Equine Infectious Anemia – Horses
Equine Infectious Anemia – Horses
Equine Infectious Anemia is a viral disease for which there is no vaccine and no cure. Though most horses succumb rapidly to EIA a percentage of infected horses appear to recover. However they still harbor the virus and during times of stress may become ill again. It is because of these healthy appearing carriers that we test horses. It insures that we do not put their pasture mates at risk.The disease is spread by horseflies. The large horsefly is the main vector. If they bite an infected horse and then bite a healthy horse the disease gets transmitted. The virus does not live for very long on the horsefly maybe as little as fifteen or thirty minutes. So for one horse to infect another they must be close to each other. This disease occurs anywhere horseflies live.
The acute horse may be difficult to diagnose because the symptoms are very general and he will not be positive on the EIA test for a month and a half. Approximately one third of infected horses will die of the acute form within a month. The chronically infected horse will having recurring acute bouts along with weight loss ventral edema swollen belly and legs and anemia. These horses will be positive on a EIA test. These horses may linger for a year or more before they die. Anemia in horses may originate from three major pathways: blood loss; increased red blood cell destruction and inadequate red blood cell production. Given the variety of pathways involved in developing anemia horses may present a fairly wide array of clinical signs. Some of the most common include decreased capacity for exercise decreased appetite depression or a trauma that causes acute blood loss.
The horse’s heart rate may be elevatednormal is about 30 beats per minuteto more than 45 or 50 beats per minute. The mucous membranes may appear very pale or white and urine may be discolored or reddish. Anemia resulting from direct blood loss is often the easiest to diagnose but is still a challenge to treat. Generally there will be signs of shock weak pulse elevated heart rate pale mucous membranes. Other signs may include profuse bleeding from the nose.
Anemia due to inadequate red blood cell production is the most common form of anemia in horses; however it is the most challenging to identify. These horses may show lowgrade exercise intolerance poor appetite and lethargy. Infections ranging from pneumonia to renal disease can if prolonged result in significant anemia. Certain types of cancer may clinically manifest as anemia as may several different viruses such as Equine Infectious Anemia EIA. Less frequently deficiencies of iron copper protein and B vitamins can impair the body’s ability to manufacture red blood cells.
Anemia resulting from increased red blood cell destruction is often accompanied by fever and yellowish mucous membranes. In more severe cases the horse’s urine will be a darkreddish brown. This category of anemia has many causes including red maple leaf toxicity. Parasites certain types of neoplasia drug toxicity particularly that which involves antiinflammatory drugs and neonatal isoerythrolysis are other causes.
The diagnosis of equine anemia is based on clinical signs that indicate reduced oxygen transport to tissues and a reduced packed cell volume. The packed cell volume PCV measures the percentage of circulating red blood cells in the bloodstream. Normally a horse has a PCV of about 40 percent with some age and breed variations. A horse with a PCV of less than 30 percent is considered anemic and efforts should be made to identify the source of the lack of red cells. To complicate matters a significant numberup to 30 percent of the total red blood cellsof red blood cells will be sequestered in the spleen of a resting horse even a fit one.
Therefore initial PCV evaluations on resting horses may be deceiving because following a period of exercise or excitement the PCV will be elevated to its normal range. If the PCV drops below 15 percent a blood transfusion may be necessary. This is often performed at a referral center where blood donors may be kept and crossmatching is performed.
While the diagnosis of anemia in horses is straightforward involving a blood sample and centrifuge the challenge is determining the primary cause. If the anemia is due to acute blood loss the source of the trauma or hemorrhage should be identified and controlled and your veterinarian should be contacted immediately.
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