An outbreak of a deadly equine virus is occurring this summer in Western Canada.
Equine infectious anemia, or EIA, is a viral disease of horses, donkeys, mules and other equine species.
Biting insects spread the blood-borne virus. Insects feed on the blood of infected horses and transfer the virus to uninfected horses in subsequent meals.
People can also spread the virus between horses by reusing contaminated needles or surgical instruments. To avoid this, use a needle only once when injecting horses.
In rare cases, infected mares can give birth to EIA-positive foals. The virus can also be spread by infected semen.
As of July, the Canadian Food Inspection Agency has confirmed cases in 26 properties in Saskatchewan, four properties in Alberta, and two each in British Columbia and the Yukon. The exact number of horses infected has not been made available. EIA is classified as a reportable disease under the federal Health of Animals Act.
EIA is diagnosed either by a Coggins test, which is named for the American veterinarian who developed the test, or the newer ELISA test. These simple blood tests are relatively fast, sensitive, reliable and standardized. In Canada, many competitive horse events and sales require horses to have a negative Coggins test before entering the venue.
All horses travelling to the United States require a negative Coggins test, which is valid for six months after testing. Testing is voluntary in Canada and paid for by owners.
If a horse tests positive, the CFIA must be notified. Horse movements on and off the property are restricted. All horses on the property and others that have had contact with the positive horse must be tested.
All horses that are positive and have signs of the disease must be euth-anized.
Positive horses that do not have clinical signs of disease are dealt with in one of two ways. They can be euthanized and the CFIA will pay compensation to a maximum of $2,000 per horse. Alternatively, owners can elect to keep the horse in permanent quarantine for the rest of its life.
Horses with EIA can live without symptoms of the disease for months to years. Sadly, this lack of illness can allow the virus to spread undetected throughout the herd.
Early in the infection, horses may have a fever and decreased appetite. As these signs are general, mild and nonspecific, early infections are often missed until blood tests are performed.
In chronic stages, horses develop edema (fluid accumulation) of the legs, belly and throat, jaundice, multiple small bleeds and weight loss. Anemia, which is abnormally low levels of red blood cells, contributes to lethargy in affected horses.
The EIA virus is similar to the Human Immunodeficiency Virus (HIV).
There is a long time between infection and symptoms and infections are life-long. There is also no vaccine or cure available.
An effective vaccine for EIA has not been developed because the virus mutates quickly. By the time the immune system recognizes the virus and tries to kill it, the virus has already changed and spread. This is a major problem facing HIV vaccine development as well.
People cannot contract the EIA virus.
The EIA virus has been used in experimental settings for cutting-edge gene therapy for specific human eye diseases such as macular degeneration, which is an age-related human eye disease.
The virus is modified to contain a small piece of human genetic material. Once injected into the diseased eye, it causes the body to produce its own healing proteins.
Eradication of EIA from Canada is possible. It infects only equine animals and there is a fast, reliable test available.
It would require a massive testing campaign of every horse in the country to identify carrier horses. Slaughter of infected horses would be necessary.
Due to the expense of this proposition, and because testing is voluntary, widespread horse industry support would be necessary.
Dr. Jamie Rothenburger is a veterinary pathology resident at the Western College of Veterinary Medicine, University of Saskatchewan.