Vaccination against canine leishmaniasis in Brazil

New paradigms in the prevention of canine vector-borne diseases

The prevention of canine vector-borne diseases (CVBDs) is pivotal for the health and welfare of dogs as well as for reducing their zoonotic risk to humans. Scientific knowledge gained in recent years contributed to the development of new strategies for the control of these diseases in different social and cultural contexts. Here, we discuss recent advances in the prevention of vector-borne pathogens (VBPs) affecting dogs with a focus on those of zoonotic relevance.

Canine leishmaniasis in the Americas: etiology, distribution, and clinical and zoonotic importance

Canine leishmaniasis is a widespread disease on the American continent, with cases reported from Uruguay to the USA and Canada. While numerous Leishmania spp. have been reported in dogs in this region, Leishmania infantum and Leishmania braziliensis are the most common etiological agents of canine leishmaniasis from a continental perspective. Nonetheless, other species may predominate locally in some countries. The participation of dogs in the transmission cycle of various Leishmania spp. has long been speculated, but evidence indicates that their role as reservoirs of species other than L. infantum is negligible. Various native wildlife (e.g., small rodents, marsupials, sloths, and monkeys) are, in fact, the primary hosts of Leishmania spp. in the Americas. In this review, an updated list of Leishmania spp. infecting dogs in the Americas is presented, along with their distribution and clinical and zoonotic importance.

Synthetic Peptides Selected by Immunoinformatics as Potential Tools for the Specific Diagnosis of Canine Visceral Leishmaniasis

Diagnosing canine visceral leishmaniasis (CVL) in Brazil faces challenges due to the limitations regarding the sensitivity and specificity of the current diagnostic protocol. Therefore, it is urgent to map new antigens or enhance the existing ones for future diagnostic techniques. Immunoinformatic tools are promising in the identification of new potential epitopes or antigen candidates. In this study, we evaluated peptides selected by epitope prediction for CVL serodiagnosis in ELISA assays. Ten B-cell epitopes were immunogenic in silico, but two peptides (peptides No. 45 and No. 48) showed the best performance in vitro. The selected peptides, both individually and in combination, were highly diagnostically accurate, with sensitivities ranging from 86.4% to 100% and with a specificity of approximately 90%. We observed that the combination of peptides showed better performance when compared to peptide alone, by detecting all asymptomatic dogs, showing lower cross-reactivity in sera from dogs with other canine infections, and did not detect vaccinated animals. Moreover, our data indicate the potential use of immunoinformatic tools associated with ELISA assays for the selection and evaluation of potential new targets, such as peptides, applied to the diagnosis of CVL.

Intramuscular Immunization with a Liposomal Multi-Epitope Chimeric Protein Induces Strong Cellular Immune Responses against Visceral Leishmaniasis

Control of the intracellular parasite Leishmania (L.) requires the activation of strong type 1 cellular immune responses. Towards this goal, in the present study, a multiepitope chimeric protein named LiChimera was encapsulated into cationic liposomes and its protective efficacy against experimental visceral leishmaniasis was investigated. Liposomal LiChimera conferred significant protection against L. infantum as evidenced by the significantly reduced parasite loads in the spleen and liver. Protection detected in Lipo:LiChimera-immunized mice was dependent on the differentiation of long-lasting cellular immune responses and particularly the induction of antigen-specific multifunctional memory CD4+ TH1 and CD8+ T cells that persisted during infection, as evidenced by the persistent high production of IFN-γ and IL-2 and proliferation activity. Notably, protected mice were also characterized by significantly low numbers of non-regulatory CD4+ T cells able to co-produce IFN-γ and IL-10, an important population for disease establishment, as compared to non-immunized control group. Collectively, these results demonstrate that cationic liposomes containing LiChimera can be considered an effective candidate vaccine against visceral leishmaniasis.

Cutaneous leishmaniasis situation analysis in the Islamic Republic of Iran in preparation for an elimination plan

Iran has invariably been under the growing public health threat of cutaneous leishmaniasis (CL), a significant barrier to local development that hinders the prevention and control efforts toward eliminating the disease. So far, no comprehensive and in-depth epidemiological analysis of the CL situation has been carried out nationwide. This study aimed to employ advanced statistical models to analyze the data collected through the Center for Diseases Control and Prevention of Communicable Diseases during 1989-2020. However, we emphasized the current trends, 2013-2020, to study temporal and spatial CL patterns. In the country, the epidemiology of CL is incredibly intricate due to various factors. This fact indicates that the basic infrastructure, the preceding supports, and the implementation plan related to preventive and therapeutic measures need crucial support. The leishmaniasis situation analysis is consistent with desperate requirements for efficient information on the control program in the area. This review provides evidence of temporally regressive and spatially expanding incidence of CL with characteristic geographical patterns and disease hotspots, signifying an urgent need for comprehensive control strategies. This information could be a suitable model and practical experience in the Eastern Mediterranean Region, where over 80% of CL is reported.

