West Nile Virus
Other names: WNV, West Nile Fever, West Nile Encephalitis
Cause: West Nile virus
Species: horses, humans, occasionally other mammals; birds act as the reservoir for the virus
Signs:
Horses – loss of appetite, depression, apprehension, fever, weakness of hind limbs, paralysis of hind limbs, impaired vision, ataxia, head pressing, aimless wandering, seizures, inability to swallow, circling, hyperexcitability, flaccid paralysis of the lower lip (droopy lip), grinding teeth, excessive sweating, muscle fasciculation, progressing to complete paralysis and coma. Death occurs in 34% of cases. For animals that survive, complete recovery is likely.
Humans – 80% asymptomatic or have mild symptoms. Of remaining 20%, most are moderate cases with fever, headache, body aches, joint pains, vomiting, diarrhea, or rash; complete recovery, but fatigue and weakness may last for months. In severe cases (mainly elderly and Immunosuppressed), high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis. Recovery may take months, and some CNS effects may be permanent. Death is rare (1% of those affected with severe illness)
Transmission: Via bite from a mosquito. Horses and humans don’t produce enough virus in their blood to infect mosquitoes. The virus can’t spread directly between horses and humans.
Diagnosis: Clinical signs combined with positive laboratory test results. Serological tests (IgM antibody, IgG antibody ELISA tests), PCR. Definitive diagnosis is important because it indicates that mosquitoes carrying the virus are in the area and need to be controlled to reduce the risk of infection to humans, horses, and other animals.
Treatment: Supportive care (anti-inflammatory drugs, pain control, sedatives, IV fluid therapy, nutritional support, nursing care)
Prevention: Vaccination of horses according to vet’s protocol (will vary based on location. Our clinic vaccinates horses against WNV every 6 months. Some areas need only yearly vaccination) Good husbandry and management to keep immune system healthy. Use insect repellents to prevent bites. Avoid outdoor activities at dawn and dusk or turning out horses at dawn and dusk when mosquitoes are most active. When you must be outdoors at dawn and dusk, wear long sleeves and long pants in addition to using insect repellent. Use fans in buildings (mosquitoes are poor fliers in wind). Cover horses with fly sheets. Control mosquitoes via IPM techniques. Do not allow birds, including domestic fowl, to roost in horse barns. Report dead birds to the local health department for testing (use gloves when handling dead birds and place in plastic bags)
Note: This is a reportable disease
Sources: Pennsylvania West Nile Virus Control Program, Rutgers New Jersey Agricultural Experiment Station, Washington State University, University of Connecticut, American Association of Equine Practitioners, CDC, Merck Veterinary Manual (image of horse being walked), Arthurveterinaryclinic.blogspot.com (image of horse that is down in the rear)
