[West Nile virus; ecology and epidemiology of an emerging pathogen in Colombia]

West Nile virus (WNV) has an enzootic mosquito-bird-mosquito cycle in nature, Culex sp mosquitoes being the main vectors. Birds are the main amplifying hosts. Humans and horses are incidental dead-end hosts. It produces a flu-like or a self-limited febrile disease in most humans. It can cause encephalitis, meningitis or meningoencephalitis in cases of neurological disease, having greater incidence and mortality from encephalitis in older people and immune-compromised patients. Outbreaks have been reported in Africa, the Middle-east, Europe and Asia. WNV first appeared in North-America in 1999 and its circulation has been documented in Mexico, the Caiman islands, Jamaica, the Dominican Republic, Martinique, Guadalupe, Cuba, Puerto Rico, El Salvador and more recently in Colombia. The public health concern regarding WNV if it becomes introduced into Middle- and South-America will depend upon the interaction of several factors. The prevailing conditions in Colombia are apt for its spread and development. There are two main hypotheses; the virus could become enzootic and endemic and cause limited human disease, or it could become epidemic and cause annual outbreaks affecting large numbers of humans and animals. It will depend upon Colombian birds' susceptibility to the virus because of biological differences and intra-specific geographical variations in mosquitoe species' vector competence and the environmental effects on its ability to transmit the virus; such factors are determinant in the primary amplifying cycle.