Insights into the drug screening approaches in leishmaniasis

Leishmaniasis, a tropically neglected disease, is responsible for the high mortality and morbidity ratio in poverty-stricken areas. Currently, no vaccine is available for the complete cure of the disease. Current chemotherapeutic regimens face the limitations of drug resistance and toxicity concerns indicating a great need to develop better chemotherapeutic leads that are orally administrable, potent, non-toxic, and cost-effective. The anti-leishmanial drug discovery process accelerated the desire for large-scale drug screening assays and high-throughput screening (HTS) technology to identify new chemo-types that can be used as potential drug molecules to control infection. Using the HTS approach, about one million compounds can be screened daily within the shortest possible time for biological activity using automation tools, miniaturized assay formats, and large-scale data analysis. Classical and modern in vitro screening assays have led to the progression of active compounds further to ex vivo and in vivo studies. In the present review, we emphasized on the HTS approaches employed in the leishmanial drug discovery program. Recent in vitro screening assays are widely explored to discover new chemical scaffolds. Developing appropriate experimental animal models and their related techniques is necessary to understand the pathophysiological processes and disease host responses, paving the way for unraveling novel therapies against leishmaniasis.

Canine Leishmaniasis in an Endemic Area for Human Leishmaniasis in Nicaragua

In this study, the frequency of canines infected with Leishmania spp. in an area endemic to leishmaniasis in humans was determined. A descriptive pilot study was conducted between the months of October and December 2020 on dogs from Rota, a community in the municipality of León, which included 45 specimens from the peridomestic area. Different variables from each specimen were monitored, such as age, sex, breed, body condition, and clinical characteristics, as well as information on the owners and cases of human leishmaniasis presented in less than 5 years. Blood samples were collected from the cephalic vein and peripheral blood was separated. A complete blood count (CBC) was performed using venous blood samples with ethylene diamine tetraacetic acid (EDTA), as well as a conventional PCR was applied for the detection of Leishmania spp. Amastigotes were found in 22% of venous or peripheral blood samples, whereas a high prevalence of 28.89% (95% CI: 14.53–43.24) was found by PCR. Only 1/12 of positive dogs in PCR presented dry exfoliative dermatitis, therefore, there was no significant difference (p ≥ 0.05), the age and sex of the dogs were also not factors associated with infection (p ≥ 0.05). This study reports for the first time the molecular detection of Leishmania in dogs in an endemic area of leishmaniasis in humans in Nicaragua. The high frequency of dogs infected with Leishmania suggests that they play an important role in the transmission cycle of human leishmaniasis.

Canine Leishmaniasis: Update on Epidemiology, Diagnosis, Treatment, and Prevention

Dog are the main reservoir of Leishmania infantum, causing canine leishmaniasis, an incurable multisystemic disease that leads to death in symptomatic dogs, when not treated. This parasite causes visceral, cutaneous, and mucosal leishmaniasis in people in the Mediterranean Basin, North Africa, South America, and West Asia. This disease is mostly unknown by veterinarians outside the endemic areas, but the disease is expanding in the Northern Hemisphere due to travel and climate change. New methodologies to study the epidemiology of the disease have found new hosts of leishmaniasis and drawn a completely new picture of the parasite biological cycle. Canine leishmaniasis diagnosis has evolved over the years through the analysis of new samples using novel molecular techniques. Given the neglected nature of leishmaniasis, progress in drug discovery is slow, and the few drugs that reach clinical stages in humans are unlikely to be commercialised for dogs, but several approaches have been developed to support chemotherapy. New-generation vaccines developed during the last decade are now widely used, along with novel prevention strategies. The implications of the epidemiology, diagnosis, treatment, and prevention of canine leishmaniasis are fundamental to public health.

