What is equine infectious anemia (EIA)?
Also known as swamp fever, equine infectious anemia is a potentially fatal, blood-borne, viral infection that’s spread between horses through horseflies, deerflies, and other biting insects. The virus is a kind of retrovirus known as a lentivirus. It’s not unlike the human HIV virus. In fact, we’ve even heard people describe equine infectious anemia as “HIV for horses.” There is no vaccine or treatment for the infection, which is a big reason why prevention programs are strictly enforced. Affected horses can often live for many years, sometimes symptom-free, and act as a carrier of the disease. Some horses never show active signs of the infection.
What are the symptoms of equine infectious anemia?
Symptoms of equine infectious anemia include things like fever, anemia, weight loss, swollen limbs, icterus, and general fatigue and weakness. There is also both an acute and chronic onset of EIA. In other words, a horse may contract EIA and die suddenly or the infection may linger, but even chronic symptoms can ultimately prove fatal. While there is no treatment, a horse may overcome the symptoms in which case the infection becomes classified as “inapparent.” Nevertheless, the horse is still a carrier of the EIA virus and can infect other horses.
What is an EIA Coggins test for horses?
Coggins testing uses some combination of antibodies and antigens from equine blood/serum samples to detect the presence of the equine infectious anemia virus. Coggins testing was originally developed in the late 1960s and early 70s by Leroy Coggins and was formally instituted as a regulatory test in 1973. This was in response to an alarming escalation of EIA cases in horses during this time period. Today, there are multiple test assays available to diagnose EIA. Today, every horse that travels across state lines, is put up for sale, or as otherwise mandated must be tested for equine infectious anemia each year.
What is an AGID test?
The Agar Gel Immunodiffusion Assay (AGID) was the original Coggins test. This diagnostic assay uses serum samples and an antigen mixture. These two fluids are placed in adjacent wells and then diffused together to detect the presence of EIA antibodies in the serum sample. This process takes considerably longer than the ELISA test, making it impractical for diagnostic labs to report test results in less than 24 hours. There are exceptions, but the AGID test is usually a couple dollars cheaper to run than the ELISA test. AGID testing has a false-negative rate of 0.025%.
What is an ELISA test?
In contrast to diffusion wells, the Enzyme-Linked Immunosorbent Assay (ELISA) uses a specially-designed plastic plate that works as a substrate for the serum sample and a prepared antigen mixture. On this plate, the antigens can be used to detect and quantify the antibodies and diagnose the presence of the EIA virus in the animal. This testing method can be completed in less than an hour. ELISA testing has a false-positive rate of 0.19%.
Are there other tests for equine infectious anemia?
Yes, the Western blot or immunoblot test is an alternative method of detection and is frequently used as a conclusive test when ELISA or AGID tests disagree or are otherwise inconclusive. The ELISA test uses specific antigen structures to search for antibodies present in the serum sample. The immunoblot test uses whole purified virus with all the structural proteins, so antibodies against multiple antigens can be detected. This three-tiered Coggins testing (AGID+ELISA+BLOT) is considered the gold standard for complex testing cases of equine infectious anemia is able to accurately identify 20% more cases of EIA than any individual test alone. An even more specialized type of EIA testing is the RT-PCR (reverse-transcription polymerase chain reaction) protocol, which is capable of testing foals born to mares who have equine infectious anemia.
How long is a Coggins test good for?
Most states will honor a negative Coggins Test for up to 12 months. Other states, like Montana and Nevada, only honor the test for up to 6 months. Either way, if you’re traveling with a horse, the Coggins Test isn’t the big time-crunch. Rather, many states only honor the Certificate of Veterinarian Inspection (CVI) for up to 30 days. In other words, you have 30 days after the certificate is issued to travel with the horse and get where you’re going. In some states, it’s as long as 6 months. In other states, it’s as little as 10 days. Some states will specifically honor the digital equine passport for up to 6 months.
How much does a Coggins test cost?
First of all, it depends if you’re a veterinarian or an animal owner/livestock producer. Many state- and university-based diagnostic laboratories offer Coggins testing as low as $3-$10, but these services are only available to accredited veterinarians. Even then, this assumes the veterinarian isn’t requesting expedited testing, or else the price can jump significantly.
