VISCERAL LEISHMANIASIS AT THE AIDS TIME - THE DIFFICULTIES OF THE BIOLOGICAL DIAGNOSIS

Numerous techniques are used in visceral leishmaniasis diagnosis, but none is completely satisfactory when used on its own. Direct diagnosis is highly reliable because false positive results are unlikely. Unfor tunately, direct examination of bone marrow samples is not sensitive e nough to avoid false negative results and direct examination of spleen aspiration, which is more sensitive, is rarely performed because of t he risk of haemorragia. Sample culture may improve the sensitivity of direct examination but it is time-consuming and sometimes leads to a f alse negative result. In order to improve the direct diagnosis, some a uthors have developed PCR assay for leishmaniasis by using amplificati on of a ribosomal RNA sequence, a kinetoplast sequence or a repetitive genomic sequence. This latest is the only one which is highly specifi c for visceral leishmaniasis agents. The reliability of the PCR based diagnosis is still being evaluated but first results are very encourag ing. Serology exhibits excellent sensitivity and specificity for the d iagnosis of new cases of visceral leishmaniasis in immunocompetent hos ts but we observed some negative serological results using several dif ferent immunological detection methods in immunocompromised patients. This lack of serological reactivity persisted throughout the course of their infections. Immunological detection methods are also difficult to use for the diagnosis of relapses in patients with previous history of visceral leishmaniasis. Indeed, patients often preserve a positive serology that would interfere with unambigous detection of relapse.