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Pathogen Page

West Nile virus

I. General Information

1. NCBI Taxonomy ID:

2. Disease:

West Nile fever

3. Introduction

West Nile virus (WNV) is a virus of the family Flaviviridae. Part of the Japanese encephalitis (JE) antigenic complex of viruses, it is found in both tropical and temperate regions. It mainly infects birds, but is known to infect humans, horses, dogs, cats, bats, chipmunks, skunks, squirrels, and domestic rabbits. The main route of human infection is through the bite of an infected mosquito (Wiki: West Nile). WNV was first detected in North America in 1999 and spread rapidly across the USA and into Canada, Mexico, and Central and South America. The virus is transmitted via mosquitoes, primarily through the bite of Culex species but also by many other genera of mosquitoes. Birds are the natural hosts and serve as the zoonotic reservoir. Mammals and reptiles are considered to be incidental hosts from which further transmission generally does not occur (Lieberman et al., 2009).

4. Microbial Pathogenesis

The mechanisms by which WNV and other neurotropic flaviviruses cross the blood-brain barrier (BBB) remain largely unknown, although tumor necrosis factor alpha (TNF-α)-mediated changes in endothelial cell permeability may facilitate CNS entry. It is likely that WNV infects the CNS at least in part via hematogenous spread, as an increased viral burden in serum correlates with earlier viral entry into the brain. Additional mechanisms may contribute to WNV CNS infection, including (i) infection or passive transport through the endothelium or choroid plexus epithelial cells, (ii) infection of olfactory neurons and spread to the olfactory bulb, (iii) a “Trojan horse” mechanism in which the virus is transported by infected immune cells that traffic to the CNS, and (iv) direct axonal retrograde transport from infected peripheral neurons (Samuel and Diamond, 2006).

5. Host Ranges and Animal Models

West Nile virus mainly infects birds, but is known to infect humans, horses, dogs, cats, bats, chipmunks, skunks, squirrels, and domestic rabbits. The main route of human infection is through the bite of an infected mosquito (Wiki: West Nile).

6. Host Protective Immunity

T-cell-mediated immunity is essential for controlling WNV infection in the CNS. Both humoral and cellular immune responses are likely essential in protection from WNV infection (Samuel and Diamond, 2006).

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