Challenges in the serological evaluation of dogs clinically suspect for canine leishmaniasis

Veterinary perspectives on the urbanization of leishmaniosis in Morocco

BACKGROUND

Leishmaniosis caused by Leishmania infantum, L. major and L. tropica is endemic in Morocco. Growing evidence of both human and canine Leishmania infections in urban centres has been reported. Since many forms of the disease are zoonotic, veterinarians play an important role in leishmaniosis control by intervening at the parasite host level. This study aimed to bring together One Health principles to connect canine and feline leishmaniosis epidemiology within urban centres of Morocco (Rabat and Fez) and assess the level of awareness of Moroccan veterinarians about facing this threat.

METHODS

A molecular survey was conducted for Leishmania DNA detection in canine (n = 155) and feline (n = 32) whole-blood samples. Three conventional polymerase chain reaction (PCR) protocols were implemented. The first PCR aimed at identifying infected animals by targeting Leishmania spp. kinetoplast minicircle DNA (kDNA). The second and third PCR targeted the Leishmania internal transcribed spacer region (ITS-1) and the Leishmania small subunit ribosomal RNA (SSUrRNA) gene, respectively, aiming at identification of the infecting species after Sanger sequencing-positive amplicons. Total immunoglobulin G (IgG) against Leishmania spp. was evaluated in 125 dogs by enzyme-linked immunosorbent assays (ELISA) using an in-house protocol, including three Leishmania-specific antigens (SPLA, rKDDR and LicTXNPx). Sera from 25 cats were screened for total IgG to Leishmania spp. by an indirect immunofluorescence antibody test (IFAT). An online questionnaire was presented to Moroccan veterinarians addressing their knowledge and practices towards animal leishmaniosis.

RESULTS

Overall, 19.4% of the dogs tested positive for Leishmania kDNA and ITS-1 and sequencing revealed infection with L. infantum among PCR-positive dogs. These animals presented a wide range of ELISA seropositivity results (16.7%, 34.9% and 51.6%) according to the tested antigens (rKDDR, SPLA and LicTXNPx, respectively). Use of kDNA-PCR revealed 12.5% cats positive to Leishmania spp. otherwise found to be seronegative by IFAT.

CONCLUSIONS

A considerable prevalence of infection was identified in dogs from urban centres of Morocco. Additionally, this is the first report of feline infection with Leishmania spp. in this country and in urban settings. Moroccan veterinarians are aware that animal leishmaniosis is endemic in Morocco, representing a public health threat, and are knowledgeable about canine leishmaniosis diagnosis and treatment.

Comparative Study of a Novel Lateral Flow Rapid Test with Conventional Serological Test Systems for the Diagnosis of Canine Leishmaniosis in Croatia and Brazil

Control of canine infections with Leishmania infantum (L. infantum), a major zoonotic disease in Brazil and southern Europe, is becoming increasingly important due to its close proximity to humans, the increasing import of dogs from endemic regions and the impact of climate change on vector spreading. Simple, rapid and reliable diagnostic tests are therefore needed to detect infected dogs. Here, we re-evaluated different serological methods for the diagnosis of canine leishmaniosis (CanL) in Croatia and Brazil. The diagnostic performance of the indirect fluorescent antibody test (IFAT) and the VetLine® Leishmania ELISA (GSD Frankfurt, Germany) was compared with three rKLi8.3-based diagnostic test systems, the rKLi8.3 ELISA (GSD Frankfurt, Germany), the INgezim® Leishma CROM (GSD Madrid, Spain) lateral flow test (LFT) and the VetBlot®Leishmania LineBlot (GSD Frankfurt, Germany). CanL symptomatic dogs were efficiently diagnosed by all tests, except the VetLine® Leishmania ELISA, which is based on whole Leishmania antigens. The advantage of rKLi8.3 was also observed in oligo- and asymptomatic dogs from Brazil and Croatia, although with reduced diagnostic efficiency compared to symptomatic dogs. Similar to IFAT and rKLi8.3 ELISA, the LFT did not cross-react with other common canine pathogens; it showed very high specificity for healthy dogs from endemic regions in both countries and did not react with healthy, vaccinated dogs in Brazil. In conclusion, serodiagnostic tests based on the rKLi8.3 antigens are superior to whole parasite antigens, and the LFT has the advantage of providing a laboratory-independent, rapid and specific diagnosis of CanL.

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.

