Comparative Study of Real-Time PCR (TaqMan Probe and Sybr Green), Serological Techniques (ELISA, IFA and DAT) and Clinical Signs Evaluation, for the Diagnosis of Canine Leishmaniasis in Experimentally Infected Dogs

A review of non-invasive samples and tools in kala-azar diagnosis and test of cure

The recurrence of visceral leishmaniasis (VL), also called kala-azar (KA), in endemic regions of tropical countries like India, is primarily attributed to asymptomatic VL, post-kala azar dermal leishmaniasis (PKDL), and human immunodeficiency virus (HIV) co-infection. To effectively manage VL cases and elimination targets, an early and rapid diagnosis as well as accurate field surveillance is highly essential. The traditional sampling methods like bone marrow (BM), spleen, and lymph node (LN) tissue aspirations are invasive, painful, tedious, and prone to nosocomial infections, require skilled persons and hospital facilities, and are not feasible in rural areas. Therefore, there is an urgent requirement for the adoption of a patient-friendly, non-invasive, non-hospitalized sampling procedure that ensures an effective VL diagnosis. This review aims to meticulously evaluate the most recent scientific research that focuses on the precision, feasibility, and applicability of non-invasive sampling (NIS) and techniques for the diagnosis and test of cure of VL, particularly in resource-limited settings. Apart from that, the non-invasive techniques (NIT) that have shown promising results while monitoring VL treatment response and relapse are also reviewed. The limitations associated with NIT and possible improvements in this regard are discussed as well to improve the diagnosis and management of VL.

Developing diagnostic tools for canine periodontitis: combining molecular techniques and machine learning models

BACKGROUND

Dental plaque microbes play a key role in the development of periodontal disease. Numerous high-throughput sequencing studies have generated understanding of the bacterial species associated with both canine periodontal health and disease. Opportunities therefore exist to utilise these bacterial biomarkers to improve disease diagnosis in conscious-based veterinary oral health checks. Here, we demonstrate that molecular techniques, specifically quantitative polymerase chain reaction (qPCR) can be utilised for the detection of microbial biomarkers associated with canine periodontal health and disease.

RESULTS

Over 40 qPCR assays targeting single microbial species associated with canine periodontal health, gingivitis and early periodontitis were developed and validated. These were used to quantify levels of the respective taxa in canine subgingival plaque samples collected across periodontal health (PD0), gingivitis (PD1) and early periodontitis (PD2). When qPCR outputs were compared to the corresponding high-throughput sequencing data there were strong correlations, including a periodontal health associated taxa, Capnocytophaga sp. COT-339 (rs =0.805), and two periodontal disease associated taxa, Peptostreptococcaceae XI [G-4] sp. COT-019 (rs=0.902) and Clostridiales sp. COT-028 (rs=0.802). The best performing models, from five machine learning approaches applied to the qPCR data for these taxa, estimated 85.7% sensitivity and 27.5% specificity for Capnocytophaga sp. COT-339, 74.3% sensitivity and 67.5% specificity for Peptostreptococcaceae XI [G-4] sp. COT-019, and 60.0% sensitivity and 80.0% specificity for Clostridiales sp. COT-028.

CONCLUSIONS

A qPCR-based approach is an accurate, sensitive, and cost-effective method for detection of microbial biomarkers associated with periodontal health and disease. Taken together, the correlation between qPCR and high-throughput sequencing outputs, and early accuracy insights, indicate the strategy offers a prospective route to the development of diagnostic tools for canine periodontal disease.

Canine visceral leishmaniasis: risk factors and spatial analysis in an endemic area of Northeastern Brazil

Canine visceral leishmaniasis is a disease caused by the protozoon Leishmania infantum, an important agent of zoonotic concern. In this study we determined the seroprevalence, risk factors and spatial distribution of infection by L. infantum among dogs in the Pajeú microregion of the Sertão region of Pernambuco, Brazil. Canine serum samples (n = 247) were tested using the Dual Path Platform (DPP®) rapid screening test and ELISA/S7® confirmatory test; and risk factors were assessed through univariate analysis and logistical regression. The spatial distribution of reactive dogs was analyzed by drawing a map using QGIS. Seroprevalence of 13.7% (34/247) was detected, with cases predominating in the municipality of Tabira (26.4%; 9/34). Age above 10 years was considered to be a risk factor associated with the presence of anti-L. infantum antibodies. The high overall prevalence and spatial distribution of positive cases showed wide dispersion of reagents dogs in the study area. Therefore, preventive measures are needed in order to reduce the risk of infection for animals and humans.

Seroprevalence of canine leishmaniosis in asymptomatic dogs in Kosovo

Canine leishmaniosis (CanL) is a neglected zoonotic disease caused by Leishmania spp. Leishmania infantum is the species responsible for the zoonotic form of the disease where dogs are reservoir hosts. This study aimed to determine the seroprevalence of CanL in asymptomatic dogs in Kosovo. Blood samples were collected from 285 dogs in all seven regions in Kosovo (35-50 samples per region) from summer 2021 to spring 2022. Sera were tested using enzyme-linked immunosorbent assay (ELISA), and the presence of anti-Leishmania IgG was confirmed by an indirect fluorescent antibody test (IFAT). The true overall seroprevalence of CanL of asymptomatic dogs in Kosovo with ELISA was 4.21% (95% CI: 2.42-7.21) while with IFAT was 3.51% (95% CI: 1.92-6.34). The highest rates were found in the Prishtina region to be 8.0% (4/50) by ELISA and 6.0% (3/50) by IFAT, and in the Mitrovica region, the prevalence was 0% (0/40). There were no significant differences among the different regions, gender, age, health status, and breed. These findings highlight the presence of CanL in most regions of Kosovo and underline the veterinary relevance of clinically asymptomatic dogs infected with Leishmania.