Elevated and sustained anti-feeding effect of Scalibor® deltamethrin collar against the sand fly Phlebotomus perniciosus in dogs confirmed for 1 year following treatment

Dogs are reservoir hosts for Leishmania infantum, a protozoan parasite transmitted by phlebotomine sand flies. The anti-feeding and fast-killing efficacy of Scalibor® deltamethrin collars against experimental Phlebotomus perniciosus challenges on dogs was determined over 1 year. Two groups of 8 dogs each were fitted with placebo (control) or deltamethrin collars (treated) on Day 0 and exposed to sand flies approximately every 28 days up to Day 364. After each exposure, anti-feeding and fast-killing efficacy rates were determined by comparing blood-fed or live insects, respectively, in the treated vs. the control group. Blood-fed and live sand flies were significantly less in treated dogs as compared to control dogs at each assessment. The anti-feeding efficacy rate exceeded 90% except on Day 337 (89%) but increased again (96%) on Day 364. Fast killing efficacy was <74% over the study when considering all flies. However, this value increased cumulatively to 98% when only blood-fed flies were compared between groups. Scalibor® collars are highly effective at preventing P. perniciosus blood-feeding and in fast-killing flies taking a blood meal for up to 1 year after application. These strong and long-lasting effects are an important strategic component for L. infantum transmission control.

Live attenuated Leishmania major p27 gene knockout as a novel vaccine candidate: A study on safety, protective immunity and efficacy against canine leishmaniasis caused by Leishmania infantum

Canine leishmaniasis (CanL) is an important parasitic e disease caused by Leishmania infantum and is transmitted by female phlebotomine sand flies primarily between canines and secondarily to humans. Recently, we showed that immunization with Leishmania major p27 gene knockout (Lmp27^-/-) as a live attenuated vaccine was safe, induced immunogenicity, and protected against the development cutaneous and visceral leishmaniasis in mice. The p27 protein is a component of the COX protein complex which is responsible for ATP production. In this study, we analyzed the Lmp27^-/- candidate vaccine potential with this regard to the safety and induction of immunogenicity and protection against CanL. Variables such a clinical manifestation, anti-Leishmania antibodies using direct agglutination test (DAT), lymphocyte proliferation, delayed-type hypersensitivity (DTH), bone marrow aspiration (BMA) and parasite burden using parasitological and molecular examinations were measured. The results demonstrated that the Lmp27^-/- vaccinated group showed no clinical signs after inoculation with Lmp27^-/- mutant during a 12-month follow-up, and had significantly higher T-cell responses (Lymphocyte proliferation and DTH), lower seroconversion and parasite burdens following a challenge inoculation with L. infantum after 6-mounth. In conclusion, vaccination with Lmp27^-/- parasites would be safe and provide significant immunoprotectivity and efficacy against infection with wild type (WT) L. infantum.

FML/QuilA-Vaccinated Dogs Naturally Infected with Leishmania infantum: Serum Cytokines, Clinicopathological Profile, and Parasitological Parameters

Dogs are the main reservoir of Leishmania infantum in endemic regions. Canine leishmaniasis, caused by L. infantum, can progress to a chronic disease resulting in death. Vaccines have been developed with a certain degree of success. The pathogenesis of this disease is not completely understood, especially in previously vaccinated dogs. We herein described clinical data, parasite load, serum levels of cytokines, and the reservoir potential in vdogs vaccinated with the fucose-mannose ligand (FML)/QuilA saponin vaccine (Leishmune™) naturally infected (Vi) and compared to vaccinated not infected dogs (Vn). Thirty-four dogs from private owners were divided into two groups: vaccinated/infected and vaccinated/uninfected. Clinical evaluation, hematological and biochemical parameters, and serum levels of cytokines were measured by conventional methods. The parasite burden in the bone marrow was measured by quantitative real-time PCR, and the transmissibility of parasites to sand flies was assessed by xenodiagnosis. Clinical, biochemical, and hematological parameters of vaccinated infected dogs were mostly normal. Vi dogs developed mild disease with low clinical scores. Serum levels of IL-10 were higher in Vi dogs, and a strong correlation was observed in IL-4 levels and the A/G ratio in Vi dogs. These results suggest a role of TH2 response in Vi dogs, although more data is needed to better understand the disease in vaccinated dogs.

