To print this page, select File-> Print from your browser menu.

Demystifying Avian Influenza

Diana Humple


Avian influenza--often simply called "bird flu" or "poultry flu"--is by now a household term throughout the world. But it's important to understand the facts of this disease, because media coverage is often sensationalized and the perceived threat to humans can result in overreactions.

There are actually 144 varieties of avian influenza. Birds are typical carriers of these viruses, which rarely cross species barriers to humans or pose a threat to the carriers themselves. The "bird flu" we hear discussed is generally H5N1, a highly pathogenic strain (referring to its high potential to kill poultry). It was first detected in domestic geese in 1996 and has since spread throughout Asia and, recently, into Europe and Africa.

Primarily a poultry disease, H5N1 also affects wild birds--in particular, waterfowl that mingle with domestic poultry. Consequently, migratory species may have a role in its spread, although the primary vector to date appears to be the transportation of poultry and poultry products.

H5N1 has not yet arrived in North America (as this Observer goes to press), but its arrival is anticipated. Asia and North America are "connected" in western Alaska, where migratory birds from both regions occur. Potentially as early as this fall, birds migrating along the Pacific Flyway could carry the disease.

Although still uncommon in humans (as of late August, H5N1 had caused the deaths of 141 people worldwide), the fatality rate is high in those infected. Fortunately, transmission is currently inefficient between humans and from bird to human, as this is not an upper respiratory tract disease (such as the common cold). Humans infected have been predominantly poultry workers in close contact with discharge from infected birds.

But epidemiologists are paying close attention to H5N1 because of its potential to mutate into more easily transmissible forms. While the virus in its current state will not produce a human pandemic, the risks associated with possible mutation are serious.

Conservation Implications
The Bar-headed Goose, an Asian species that is already threatened, has suffered mortality from "poultry flu." Photo by John Graham Holmes/VIREO

Often overlooked in the face of anthropocentric fears are the potential impacts of H5N1 on wildlife. Among biologists, concern is growing about implications for wild bird populations. The virus has already infected numerous waterbirds--geese, ducks, swans, gulls, cormorants, shorebirds and others--as well as landbirds such as songbirds, raptors, pigeons and doves. The greatest documented effect has been upon Bar-headed Geese (Anser indicus) at Qinghai Lake in China, where up to 10% of the world population of this threatened species has died from H5N1. Population-level effects on all wildlife are largely undetermined and require close monitoring. Impacts also include misinformed management decisions in some regions to cull wildlife, due to fears of H5N1's spread.

The World Health Organization has recommended specific actions to reduce the likelihood of a pandemic. These include strengthening national preparedness to reduce opportunities for spread in poultry, and improving early-detection systems. Bird monitoring studies help trace the spread of H5N1. Scientists in North America have launched programs to test wild birds, to gain knowledge about the spread of all avian influenzas and for early detection of H5N1--especially in Alaska.

PRBO is participating in national efforts to collect potential influenza samples from shorebirds and landbirds. During the banding process, we gently take swabs from the cloaca (the body cavity through which birds excrete and reproduce) and, in shorebirds, the throat, obtaining samples that would contain virus cells of any influenzas present. Our shorebird sampling, led by PRBO's Nils Warnock, PhD, in collaboration with USGS and USFWS, is done in California and Alaska. Our landbird sampling--in collaboration with UCLA, the Institute for Bird Populations, and the Landbird Migration Monitoring Network of the Americas--is done in California.

With our expertise in bird migration and population monitoring, PRBO is in a position to contribute to a greater scientific understanding of "bird flu"--necessary for addressing potential effects of this disease.