The Pantanal hosts diverse wildlife species and therefore is a hotspot for arbovirus studies in South America. A serosurvey for Mayaro virus (MAYV), eastern (EEEV), western (WEEV) and Venezuelan (VEEV) equine encephalitis viruses was conducted with 237 sheep, 87 free-ranging caimans and 748 equids, including 37 collected from a ranch where a neurologic disorder outbreak had been recently reported. Sera were tested for specific viral antibodies using plaque-reduction neutralisation test. From a total of 748 equids, of which 264 were immunised with vaccine composed of EEEV and WEEV and 484 had no history of immunisation, 10 (1.3%) were seropositive for MAYV and two (0.3%) for VEEV using criteria of a ≥ 4-fold antibody titre difference. Among the 484 equids without history of immunisation, 48 (9.9%) were seropositive for EEEV and four (0.8%) for WEEV using the same criteria. Among the sheep, five were sero- positive for equine encephalitis alphaviruses, with one (0.4%) for EEEV, one (0.4%) for WEEV and three (1.3%) for VEEV. Regarding free-ranging caimans, one (1.1%) and three (3.4%), respectively, had low titres for neutralising antibodies to VEEV and undetermined alphaviruses. The neurological disorder outbreak could not be linked to the alphaviruses tested. Our findings represent strong evidence that MAYV and all equine encephalitis alphaviruses circulated in the Pantanal.

In an effort to detect West Nile virus (WNV) in Brazil, we sampled serum from horses and chickens from the Pantanal region of the state of Mato Grosso and tested for flavivirus-reactive antibodies by blocking ELISA. The positive samples were further confirmed for serological evidence of WNV infection in three (8%) of the 38 horses and one (3.2%) of the 31 chickens using an 80% plaque-reduction neutralisation test (PRNT80). These results provide evidence of the circulation of WNV in chickens and horses in Pantanal.

We prospectively sampled flavivirus-naïve horses in northern Colombia to detect West Nile virus (WNV) and St. Louis encephalitis virus (SLEV) seroconversion events, which would indicate the current circulation of these viruses. Overall, 331 (34.1%) of the 971 horses screened were positive for past infection with flaviviruses upon initial sampling in July 2006. During the 12-month study from July 2006-June 2007, 33 WNV seroconversions and 14 SLEV seroconversions were detected, most of which occurred in the department of Bolivar. The seroconversion rates of horses in Bolivar for the period of March-June 2007 reached 12.4% for WNV and 6.7% for SLEV. These results comprise the first serologic evidence of SLEV circulation in Colombia. None of the horses sampled developed symptoms of encephalitis within three years of initial sampling. Using seroconversions in sentinel horses, we demonstrated an active circulation of WNV and SLEV in northern Colombia, particularly in the department of Bolivar. The absence of WNV-attributed equine or human disease in Colombia and elsewhere in the Caribbean Basin remains a topic of debate and speculation.

OBJECTIVES: West Nile virus (Flavivirus: Flaviviridae; WNV) has spread rapidly throughout the Caribbean Basin since its initial detection there in 2001. This report summarizes our current knowledge of WNV transmission in tropical America. METHODS: We reviewed the published literature and consulted with key public health officials to obtain unpublished data. RESULTS: West Nile virus infections first appeared in human residents of the Cayman Islands and the Florida Keys in 2001, and in apparently healthy Jamaican birds sampled early in 2002. Serologic evidence of WNV infection in 2002 was detected in horses, chickens and resident free-ranging birds in Guadeloupe, the Dominican Republic, and eastern Mexico. In 2003, WNV spread in Mexico and northern Central America, and serologic evidence was detected in the Bahamas, Puerto Rico and Cuba. In 2004, the first serologic evidence of WNV activity in South American ecosystems surfaced in September-October in Colombia and Trinidad, where domestic animals circulated WNV-neutralizing antibodies. CONCLUSIONS: The sparse reports of equine, human and avian disease in Latin America and the Caribbean is puzzling. Isolates are needed to evaluate viral attenuation or other possible explanations for reduced disease burden in tropical ecosystems.

