West Nile virus has been detected in numerous countries of the Old World, including Africa, Near East and Asia. In Eurasia, WNV has been shown to cause meningoencephalitis in humans and horses (e.g. in Southern France, Romania, Italy and Russia). It first occurred in 1999 in New York City, but has extended its range throughout much of the eastern parts of the USA, and entered South-Central Canada and the Caribbean region.
A study with experimentally infected dogs and cats in 2004 showed viraemia of different extent and no occurrence of clinical signs in dogs and mild, non-neurologic signs in some cats (Austgen et al., 2004). In another study, only serum creatine kinase was altered in infected dogs suggesting a mild and recurrent myopathy (Blackburn et al., 1989). Generally, WNV infection is suggested not to be associated with clinical disease, especially in dogs, but single case reports of clinical signs and disease have been published (e.g., Lichtensteiger et al., 2003).
Human health risk
Most human infections with WNV are subclinical. If clinical signs occur, flu-like illness can be observed, which is characterized by high fever and chills, malaise, headache, backache and myalgia. In epidemics, fever, a flushed face, conjunctival injection and generalised lymphadenopathy were common. Severe cases exhibit neurological manifestations like meningitis, encephalitis and myelitis.
Blackburn NK, Reyers F, Berry WL, et al.: Susceptibility of dogs to West Nile virus: A survey and pathogenicity trial. J Comp Pathol. 1989, 100, 59-66