Voluntary Surveillance Program for Equine Influenza Virus in the United States from 2008 - 2021

Abstract: Background

Equine influenza virus (EIV) is an enzootic cause of respiratory disease in equids as documented in studies from most of the world. Horses with EIV infection have consistent clinical signs of fever, nasal discharge and cough. Current knowledge of patterns of EIV is relevant to the Internist.

Objectives

This study evaluated epidemiologic and clinical features of horses with signs of infectious respiratory disease sampled through a biosurveillance program.

Animals

Veterinarians in practice submitted samples from sentinel horses showing signs compatible with infectious respiratory disease. A total of 9,740 horses, mules, and donkeys were included.

Methods

Samples obtained from December 2008 - June 2021 were analyzed. A questionnaire was used to collect clinical history and case information. Whole blood and nasal secretions were sampled from horses with fever ( >101.5^oF) and signs of acute upper respiratory disease. Samples were evaluated with real-time PCR for equine herpesvirus type 1 and 4, equine influenza virus, equine rhinitis virus A & B and Streptococcus equi subs. equi.

Results

966 equids tested positive for EIV yielding a 9.9% positivity rate. The study documented comparable incidence to equine herpesvirus type 4, age of incidence mostly commonly in 1- to 9-year-old equids, primary seasonality in winter to early spring (though identified throughout the year) and occurrence of prior travel in positive individuals.

Conclusions

This analysis supports the importance of EIV as a frequent pathogen associated with equine upper respiratory disease in the United States and provides contemporary data from EIV detection in the United States.