Epidemiological surveillance of West Nile virus in the world and Brazil

West Nile virus (WNV) is a neurovirulent mosquito-borne Flavivirus that is maintained in nature by a zoonotic transmission cycle between avian hosts and ornithophilic mosquito vectors, mostly from the Culex genus. Until the 1990s, WNV was considered to be an old-world arbovirus, but in 1999, WNV emerged in the United States (US) and spread rapidly, becoming a major threat to public health. WNV adapted to the transmission cycle involving American mosquitoes and birds and reached Central and South America in subsequent years. In 2003, the National West Nile Fever Surveillance System was created in Brazil based on serological screening of animals and sentinel vectors, as recommended by the Pan American Health Organization (PAHO) and the World Health Organization (WHO). Since 2008, serological evidence of WNV infection in Brazilian horses has been reported, and the circulation of WNV has been monitored through the regular serological screening of sentinel horses and reporting of encephalomyelitis cases. Horses are highly susceptible to WNV infection, and outbreaks of neurological disease among horses often precede human cases. In this regard, equine surveillance has been essential in providing early warning to public and animal health authorities in several countries, including Brazil. This demonstrates the need for animal and public health intervention programs to allocate resources to make veterinarians aware of the role they can play in the human surveillance processes by monitoring horses. This review discusses the importance of equine surveillance and the gap that veterinarians can fill on the front line in human surveillance, in Brazil and worldwide, in the context of “One Health”