Animal HealthDiseasesEquine Infectious AnemiaEpidemiology

Equine Infectious Anemia (EIA) Epidemiology

The incidence and distribution in Montana and elsewhere, along with the information regarding the spread of the disease.

Mode of Transmission

Insects, primarily horse flies and deer flies that feed on blood, are the usual means by which EIA is transmitted. In addition, common needles, or any object that can carry blood from one equine to another, may be a means of transmitting the disease.

Insect transmission of EIAV is dependent on the number and habits of the insects, the density of the horse population, the number of times the insect bites the same and other horses, the amount of blood transferred between horses, and the level of virus in the blood of the infected horse from which the initial blood meal was obtained. The rate of transmission cannot be predicted accurately because of these variables.

EIA in Montana

Since 1979, a total of 167 cases of Equine Infectious Anemia (EIA) have been diagnosed in Montana.

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Contact Information

Department of Livestock
Animal Health Bureau
PO Box 202001
Helena, MT 59620-2001
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