Mosquito-Borne Diseases

West Nile fever is caused by the West Nile virus (WNV), a mosquito-borne flavivirus and human, equine, and avian neuropathogen. Birds are the natural reservoir host, and the virus is maintained in nature in a mosquito-bird-mosquito transmission cycle. The virus has also been isolated  from dogs.

A serological survey of dogs from the Highveld region of South Africa showed that 37% (138 of 377) had neutralising antibodies to West Nile virus (WNV). Two of three dogs infected with WNV had a mild recurrent myopathy, but no other abnormalities were detected in the biochemical or hematological tests performed on any of the dogs. It was concluded that dogs do not play an important role in the epidemiology of WNV but they possibly contribute to the maintenance of the virus in a region.

Distribution

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.

Clinic

A study with experimentally infected dogs in 2004 showed no occurrence of clinical signs after WNV infection. In another study, only serum creatine kinase was altered in infected dogs suggesting a mild and recurrent myopathy. A clinical case in a dog in Botswana, Africa, showed severe diarrhea, comatose attitude and convulsions. Finally the dog died.

Human health risk

Most human infections with WNV are subclinical. If clinical symptoms occur, flu-like illness can be observed, which is characterised 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.

   

Further information

• 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