One horse has died and another is suffering neurologic defects after being bitten by infected mosquitoes in Lambton County.
According to the Equine Disease Communication Center (EDCC), a three year old unvaccinated standardbred filly was found laying down by its owner on September 16.
It had developed muscle fasciculations of the head and shoulder and died. West Nile Virus (WNV) was identified as the cause of death on September 17.
Ontario's Ministry of Agriculture, Food and Agribusiness told Sarnia News Today WNV in horses is spread through mosquito bites and affects the horse’s central nervous system.
WNV vaccines are available for horses and are highly effective when administered.
Symptoms in horses range from fever, fatigue, trembling, depression, loss of appetite, incoordination, head tilting and partial paralysis, to convulsions and sometimes death.
Once contracted, the ministry said there is no specific treatment for WNV in horses, and just over one third of horses showing clinical disease may die as a result.
Horses are a dead-end host for WNV and therefore cannot transmit the virus to other horses, animals or people.
On September 20, Eastern Equine Encephalitis Virus (EEEV) was confirmed in a 13 year-old quarter horse. EEEV is also spread by infected mosquitoes.
EDCC said the under vaccinated gelding developed ataxia with weakness in the right front and hind limbs on August 29. He was clinically normal on August 28.
EDCC said he was treated supportively and remains alive, but with some neurologic deficits.
Lambton Public Health (LPH) said, like West Nile, EEEV is typically found in wild birds and mosquitoes, but can be spread to horses and, in rare cases, humans, through an infected mosquito’s bite.
LPH said humans cannot be infected with EEEV from another horse or human.
Horses can be protected by a vaccine against EEEV, however there is no vaccine for humans and while human cases are rare, the disease can cause serious neurological complications and even death.
LPH is reminding residents that preventing mosquito bites is the best way to protect against both WNV and EEEV.
To reduce the risk of being bitten by mosquitoes:
• Avoid areas with high mosquito populations.
• Take extra precautions from dusk to dawn when mosquito activity is high.
• Wear protective, light-coloured clothing.
• Use repellents containing DEET or Icaridin. Follow label instructions carefully.
To reduce mosquito breeding areas:
• Drain areas of standing or stagnant water on your property.
• Remove old tires; turn over pails, toys, and wheelbarrows.
• Change water in bird baths (at least weekly).
• Keep eaves clear to avoid trapped water
In August, LPH reported its first lab-confirmed human case of WNV in 2024.
The news came shortly after WNV was detected in a mosquito trap in Corunna on August 14.
EEEV is not a reportable disease in Ontario and no mosquito traps have tested positive for it in Lambton County.