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

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

Serodiagnosis of canine leishmaniasis using a novel recombinant chimeric protein constructed with distinct B-cell epitopes from antigenic Leishmania infantum proteins

Visceral leishmaniasis (VL) is an important public health problem in the world, and control measures are insufficient to avoid the spread of this neglected disease. Dogs are important domestic reservoirs of Leishmania parasites in countries where VL is a zoonosis, representing a major source of infection between sand fly vectors and humans. In this context, a precise diagnosis of canine leishmaniasis (CanL) could help to reduce the number of human cases. Distinct approaches for the diagnosis of CanL have used recombinant proteins in serological assays. However, variable results of the antigens have been found, mainly to diagnosis asymptomatic cases. The present study used bioinformatics to select specific B-cell epitopes of four Leishmania infantum proteins, which had previously been proven to be antigenic in VL, aiming to produce a novel chimeric protein and to evaluate it for the diagnosis of CanL. Seven B-cell epitopes were identified and used to construct the chimera, which was analyzed in a recombinant format through an ELISA assay against a canine serological panel. A soluble Leishmania antigenic extract (SLA) was used as an antigen control. Results showed 100 % sensitivity and specificity for chimera, while when using SLA the values were 26.0 % and 96.4 %, respectively. The performance of chimera was compared with a commercial kit using asymptomatic and symptomatic dog sera, and the data showed that no false-negative result was found when the recombinant protein was used. However, when using the commercial kit, 40.0 % and 16.0 % of the false-negative results were found, respectively. In conclusion, the recombinant chimera showed an antigenic potential to be evaluated in new studies against a larger serological panel for the diagnosis of CanL.

In vivo evaluation of anti-Leishmania activity of alkyltriazoles and alkylphosphocholines by oral route

The failures in the treatment of leishmaniasis is an increasing problem around the world, especially related to resistance. Thus, we describe the synthesis and in vivo anti-Leishmania activity of alkylphosphocholine and alkyltriazoles; besides, their likely action mechanisms stem from some eventual inhibition of parasite enzymes using computational tools. These compounds were tested in an in vivo hamster model infected with Leishmania Leishmania infantum chagasi. Fifty days after parasite inoculation, the two compounds 12-azidedodecylphosphocholine (3) and 3-(1-(12-fluorododecyl)-1H-1,2,3-triazol-1-yl)propano-1-ol (9), were separately administered once a day as oral suspensions (25 and 12.5 mg/kg/day, respectively) during ten days, and their efficacy was compared to the reference compound pentavalent antimonial Glucantime (GLU). Compound 3 significantly reduced the number of parasites in the spleen (4.93 × 10² amastigotes/g) and liver (4.52 × 10³ amastigotes/g). Compound 9 reduced the number of amastigotes in the spleen to 1.30 × 10⁴ and 1.36 × 10³ amastigotes/g in the liver. GLU was the most effective overall treatment (7.50 × 10¹ and 2.28 × 10² amastigotes/g in the spleen and liver, respectively). The high activity levels of these compounds in vivo may stem from their high in vitro leishmanicidal activity and lipophilicity. The in silico absorption, distribution, metabolism, and excretion studies also showed some anti-Leishmania potential. Compound 9 had more lipophilic characteristics than those of compound 3. In silico studies of the nine enzymes of compounds 3 and 9 showed significant evidence of interactions with nicotimidase and tyrosine aminotransferase, demonstrating possible inhibition enzymes present in L. (L.) infantum chagasi. These compounds could be a promising template for developing a new class of leishmanicidal agents, by oral route, and deserve further investigation to explore different therapeutic regimens.

Effectiveness of insecticide-impregnated dog collars in reducing incidence rate of canine visceral leishmaniasis: A systematic review and meta-analysis

Canines are proven reservoir hosts of Leishmania infantum, the causative agent of human zoonotic visceral leishmaniasis, and therefore domestic dogs play a central role in transmitting the disease to humans. Studies on the effect of insecticide-impregnated dog collars for controlling canine visceral leishmaniasis (CanL) have been increasing; however, meta-analysis has not been conducted. This study assessed the effectiveness of insecticide-impregnated dog collars for preventing CanL. We searched (PubMed, Web of Science, Scopus, Embase, Ovid Medline(R), and Cochrane library), from inception until 2 May 2020. Two authors independently performed articles screening and data extraction. We applied the RoB 2.0 tool to evaluate the risk of bias in randomized trials, while the ROBINS-I tool was used for non-randomized trials. I-squared statistics(I²) and funnel plot and Egger’s test, respectively, were used to assesses heterogeneity between studies and publication bias. Relative Risk (RR) and 95% Confidence Interval (CI) were calculated using the random-effects model in Stata 14 software. Out of 242 citations identified, 14 studies comprising 3786 collared dogs and 3428 uncollared dogs were eligible for meta-analysis. The use of deltamethrin-impregnated dog collars(DMC) showed an overall effectiveness of 54% (95%CI: 35–65%, I² = 63.2%, P = 0.002) in decreasing incidence of CanL, while 10% imidacloprid and 4.5% flumethrin collars provided an overall effectiveness of 90% (95%CI: 80–96%, I² = 0.0%, P = 0.376). DMC efficacy stratified by follow-up duration was estimated to be 58% (RR = 0.42, 95%CI: 0.20–0.87), 54% (RR = 0.46, 95%CI: 0.31–0.68), 53% (RR = 0.47, 95%CI: 0.29–0.82) for follow-up periods of 5 to 6 months, 1 year and 2 years, respectively. The current evidence indicates that using insecticide-impregnated dog collars can reduce the risk of CanL caused by L. infantum. Therefore, insecticide-impregnated dog collars could be a viable alternative for inclusion as a public health measure for controlling CanL.

