West Nile Virus (WNV) is an encapsulated flavivirus that is spread from infected birds to humans by mosquito bites. It can also be transmitted by receipt of blood transfusions and organ transplants. It was introduced into the United States in 1999. It has been reported in most states and the District of Columbia. About 20% of cases of WNV infection result in mild symptoms of West Nile Fever: sudden onset of fever, often accompanied by malaise, headache, myalgia, anorexia, nausea, vomiting, lymphadenopathy and rash. These symptoms last 3-6 days and are self-limited. Approximately 0.5-1% of infections result in severe neurologic disease, especially in older individuals. Symptoms include encephalitis, meningitis, Parkinson-like symptoms, and flaccid paralysis. A few patients may exhibit optic neuritis, cranial nerve abnormalities, seizures, and myoclonus. The death rate in individuals with central nervous system symptoms is approximately 10%.

No person with hemophilia A or B has been reported with WNV. Because WNV is an encapsulated virus, it appears to be inactivated by the heat and solvent detergent processes used to produce plasma-derived clotting factor concentrates. However, individuals with rare bleeding disorders may require transfusions of plasma, and individuals with hemophilia A and B may need transfusions of red blood cells. Thus individuals with bleeding disorders may develop symptoms of WNV due to receipt of these blood components.

MASAC recommends that HTC personnel keep in mind the symptoms of WNV infection and report any possible infections in persons with bleeding disorders to their local and state health departments and to the Hematologic Diseases Branch of the CDC promptly so that appropriate investigations may be initiated in a timely manner.