Studies on the control of visceral leishmaniasis: validation of the Falcon assay screening test--enzyme-linked immunosorbent assay (FAST-ELISA) for field diagnosis of canine visceral leishmaniasis.

The Falcon assay screening test-enzyme-linked immunosorbent assay (FAST-ELISA), the latest version of the enzyme-linked immunosorbent assay, uses antigen-coated beads. A 96-well plate can be run in 20 min without electricity or expensive equipment. We compared the FAST-ELISA, a standard ELISA, and an indirect immunofluorescent assay (IFA) for evaluation of canine leishmaniasis under field conditions using samples from 161 dogs from our longitudinal study in the endemic area of Jacobina, Bahia, Brazil. Organisms were isolated by culture (NN medium) or by inoculation of hamsters with samples from 59 of the dogs. When plasma were tested, we found a sensitivity of 88% and a specificity of 90% using the FAST-ELISA with a spectrophotometer. Using the same plasma samples, the IFA had a sensitivity of 75% and a specificity of 93%. The standard ELISA had a sensitivity of 90% and a specificity of 85%. When whole blood was tested with the FAST-ELISA, we found a sensitivity of 85%. There was no significant difference between visual and spectrophotometric results with plasma or whole blood. The FAST-ELISA system provides a sensitive, specific, and field-adaptable test for canine visceral leishmaniasis, which can be evaluated quickly without the use of a microscope or spectrophotometer.

Comparison of the polymerase chain reaction and serology for the detection of canine visceral leishmaniasis.

The polymerase chain reaction (PCR) and serology was evaluated for the diagnosis of canine visceral leishmaniasis in Bahia, Brazil in a study of 125 dogs. The PCR was 100% sensitive in 25 dogs that had Leishmania demonstrated by either culture or hamster inoculation. It was 100% specific for 35 dogs from the northeastern United States, all were PCR negative. However, 22 of 54 Brazilian dogs that were culture-hamster inoculation-negative were positive by PCR. The nature of the PCR product was identified by hybridization with specific Leishmania probes. Whereas the sensitivity of serology in relationship to infection, as determined by hamster or culture assay was more than 80%, sensitivity of serology was only 63% when compared with PCR. These results raise questions about the use of serology to detect Leishmania infection in dogs, and suggest that the PCR might serve as a better gold standard to define Leishmania infection than culture or hamster inoculation.

Visceral leishmaniasis in a new ecological niche near a major metropolitan area of Brazil.

In 1991, a community cross-sectional study was conducted in a village situated near the beach and close to Salvador, the capital city of Bahia, in Brazil, to determine the prevalence of visceral leishmaniasis since 1989. A serological survey was made of human and canine reservoirs and an intradermal skin test for leishmaniasis was used to assess cellular immune responses. Nearly 30% of the 243 individuals in the study area had positive skin tests and 14% had positive serology, the latter being compatible with recent infection; 29 of 460 dogs examined were seropositive. A possible association was observed between human infection and the presence of dogs in or near residences, but not between human infection and malnutrition. This report describes the evolution of a new focus of visceral leishmaniasis, its expansion toward a metropolitan area, and current measures taken to control the epidemic.