Serological Evidence of Widespread Circulation of West Nile Virus and Other Flaviviruses in Equines of the Pantanal, Brazil

Abstract

A recent study reported neutralizing antibodies to West Nile virus (WNV) in horses from four ranches of southern Pantanal. To extend that study, a serosurvey for WNV and 11 Brazilian flaviviruses was conducted with 760 equines, 238 sheep and 61 caimans from 17 local cattle ranches. Among the tested equines, 32 were collected from a ranch where a neurologic disorder outbreak had been recently reported. The sera were initially screened by using a blocking ELISA and then titrated by 90% plaque-reduction neutralization test (PRNT90) for 12 flaviviruses. Employing the criterion of 4-fold greater titer, 78 (10.3%) equines were seropositive for Ilheus virus, 59 (7.8%) for Saint Louis encephalitis virus, 24 (3.2%) for WNV, two (0.3%) for Cacipacore virus and one (0.1%) for Rocio virus. No serological evidence was found linking the neurological disease that affected local equines to WNV. All caimans and sheep were negative by blocking ELISA for flaviviruses. There were no seropositive equines for Bussuquara, Iguape, Yellow fever and all four Dengue virus serotypes. The detection of WNV-seropositive equines in ten ranches and ILHV and SLEV-seropositive equines in fourteen ranches of two different sub-regions of Pantanal is strong evidence of widespread circulation of these flaviviruses in the region.

Características gerais e epidemiologia dos arbovírus emergentes no Brasil

“…Posteriormente, outro estudo realizado na mesma região detectou a presença de anticorpos neutralizantes não somente contra o WNV, mas também, a outros flavivírus (ILHV, SLEV, CACV e ROCV), em equinos, ovinos e jacarés, evidenciando ampla circulação destes vírus na região 30 . Contudo, no Brasil 31 , ainda não houve associação do WNV à doença em humanos, apesar da abundância de potenciais vetores e hospedeiros vertebrados, nesta vasta reserva ecológica, o Pantanal.…”

“…Uma proteína do envelope do WNV (domínio III -rDIII) foi preconizada como potencial candidata a ser utilizada em testes imunoenzimáticos para detecção do vírus 32 . 30 .…”

Nhumirim virus, a novel flavivirus isolated from mosquitoes from the Pantanal, Brazil

“…In addition to WNV, neutralizing antibodies for eight flaviviruses including SLEV, ROCV, ILHV, CPCV, Bussuquara, dengue, yellow fever and Iguape viruses, were also recently detected in Pantanal equines. However, considering the high cross-reactivity observed among flaviviruses, only the circulation of WNV, CPCV, ILHV, SLEV and ROCV could be inferred in Pantanal equines [12]. Prevalence data for specific flaviviruses in the Pantanal has relied mainly on serologic surveys rather than direct isolation.…”

A Saint Louis encephalitis and Rocio virus serosurvey in Brazilian horses

“…Moreover, 93 (12.3%) of the horses presented monotypic reactions to SLEV, and 46 (6.1%) presented monotypic reactions to ROCV. These seropositivity levels are high, indicating that fl aviviruses may circulate widely in Brazil 14,21 . We also show the fi rst evidence of widespread ROCV infection among horses in Brazil.…”