By Bruce Batt, Ph.D.
The press is bombarding us with information as a new strain of bird flu has devastated domestic poultry by the hundreds of millions in Southeast Asia and has, in a few cases, sickened or killed people. This is a bird disease that has spread over parts of Asia, Europe, and North Africa, and many experts believe its arrival in North America is inevitable. Some think it will happen this year. One way the virus could arrive is to be carried by waterfowl and other wild birds. Therein lies the connection with waterfowl and the threat to waterfowl conservation in North America, even though there has never been a case in which the disease is known to have been transmitted from a wild bird to a human.
WHAT IS AVIAN INFLUENZA?
The term avian influenza refers to viruses that occur in birds. Birds easily shake off most strains of bird flu, and most types have low pathogenicity (ability to produce disease). But genetic mutation occurs frequently in viruses, and sometimes a harmless virus will change to one that is highly pathogenic and can cause severe sickness and death. This is what has happened with the emergence of the strain of bird flu that is causing worldwide concern among poultry scientists, human health experts, and waterfowl managers. The new strain, which was identified in 1996, is known as the Asian H5N1 virus.
WHAT DOES AVIAN FLU HAVE TO DO WITH HUMAN HEALTH?
Rarely is an avian flu transmitted from birds to other kinds of animals. But the new Asian strain has infected more than 200 people, mostly in Southeast Asia. Almost all of them caught it directly from domestic poultry. More than 100 people have died—a very high mortality rate for any flu. By comparison, a few million Americans get the “normal” flu every winter, and an average of 36,000 die each year.
In nearly every case studied, people infected with the Asian bird flu have lived and worked in close contact with domestic poultry where they shared the same air, soil, and water. This degree of exposure is highly unusual in developed countries where poultry are generally raised in large sanitary “factories.” There have been at least three instances where the virus has been transferred from human to human within families. But even though in its present form the virus infects humans only with difficulty, additional mutations could allow it to spread more easily from human to human, eventually becoming widespread in people. This situation would be called a pandemic.
Even if such a genetic change were to occur, the mutated virus might be less virulent in people in its new form. Or, it could be just as deadly as the current form, and that’s why human health authorities are so concerned. They must prepare for the worst-case scenario because the consequences of failing to do so could be severe. That’s why we see bird flu in the news so much. International agreements have dedicated several billion dollars to everything from vaccine development to trade restrictions and surveillance of wild birds. These actions carry significant political and economic implications and are thus big news.
HOW ARE WILD WATERFOWL INVOLVED?
Wild birds, including waterfowl and other water birds, are sometimes killed by the new strain of bird flu, but most of them appear to be resistant. As a result, some can become carriers of the disease—that is, they have the disease in their bodies but are not sick and live normally. In this condition, infected birds may carry the disease to other locations and affect other wild and domestic flocks. Nevertheless, in almost every case where wild birds have died from the disease, the origin has been traced to infected flocks of domestic poultry. There are a few cases, however, where the disease arrived in remote locations where it was more likely transported by wild birds.
Although Asian H5N1 can be lethal to individual wild waterfowl, only a few large die-offs have occurred in the wild. The most serious happened in western China last summer when more than 6,000 wild birds died in a nature preserve. Among these were 2,000 bar-headed geese, an endangered species in Asia. This represented about 20 percent of the world’s known population, so the loss was significant for this species.
Beyond this case, most other outbreaks in wild waterfowl this past winter typically killed a few individual birds and rarely more than a few hundred. This is a bit of “good” news, as it lessens the concern that massive die-offs of waterfowl, in the hundreds of thousands or millions, are likely to occur if the disease comes to North America. We are still concerned about the effects of the disease, however, because of the large concentrations of ducks and geese that we see in North America during migration and winter.
A recent United Nations report recommended that protecting and restoring wetlands was a sound mechanism for dispersing large concentrations of wild birds to help keep them away from domestic flocks. For seven decades, DU has been advocating wetland conservation for different reasons. Such independent advocacy for wetlands is welcome and could benefit waterfowl in the long term.