Serological and Molecular Survey of Leishmania infantum in a Population of Iberian Lynxes (Lynx pardinus)

Leishmania infantum, the sand fly-transmitted protozoan parasite responsible for leishmaniasis in humans, dogs, and cats, is endemic in the Iberian Peninsula. However, the impact of L. infantum infection on the conservation of the endangered Iberian lynx (Lynx pardinus) is unknown. Herein, we describe for the first time the occurrence of L. infantum infection among a population of reintroduced and wild-born L. pardinus living in the Portuguese Guadiana Valley Park. The presence of infection was addressed by molecular detection of Leishmania kinetoplast DNA (kDNA) in 35 lynxes, with further confirmation of L. infantum species performed by an internally transcribed spacer (ITS)-1 sequencing. Eight blood samples were positive for kDNA, and ITS-1 sequencing confirmed the presence of L. infantum in two of those samples. Exposure to Leishmania was screened in a group of 36 lynxes using an immunofluorescence antibody test (IFAT) and a multi-antigen enzyme-linked immunosorbent assay (ELISA), using SPLA, rK39, and CPX as Leishmania-specific antigens. Four animals presented a positive IFAT at a dilution of 1:40. Eight samples were considered seropositive to all ELISA Leishmania-specific antigens. Agreement between PCR, IFAT, and all ELISA antigens was found for 1 in 27 samples. These results highlight the susceptibility of autochthonous L. pardinus to L. infantum infection. Further investigation is required to assess the impact of L. infantum infection on this wild species conservation.

Establishment of an indicator framework for the transmission risk of the mountain-type zoonotic visceral leishmaniasis based on the Delphi-entropy weight method

BACKGROUND

Visceral leishmaniasis (VL) is one of the most important neglected tropical diseases. Although VL was controlled in several regions of China during the last century, the mountain-type zoonotic visceral leishmaniasis (MT-ZVL) has reemerged in the hilly areas of China in recent decades. The purpose of this study was to construct an indicator framework for assessing the risk of the MT-ZVL in China, and to provide guidance for preventing disease.

METHODS

Based on a literature review and expert interview, a 3-level indicator framework was initially established in November 2021, and 28 experts were selected to perform two rounds of consultation using the Delphi method. The comprehensive weight of the tertiary indicators was determined by the Delphi and the entropy weight methods.

RESULTS

Two rounds of Delphi consultation were conducted. Four primary indicators, 11 secondary indicators, and 35 tertiary indicators were identified. The Delphi-entropy weight method was performed to calculate the comprehensive weight of the tertiary indicators. The normalized weights of the primary indicators were 0.268, 0.261, 0.242, and 0.229, respectively, for biological factors, interventions, environmental factors, and social factors. The normalized weights of the top four secondary indicators were 0.122, 0.120, 0.098, and 0.096, respectively, for climatic features, geographical features, sandflies, and dogs. Among the tertiary indicators, the top four normalized comprehensive weights were the population density of sandflies (0.076), topography (0.057), the population density of dogs, including tethering (0.056), and use of bed nets or other protective measures (0.056).

CONCLUSIONS

An indicator framework of transmission risk assessment for MT-ZVL was established using the Delphi-entropy weight method. The framework provides a practical tool to evaluate transmission risk in endemic areas.

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

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

Serological and molecular detection of Leishmania species in dog peripheral blood from Bobo-Dioulasso city, a confirmation of canine leishmaniasis enzootic area for Burkina Faso

Canine leishmaniasis is increasingly reported worldwide and represent a threat to both animal and human health. In a previous pilot study conducted in Bobo-Dioulasso, the second town of Burkina Faso, we reported five cases of canine leishmaniasis. With the perspective of a One Health action plan, and in the context of increasing urbanization, this study aimed to provide new information on Leishmania spp in dogs in this city. A cross-sectional survey was carried out from May to August 2018 in six districts of the city in order to record clinical and biological data from domestic dogs randomly selected per district. Blood samples were collected into EDTA tubes (4-5 mL), treated and stored at -20 °C until further analyses. The infection status of the dogs was performed by serological tests using plasma, and real time-PCR (RT-PCR) to detect Leishmania parasites using buffy coats. Nested PCR was used for typing the Leishmania species in dogs which were found to be RT-PCR positive. A total of 147 dogs were examined clinically and sampled for blood collection, including 53.7% females and 46.3% of males with a median age of 3 years. The seroincidence of Leishmania parasites within this dog population was 4.76% (95% CI:2.26-9.72). The incidence of Leishmania was 10.88% (95% CI: 6.73-17.11) by RT-PCR which was significantly more sensitive (p = 0,047) and a fair concordance was observed between both tests (Kappa = 0.39, p < 0.001). The characterization of Leishmania species revealed that L. major was circulating in this domestic dog population. Our results confirmed the persistence of zoonotic circulation of Leishmania parasites such as L. major currently in Bobo-Dioulasso city and highlight the need for targeted interventions in order to control transmission of leishmaniasis in this region.

Leishmania exposure in dogs from two endemic countries from New and Old Worlds (Brazil and Portugal): evaluation of three serological tests using Bayesian Latent Class Models

BACKGROUND

Zoonotic leishmaniosis caused by Leishmania infantum is endemic in several countries of the Mediterranean Basin, Latin America, and Asia. Dogs are the main hosts and reservoirs of human infection. Thus, from a One Health perspective, early diagnosis of Leishmania infection in dogs is essential to control the dissemination of the parasite among other dogs and to humans. The aim of this study was to estimate the diagnosis accuracy of three serological tests to detect antibodies to Leishmania in dogs from two endemic settings using Bayesian latent class models (BLCM).

