An Epidemiological Overview of the Equine Influenza Epidemic in Great Britain During 2019

This retrospective descriptive study aims to describe the epidemiology of the 2019 equine influenza epidemic within GB.

Fleur Whitlock, John Grewar, Richard Newton

A horse looks over the stall door. During an equine influenza epidemic, horses need to be quarantined.
There were 412 confirmed cases of EI during the 2019 epidemic in Great Britain, which researchers are now linking to low levels of vaccine coverage and limited biosecurity measures. iStock

During 2019, an epidemic of equine influenza (EI) occurred in Europe. This retrospective descriptive study aims to describe the epidemiology of the 2019 EI epidemic within GB.

Veterinary surgeons provided epidemiological data from referring samples for EI virus testing. Where available, researchers collated and described data on confirmed cases and their wider resident population on EI-infected premises. On a national level, spatial and temporal representations, consisting of choropleth maps and epidemic curves, described the spread of EI. Researchers investigated EI-infected premises-level factors associated with the first of two epidemic phases using ordinary logistic regression analysis.

About the 2019 Equine Influenza Epidemic

The EI epidemic consisted of 412 confirmed cases and 234 EI-infected premises. The first of two epidemic phases occurred between January and April, followed by a second phase through to August. The median age of confirmed cases was 5 years. Sports horses (24%) and Cobs (16%) made up the highest proportions by general horse type and breed. Among confirmed cases, 72% were unvaccinated, and 18% were vaccinated against EI. Forty-two percent of EI-infected premises reported that new horses had arrived within 2 weeks of a confirmed case. Investigation of EI-infected premises biosecurity measures indicated that 23% quarantined new arrivals, 37% had isolation facilities and 57% of resident horses were vaccinated. EI-infected premises were more likely in the first than second epidemic phase to be classified as professional, have a vaccinated confirmed case and EI confirmed in a newly arrived animal.

Bottom Line

During the equine influenza epidemic, EI-infected premises generally had low levels of population vaccine coverage and implemented limited preventive biosecurity measures, particularly linked to horse movements.

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