Serologic evidence of natural togavirus infections in Panamanian sloths and other vertebrates.

Plasmas of sloths and other Central Panamanian wild vertebrates were tested for plaque-reduction neutralizing (PRN) antibodies against four flaviviruses and one alpha-virus. Forty percent of 97 two-toed sloths, Choloepus hoffmanni, and 8% of 168 three-toed sloths, Bradypus variegatus, were specifically positive against St. Louis encephalitis (SLE) virus. The prevalence of antibody against SLE virus was considerably higher in sloths than in any other group of wild vertebrates tested, including birds, and was found mainly in adult sloths. Specific PRN antibody against yellow fever (YF) virus was found only in monkeys. A high prevalence of PRN antibody against Ilheus and Mayaro viruses was detected in agoutis, Dasyprocta punctata, and against Mayaro virus in howler monkeys, Alouatta villosa. No plasma was specifically positive against Bussuquara virus. The results are interpreted as evidence that sloths are probably not important hosts in jungle YF cycles, but may be significant amplifying hosts in tropical SLE virus cycles.