Outbreak of equine herpesvirus 4 (EHV-4) in Denmark: tracing patient zero and viral characterization.
Authors: Ryt-Hansen Pia, Johansen Victoria Kyhl, Cuicani Marta Maria, Larsen Lars Erik, Hansen Sanni
Journal: BMC veterinary research
Summary
# Editorial Summary: EHV-4 Outbreak Investigation at University of Copenhagen Teaching Hospital During spring 2022, a seven-week EHV-4 outbreak at the Large Animal Teaching Hospital in Copenhagen affected nine hospitalised horses, with a tenth animal testing positive approximately three weeks after the primary cluster resolved—prompting investigation into transmission routes and viral characteristics. Researchers employed detailed clinical monitoring, qPCR testing of nasal swabs, serological analysis, and partial and full genome sequencing to trace the outbreak's origin and characterise the circulating virus, correlating these findings with documented horse movements and locations throughout the facility. Nine horses developed positive qPCR results within the outbreak window, whilst Eq10's delayed positive result raised questions about either prolonged viral shedding from the initial cluster, reinfection, or a separate exposure event. Partial and full genome sequencing enabled researchers to determine whether Eq10 carried the same viral strain or a distinct introduction, informing understanding of outbreak dynamics and control measures. These findings underscore the infection-control challenges posed by endemic EHV-4 in hospital settings where multiple compromised horses congregate, highlighting the importance of implementing rigorous biosecurity protocols during outbreaks and maintaining detailed records of patient movement to facilitate epidemiological investigations and minimise nosocomial transmission.
Read the full abstract on PubMed
Practical Takeaways
- •Hospital outbreaks of EHV-4 can be prolonged; implement strict quarantine and movement protocols for suspected cases to prevent spread across populations
- •Monitor horses for 3+ weeks after the apparent end of an outbreak, as late positive cases suggest the virus may persist or transmit longer than initially expected
- •Use qPCR testing of nasal swabs alongside serology and detailed movement tracking to identify outbreak source and transmission routes in multi-horse facilities
Key Findings
- •An EHV-4 outbreak at a teaching hospital lasted approximately seven weeks with nine horses testing positive during the acute outbreak period
- •A tenth horse tested EHV-4 positive almost three weeks after the last outbreak case, suggesting potential persistent shedding or delayed infection
- •Detailed clinical registrations, movement tracking, and qPCR testing identified epidemiological patterns within the hospitalized population
- •Genome sequencing characterized the viral strain and provided evidence for viral transmission pathways during the outbreak