July 19, 2005
West Nile Virus
Now that we're in the midst of prime mosquito season throughout the U.S., it's likely cam watchers have been hearing reports about the West Nile virus. As many know, the WNV infects mosquitoes after they feed on infected birds, and once mosquitoes are infected, they can then transmit the West Nile virus to humans, animals, and other birds while biting to take blood.
Despite the extensive media coverage that is often given to the West Nile virus, the reality is that the virus does not present a large threat to people here in America. In areas where the virus exists, a small number of mosquitoes carry it, and of those humans who do become infected, only about 1% become seriously ill. To illustrate, the Centers for Disease Control reported that in 2004 approximately 100 people died from WNV in the U.S., which is about the same amount as died from reactions to bee stings. This does not mean, however, that the virus should be taken lightly, especially by those who are the most susceptible, such as the elderly, the very young, and those who have a weakened immune system.
As it stands now, however, the West Nile virus is hitting bird populations the hardest. Since 1999, WNV has been detected in over 225 wild and captive bird species in the U.S., as birds are the natural hosts of the virus, and over 12,000 have died as a result (although death estimates are likely underestimated because many birds die of WNV and are never found).
Crows and jays were originally the most affected, but soon it was discovered that raptors (especially in the Midwest) were becoming victims as well. Among the raptors that were hardest hit were great horned owls, which are one of the few birds of prey that will eat crows.
Infected bald eagles and ospreys have also been discovered, and some have died from the virus, but the deaths have not been in huge numbers. Ospreys and bald eagles are aided by the fact that their main food source is fish, which lessens the likelihood that they will contract the virus from infected birds (although an added danger does exist because they use bird carcasses and body parts as nesting material).
Of special concern now are rare birds held in zoos, as well as the state of Hawaii, where the WNV has not established itself but represents a looming threat to the many unique and threatened birds living on the islands.
Blackwater Refuge is located in Maryland, and at this time the Maryland Department of Natural Resources reports that no infected ospreys have been found in the state, although they admit that significant testing has not been done (dead ospreys that are found can be tested to determine if the virus was possibly the cause of death). In Virginia -- our neighboring state -- the public state veterinarian reports that five dead ospreys were tested for the virus but all the birds tested negative.
Several research groups are currently working on a West Nile virus vaccine that can be used on birds. Presently there is a vaccine for horses that has been tried on captive birds, but the results have been mixed, so an avian vaccine is being researched at this time. A vaccine would be especially helpful for protecting captive birds that belong to endangered and threatened species rehabilitation programs.
In the wild, surviving birds seem to be developing an immunity to the virus. Over time this trend will likely grow as those birds that are resistant to the West Nile virus will give birth to a new generation and pass on these virus-resistant traits to their young.
As for humans, we can do more to reduce the local mosquito population by following some simple steps around the home, such as eliminating standing water in gutters and yard containers. If you'd like to learn more about the West Nile virus and prevention methods you can take, visit the Centers for Disease Control's West Nile Virus website to get more information.
Until next time,
Lisa - webmaster