Avian Flu: What it could mean for wild birds (and birders)

by Pepper Trail, reprinted with permission from the Rogue Valley Audubon newsletter, The Chat.

This month I've decided to devote the column to something that may seem rather far removed from bird conservation: the growing concern about avian flu and the possibility that this could spread to humans and become a deadly global epidemic. While this disease has so far had little actual impact on humans, it has the potential to radically alter public attitudes and interactions with wild birds. Furthermore, there is growing evidence that avian flu is already having a drastic effect on some bird populations.

"Regular" Avian Flu and H5N1
As is the case with human influenza, there are many different strains of avian flu--over 140 by last count. Many of these circulate in wild birds (especially waterfowl) at low levels and cause only mild disease symptoms. Highly pathogenic avian influenza viruses can cause great mortality in domestic poultry flocks but are very rare in wild birds. The particular avian flu virus that is the center of all the current concern is called H5N1. This highly pathogenic strain was never recorded in wild birds before the recent outbreaks in Southeast Asia, Russia and countries around the Black Sea. It is likely that it originated in domestic poultry through mutation of low pathogenic strains and was then passed from poultry to wild birds.

H5N1 and People
So far, about 120 people (all in Southeast Asia) have been infected with H5N1, almost all of whom had close contact with poultry. Of these, more than 60 have died. Thus, this is a very serious disease if it is acquired. The good news is that the present virus does not spread easily to humans, even those working closely with infected poultry. While human-to-human transmission is suspected in a handful of cases, it is clearly very rare. The great fear among public heath officials (and the basis for the current media frenzy) is the possibility that this virus could mutate into a form that is highly infectious to, and between, humans. Such mutations have occurred in earlier strains of avian flu, including the strain responsible for the great "Spanish Flu" pandemic of 1918, which killed 40-50 million people worldwide. However, there is nothing inevitable about this transformation: it is a possibility, but by no means a certainty.

H5N1 and Wild Birds
In Southeast Asia, domestic flocks are often allowed to mix freely with wild birds, especially waterfowl. This facilitates the transmission to migratory waterbirds, leading to several reported die-offs. The question is: can infected wild birds spread H5N1 to new areas, or is the strain so deadly that it kills birds "on the spot?" This has become the subject of intense research.

Most cases of the spread of the virus are clearly explained by trade in infected poultry, not by the movements of wild birds. However, in August, an outbreak of H5N1 was detected at a remote lake in northern Mongolia, far from known poultry sources. This has led many researchers to conclude that at least in some cases, wild birds can spread the virus along their migratory routes. Remember: the "spread" we're talking about here is from wild birds to poultry, not to people. Global testing of both domestic waterfowl and wild birds is needed in order to monitor the extent and spread of the virus in domestic flocks and wild bird populations.

In addition to its economic and public health impacts, H5N1 may also pose both direct and indirect threats to wild bird populations. In the "direct" category, for example, it is estimated that up to 10% of the world population of the rare Bar-headed Goose perished in a recent outbreak in China. In the "indirect" category, campaigns of killing ("culling") wild birds in an effort to contain the virus have been proposed in some areas, including Thailand, where wild Asian Openbill Storks were targeted. These culls are highly unlikely to stop the spread of the disease. This view is shared by the World Health Organization, Food and Agriculture Organization of the United Nations, and the World Organization for Animal Health, as well as conservation groups like BirdLife International. Indeed, culls have the potential to make the situation worse by dispersing infected individuals and stressing healthy birds, making them more prone to disease. Moreover, it would divert resources away from important disease control measures.

It is important to emphasize that there is no evidence that humans have ever been infected with H5N1 through contact with wild birds. Human infections have only occurred in people who have been closely associated with poultry. However, should H5N1 spread to North America, bird-banders and others who handle wild birds may need to adopt new precautions.

Controlling the spread of H5N1
The most efficient control techniques involve improved biosecurity, primarily of the poultry industry, to reduce the likelihood of contact between domestic stock and wild birds or infected water sources. This needs to be coupled with swift and complete culls of infected poultry flocks in the event of an outbreak. Further measures that should be considered include stricter controls on wild bird markets, and movements of domestic poultry. Such measures should be introduced worldwide. Countries currently free of the disease should consider a ban on imports of domestic poultry and wild birds for the pet trade from affected regions.

Concerns about the role of the bird trade in spreading avian flu have unfortunately been proven correct. In 2004, two Crested Hawk Eagles being smuggled into Belgium on a flight from Thailand were found to be infected with H5N1, and just last week, a parrot being imported into England from Taiwan also tested positive. The scale of the wild bird trade in Asia is huge, involving millions of birds per year. Shutting down this trade would not only close a possible avenue for the spread of avian flu, but would be of immediate benefit to wild bird populations throughout Asia.

What about North America?
H5N1 has not yet been reported from either North or South America. Since the 1990s, the U.S. Department of Agriculture has sampled more than 10,000 migratory waterfowl crossing the Bering Sea from Asia to Alaska, but has not found a single bird carrying the H5N1 virus.

Few birds migrate from Asia all the way into the lower 48, but many mingle in Alaska with local populations of waterfowl and shorebirds whose migratory pathways bring them through Oregon, including the Klamath Basin. In response to increased concern about avian flu, a consortium of government agencies is seeking $5 million over the next three years to expand virus testing to birds along their migratory routes in the lower 48 states beginning next spring. This is a prudent step that deserves our full support.

Amid all the concerns that avian flu raises, the good news is this: even in areas where H5N1 has been reported, the observation and enjoyment of birds in the wild are not associated with any increased risk of avian flu. Birding remains what it has always been, what we need now more than ever: a blessed escape from the worries of the world.

For more information:

• National Audubon Society
• BirdLife International
• Avian flu and the wild bird trade
• Guidelines for handling wild birds from the National Wildlife Health Center