Is the Danger Real?
Sensible precautions should protect hunters from West Nile virus and bird flu.
By Arturo Longoria
West Nile virus was first introduced into the New York City area in 1999 after migrating across the Atlantic from its normal haunts in Africa, Europe and the Middle East. By 2003 the disease had made it all the way westward to California. The virus’s usual route of transmission from birds to humans is through mosquitoes that prey on both. In the case of avian influenza (bird flu), North America is now in a “wait and see” or surveillance mode, with public health officials, epidemiologists and field biologists alert for the possible arrival of a more virulent form of bird flu from Asia.
But just how vulnerable are hunters to these pathogens, and what measures should they take to protect themselves from the illnesses they cause? Do birds afflicted with West Nile virus (WNV) show any overt signs of infection? Not according to Dr. Eric Fonken, a research veterinarian and veterinary epidemiologist in the Zoonosis Control Branch of the Texas Department of State Health Services.
“There is no way to tell by looking at a bird if it has WNV or most any other infectious disease,” says Fonken, who also stresses that common bacterial illnesses like salmonella are more prevalent in bird feces and pose greater risks to hunters than WNV. “Still, most game birds will show no symptoms at all, but others may exhibit weakness, be unable to fly, or be in poor physical condition. Many WNV-infected birds are simply found dead. Hunters should avoid handling sick or dead birds,” Fonken says.
The experts are all in agreement that a hunter’s most likely scenario for contracting WNV is from the bite of an infected mosquito. Fonken notes that to date the U.S. Centers for Disease Control has not issued any reports of anyone becoming infected with WNV from handling an infected bird even though there is a “theoretical risk” that direct contact might transfer the virus to a human.
With those facts in mind, what age group has the highest probability to contract WNV?
“All age groups are at essentially equal risk of becoming infected,” Fonken says. “However, persons over 50 years of age are at much greater risk for developing WNV neuroinvasive disease [an encephalitic infection of the brain, spinal cord or tissue surrounding the brain and spinal cord], which is quite serious and can result in significant long-term disability or death.” Fonken also notes that humans face the greatest probability of being at risk of mosquito bites during the warm and rainy months of August and September. South Texas, with its perpetual warm weather, has the potential for year-round cases of WNV, says Fonken.
But if a hunter is bitten by mosquitoes, and then later experiences achy, feverish symptoms, does this warrant prompt medical attention?
“There are many diseases that are more common than WNV that also start out with vague, flu-like symptoms,” Fonken says. “If a person becomes ill enough that they seek medical attention, they should tell their healthcare provider about their outdoor activities, animal exposures and any insect or tick bites they may have incurred. That way, the physician can consider the possibility of animal-, tick- or insect-borne disease, including WNV.”
When it comes to eating birds or mammals infected with WNV, there are two things to keep in mind. First, according to the experts, including Fonken, properly cooked meat destroys the virus. But what about dried meat that has not been cooked? Experts are not willing to offer definitive answers to that question just yet. Most epidemiologists have concluded that although game mammals can become infected with WNV, their tissues do not generally have sufficient quantities of the virus to pass it on to humans. They also suspect that stomach acids will kill the virus when ingested. Still, those conclusions are tentative and no one in the scientific community is willing at this time to offer an irrefutable declaration.
The bottom line regarding West Nile virus is that its potential to ruin the hunt is extremely low. As Fonken explains, “WNV is a real threat, but when put into perspective, there is no reason for panic or to avoid outdoor activity. About 80 percent of the people infected with WNV will not develop any symptoms at all. About 20 percent of those infected will develop West Nile fever, and less than one percent will develop a more severe West Nile neuroinvasive disease.”
The danger, however, is more evident when it comes to avian influenza, though only in highly virulent forms.
“From what we know about human cases of avian influenza, it appears to take a significant amount of exposure to infected birds for a person to become infected, and then almost only when the virus is a highly pathogenic strain,” Fonken says. “In general, feces, saliva and respiratory secretions from influenza-infected birds are potentially infectious. There is a very low prevalence of avian influenza in waterfowl populations, and these viruses do not generally infect non-waterfowl species, such as backyard songbirds. So the potential for the average person to be exposed to avian influenza is extremely small.”
Other factors lessen the danger to humans as well, Fonken points out. “Most types of avian influenza do not appear to be infectious to humans,” he explains. “A big exception to that is the current strain of highly pathogenic H5N1 avian influenza circulating in Asia, Africa, the Middle East and Europe. We do not currently have that H5N1 strain in North America, however. [Furthermore], highly pathogenic avian influenza viruses typically develop and circulate only in domestic poultry, although on rare occasions circulate in wild birds. So at this point in time, for a hunter in North America, I would rate the risk of contracting avian influenza from a wild bird to be an extremely slight probability.”
Of course, slight probability does not mean zero probability. As proof of this, Fonken says there is evidence from a study in Iowa of rare infection, but no clinical disease, with avian influenza virus in hunters and wildlife biologists who had extensive contact with wild waterfowl over a period of years.
What if a bird flu pandemic strikes U.S. soil?
“If a highly pathogenic strain of avian influenza begins to circulate widely in wild North American game birds, a rather unlikely scenario, scientists will use all available information to determine the risk to hunters and others having contact with these birds. Using an objective risk assessment process, public health authorities would then determine reasonable and appropriate measures for hunters and others to take to minimize their risk of infection,” Fonken says.
Still, areas in the state with seasonal waterfowl populations will receive the greatest surveillance for avian influenza, particularly the H5N1 strain.
“There is really no way to predict with any certainty the likelihood of seeing avian influenza in a given part of the state, beyond saying in general that areas with large populations of waterfowl and/or shorebirds would be more likely to have infected birds,” Fonken says. “To give an accurate estimate, you would first need to know which bird species were infected, which subpopulations of those species were affected, where those species stopover and/or winter within the state, how long they spend in those locations, and the number of birds at any given location, among other considerations.”