Chief biosecurity officer Jim Thompson said a private vet had attended the sick horse on Sunday and took samples, which were sent off for testing.
The horse died yesterday morning.
"Initial reports are that there are 37 other horses on the property," Thompson said.
"We are in the process of quarantining the property, with Biosecurity Queensland officers already in contact with the owners.
"This property will be quarantined to restrict the movement of horses on and off.
"Tracing will be a priority to determine what contact the deceased horse had with other animals on the property.
"Queensland Health, key horse industry groups and the Australian Veterinary Association have been notified of this latest case."
Staff from Queensland Health's Cairns Public Health Unit are on the way to the property to assess the situation and offer any testing or treatment to people that may be required.
It is not yet clear how much exposure people had to the horse and virus. However, more will be known once staff are on site.