Teste de aglutinaçäo directa no sorodiagnóstico da leishmaniose visceral no estado do Pará / Direct agglutination test in the serodiagnosis of human visceral leishmaniases in the State of Pará, Brazil

RESUMO

The direct agglutination test (DAT) was evaluated for serodiagnosis of visceral leishmaniasis (VL) in human and canids (dogs and foxes Cerdocyon thous). The results were compared with those of the immunofluorescent antibody assay (IFAT) and enzyme-linked immunosorbent assay (ELISA). The sera used were from humans (303) confirmed VL (16), suspected VL (65), other conditions (102), negative controls (15) and individuals from an endemic area (105); dogs (82) from an endemic area (68), Salvaterra/Marajó/Pará (21 of which were parasitologically positive), and negative controls (14), from Belém; foxes (9) caught on Marajó Island. Antigens for DAT were prepared from promastigots of L. (L.) donovani, L. (L.) chagasi. Antigens used in ELISA and IFAT were prepared from promastigotes (soluble antigen) and amastigotes respectively of L. (L.) chagasi. In humans, the specificity and sensitivity of DAT using L. (L.) donovani were high (98.4 per cent and 100 per cent respectively) and comparable to that of IFAT (97.5 per cent and 100 per cent). ELISA was less specific (84.8 per cent) although similarly sensitive (100 per cent). In dogs, DAT was more specific using L. (L.) donovani as antigen than using L. (L.) chagasi. However, both DAT and ELISA were less sensitive (both 71.4 per cent) than IFAT (100 per cent). This difference was reflected in the results from endemic dogs, 87 per centof which were positive by IFAT but only 54 per cent by ELISA and 49 per cent by DAT. Similarly, all 9 fox sera were positive by IFAT, 7 of 9 (78 per cent) by ELISA but none by DAT. In conclusion, DAT using L. (L.) donovani antigen can provide a useful test for human VL; utilization on a large scale would be possible with a suitable reference laboratory to monitor antigen quality. However, DAT appears less useful for canine studies, as it was less sensitive than ELISA and especially IFAT in detecting canine infection.