i live in the epi center for West Nile Virus in US- (the first cases of humans contracting it were less than 1 mile from my home at the time..

NYC has made a real effort to curb the disease. (as i recall, it was the vets at the NYZoological Society that first identified the virus, (with the help of CDC). several of the birds in captivity contracted the disease, since several of NYZS aviaries are large 'cages' made with fine mesh, so the birds have 'an outdoor' environment.
(the zoo doen't really 'collect' most species of water fowl, it just make really friendly environments, and attracts native birds to nest --some become year round residents!) the same is true for the peacocks.. they have the whole zoo as there 'cage'. out side the zoo is mostly concrete and traffic, the pea cocks and hens are not attracted to it. (once in while a pea cock or pea hen will decide to 'take up residence' in the area for the lions.. its always a bad idea!)