West Nile virus, abbreviated as WNV, belongs to the family of Flaviviridae and mainly has been found in tropical or temperate regions of the world. In 1937, it was identified in Uganda of the West Nile region of East African. At first, people believed in that this genus would cause a minor risk for humans because the diseases related to this kind of virus were found scarcely in the world until the year 1996 when an outbreak in Romania, where a huge number of cases with neuroinvasive disease. West Nile virus now becomes an endemic pathogen which threated people’s health of Africa, Asia, Australia, the Middle East, Europe and the United States, where those counties have experienced a worst epidemic of this virus in 2012. In this year, WNV killed 286 people in the United States, especially the state of Texas being hard hit by this virus. Figure 1 shows that family tree of West Nile virus.
West Nile Virus causes a symptom that seems like people catching the characteristics of flu and only a small proportion of patients will advance into West Nile Encephalitis, a symptom that viruses get through blood-brain barrier and infect nervous system. WNV contains a single-stranded RNA and its envelope consists of E and M proteins. E protein mainly regulates the virion assembly, recognition of cell receptors, cell endosomal membrane fusion, agglutination of red blood cells, and induction of immune responses. WNV maintains a life cycle illustrated as figure 1.
Fig. 1 Life Cycle of West Nile Virus
WNV maintains a life cycle in nature between mosquitoes and birds. A mosquito containing virus bites an uninfected bird, then the virus amplifies within a host bird, an uninfected mosquito is infected when it bites this infected bird. Incidental infections, such as humans and horses, because virus does not proliferate well within these species, they are considered as dead-end hosts.
Figure 2 shows the cellular signal pathway of West Nile Virus: after binding, virus fuses its envelope with cellular membrane, followed by uncoating of the nucleocapsid and then releases its genetic substance-RNA genome into cell.
The viral genome serves as a positive RNA by which the virus synthesizes its own gradients (genetic substance RNA) by using host stuff. Those replicants are packaged subsequently into new virus particles that are transported in vesicles to the cell membrane.
Fig. 2 Signal Pathway of Life Cycle of West Nile Virus