Aspirin and Valacyclovir to Treat EHV-1 in Horses

While aspirin did not alter the number of EHM horses that developed recumbency, it did improve survival.
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While aspirin did not alter the number of EHM horses that developed recumbency, it did improve survival. It was estimated that there would be 45 times greater risk of euthanasia without the use of aspirin.

A presentation by Susannah Lewis, DVM, PhD, at the 2019 AAEP Convention, discussed a retrospective review of an EHV-1 outbreak of 63 horses at boarding and training farms. Horses had clinical signs of fever, respiratory illness, abortion, and/or equine herpesvirus myeloencephalopathy (EHM, or neurologic herpesvirus).

Valacyclovir—used in 33 horses in hopes of inhibiting viral replication—was administered at 27 mt/kg orally every 8 hours for two days, then dropped to 18 mg/kg every 12 hours for 10 days. 

Aspirin was dosed at 10 mg/kg orally every 24 hours to inhibit platelet aggregation in four horses with EHM.

Of the 63 horses, fever greater than 101.5 degrees Fahrenheit developed in 44, while 12 developed EHM and seven were euthanized.

The study identified that valacyclovir did not affect the duration or magnitude of fever, but it seemed to decrease the number of new fevers. Valacyclovir also did not affect the number of cases that developed EHM (27%) or the likelihood of euthanasia. 

While aspirin did not alter the number of EHM horses that developed recumbency, it did improve survival. It was estimated that there would be 45 times greater risk of euthanasia without the use of aspirin.

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