Effectiveness of insecticide-impregnated collars for the control of canine visceral leishmaniasis

Visceral leishmaniasis is a neglected tropical disease widely distributed worldwide. In Brazil, the control measures adopted in the last decades have not been able to prevent the spread of the disease. This study aimed to evaluate the effectiveness of a population-based intervention using 4% deltamethrin-impregnated dog collars on the incidence of canine visceral leishmaniasis. A community intervention study was carried out in two areas of the city of Montes Claros, State of Minas Gerais, Brazil. In the control area, the preventive measures recommended by the Brazilian Program for Surveillance and Control of Visceral Leishmaniasis were implemented (culling of infected dogs and vector control with residual insecticides). In the intervention area, deltamethrin-impregnated collars were fit to domiciled dogs, in addition to the above mentioned preventive measures. At the beginning of the study, a census survey was carried out among domiciled dogs to detect the prevalence of L. infantum infection. Dogs found seronegative at recruitment were longitudinally followed-up to evaluate the incidence of infection. Monitoring of canine infection (control and intervention areas) and replacement of collars (intervention area) occurred through sequential surveys at 12, 18, and 24 months after the initial survey. At each survey, dogs were tested, and the owner answered a questionnaire about the general characteristics of the animal. Multilevel logistic regression models were used to test the effect of collars on the risk of canine infection, with households considered as aggregation units. Associations were expressed as odds ratios (OR) and respective 95% confidence intervals (95%CI). The prevalence of infection in the initial survey was 9.7% and 9.9% in the intervention and control areas, respectively (p = 0.732). Among a total of 20,477 dogs participating in the study, 9,770 were seronegative at recruitment. The cumulative incidence of infection was 4.1% in the intervention area and 7.9% in the control area (p < 0.001). In the multivariable analysis, the risk of infection was 52% lower in the intervention area as compared to the control area (OR = 0.48, 95%CI:0.39-0.59), after adjusting for the number of dogs in the house, period of recruitment, time of dog ownership, and age, sex, length of fur and breed. The use of 4% deltamethrin-impregnated dog collars was effective in reducing the incidence of canine leishmaniasis. Cost-effectiveness studies are recommended before the incorporation of collars in the arsenal of control measures of the Brazilian Program for Surveillance and Control of Visceral Leishmaniasis.

TroCCAP recommendations for the diagnosis, prevention and treatment of parasitic infections in dogs and cats in the tropics

The Tropical Council for Companion Animal Parasites Ltd. (TroCCAP) is a not-for-profit organisation whose mission is to independently inform, guide and make best-practice recommendations for the diagnosis, treatment and control of companion animal parasites in the tropics and sub-tropics, with the aim of protecting animal and human health. In line with this primary mission, TroCCAP recently developed guidelines for the diagnosis, treatment and control of feline and canine parasites in the tropics. The development of these guidelines required unique and complex considerations to be addressed, often inapplicable to developed nations. Much of the tropics encompass middle-to-low income countries in which poor standards of environmental hygiene and large populations of stray dogs and cats coexist. In these regions, a range of parasites pose a high risk to companion animals, which ultimately may place their owners at risk of acquiring parasitic zoonoses. These considerations led to the development of unique recommendations with regard, for example, to deworming and endoparasite testing intervals for the control of both global and 'region-specific' parasites in the tropics. Moreover, the 'off-' or 'extra'-label use of drugs for the treatment and control of parasitic infections is common practice in many tropical countries and many generic products lack manufacturers' information on efficacy, safety, and quality control. Recommendations and advice concerning the use of such drugs and protocols are also addressed in these guidelines. The formation of these guidelines is an important first step towards improving the education of veterinarians specifically regarding best-practice for the diagnosis, treatment and control of canine and feline parasites in the tropics.