Equine Herpes Virus-1 (EHV-1) Recrudescence and Viremia in Hospitalized Critically Ill Horses
Outbreaks of EHV-1 appear to be occurring with increased frequency and reports of spread within a hospital population exist. Equine herpes virus-1 infection occurs through exposure to viral particles shed in nasal secretions or placenta and tissues of an aborted fetus. Once infected, latency is a hallmark of herpes viruses. Recrudescence and nasal shedding can occur in animals with or without clinical evidence of disease making identification of potentially infectious horses challenging. Risk factors for recrudescence and shedding are poorly documented but many types of stressors (e.g., weaning, castration, long-distance transport, movement to a new facility and immunosuppression) have been suggested. Horses presenting to referral hospitals with severe illnesses are typically under significant stress and elevated serum cortisol and catecholamine concentrations have been documented in such horses. Little information exists on the effect of acute critical illness on EHV-1 recrudescence and shedding. Knowledge about this potential risk would be important for development of effective biosecurity policies to limit the risk of EHV-1 transmission in a hospital setting.
Horses greater than 6 months of age presenting with acute abdominal disorders (surgical colic or colitis) were included in the study. For inclusion, horses with colic had to have had an exploratory celiotomy as part of their treatment course. Horses with colitis had to have evidence of systemic inflammatory response syndrome including at least 3 of the following criteria; heart rate > 60 bpm, plasma lactate > 3.0 mmol/liter, rectal temperature > 102.5F, or absolute neutropenia or neutrophilia. Whole blood and nasal secretions were collected on day 1, day 4-7 and day 10-12. All samples (uncoagulated blood, nasal secretions) were processed for nucleic acid purification and tested for EHV-1 using real-time PCR assays targeting the glycoprotein B (gB) gene and the polymerase (ORF 30) gene.
One hundred and twenty two horses met the inclusion criteria. There were 89 surgical colics and 33 colitis cases. Age ranged from 6 months to 28 years with a median age of 12 years. There were 56 mares (46%) 61 geldings (50%) and 5 stallions (4%). Samples were collected from all horses on day 1, 75 horses (61%) on days 4-7 and 19 horses (16%) on days 10-12. One hundred and seven horses survived to discharge. None of the samples were positive for EHV-1 DNA.
These results suggest that nasal shedding and viremia of EHV-1 in hospitalized critically ill horses with acute abdominal disorder is extremely rare. These results may be useful in the implementation of biosecurity protocols for decreasing the risk of EHV-1 infection in the hospital setting.