Clinical Signs
The incubation period of equine infectiou anemia virus, or the time between initial infection and when signs begin to appear, is generally 2-4 weeks; however it can range from one week up to three months (CFIA 2013). The virus generally replicates in the horse’s cells for days or weeks before antibody to the virus can even be detected (Merck Veterinary Manual 2012).
EIAV can take on three different forms:
ACUTE:
This phase, where viremia peaks, usually occurs during a febrile episode before the horse becomes seropositive (Merck Veterinary Manual 2012). This form may develop at the initial attack or at subsequent attacks and often terminates in death within 3-14 days. Signs one may observe:
EIAV can take on three different forms:
ACUTE:
This phase, where viremia peaks, usually occurs during a febrile episode before the horse becomes seropositive (Merck Veterinary Manual 2012). This form may develop at the initial attack or at subsequent attacks and often terminates in death within 3-14 days. Signs one may observe:
- Sudden onset
- High fever (104-108°F)
- Severe depression
- Decreased appetite
- Rapid decrease of body condition
- Profound weakness, incoordination, recumbancy, prostration
- Jaundice
- Edema of ventral abdomen, and extremities +/- petechial hemorrhages of the mucous membranes at the tongue base and on the conjunctiva
- Heart rate and intensity of heart sounds are increased with moderate exercise
- Yellowish or bloody nasal discharge
- Splenomegaly
- Severe anemia (which can lead to death)
SUBACUTE:
This phase is often the most common. The signs that you may observe here are similar to those listed above in the acute form, but generally are not as severe, and death is rare. Recovery is often noted after 7-20 days and horses may remain asymptomatic for weeks or months (North Carolina Department of Agriculture and Consumer Services, undated). Relapses may occur and have been found to be associated with factors such as the use of steroid drugs, or periods of stress such as hard work, hot weather, racing, showing, pregnancy, etc. (CFIA 2013).
CHRONIC:
This phase can follow initial or subsequent acute or subacute outbreaks. At any time this form can revert back to the subacute or acute form and later become chronic again. Signs that may be observed with this form include:
- Unthriftyness
- Lack of stamina
- Periodic anemia
- Inability to perform hard work
- Unsatisfactory breeding performance
Despite the above breakdown into three forms with associated signs, clinical presentation can vary greatly: in some cases loss of coordination may be the only sign; some cases may be completely asymptomatic; others may show acute signs followed soon after by death (Raabe et al. 1998). Many horses may also end up being euthanized because of impending death (North Carolina Department of Agriculture and Consumer Services, undated).
Pregnant mares who become infected may abort the fetus; foals that are born infected could die within the following two months (CFIA 2013).