Coggins test still vital cog in EIA screening
The standard in equine infectious anemia (EIA) screening is a test known to horse owners everywhere as the Coggins test. A “negative Coggins” is required for import and export of horses and is recommended for any situation in which horses are gathered together, such as a competition or boarding stable.
But what exactly is a Coggins test, and how is a positive determined? When so much is riding on the results, horse owners want to be sure they can have faith in the system.
“It starts with a simple blood test,” explains Dr. Steve Manning, an equine field service veterinarian with the Western College of Veterinary Medicine’s Veterinary Medical Centre.
“First we examine the horse to make sure that it’s healthy,” says Manning. “We fill out a form describing the colour, markings and any visible scars, as well as the horse’s age, breed and the owner’s contact information. We also have to make a note of the land location at which the horse resides.”
Next, blood is drawn and submitted along with the form to a lab for testing. Blood must be taken by a Canadian Food Inspection Agency (CFIA)-accredited veterinarian and tested at a CFIA-accredited lab. Most large animal veterinarians are accredited; the certification must be renewed every two or three years.
The system is designed to ensure accuracy at every stage. “Because testing is a two-step procedure, the chances of a false positive are very small,” explains Dr. Betty Althouse, a former veterinary program specialist with the CFIA.
“The first test is a very sensitive ELISA (enzyme-linked immunosorbent assay). You want to catch as many positives as possible at this point – a false positive is not as much of a worry as a false negative.”
If the first test comes back positive, a CFIA lab repeats the ELISA test. If this second ELISA is negative, the horse is negative. If the second test also comes back positive, an actual AGID Coggins test is performed. If the Coggins (AGID test) is negative, the animal is declared negative, but a retest is recommended. If the Coggins test is positive, the horse is declared to have EIA.
“Because a horse can not clear the virus from its system,” says Althouse, “a positive (AGID) Coggins test definitively means that the horse is a carrier for EIA.”
A number of horses involved in the recent outbreak in northern Saskatchewan showed a positive ELISA and a negative Coggins test. However, when re-tested, those horses came back with a positive Coggins result as well.
In 2011, positive EIA findings ranged from only one horse in a herd of 300 to as high as nine in 10 and 43 in a herd of 69. However, more cases found in 2012 have been a single horse within a herd.
A negative Coggins test is a snapshot of a horse’s health status at a particular point in time. Different organizations will have different requirements as to how recent a horse’s test should be — suggested time frames can range from 30 days to six months to one year.
“How long a Coggins is good for depends on why it’s being drawn,” explains Manning. “From a practical standpoint, within six months or within the current fly season is reasonable. For export purposes, the test is good for 180 days.”
A Coggins test currently costs around $60. If he’s discussing the Coggins test with clients who regularly travel with their horses to shows and other events, Manning recommends yearly testing as a matter of course.
“It (EIA) can easily cause a problem in large herds,” he says. “You get one or two positives in there and then it spreads — it’s best to be proactive.”
Manning says the best course of action is for horse owners to discuss the risks of EIA with their local veterinarian. More detailed information about the disease is also available on the CFIA web site and on the Saskatchewan Ministry of Agriculture site.