The Renfrew County and District Health Unit says there is a confirmed case of a horse with Eastern Equine Encephalitis Virus.
They say the horse was not up to date on vaccines and had no history of travel.
They add that though this indicates local virus activity, the risk to humans remains low.
The virus is borne by mosquitoes and can on occasion spread to horses, but rarely humans.
The heath unit says it does not spread from horse to person or from person to person.
The virus causes neurological illness and can be fatal.
To protect yourself against mosquito-borne infections, the health unit advises using a repellent approved by Health Canada, covering exposed skin and removing any stagnant water around your home, where mosquitoes usually lay eggs.
