West Nile fever

West Nile fever is caused by The West Nile virus (WNV),  a member of the Flaviviridae family, the best-known member of which is Yellow Fever Virus. The Flaviviridae are single-stranded RNA viruses in which the virion strand is also the mRNA, and which assemble in the cytoplasm into icosahedral virions composed of one type of capsid protein. While the majority (90 %) of West Nile virus infections in humans are innocuous, some infections produce meningitis and encephalitis, and are noted for long-term convalescence and fatigue (Kramer et al. 2007).

A bit of science

For those who are interested , the capsid of WNV is a major pathogenic protein that is associated with growth arrest of host cells.  WNV capsid protein binds to the substrate-binding domain of Hsp70 in the cytoplasm of infected cells. Capsid binding to Hsp70 disrupts the functional role of Hsp70 in ensuring protein folding. Specifically, the folding function of Hsp70 and Hsp40 complexes in restoring enzyme activity is impaired as viral titers increase. Furthermore, WNV capsid induces cytotoxicity—via caspase-induced apoptosis and mitochondrial dysfunction—that is attenuated by Hsp70. The data support the notion that direct binding of WNV capsid to Hsp70 may mediate illness severity in the host (Oh and Song 2006).

Example outbreak

The West Nile virus quickly spread across the United States after the first reported cases in Queens New York in 1999. The virus is believed to have entered in an infected bird or mosquito, although there is no clear evidence.  It is worth noting that the WNV is the subject of extensive experimentation in laboratories in the USA with new virulent strains being examined and mutants being produced of the older strains. 

The disease spread quickly through infected birds. Mosquitoes spread the disease to mammals. It was mainly noted in horses but also appeared in a number of other species. The first human cases usually followed within three months of the first appearance of infected birds in the area except where cold weather interrupted the mosquito vectors.

According to very conservative estimates, the reported number of infected in 2009 was 720, but the estimated total number of infected the same year exceeded 54,000. Many cases were believed to have gone unreported because the symptoms were 'not serious enough' or went undiagnosed. In addition, “some more severe but non-neuroinvasive cases were not reported to the CDC”.

More cases have continued to appear via blood donation screening. 1,039 West Nile-tainted blood donations were discovered between 2003 and mid-2005. There have been 30 cases of West Nile from blood transfusion, the majority from 2002 before blood screening was instituted.   

Since the virus ‘arrived’ in the U.S., there have been over 1,100 deaths with cases reported from every U.S. state except Maine, Alaska and Hawaii. The number of animals killed is, of course, unknown.   Animal cases have been occasionally found in Maine and in Puerto Rico.  In 2012, there was a widespread re-outbreak with the second-highest total case numbers of humans.