METHODS

A total of 378 dogs from two Portuguese and Brazilian endemic areas of leishmaniosis (194 animals from Portugal and 184 from Brazil) were screened. Detection of anti-Leishmania antibodies was performed using two commercial ELISA (L. infantum IgG-ELISA® and EIE-LVC®) and a rapid immunochromatographic test (DPP-LVC®). Bayesian latent class models were used to estimate Leishmania infection prevalence, together with sensitivities and specificities of the three diagnostic tests, in the two dog populations simultaneously. Predictive values were also calculated. Credibility intervals (CI) were obtained, considering different types of prior information.

RESULTS

A posterior median Leishmania seroprevalence of 13.4% (95% CI 9.0-18.7) and of 21.6% (15.0-28.3) was estimated to the Portuguese and Brazilian dog subpopulations, respectively. The Bayesian analysis indicated that all tests were highly specific (specificity above 90%), and that the DPP-LVC® was more sensitive (96.6%; 83.1-99.9) than both ELISAs in the Portuguese subpopulation, while in the Brazilian subpopulation, EIE-LVC® and L. infantum IgG-ELISA®, had the highest sensitivity (88.2%; 73.7-97.0) and specificity (98.7%; 95.1-99.9), respectively.

CONCLUSIONS

In general, the levels of diagnosis accuracy of the three serological tests to detect Leishmania antibodies assessed by BLCM indicate their utility in canine epidemiological studies. The same approach should be used to assess the performance of these techniques in the clinical management of infected and sick dogs using representative samples from the wide spectrum of clinical situations, namely from subclinical infection to manifest disease. The low positive predictive value of the serological tests used in the current protocol of the Brazilian Ministry of Health suggests that they should not be used individually and may not be sufficient to target reservoir-based control interventions.

Leishmaniosis caused by Leishmania infantum in ferrets: Update review

Leishmaniosis in domestic ferrets (Mustela putorius furo) is a disease caused by Leishmania infantum, a parasite transmitted through the bite of an infected female phlebotomine sand fly. Among vertebrates, the dog is the primary domestic reservoir of the parasite; however, other domestic animals can be implicated such as cats. The first description of a clinical case of leishmaniosis in domestic ferrets was reported recently. As a result, new knowledge has been published including empirically based treatment protocols, confirmatory techniques to detect the presence of the parasite infection and seasonal variation in the antibodies against Leishmania in apparently healthy domestic ferrets. The most common clinical signs observed are enlargement of peripheral lymph nodes and skin lesions such as papular and/or ulcerative dermatitis. Additionally, the most frequent laboratory alterations seen are hyperproteinaemia with hyperglobulinaemia and biochemical analytes alterations depending on the affected tissue. Two different therapeutic protocols have been described to treat domestic ferrets with leishmaniosis: meglumine antimoniate plus allopurinol protocol or miltefosine plus allopurinol protocol. These treatment protocols seemed to be able to control the Leishmania infection, although the presence of xanthinuria could be detected. The susceptibility of domestic ferrets to Leishmania infantum, the clinical picture, treatment of infected animals and prevention are poorly understood, due to the scarcity of recent description in the literature. Different proposed diagnostic algorithms have been included for domestic ferrets with suspected leishmaniosis, clinically healthy domestic ferrets and animals as blood donors. In this sense, the present review provides updated data on scientific knowledge of leishmaniosis in ferrets.

Polymerase chain reaction using conjunctival swab samples for detecting Leishmania DNA in dogs

The dog is the main domestic reservoir of Leishmania and font of infection for the vector, constituting an important host for the transmission of the parasite to humans. Non-invasive collection of swab samples for leishmaniasis diagnosis has been a promising alternative. This study analyzed the positivity of polymerase chain reaction (PCR) for the diagnosis of canine leishmaniasis in conjunctiva samples. DNA extraction was performed using SDS 20% and PCR was performed using 13A/13B primers that amplify 120-bp of Leishmania kDNA. Of the 77 dogs analyzed, 50 (64.93%) had ocular changes: 25 (32.47%) dogs had periocular lesion, 41 (53.25%) dogs had purulent eye discharge, and 17 (22.08%) dogs had both signals. PCR was positive in 35 dogs (45.45%), and there was no significant difference between dogs with and without ocular signals (p=0.4074). PCR positivity was significant higher in dogs without periocular injury (p=0.0018). Conjunctive PCR, a less invasive, fast, and painless collection technique, is indicated to complement the diagnosis, especially in dogs without periocular injury, independent of the presence of purulent eye discharge.

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.