Characterization of virulence variants of African horsesickness virus.

This research investigates the effects of three different variants of the African horsesickness virus on naive North American horses, demonstrating that the disease form manifested in the horses is determined by the specific strain of the virus used in inoculation.

Background

• The African horsesickness (AHS) virus can lead to three different syndromes in horses, namely, pulmonary, cardiac, and fever forms. These disorders are categorized based on the organs affected, the severity of lesions, the commencement of clinical signs, and mortality rates.
• The researchers studied these effects through an experiment involving three different AHS virus variants, all grown in cell culture and then introduced to naive North American horses. Naive horses are those that haven’t been previously exposed to AHS and therefore have no immunity against it.

Study Findings

• A virus called AHS/4SP consistently triggered the pulmonary form of AHS, leading to immediate onset of severe pulmonary edema – fluid accumulation in the lungs – and a 100% mortality rate.
• The AHS/9PI variant caused symptoms typical for the cardiac version of AHS; these included pericardial effusion (fluid around the heart), subendocardial hemorrhage (bleeding under the heart’s inner lining), and widespread subcutaneous edema (under-skin fluid accumulation). This variant had a mortality rate of approximately 70%.
• The third virus, AHS/4PI, led to mild illnesses or subclinical disease, which often only presented as short-lived mild fever. There were no deaths among the horses infected with this strain of the virus.
• All horses that survived the infection developed both neutralizing and ELISA-reactive antibodies, confirming exposure to the virus and an immune response.

Conclusion

• The findings of the study indicate that the form of AHS observed in naive horses is a characteristic of the specific AHS virus variant used for inoculation. Such characterization of virulence variants could influence approaches to prevention and treatment of AHS.