dL) and creatinine (0.7, 0.4–0.8 mg/dL) were significantly lower and the serum levels of aspartate aminotransferase were significantly higher (57, 39–95 U) in animals with spleen type 3 than in animals with spleen type 1 (2.8, 2.4–3.4 g/dL; 0.9, 0.7–1.2 mg/dL and 23, 20–32 U, respectively). Our data confirm the hypothesis that disruption of the splenic lymphoid tissue is associated with a more severe clinical presentation of canine visceral leishmaniasis.

Activity of Thymus capitellatus volatile extract, 1,8-cineole and borneol against Leishmania species

In the search for new leishmanicidal agents, Thymus capitellatus Hoffmanns. & Link (family Lamiaceae) volatile extract and its major compounds, 1,8-cineole and borneol, were tested against Leishmania infantum, Leishmania tropica and Leishmania major. Plant volatile extract (essential oil) was analysed by GC and GC-MS and the activity of essential oil on Leishmania promastigotes viability was assessed using tetrazolium-dye colorimetric method (MTT). The MTT test was also used to assess the cytotoxicity of essential oil on macrophages and bovine aortic endothelial cells. Effects on parasites were also analyzed by flow cytometry in order to assess mitochondrial transmembrane electrochemical gradient (JC-1), analyze phosphatidylserine externalization (annexin V-FITC, propidium iodide) and evaluate cell cycle (DNase-free, RNase, PI). Morphological and ultrastructural studies were performed by light, scanning and transmission electron microscopy. T. capitellatus volatile extract exhibited anti-parasite activity on Leishmania species, with IC50 values ranging from 35 to 62 μg/ml. However, major compounds 1,8-cineole and borneol did not showed biological activity suggesting that these monoterpenes are not responsible for the antileishmanial activity of T. capitellatus essential oil. Appearance of aberrant-shaped cells, mitochondrial swelling and autophagosomal structures were some of the ultrastructural alterations exhibited among treated promastigote cells. T. capitellatus promoted leishmanicidal effect by triggering a programmed cell death as evidenced by externalization of phosphatidylserine, loss of mitochondrial membrane potential, and cell-cycle arrest at the G(0)/G(1) phase. The volatile extract did not induced cytotoxic effects on mammalian cells. Taken together, these results suggest that T. capitellatus may represent a valuable source for therapeutic control of leishmaniasis in humans and animals.