Katherine Kamminga, Ph.D., Assistant Professor of Entomology
General Information
West Nile Virus (WNV) is a mosquito-borne virus that primarily spreads during the summer months. While most infections show no symptoms, the virus can lead to severe neurological health issues, including encephalitis, in both humans and horses.
Transmission Cycle
Symptoms and Severity
Impact Level
Frequency
Clinical Presentation
Asymptomatic
80%
No visible symptoms; most people are unaware that they are infected
Mild
19%
Presents as a mild cold or flu-like symptoms; rarely diagnosed
Severe
1%
Requires hospitalization and can lead to permanent neurological damage or even death
WNV does not spread directly from person to person, but by a specific biological cycle:
Reservoirs: Birds act as the primary "reservoir" for the virus.
In Humans
Vectors: Mosquitoes become infected when they feed on infected birds, then transmit the virus to other animals through bites.
Headaches and fever.
Inflammation of the brain and spinal cord.
Vision problems or coma in severe cases.
Dead-End Hosts: Humans and horses can contract the virus, but they do not develop high enough viral levels to pass it to other humans, animals, or back to mosquitoes.
Note: Most infected persons develop long-term immunity.
In Horses
Rare Cases: Transmission can occur through blood transfusions or organ transplants, though this is rare.
Encephalomyelitis: Inflammation of the brain with loss of coordination (ataxia), teeth grinding, muscle spasms, or blindness.
Mortality: Approximately 30% of horses that develop encephalomyelitis do not survive.
Prevention and Protection
Rainy and warm weather increases mosquito populations and infection risks. There is no vaccine or specific treatment for humans; prevention is the only defense.
Action Steps:
Eliminate Mosquito Habitat: Empty troughs, puddles, and old tires that collect rain water.
Biological Control: Introduce mosquito-eating fish into small, contained ponds.
Vaccination: Ensure horses are vaccinated annually. Human vaccines are not available.
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