This is an archived Horseadvice.com Discussion. The parent article and menus are available on the navigation menu below:
HorseAdvice.com » Diseases of Horses » Cardiovascular, Blood, and Immune System » Equine Infectious Anemia (EIA) and the Coggins Test »
  Discussion on Coggins Test
Author Message

Posted on Sunday, Jul 28, 2002 - 12:46 am:

A couple of horses have recently been euthanized in our area for a positive Coggins Test. I've been reading through the articles to refresh my memory on what the Coggins Test actually tests for. It is my understanding from what I've read that the test shows the presence of antibodies for EIA in the bloodstream. What I don't understand is how that in turn proves the horse as a carrier for the disease. I would assume that since I was vaccinated for measles when I was young, I carry the antibodies for the disease, but I'm not a measles carrier. Obviously, I'm not getting something.

Also, I thought there was a study done back in the late 60s/early 70s where a herd of positive horses was put in with a herd of negative horses. Then after a year, everyone was retested and none of the negatives came up positive. Has anyone heard of that study or something similar where the results were different? I guess I'm wondering what the risk of transmission really is.

If this is already covered, just point me to the article. I just haven't run across it yet.

Thanks!
Nancy

Posted on Sunday, Jul 28, 2002 - 11:00 am:

Since there is no vaccine for EIA your example does not apply to this disease. Research has shown that animals that have a titer on the Coggins test are also carrying the organism, with the unusual exception of some foals born to infected mares, this is explained in the article. The article also explains the transmission of this disease. Though I have not seen that particular paper it is entirely possible if ANY of the following are true:
1) biting flies were not much of a problem
2) none of the infected horses had a viremic episode during the year
3) the chance occurrence of a fly biting a viremic horse bit a noninfected horse within 15 minutes.
DrO

Posted on Tuesday, Jul 30, 2002 - 3:04 pm:

Oh, I see. I didn't understand that the test not only checked for antibodies, but also for the presence of the virus. Does that mean if the antibodies for the disease were present, but not the virus that the test would come back as negative? A little off topic, but in reference to your comment about the measles vaccine, why would it make a difference how the antibodies were caused in the blood stream?

In rereading the articles, I have another couple of questions. In the studies "A propagating epizootic of equine infectious anemia on a horse farm" and "Transmission of equine infectious anemia virus by Tabanus fuscicostatus.", they talk about horses becoming infected. Does that mean the horses actually became ill or that they tested positive to the Coggins Test? Also, what does seroconverted mean? I tried my dictionary but no luck.

Thanks again for clearing this up. I've had an opinion on the Coggins Test for years, but I thought it was about time I made it an informed one.

Nancy

Posted on Wednesday, Jul 31, 2002 - 6:39 am:

Hello Nancy,
The test does not check for presense of the virus, just for the antibody. But research has shown that where there are antibodies there is virus. In other words the test has a very low incidence of false positives and when they occur are usually do to the test being run incorrectly.

The reason the cause of antibody production is important is if the antibodies can be caused by things other than the virus, say a vaccine, then it would not be a reliable indicator of the presence of the virus.

Seroconversion: Development of detectable specific antibodies in the serum as a result of infection or immunization. (Don't forget that each article has a link to a medical dictionary at the top of it).

I am not sure what the clinical status was of the horses in that article but I will see if I still have a copy and if so will review it to see if it is given.
DrO

Posted on Friday, Aug 2, 2002 - 9:43 pm:

Thanks Dr O. I missed the medical dictionary link! I'm looking forward to hearing about the status of the infected horses in that study.

So here is my understanding of how this works from reading the articles and from what you've told me ... Horses who recover for EIAV normally get rid of all the virus. When they do, they stop producing antibodies for the disease. Thus, if the antibodies are presence so must be the virus; however, there are a small group of horses who for an unknown reason are unable to completely rid themselves of the virus. While these horses may not exhibit symptoms, they continue to produce the antibodies for the disease and test positive to the Coggins test. Also, these horses will sometimes have a reoccurence of the disease. These horses are also the only known long-term carriers of the disease. If you find that the studies we have been talking about only proved that the previously uninfected horses tested postively, but did not show any clinical signs of the disease, then as far as I have understood there is still no scientific proof that the positively testing horses can actually pass the disease to the extent that another horse will exhibit symptoms.

How am I doing?

Have the quarantine farms kept any kind of statistics about what percentage of horses with positive tests have flair ups?

Thanks for the clarification and your patience!
Nancy

Posted on Saturday, Aug 3, 2002 - 7:29 am:

That is incorrect: horses that appear to recover still carry the virus and that is the reason for the reoccuring episodes later. During the times they appear disease free they are unlikely to be contagious but during there recurring bouts the virus is in high enough concentration in the blood to be contagious. But all this is already explained in greater detail in the article, Nancy.
DrO
Home Page | Top of Page | Join Us!
Horseadvice.com is a BBB Accredited Business. Click for the BBB Business Review of this Horse Training in Stokesdale NC