If you’re an animal owner, a Coggins Test may cost something more like $20 to $100 or more. In this case, much of the cost difference is simply a matter of how the clinic prefers to itemize their costs and services. Rather than standalone testing costs, many vet clinics have package deals that will quote you one price for the horse exam, blood draw, travel fee (if making a farm call), Coggins Test, health certificate, and online reporting.
How common is equine infectious anemia?
Today, equine infectious anemia is rare. In 2018, there were 51 cases in the United States according to the USDA. There were 80 cases in 2017 and 52 cases in 2016. These cases are out of an estimated 9 million horses. Rates of equine infectious anemia have risen and fallen dramatically over the last century. Anecdotal reports of the disease go back several centuries, but there was a noticeable rise in the incidence of equine infectious anemia starting in the 1930s. This rise continued throughout the middle part of the century and started to create serious concern in the equine community during the 1960s and 70s. In 1975, for example, there were 10,371 cases according to the American Association of Equine Practitioners.
It hasn’t always been a straight line, but Coggins testing and quarantine protocols have been extremely effective at reducing the number of cases. Nowadays, it’s about as common to get a false positive from an ELISA Coggins test as it is for a horse to contract equine infectious anemia.
What regions are most affected by equine infectious anemia?
The most common states for equine infectious anemia in 2018 were Georgia and Texas. Generally speaking, the Gulf Coast states are most affected by EIA. That’s because the high humidity and warm temperatures year-round create a friendly environment and greater exposure to the deer flies, horse flies, and other biting insects that are vectors of the disease. Other risk factors include horses that are frequently around different groups of horses, especially equines that have not been required to undergo regulatory Coggins testing.
What happens with a positive Coggins test result?
As rare as equine infectious anemia has become, the most common reason for a positive Coggins test result is a false-positive. A large-scale research study of Coggins testing efficacy found that ELISA testing, the most common type of Coggins test, has a false-positive rate of about 0.19%. And so, the first thing that’s done is a second, confirmatory test. Many veterinary diagnostic labs will submit positive Coggins test results and samples to the National Veterinary Services Laboratory for confirmatory testing of equine infectious anemia. A regular AGID Coggins test can confirm a positive case of equine infectious anemia. However, the AGID Coggins testing also has a false-negative rate of 0.025%. So, when two different Coggins tests disagree, the third testing protocol, the immunoblot (or Western Blot) EIA test is used.
How dangerous is equine infectious anemia to individual horses?
When a positive case of equine infectious anemia is confirmed, there are only two options for the horse: Euthanasia or permanent quarantine. Equine infectious anemia can spread among horses and then go undetected for months or years, potentially infecting nearly an entire stable of horses, or worse. In the 1960s and 1970s, before Coggins testing proved effective and started separating infected equine from healthy stablemates, there was widespread uncertainty about the future of horse racing, ranching, rodeos, equestrianism, and the entire equine industry. So, whether you need to say good-bye to a beloved horse or foot the bill for quarantine-based care, don’t try to subvert the rules. The consequences are never good.
How dangerous is equine infectious anemia to horse populations?
On a global scale, not very dangerous at all. Most every developed country has some form of effective disease control and monitoring program in place. In 2018, only one of out of every 250,000 horses in the US had a confirmed case of equine infectious anemia. This low incidence rate is a testament to the effective implementation of decades’ worth of Coggins testing and quarantine practices. Even still, there are dangers to local equine populations. Given that the highest risk of equine infectious anemia occurs in the Gulf Coast states, for example, we worry about a bad outbreak of the disease hitting the population of Florida Cracker Horses, an endangered and, arguably, historically significant horse breed.
Is there a vaccine for Equine Infectious Anemia?
Yes and no. There are multiple vaccines for equine infectious anemia in development but few are widely used. In one notable exception, China is making attempts to vaccinate its equine populations to control or eradicate the disease inside its borders altogether. With regulatory testing practices in place, the U.S. is in no hurry to invest resources developing and implementing a vaccination program which still may not be 100% effective in completely eradicating the disease.