OBJETIVOS: El virus del Nilo occidental (VNO, familia Flaviviridae, género Flavivirus) se ha propagado rápidamente por toda la cuenca del Caribe desde que se detectó por primera vez en 2001. En este informe se resumen nuestros conocimientos actuales acerca de la transmisión del VNO en zonas tropicales del continente americano. MÉTODOS: Revisamos todo lo que se ha publicado sobre el tema y consultamos a autoridades de salud clave para obtener datos inéditos. RESULTADOS: Las infecciones por el virus del Nilo occidental aparecieron por primera vez en seres humanos residentes de las Islas Caimán y de los Cayos de la Florida en 2001, y en pájaros de aspecto sano de los cuales se obtuvieron muestras a principios de 2002. En 2002 se encontraron pruebas serológicas de infección por el VNO en caballos, pollos y aves de corral no estabuladas oriundas de Guadalupe, la República Dominicana y la parte oriental de México. En 2003, el VNO se diseminó dentro de México y por la parte norte de Centroamérica y se encontraron pruebas serológicas en las Bahamas, Puerto Rico y Cuba. En 2004, las primeras pruebas serológicas de actividad vírica en ecosistemas sudamericanos se detectaron en septiembre y octubre en Colombia y Trinidad, donde se observaron anticuerpos neutralizantes contra el VNO en animales domésticos. CONCLUSIONES: Estos informes esporádicos de enfermedad equina, humana y aviar en América Latina y el Caribe son desconcertantes. Es necesario aislar las cepas para determinar si la atenuación del virus u otro factor explica la carga de enfermedad reducida en ecosistemas tropicales.

El virus del Oeste del Nilo (VON) género Flavivirus, familia Flaviviridae, es mantenido en la naturaleza en un ciclo enzoótico ave-mosquito-ave. Las aves son los hospederos amplificadores primarios. Humanos y caballos son hospederos incidentales finales. En humanos las infecciones se manifiestan como enfermedad febril autolimitada. También puede presentarse encefalitis o meningoencefalitis. El virus se ha establecido en Norte América y se ha documentado su circulación en México, Jamaica, República Dominicana, Guadalupe, Cuba, Puerto Rico, El Salvador y recientemente en Colombia. Se realizó una vigilancia centinela en culícidos y aves domésticas para hacer un seguimiento a la circulación en el departamento de Córdoba e identificar que especies de mosquitos estaban infectadas con el virus. Se analizaron 4942 mosquitos en 99 pooles por la técnica Vec TestTM (Medical System, Inc. Camarillo, CA) y 162 sueros de aves de corral fueron enviadas al Centers for Disease Control and Prevention Division of Vector-Borne Infectious Diseases Fort Collins, USA, para ser analizadas por MAC-ELISA y debido a las reacciones cruzadas que se dan entre el VON y otros virus del serocomplejo de la encefalitis japonesa se utilizó el test de reducción de la neutralización en placa (PRNT). No se obtuvieron mosquitos o aves positivos.

West Nile Virus (WNV) genus flavivirus, family Flaviviridae, is maintained in nature in an enzootic cycle mosquito-bird-mosquito. Birds are the main amplifying hosts. Humans and horses are incidental dead-end hosts. In humans it yields a self-limited febrile disease; it can produce encephalitis and meningoencephalitis as well. WNV is wide spread in North America and its circulation has been documented in México, Jamaica, Dominican Republic, Guadalupe, Cuba, Puerto Rico, El Salvador and recently Colombia. It was performed a sentinel surveillance in Culicides and domestic birds to follow-up WNV circulation in the department of Córdoba taking into account its circulation evidence in horses of this region and identifying mosquito species infected with the virus. 4.942 mosquitoes were assessed in 99 pools were assessed by Vec TesttTM (Medical System, Inc. Camarillo, CA) and 162 serums of domestic birds were analyzed by MAC-ELISA in the Centers for Disease Control and Prevention, Division of Vector-Borne Infectious Diseases, Fort Collins, USA. Due to the crossed reactions among WNV and others virus of the Japonese Encephalitis, a plaque reduction neutralization test (PRNT) was used. There was not nor positive mosquitoes neither positives birds.