Bird flu: A real threat or just fiction?

The implications of a worldwide avian influenza (bird flu) pandemic are real and of dire concern to people worldwide. Some of the connections between agriculture are real and some are as fictional as a dime store novel.

Avian influenza (AI) or bird flu is primarily just that — a disease of birds. In rare cases the virus has spread to humans and in a few cases — the 1918 flu pandemic, the 1957 Hong Cong Flu Epidemic and the 1962 Asian Flu Epidemic, it spread rapidly among humans.

Bird flu occurs when any of 16 known hemagluttinin (HA) and nine neuraminidase (NA) proteins interact and cause changes in the cellular structure of the avian influenza gene. In 1918, the combination of H1N1 proteins caused a mutation that spread freely among humans and killed somewhere between 30 and 50 million people worldwide.

Most experts agree the pandemic got its beginnings from backyard poultry in the Midwest, which was most likely infected by migratory birds.

In 2005, a different strain of the bird flu, H5N1, has made the jump from birds to humans in six Asian and one European country (Turkey). As of Feb. 1, 2006, 160 people in these countries were infected with H5N1 bird flu and approximately 83 of them died. The mortalities were among young, otherwise healthy men and women, and in only one case was this strain of bird flu contracted by one person from another person. All other cases came from direct contact with infected birds.

The H5N1 strain has now been diagnosed in birds in Romania, Croatia, Ukraine and other European countries. Many virologists who study influenza believe the H5N1 strain will be the next epidemic or pandemic flu.

From the hysteria of these tragic cases in 2005-2006 has sprung a number of widely circulated myths about bird flu — some of them directly related to farmers and farming.

Myth one: Using poultry litter for fertilizer increases the risk of spreading bird flu. No form of avian influenza has been known to survive outside a live animal or person for longer than a few hours, except in extreme cases — as in Pennsylvania in the 1990s for 100 days in semi-frozen manure.

Recent concerns about AI viruses persisting in poultry litter and subsequently surviving in the soil when applied as fertilizer and subsequently infecting people who eat food crops grown on this land are myth. The high cost of fertilizer and availability of litter as a source of nitrogen and other soil nutrients likely means a record amount of litter will be used on crops in the Southeast.

A leading expert on avian influenza in the U.S. describes the connection between bird flu and poultry litter this way: “No scientist is going to say anything is impossible, but the chances of an AI virus living in poultry litter and in the soil and being transmitted to a plant and into humans is much less likely than winning the National Powerball Lottery a hundred times in a row.”

Myth two: I live and work on a farm in a rural area of the country, so I am less likely to catch bird flu. Avian influenza experts agree the first jump from birds to humans is most likely to occur from wild birds, probably migratory water fowls to backyard chicken flocks — which are much more prevalent in rural areas. Living in rural areas may actually be a more likely location for early cases of bird flu in humans. However, in later stages of a worldwide flu pandemic where one lives won't likely make much difference.

Myth three: If I eat chicken or turkey, I am more likely to contract bird flu. No evidence exists that any sub-type of bird flu has ever been contracted by eating properly cooked chicken or turkey. Properly cooked is open to debate, but the same cooking guidelines that protect against salmonella will be sufficient. Despite the safety of eating poultry products, poultry consumption worldwide has dropped more than 35 percent since the latest cases of H5N1 bird flu surfaced in 2005.

Myth four: If I deliver grain or collect litter from poultry houses or operations in which chickens have died from bird flu, I will likely catch the virus. No, commercial layer and broiler operations are actually a fairly low risk for avian influenza. Even on poultry farms where birds are diagnosed with avian influenza, the virus has to mutate to a form that affects humans and this is not likely to occur in a commercial poultry operation.

Avirulent, or non-lethal strains of avian influenza occur fairly often, but only those determined to be virulent mandate automatic eradication of infected birds. Because of its past ability to mutate into forms that infect humans, all cases of H5 and H7 influenza are being treated as a virulent form, even though most strains remain avirulent. Before any strain of bird flu can infect humans, it has to mutate into a form that can be transmitted from animal to animal, then animal to human, then make the biggest and most rare jump of all to a form that can be passed from one human to another.

The last jump from chickens to humans has occurred several times throughout history, most recently with the H5N1 virus in Asia and Turkey. In 2003, in New York, one poultry worker was diagnosed with H7N2 bird flu. He recovered and no spread of the virus was documented. In 2004, in British Columbia in western Canada, two poultry workers were diagnosed with H7N3 bird flu. Both were treated with oseltamivir, both recovered, and no spread of the strain was documented.

In both the Canadian and New York cases, the human infection was traced back to live markets. Charlie Beard, retired USDA poultry scientist and one of the first to track avian influenza, calls live markets a ticking time bomb. Beard contends these live markets are a likely source of future bird flu epidemics.

Myth five: The flu vaccine I take annually will protect me from bird flu. The most likely strain of bird flu to infect humans is the H5N1 strain currently causing problems in Asia and Turkey. This and similar strains are resistant to commonly used flu vaccines. The only vaccines known to reduce the severity of these strains are oseltamivir and zanamivir. Both are used sparingly worldwide to prevent resistance problems.

The reality is that avian influenza isn't likely to affect either farmers or the general public by contact with chickens or turkey, rather with wild birds, especially ducks. Farmers who duck hunt should be particularly aware of birds that appear listless or less vigorous than other ducks in the flock or that have discolored or shedding feathers. Likewise processing and handling wild ducks or other migratory birds should be done with care.

Migratory ducks are known carriers of avian influenza. In the H5N1 cases in Asia and Turkey, a much higher level of feather shed, characteristic of AI infection as been detected in wild ducks. In some of the 2005-2006 cases of bird flu in humans in Asia, the infection came from direct contact with wild ducks.

For farmers with chickens, there is a greater risk that these backyard flocks will become infected by contacting saliva or feces of wild ducks, most likely via a sharing of feed. Sheltering backyard chickens from wild birds, especially migratory ducks is good insurance against bird flu and other diseases vectored by these birds.

“Most of us who have followed bird flu, or avian influenza, for a long time agree that a pandemic will occur, but there is less agreement on when, where and how severe the problem will be,” Beard says.

Beard, who developed the first test to detect avian influenza back in 1971, explains that humans have no immunity to newer strains of bird flu. The H1N1 flu that has been around since the 1918 pandemic still kills approximately 35,000 people in the U.S. each year. If a strain with close to the virulence of the H5N1 strain that has killed approximately 50 percent of humans infected in 2005-2006 makes the jump to a form that spreads from humans to humans, this would be a catastrophic pandemic that would literally affect the whole world in a matter of days, Beard warns.

Far from being a forecaster of worldwide destruction, Beard contends everyone involved in diagnosing and managing bird flu should plan for the worst and hope for the best. He points out that flu vaccines, modern communication, and sophisticated diagnostic tests are factors in favor of managing a worldwide flu pandemic.

While the risk to humans from bird flu is real and the likelihood of a worldwide pandemic is certainly a potential threat to people worldwide, many of the myths surrounding this disease may affect management of farming operations and these should be weighed carefully against reality.

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