Detecting Leishmania in dogs: A hierarchical-modeling approach to investigate the performance of parasitological and qPCR-based diagnostic procedures

BACKGROUND

Domestic dogs are primary reservoir hosts of Leishmania infantum, the agent of visceral leishmaniasis. Detecting dog infections is central to epidemiological inference, disease prevention, and veterinary practice. Error-free diagnostic procedures, however, are lacking, and the performance of those available is difficult to measure in the absence of fail-safe "reference standards". Here, we illustrate how a hierarchical-modeling approach can be used to formally account for false-negative and false-positive results when investigating the process of Leishmania detection in dogs.

METHODS/FINDINGS

We studied 294 field-sampled dogs of unknown infection status from a Leishmania-endemic region. We ran 350 parasitological tests (bone-marrow microscopy and culture) and 1,016 qPCR assays (blood, bone-marrow, and eye-swab samples with amplifiable DNA). Using replicate test results and site-occupancy models, we estimated (a) clinical sensitivity for each diagnostic procedure and (b) clinical specificity for qPCRs; parasitological tests were assumed 100% specific. Initial modeling revealed qPCR specificity < 94%; we tracked the source of this unexpected result to some qPCR plates having subtle signs of possible contamination. Using multi-model inference, we formally accounted for suspected plate contamination and estimated qPCR sensitivity at 49-53% across sample types and dog clinical conditions; qPCR specificity was high (95-96%), but fell to 81-82% for assays run in plates with suspected contamination. The sensitivity of parasitological procedures was low (~12-13%), but increased to ~33% (with substantial uncertainty) for bone-marrow culture in seriously-diseased dogs. Leishmania-infection frequency estimates (~49-50% across clinical conditions) were lower than observed (~60%).

CONCLUSIONS

We provide statistical estimates of key performance parameters for five diagnostic procedures used to detect Leishmania in dogs. Low clinical sensitivies likely reflect the absence of Leishmania parasites/DNA in perhaps ~50-70% of samples drawn from infected dogs. Although qPCR performance was similar across sample types, non-invasive eye-swabs were overall less likely to contain amplifiable DNA. Finally, modeling was instrumental to discovering (and formally accounting for) possible qPCR-plate contamination; even with stringent negative/blank-control scoring, ~4-5% of positive qPCRs were most likely false-positives. This work shows, in sum, how hierarchical site-occupancy models can sharpen our understanding of the problem of diagnosing host infections with hard-to-detect pathogens including Leishmania.

Atypical Lesions in Canine Leishmaniosis: Description of New Cases

Simple Summary

Canine leishmaniosis is a zoonotic disease caused mainly by the protozoan Leishmania infantum that is endemic in the Mediterranean basin. The clinical signs and pathological characteristics have been extensively described; however, atypical lesions leading to clinical and pathological misdiagnosis have been sporadically reported. This study presents three cases of dogs experimentally infected with Leishmania infantum that showed gross lesions considered atypical of canine leishmaniosis and not previously reported. Macroscopic lesions were observed in the liver, spleen, and peritoneal cavity that corresponded to tan to whitish nodular lesions in all organs and multifocal irregular and linear whitish lesions in one of the livers that mimicked tumors. Microscopically, a marked granulomatous inflammation with a relative scarcity of parasites was observed in all the organs. In conclusion, microscopic and parasitological studies should be performed on atypical lesions observed in Leishmania-infected and non-infected dogs, especially in endemic regions. In addition, due to its zoonotic importance, leishmaniosis should be considered when atypical nodular lesions are observed in dogs from non-endemic regions with a history of travel to endemic regions.

Abstract

Pathological characteristics are well described in canine leishmaniosis (CanL). However, atypical lesions that can be confused with other pathologies or trigger unusual clinical signs are sporadically reported. Atypical lesions were observed during routine postmortem examination in three Leishmania-infected dogs and samples were taken for histopathological and immunohistochemical studies. Clinical signs, biochemical parameters, level of antibodies, and parasite detection by PCR were also evaluated. Atypical lesions were found in the peritoneal cavity, liver, and spleen. Splenomegalia and hepatomegalia were observed in all dogs. In addition, multifocal dark to white nodules of variable size were observed in the peritoneal cavity, liver, and spleen of one dog and in the spleen of the other two dogs. One dog presented diffuse irregular whitish lines with a threadlike appearance and another an intense fibrotic depression in the intermediate lobe. Microscopically, an intense granulomatous inflammation with abundant macrophages, a variable number of lymphocytes, and a low to moderate number of parasites was observed. This study represents the first description of granulomatous peritonitis associated with Leishmania in dogs. It also shows atypical macroscopic expression of hepatitis in CanL. In the absence of an adequate clinical history and laboratory analyses, certain lesions observed in CanL could admit alternative diagnoses.