SEROLOGICAL DIAGNOSIS OF LEISHMANIASIS - ON DETECTING INFECTION AS WELL AS DISEASE

Serological tests are very frequently used in epidemiological surveys of leishmaniasis and other parasitoses. Their sensitivity and specific ity are generally defined with respect to parasitism and disease, rath er than infection. The reason is that known positives are those indivi duals most likely to yield parasites, or who have distinctive clinical signs, and concomitantly high antibody titres. This paper investigate s the performance of one serological method, the indirect fluorescent antibody test (IFAT), in detecting Leishmania infantum infection durin g an intensive 2-year cohort study of dogs in southern France. The res ults show that sensitivity and specificity with respect to infection c an be simultaneously high, but maximum sensitivity is probably < 80 %, and lasts for a relatively short period of 2-3 months after a lengthy incubation period. The IFAT gave the incidence of infection as 18-65 % in the first year, whereas the best estimate of incidence based on p arasite isolation and clinical observation was 72 %. But data from the second year suggest that the 72 % was itself an underestimate. We arg ue that, during epidemiological surveys, the IFAT in particular, and s erological tests for leishmania in general, will underestimate prevale nce, incidence and hence the scale of the control problem. However, th ere is evidence that tests for canine leishmaniasis employing high thr eshold titres will identify the most infectious animals, allowing sele ctive treatment or culling of those which contribute disproportionatel y to transmission.