The first human case of West Nile virus (WNV) for 2005 was reported to have occurred in Kansas in late June. The CDC has released few details on the patient but has confirmed this being 2005's first documented incidence of the mosquito borne disease in the US.
WNVis a positive single-stranded RNA flavivirus of about 11 kb. It primarily infects birds and mosquitoes, with humans, horses, and other vertebrates serving as incidental hosts. The virus was first isolated from a febrile patient in the West Nile region of Uganda in 1937. It remained a little-understood cause of febrile illness and sporadic encephalitis in parts of Africa, Europe, and Asia until the late summer of 1999, when outbreak surveillance identified 59 patients hospitalized with West Nile virus infection in the New York City area. The following year, the Centers for Disease Control and Prevention, in collaboration with regional health departments, established ArboNET to track WNV infections in the US. Data from ArboNet have documented the dramatic westward spread of WNV across North America. As of January, 2005, avian or animal infections have been reported from 47 states and Puerto Rico, and human infections have been reported in 40 states.
By October, 2004, ArboNET had received reports of WNV infection in 58 mosquito species and 284 bird species and had recorded 6690 cases of neuroinvasive WNV disease (meningitis, encephalitis, or acute flaccid paralysis) among persons in the United States. ArboNet has also recorded 629 deaths. Serologic surveys indicate that symptoms develop in approximately 20 percent of infected people and that neuroinvasive disease occurs in 1 in 140. The risk of neuroinvasive disease and death increases with age.
Following a WNV infected mosquito bite, transient viremia occurs during the incubation period and lasts a mean of 6 days. Viremia resolves with the appearance of IgM and with the onset of cl