Preliminary observations on the diagnosis and transmissibility of canine visceral leishmaniasis in Teresina, n.e. Brazil.

A pilot group of 49 dogs and control groups from non-endemic areas were examined serologically for the presence of visceral leishmaniasis (VL) by direct agglutination test (DAT), indirect immunofluorescence (IFAT) enzyme-linked immunosorbent assay (ELISA) and DOT-ELISA. Results indicated that DAT is less sensitive than the other assays and that serology with filter paper blood samples is less sensitive than with serum. Promastigote infections were common in fed Lutzomyia longipalpis taken from a dog kennel inhabited by a dog carrying Leishmania chagasi. Colony-bred Lu. longipalpis readily acquired L. chagasi infection when fed on skin lesions of dogs naturally infected with L. chagasi: a small proportion of flies also became infected when fed on apparently normal skin. Widespread distribution of amastigotes in normal skin of asymptomatic animals was shown both by intensive microscopy and by probing skin biopsy samples with the Lmet2 L. donovani-complex specific DNA probe. It was demonstrated that an immunologically naive dog could be infected by a single experimentally infected sand fly. Abundant amastigotes present within the resultant lesion 22 days later were transmissible to sand flies but serology remained negative at least 45 days after the infective bite. Experimental transmission of canine VL by sand fly bite is a valuable approach for determining which diagnostic procedures are most sensitive, specific and suitable for field application in suburban households.