Early detection and persistent positivity of anti-Leishmania antibodies using a recombinant protein-based ELISA in naturally infected dogs in Brazil

Matheus Silva De Jesus,Manuela Da Silva Solcà,Lairton Souza Borja,Lívia Brito Coelho,Deborah Bittencourt Mothé Fraga,João Victor Andrade Cruz,Edmilson Domingos Da Silva,Claudia Ida Brodskyn

doi:10.1186/s13071-021-04895-z

Abstract

BackgroundVisceral leishmaniasis (VL) is a zoonotic disease caused by Leishmania infantum, for which dogs constitute the main urban parasite reservoir. Control measures and the treatment of canine visceral leishmaniasis (CVL) are essential to reduce VL cases. Early and accurate detection of L. infantum-infected dogs is crucial to the success of VL control. To improve the serological detection of L. infantum-exposed dogs, we evaluated the early diagnosis capacity of a recombinant protein (rLci5) in an immunosorbent assay (ELISA) to detect naturally infected dogs. Additionally, we evaluated the persistence of the positive results obtained by rLci5 ELISA in comparison to other conventional diagnostic test methods.MethodsSerum samples obtained from 48 L. infantum-infected dogs involved in a cohort study were evaluated using different diagnostic methods (qPCR, EIE-LVC, DPP-LVC and splenic culture). The results were compared to rLci5 ELISA to determine its capacity to diagnose L. infantum infection at earlier infection time points. The persistence of positive diagnostic test results was also compared for each dog evaluated.ResultsrLci5 ELISA presented higher rates of positive results at early time points compared to the other diagnostic tests employed in the cohort study, as early as 24 months prior to detection by other tests. rLci5 ELISA positivity was 52.1% (25/48) at baseline, while qPCR was 35.4% (17/48), DPP-LVC 27.1% (13/48), EIE-LVC 22.9% (11/48) and culture only 4.2% (2/48). In at least one of the time points of the 24-month cohort study, rLci5 ELISA was positive in 100% (48/48) of the dogs, versus 83% (40/48) for qPCR, 75% (36/48) for DPP-LVC, 65% (31/48) for EIE-LVC and 31% (15/48) for culture. Investigating clinical signs in association with diagnostic test positivity, rLci5 ELISA successfully detected CVL in 62.9% (95/151) of the clinical evaluations with a score of 0–3, 64.3% (45/70) with scores between 4 and 7, and 73.7% (14/19) with scores > 7, providing higher rates of positivity than all other methods evaluated. Moreover, rLci5 ELISA presented the greatest persistence with respect to test positivity: 45.8% of the dogs evaluated.ConclusionFour diagnostic tests were compared to rLci5 ELISA, which presented earlier infection diagnosis and a greater persistence of positive test results. Accordingly, the use of the rLci5 ELISA can improve CVL diagnostic performance by detecting infected dogs sooner than other testing methods, with enhanced persistence of positive results over the course of the infection.Graphic abstract

Highlights

Visceral leishmaniasis (VL) is a zoonotic disease caused by Leishmania infantum, for which dogs constitute the main urban parasite reservoir
100% tested positive on rLci5 enzyme-linked immunosorbent assay (ELISA) at least one time point, while 83% (40/48) were positive by Real-time or quantitative PCR (qPCR), 75% (36/48) on Dual Path Platform (DPP)-LVC, 65% (31/48) on Immunoenzymatic assay (EIE)-LVC and 31% (15/48) by culture
Parasite cultures presented the lowest rate of positivity, resulting in an average 10% detection rate over the five time points evaluated in the cohort study. qPCR detected an average of 30% of dogs as positive, while DPP-LVC and EIELVC averaged 34% and 38%, respectively. rLci5 ELISA detected significantly higher numbers of positive dogs throughout the study, ranging from 46 to 81%, with an average 64% positive detection rate over five evaluation time points (Table 1)

Summary

Introduction

Visceral leishmaniasis (VL) is a zoonotic disease caused by Leishmania infantum, for which dogs constitute the main urban parasite reservoir. Control measures and the treatment of canine visceral leishmaniasis (CVL) are essential to reduce VL cases. To improve the serological detection of L. infantum-exposed dogs, we evaluated the early diagnosis capacity of a recombinant protein (rLci5) in an immunosorbent assay (ELISA) to detect naturally infected dogs. The protozoan parasite Leishmania infantum is the main etiological agent of human visceral leishmaniasis (VL) in Brazil, an endemic zoonosis commonly found in tropical countries [1]. Dogs are the main urban reservoirs of L. infantum, which may play an important role in the transmission and maintenance of VL, resulting in the accidental infection of humans [4, 5]. Among the available diagnostic methods, serological assays offer several advantages including low cost, feasibility in field settings and rapid test results, as well as adequate parameters of sensitivity and specificity when appropriate antigens are employed [8]

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Discussion

Conclusion