Canine leishmaniasis: Identification of asymptomatic carriers by polymerase chain reaction and immunoblotting

A major limitation to the study of the epidemiology of canine visceral leishmaniasis is the inability to identify and count asymptomatic carriers because classic diagnostic tests are insufficiently sensitive. We investigated the capacity of the polymerase chain reaction (PCR) to detect the parasite and immunoblotting to detect specific antibodies in samples from dogs living in an endemic area without any symptoms of leishmaniasis. Results of classic serologic tests (immunofluorescence and enzyme-linked immunosorbent assay) were negative. Two independent PCR assays detected the parasite in skin and conjunctival samples from 80% of the dogs. We found specific antibodies by immunoblot in 66% and 56% of the dogs had both specific antibodies and parasite DNA. As controls, samples from dogs with clinical manifestations of the disease before and after treatment were assayed. The frequency of positive PCR samples decreased after treatment, and although antibody levels decreased with cure of the disease, they remained detectable by immunoblot. Results showed that most of the dogs living in an endemic area had been exposed to Leishmania. Both PCR and immunoblot are sensitive enough to detect asyptomatic infection and could be valuable tools for studies monitoring the transmission of the disease and vaccination trials.