As in
humans , sub-clinical
infection by
arboviruses in
domestic animals is common; however, its
detection only occurs during epizootics and the silent circulation of some
arboviruses may remain undetected. The objective of the present
paper was to assess the current circulation of
arboviruses in the Nhecolândia sub-region of South Pantanal,
Brazil . Sera from a total of 135
horses , of which 75 were immunized with
bivalent vaccine composed of inactive
Eastern equine encephalitis virus (EEEV) and
Western equine encephalitis virus (WEEV) and 60 were unvaccinated, were submitted to thorough viral isolation,
reverse transcriptase polymerase chain reaction (RT-PCR) and
neutralization tests for
Saint Louis encephalitis virus (SLEV), EEEV, WEEV and Mayaro
virus (MAYV). No
virus was isolated and viral nucleic-
acid detection by RT-PCR was also negative. Nevertheless, the
prevalence of
neutralizing antibodies in
horses older than seven months was 43.7 percent for SLEV in equines regardless of
vaccine status, and 36.4 percent for WEEV and 47.7 percent for EEEV in unvaccinated
horses . There was no evidence of MAYV
infections . The serologic evidence of circulation of
arboviruses responsible for equine and
human encephalitis , without recent official
reports of clinical
infections in the area, suggests that the Nhecolândia sub-region in South Pantanal is an important area for
detection of silent activity of
arboviruses in
Brazil .