South Dublin Branch News

West Nile virus.
November 2002

This year 177 people have died in North America from the virus which is a virulent strain first identified in Israel in 1998. West Nile virus is on the increase but this bird hosted virus is also a major threat to some of its hosts.

The virus lives mainly in birds and is carried by mosquitoes. Since its arrival in New York in 1999 it has spread to most US states and Canadian provinces and this spread has been at a rate consistent with the dispersal of non-migratory birds. The House Sparrow is one identified host, which as an Old World immigrant is resistant to the virus and is a prime suspect. Outbreaks in humans happen mainly in late summer, after the season's mosquitoes have spread the virus among birds, but it is not likely to become a major public health problem in a temperate zone. Crows however are a susceptible species, in the worst affected areas 90% are gone, and related birds such as the Blue Jay may also be at risk. This year birds of prey also are dying in several states. Classically, a wildlife virus should become less lethal after its initial attack, it is not in its interest to kill off all its hosts. One hundred North American birds are known to be susceptible and at least one, the sparrow, doesn't fall ill. The virus could persist where there are sparrows, no matter how many other species it kills off - it has no reason to evolve into something less harmful.

Endangered species such as the Florida Scrub Jay could disappear. Bald Eagles which are recovering in numbers are also at risk. Matters are not helped by local authorities using malathion, a highly toxic spray, to kill mosquitoes.

It is hoped that American birds can develop a resistance to West Nile like their Old World counterparts. As for humans, the prospect for a vaccine looks good. West Nile is a flavivirus close to yellow fever and Japanese encepholitis viruses which already have vaccines and these may even offer some protection. Don't leave home without one!

See report
26.10.2002