WEST NILE VIRUS

The West Nile virus (WNV) is a flavivirus that has been present in the United States since 1999. Like many viruses, WNV has the ability to change or mutate over time, becoming more or less pathogenic to the species it infects; although WNV has been recognized for many decades in northern Africa, the Mediterranean and parts of Europe, the degree of pathogenicity we see now has only been present since the 1990’s. Transmission is mainly through mosquito bites, but eating infected mice or drinking contaminated water can potentially infect birds. As of this writing, WNV is present in all 48 continental states, and is expected to continue to spread through Central and South America. Birds of many species, humans, and horses seem to be the most susceptible to WNV disease.

The symptoms caused by WNV tend to be neurological in nature. Birds will present with signs such as unexplained weakness, torticollis (twisting of the head and neck), seizures, or circling; in many cases sudden death is the only indicator of disease. Not all species of birds are affected evenly, with some, such as crows and jays, being considered more susceptible, while others, like chickens, being fairly resistant. Research in the US is still very new in this area, and new susceptible species are being added to the list on a regular basis. Until proven otherwise, all species should be considered susceptible.

Diagnosis of WNV infected birds at Liberty Wildlife is based tentatively on clinical signs. Blood testing is available, but due to the rapidity of the disease process is not always a feasible option. Unfortunately, definitive diagnosis is often confirmed at necropsy (postmortem exam). Treatment of WNV consists solely of supportive care. Anti-inflammatory drugs, anti-seizure medications, fluid therapy, etc. have all been tried with inconsistent results.

Prevention of infection is always considered the best treatment. Control of the environment is the most reliable method of prevention at this point. Eliminating standing water and spraying for mosquitoes with safe insecticides will greatly reduce the rate of spread. Vaccination against WNV is also available. To date the only vaccines on the market are labeled for use in horses, although several zoos and other bird collections have been vaccinating their birds with the equine product. While the vaccine has not caused any ill effects in birds, its efficacy is still being tested. Liberty Wildlife is vaccinating their Education birds with the available equine vaccine. While much has been learned about WNV over the last 5 years, we are only at the tip of the iceberg. Close monitoring of populations and their responses to the virus, as is often noted firsthand in rehabilitation, will continue to be of great importance to researchers.