West Nile Virus and Wild Turkeys

By: Bob Eriksen, NWTF Regional Biologist

West Nile Virus arrived in North America in the summer of 1999. Before emerging as a problem in the northeastern United States, the virus had been documented in Africa, Europe, the Middle East and western and central Asia. The most serious threat of West Nile Virus is encephalitis (inflammation of the brain) in humans and horses. The virus is spread by an insect vector. A vector is an insect that draws blood from an infected animal, keeps the virus in its system and then bites and infects another animal or human. There has also been some mortality from this disease in certain wild and domestic birds. West Nile Virus was first noticed around New York City in the summer of 1999 when crows and other birds were found dead or struggling and near death. At the same time a number of people became ill with an unknown neurologic disease. Disease experts with the Center for Disease Control and the Southeast Poultry Research Laboratory in Athens, Georgia began testing dead crows and blood drawn from humans who were ill with encephalitis. These disease detectives were able to isolate and identify the virus, solving the mystery of what disease was causing the trouble. It is still not known how West Nile virus got from Europe to the United States.

The medical profession was greatly concerned about the potential for this disease to cause substantial illness among humans. Though anyone may become infected with West Nile Virus, children, people over the age of fifty and people with compromised immune systems develop the most severe cases. People in poor health can die from the disease. Horses are severely affected and often die when they develop the virus. Monitoring efforts began that summer and continue in the northeast to document the spread of the virus by testing mosquitoes and checking blood samples from sentinel chickens (chickens kept in cages near mosquito-infested areas). The agricultural community, especially horse owners and the poultry industry worried about the potential impact the virus could have on the livelihood of farmers. Horses are particularly susceptible to the disease and it is apparent that certain birds can carry, transmit and die from the virus. Chicken and turkey farmers were fearful of the impact the disease might have on their operations.

Disease experts were worried that turkeys might be a potential reservoir for the virus because there are high-density turkey farming operations and large wild turkey populations in the eastern United States. Turkey hunters were also concerned about the new disease. Could it affect wild turkey populations? Could eating a wild turkey infected with the virus transmit the disease to the hunter’s family? Researchers at the Southeast Poultry Research Laboratory tested domestic turkey poults to answer some of the questions about the disease and turkeys. The results of the testing were published in “Avian Diseases”, a journal read by pathologists and veterinarians (Avian Diseases 44:932-937, 2000).

Turkey poults were inoculated with a dose of the West Nile Virus large enough to cause infection and were observed and tested for a period of time. If domestic turkeys were highly susceptible to West Nile Virus, wild turkeys probably would be too. All of the turkey poults deliberately injected with the virus developed the virus and had antibodies in their blood within seven days of being exposed. However, the poults did not appear to develop severe symptoms of the disease. Only one of the tested poults died, but it did not die from the virus. The level of virus in the blood of the infected turkeys was too low for the disease to be transmitted from the turkeys to other animals or humans by mosquitoes. There was no transmission of the virus from the infected turkeys to other turkeys kept in the same pens. The experts concluded that there is very little potential for West Nile Virus to become a major new disease in either domestic or wild turkeys. West Nile is not transmitted from one turkey to another just by being in close proximity to one another. Too little virus is found in the blood of infected turkeys to enable mosquitoes to transmit the disease from turkeys to other turkeys or from turkeys to other species. The virologists concluded that neither domestic nor wild turkeys will be a host or reservoir for the virus. That is good news for wild turkey enthusiasts and the poultry industry!

All this does not mean that wild turkeys cannot come down with West Nile Virus. Wild turkeys can contract the disease, but it is not likely to cause death or any permanent problems. On the other hand, crows, jays and some other bird species are severely affected by West Nile Virus. Two or three wild turkeys have tested positive for exposure to West Nile Virus in New York State, but none of the birds were thought to have died from West Nile. It looks like we need not worry about our wild turkey flocks being decimated or even greatly impacted by West Nile Virus. Turkey hunters should not worry about eating any wild turkey that appears to act normally before being harvested. Your chances of contracting any disease from cooked wild game are very low. Obviously sick wild turkeys should be reported to the Game Commission and should be submitted for testing. Sick crows and other birds should be reported to local health officials.