This is an archived Horseadvice.com Discussion. The parent article and menus are available on the navigation menu below:
HorseAdvice.com » Diseases of Horses » Fever of Unknown Origin »
  Discussion on Fever and positive Coomb's test
Author Message
Member:
Herrin

Posted on Thursday, Jul 14, 2005 - 1:50 pm:

Dr. Oglesby,

My horse was vaccinated in April for everything possible, including strangles and WNV. A few days later he had a temperature of 103 and rapid, shallow breathing. He did this off and on for over a month with intermittent signs of colic. The vet thought he had an impaction due to the stress of vaccinations. Finally, he seemed to come out of it, however, the past Sunday, he was lethargic and when I took his temperature (three times with different thermometers) his temperature was 106.2. The vet came immediately. We got his temperature down and fluids him. The vet drew blood which indicated anemia (I've read your article). The vet did not want to stress my horse by exercise. My horse continued to have a fever around 104 unless given banamine. He ate and drank fine except the first day. The vet drew blood again Tuesday and told me yesterday that my horse tested positive with the Coomb's test and that he had Autoimmune haemolytic anaemia. I understand that that is a secondary problem to something else going on. My question is; what are some of the primary causes that could be causing the positive Coomb's test? My vet feels that the vaccinations could possibly have set off the immune response. Is this something you have ever seen?
Thank you,
Sheri
Moderator:
DrO

Posted on Friday, Jul 15, 2005 - 6:30 am:

Hello Sheri,
A few questions Sheri. What were the values for the Hct (sometimes called the PCV) and hemoglobin? Also was he positive to the direct or indirect Coombs, or both? Lastly, while your horse was having the episodes of fever was penicillin used to treat it at any time even just once?

I think you are confused over what the Coombs test is and does. It does measure the tendency of the body's immune system to attack RBC's so measures the autoimmune hemolytic anemia directly. While it misses some mild chronic cases, the direct test when positive is pretty accurate.

It is the autoimmune hemolytic anemia (AIHA) itself that can be primary or secondary. Primary acquired AIHA is also called idiopathic: we don't know why it starts. Secondary AIHA is caused by a known stimulus. Though vaccination could be considered a trigger it is not common and I have not seen such nor can I find such a case. On the other hand penicillin is a very common cause of secondary AHIA.

Here is a study that summaries 8 cases, note that the prognosis of 50% death is unusally high and probably reflects the large number of primary cases (usually much rarer than secondary) in this study:

Vet Rec. 1990 Jan 20;126(3):51-3.
Autoimmune haemolytic anaemia in eight horses.

Mair TS, Taylor FG, Hillyer MH.
Department of Veterinary Medicine, University of Bristol, School of Veterinary Science, Langford.

Autoimmune haemolytic anaemia was diagnosed in eight horses on the basis of a positive Coomb's test. The disease was considered to be idiopathic in three cases and secondary to another condition in five. The clinical signs included dullness and depression, pyrexia, jaundice and haemoglobinuria. In addition to anaemia, haematological evaluation commonly revealed auto-agglutination of red cells and anisocytosis; reticulocytosis and an increased mean corpuscular volume were less commonly observed. Four horses were successfully treated with dexamethasone, but the other four were destroyed or died because of the underlying disease.
DrO
Member:
Herrin

Posted on Friday, Jul 15, 2005 - 9:07 pm:

Dr. Oglesby,

My horse has had two rounds of bloodwork so far. The initial one, when his fever was 106.2 and another one a few days later. I only have a copy of the results from the first one, but the vet indicated that the second one showed my horse was still anemic. According to the first blood test, Mac's HCT level was 27.9 percent. I don't see Hemoglobin on the lab report, but there is something called HGB. If that's the hemoglobin, the results on it were 10.7 g/dl

It was the direct and indirect Coomb's test. Mac had not received any penicillin during any of his treatment.

Thank you for pointing out that I was confused about what the Coomb's test is and what it does. Your answer, and talking with my vet clarified some of my confusion, however, it is still difficult to understand what AIHA is and what the prognosis is. At this point, we do not know why he has developed the AIHA. My vet has put him on prednalazone (I don't have the bottle in front of me for proper spelling). My vet has recommended a month of steroid treatment with a gradual reduction in the dose over the course of the month. The vet will also monitor his blood work periodically to see how Mac is progressing. Do you have any suggestions for tests that might determine if there is a condition that is causing the AIHA? My vet has advised me to wait until the month of steroids is over and see how Mac does.

Since we've ruled out penicillin as a secondary cause, what are some of the other things that could cause this? Do horses with AIHA as a primary cause eventually die from it? Or, can it be managed?

Thank you so much for the excellent website. It is a great resource of credible information.

Sheri
Member:
Herrin

Posted on Friday, Jul 15, 2005 - 9:10 pm:

Dr. O,

I had just had another thought. Mac did not receive any penicillin the first time. He did however, receive one dose of SMZ tablets. I don't know if there is penicillin in the SMZ? Also, when Mac ran a high fever this past sunday, he was given Genomicin. Is this in the penicillin family?
Sheri
Moderator:
DrO

Posted on Saturday, Jul 16, 2005 - 7:58 am:

The HGB to HCT ratio is suspicious for ongoing but mild hemolysis but you did not say which of the Coombs tests were positive.

The way to look at this is your horses immune system is attacking his own RBC's, it is like an allergy has developed to the RBC's. Often we don't know why this happens. The non-specific immune stimulation of the adjuvants in the vaccines may have taken a horse predisposed to this and been the "straw that broke the camels back" or it may have be an unusual reaction to one of the other drugs, or a possible complication of a otherwise mild infection: these are all possibilites that there is no good way to differentiate.

The prognosis is fair for complete recovery from AIHA. Often following a course of steroid therapy the problem will just disappear though this may take up to 4 months. We presume whatever is causing the immune system to see the RBC's as foreign has gone.

TMP/SMZ tablets are not in the penicillin family and has not been associated with hemolytic anemia, but that does not mean this is not possible. What exact form of steroid are you using and what is the dosage rate and frequency?
DrO
Member:
Herrin

Posted on Saturday, Jul 16, 2005 - 8:37 am:

Dr. O,

I will have to check with the vet to see which test was positive.

So far, Mac has had two days of Prednisolone - thirty tablets once a day. I do not know the strength of the tablets but will check later today.

He is not to receive any Prednisolone today and then another thirty pills Monday. Skip Tuesday and thirty on Wednesday. Then, go to 10 tablets every other day.

Thanks again for helping me understand this!
Sheri
Moderator:
DrO

Posted on Saturday, Jul 16, 2005 - 1:53 pm:

I would not personally lower the dose of the Pred until I saw a clinical response but many veterinarians are afraid (unnecessarily) of the use of glucocorticoids in horses. You should not make a change without approval from your vet however. For more on this study Equine Medications and Nutriceuticals » Anti-inflammatories (NSAID's, Steroids, Arthritis Rx) » Overview of the Steroidal Anti-inflammatory Drugs.
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