The diagnosis of visceral leishmaniasis remains difficult in rural areas where the disease is endemic, and serologic methods still need assessment, as they are not very sensitive for the detection of asymptomatic infectious dogs. Here we present data on the development of enzyme-linked immunosorbent assay (ELISA)-based methods for the detection of antibodies against recombinant leishmanial antigens (namely, the recombinant K26 [rK26] and rK39 antigens from Leishmania infantum and the rA2 protein from Leishmania donovani) in comparison to ELISAs employing crude soluble antigen (CSA). The assays utilized sera from known negative controls (n ؍ 25) and clinically asymptomatic (n ؍ 50) and symptomatic (n ؍ 50) dogs with confirmed L. infantum infections. Additional studies were also done using sera from animals harboring other infections (n ؍ 14) for the evaluation of cross-reactivity. Our study indicated that rK26 and rK39 used in ELISAs provided very high sensitivities for the detection of symptomatic dogs (94% and 100%, respectively), followed by CSA (88%) and rA2 (70%). Conversely, rA2 was more sensitive for asymptomatic dogs (88%) than rK39 and rK26 (both 66%) and CSA (30%). Some cross-reactivity in sera from dogs with other infections (Leishmania braziliensis and Leptospira interrogans) was identified, but the rA2 protein provided the greatest specificity (98%). Data further indicate that all three recombinant proteins must be used in parallel to detect essentially all infected dogs. Efforts should be made to develop a cheap and reliable serologic test based on epitope selection from these diagnostic markers for the sensitive detection of L. infantum-infected dogs.
This study evaluates cross-immunity in rhesus monkeys (Macaca mulatta) previously infected with one species of Leishmania and have had self-cured disease or were cured by antimony-based therapy upon development of full-blown disease. We found that a self-healing cutaneous leishmaniasis (CL) following experimental infection with Leishmania (Leishmania) major induces significant protection for L. (L.) amazonensis and L. (Viannia) guyanensis, and was dependent on time of re-challenge by L (L.) amazonensis after animals had recovered from primary lesions, but lacked protection against L. (V.) braziliensis. In contrast, monkeys that recovered from L. (V.) braziliensis CL or L. (L.) chagasi visceral leishmaniasis following chemotherapeutic intervention were protected by challenge with L. (V.) braziliensis and L (L.) amazonensis. These findings indicate the relative variability in protection after self-cure or drug-cured experimental leishmaniasis to challenge by heterologous leishmanial parasites. Further studying the immune response may provide information regarding relevant factors influencing cross-protective immunity.
In an endemic rural area of southeast Brazil, surveys confirmed that dogs serve as peridomestic reservoirs of Leishmania infantum. It is likely that the lack of efficient control is because presently used diagnostic tests miss positive dogs. Overall, 57% of the dogs had specific antibodies, but the canine infection was not uniformly fatal and many seropositive dogs remained asymptomatic or even spontaneously recovered. Furthermore, 42% of the human residents became leishmanin-positive reactors and 47% had positive serology at the initial survey, but our estimates also point at a high recovery rate among the infected population with time. The delayed-type hypersensitivity (DTH) reaction to Leishmania was a good indicator of resistance to infection in this particular epidemiologic situation. The lack of any significant differences in infection rates by gender or age indicate that all of the population was at an equal risk of infection and most people were infected in the peridomestic setting.
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