For the Birds Radio Program: West Nile Virus
Laura gives a history of West Nile Virus and other mosquito-borne illnesses, on birds and humans, and talks about why we must be careful about how we approach the mosquito problem to ensure that the cure isn’t worse than the disease.
One of the saddest news stories in the world of birds is the spread of West Nile Virus in the US. This virus, which causes inflammation of the spinal cord and brain, was first isolated in Uganda in 1937. An outbreak in Israel in 1957 killed many elderly patients, and the disease spread to Egypt and France in the early 60s. The disease arrived in America in 1999, with the first cases noted in horses and humans, but very quickly people started noticing dead crows littering cities along the eastern seaboard. West Nile Virus is far more lethal to birds than it is to humans.
Individuals of at least 70 species of birds have died from the virus, and it seems to take its heaviest toll on the crow family, including Blue Jays. Infected crows have close to I 00% mortality when exposed to West Nile Virus. And the disease is spreading rapidly: this year there has been confirmation of infected birds in Michigan, Illinois, and Wisconsin.
Mosquito-borne diseases of many kinds have taken a heavy toll on birds, leading to the total annihilation of several native species in Pacific islands. Hawaii was isolated from mosquitoes from the moment spewing volcanoes formed the islands, and the birds that eventually found their way there lived in a mosquito-free paradise for millennia. Then in the 1820s, a spiteful ship captain introduced mosquitoes to Hawaii, in what was both a case of biological warfare and an ecological crime of enormous magnitude. Neither the Hawaiian people nor the birds had any defenses against mosquito-borne diseases, and both died in huge numbers. The native birds of Oahu had largely disappeared by the 1860s. On Kauai, Molokai, Maui, and Hawaii, a major population crash of forest birds occurred in the 1890s and early 1900s. Birds on Lanai survived until the establishment of Lanai City in the early 1920s, when suddenly their population also crashed. Now virtually all the native birds seen in Hawaii are seen at high elevations, where mosquitoes are not found. A handful of native birds are still doing okay, but many others simply could not adapt to the restricted range and have died out. And ominously, Hawaiian mosquitoes seem to be adapting to higher and higher elevations even as Hawaiian birds don’t seem to be developing any immunities whatsoever to the diseases those mosquitoes carry.
As scary as West Nile Virus is, and as important as mosquito control is for humans and birds both, sometimes the cure is even more dangerous than the disease. Last year New York State asked New York counties to send in dead birds for analysis to trace the spread of the disease. More than 80,000 birds were turned in and examined. Although many of them had died from West Nile Virus, the leading cause of death wasn’t the virus at all, but rather was pesticides, especially common lawn care products, all approved by the EPA.
Ironically, some of the pesticides used in mosquito abatement are suspected of reducing immunity in birds, making them more vulnerable to West Nile Virus. The wisest course of action in using pesticides to prevent the disease is to control mosquitoes at the larval stage using less toxic methods than aerial spraying–aerial spraying has been totally ineffective at holding the disease at bay because it’s so ineffective at killing adult mosquitoes. So far, West Nile Virus is known to have killed eight humans in the two years since it first appeared here, and the recent death of an elderly woman in Connecticut may have also been caused by the virus. Meanwhile, thousands of birds have died from the virus, and tens of thousands of birds have died from the pesticides used to kill the mosquitoes that carry the virus. Frank Gill, Senior Vice President of Science of the National Audubon Society, said, “Like canaries in a coalmine, birds warn of danger in our environment. If these chemicals kill birds, what are they doing to our kids?”