Venezuelan Equine Encephalomyelitis (VEE) Fact Sheet

What is Venezuelan equine encephalomyelitis?

Venezuelan equine encephalomyelitis (VEE) is caused by a mosquito-borne virus that affects horses, mules, donkeys and zebras.

Is VEE a risk to human health?

Bites from infected mosquitos spread the disease to humans. Outbreaks of human disease usually happen a few weeks after horse cases occur. Healthy adults may develop flu-like symptoms such as a high fever and headaches. People with weak immune systems, young children and the elderly can become very ill.

What are the clinical signs of VEE?

There are four ways horses infected by the VEE virus may show clinical signs:

• Sub-clinical: Some strains of the VEE virus will usually not cause apparent clinical signs in horses.
• Moderate: Fever, decreased appetite and lethargy
• Severe: High fever with decreased appetite, dullness, and high heart rate followed by neurological signs. Neurological signs may include muscle twitching, incoordination, pressing their head against solid objects, and paddling their legs when lying down. Some horses can have diarrhea or show signs of colic.
• Fatal: Horses suffer the clinical signs described above, but end in death.

Where is VEE found?

VEE has never been reported in Canada. The disease has occurred only in the western hemisphere, in particular South and Central American countries. In 1972, an outbreak of VEE extended into Texas.

How is VEE transmitted and spread?

Mosquitos spread VEE by biting. When a horse is infected by a mosquito, they develop a large amount of the virus in their blood. Other mosquitos that bite this horse then become infected and go on to infect more horses. For this reason, horses are considered amplifying hosts.

Horses can also shed the virus in their urine, saliva and other bodily fluids. Horse owners need to follow strict biosecurity principles when dealing with infected horses in order to protect themselves and other horses. Needle sharing, wounds and contaminated surgical equipment are all possible routes of transmission.

More information on biosecurity can be found on the CFIA Animal Biosecurity webpage.

How is VEE diagnosed?

A vet may suspect VEE based on clinical exam findings in a horse with a recent history of travel to an area with VEE or contact with such horses.

The only way to definitively diagnose VEE is through laboratory testing.

How is VEE treated?

While a vaccine is used in horses in countries that have experienced VEE, there is no treatment for the disease.

What is done to protect Canadian livestock from VEE?

The Canadian Food Inspection Agency (CFIA) has strict regulations on the import of animals and animal products from countries where VEE is known to occur. These regulations are enforced through port-of-entry inspections conducted by both the CFIA and Canada Border Services Agency.

VEE is a reportable disease under the Health of Animals Act. All suspected cases must be reported to the CFIA for immediate investigation by inspectors.

How would the CFIA respond to an outbreak of VEE in Canada?

Canada's emergency response strategy in the event of an outbreak of VEE virus would be to:

• eliminate the disease
• re-establish Canada's disease-free status as quickly as possible

In an effort to eliminate VEE, the CFIA may employ some or all of the following disease control methods:

• humane euthanasia of infected animals
• surveillance and tracing of potentially infected or exposed animals
• strict quarantine and animal movement controls to prevent spread
• strict cleaning and disinfection of infected premises
• zoning to define infected and disease-free areas

If VEE becomes widespread in the mosquito population, the strategy may be modified to include vaccination of susceptible horses.

Owners whose animals are ordered to be euthanized may be eligible for compensation

Additional information

• Chronic wasting disease of deer and elk
• Animal Health Offices
• CWD herd certification programs
• CWD – What to expect if your animals may be infected