This fall, equine herpesvirus-1 (EHV-1) spread among patients in the veterinary hospital at Colorado State University (CSU), despite the fact the school runs one of the nation’s top veterinary biosecurity programs. The finding forced 20 hospitalized horses into a quarantine, which is expected to be lifted Nov. 17.

The outbreak apparently began after hospital staff admitted a critically ill and partially paralyzed horse on Oct. 23. Because EHV-1 was suspected, the horse was isolated from the hospital population and managed with increased biosecurity precautions. Lab tests did not confirm the diagnosis for 10 days, but in the interim, two horses hospitalized for other reasons developed unexplained fevers.