A five-year-old unvaccinated horse in the Parry Sound district has tested positive for West Nile virus, according to a report from Public Health Ontario received by the North Bay Parry Sound District Health Unit. Health officials report that the animal developed signs of the infection on Aug. 21 and is currently improving after receiving treatment.
Mosquito Activity and Bird Reservoirs
According to the North Bay Parry Sound District Health Unit, the positive test confirms that local mosquitoes may be spreading the infection. Mosquitoes acquire the virus by feeding on infected birds, which act as the primary reservoir host, and transmit it to humans and animals exclusively through bites.
According to PetMD, horses and people cannot transmit the virus back to mosquitoes because the pathogen does not stay in their bloodstreams in sufficient quantities. The Parry Sound case follows a recent confirmation by Public Health Sudbury & Districts involving a crow from Espanola infected with West Nile virus, alongside a Broad-Winged Hawk case noted by the North Bay Parry Sound District Health Unit.
Symptoms and Medical Risks
Symptoms of West Nile virus in humans are typically mild and appear within two to 15 days after infection, with 70 to 80 per cent of infected individuals experiencing no symptoms at all, according to CTV News. However, the health unit warns that the virus can occasionally cause severe outcomes affecting the brain and nervous system, particularly in elderly individuals and those with weakened immune systems.
When symptomatic, human cases may involve a rapid onset of severe headache, high fever, stiff neck, nausea, vomiting, difficulty swallowing, drowsiness, and confusion. There is no human vaccine available for West Nile virus, though symptoms can be treated, and health authorities advise anyone experiencing concerning symptoms to seek medical attention.
In horses, PetMD notes that early signs include fever, decreased appetite, and decreased energy. If the virus crosses the blood-brain barrier, animals may display neurologic signs such as muscle twitching, disorientation, circling, weakness, ataxia, and changes in mental state.
Prevention and Protective Measures
Because mosquitoes are most active between dusk and dawn, the health unit advises residents to take specific protective measures to reduce their exposure risk:
- Wear light-coloured clothing, including long-sleeved shirts, pants, socks, and shoes.
- Use bug spray containing DEET or Icaridin.
- Install or repair window and door screens.
- Eliminate any standing water on your property so mosquitoes cannot breed.
Did You Know? Horses can be vaccinated against West Nile virus, and unvaccinated animals face the highest risk of developing severe neurologic symptoms if bitten by an infected mosquito, according to veterinary guidelines from PetMD.
Frequently Asked Questions
Can humans catch West Nile virus directly from a horse?
No. According to PetMD, humans and horses cannot transmit the virus to each other because the pathogen does not remain in their bloodstreams in high enough concentrations for mosquitoes to pick it up.
What are the peak activity times for disease-carrying mosquitoes?
According to the North Bay Parry Sound District Health Unit, mosquitoes are most active between dusk and dawn.
Is there a vaccine for humans?
No, there is no vaccine available to humans for West Nile virus, though symptoms can be treated by medical professionals, per public health guidance.