Serological evidence of equine influenza infections among persons with horse exposure, Iowa

Kerry R.Leedom Larson, Gary L. Heil, Thomas M. Chambers, Ana Capuano, Sarah K. White, Gregory C. Gray

Research output: Contribution to journalArticlepeer-review

21 Scopus citations


Background: Equine influenza virus (EIV) is considered enzootic in North America and experimental studies have documented human EIV infections. Study design: This cross-sectional study examined 94 horse-exposed and 34 non-exposed controls for serological evidence of EIV infection. Sera were evaluated for antibodies against three EIV and two human H3N2 viruses using microneutralization (MN), neuraminidase inhibition (NI), enzyme-linked lectin (ELLA), and hemagglutination inhibition (HI) serological assays. Risk factor analyses were conducted using logistic regression and proportional odds modeling. Results: There was evidence of previous infection by MN assay against A/equine/Ohio/2003(H3N8) but not the other 2 EIVs. Eleven (11.7%, maximum titer 1:320) horse-exposed and 2 (5.9%, maximum titer 1:160) control subjects had MN titers ≥1:80. Among the horse-exposed, 18 (19.1%) were positive by NI assay and 8 (8.5%) had elevated ELLA titers ≥1:10. Logistic regression modeling among horse-exposed revealed that having an elevated MN or ELLA titer (≤1:10) was associated with having a positive NI titer (OR. =. 4.9; 95% CI. =. 1.3-18.7, and OR. =. 53.2; 95% CI. =. 5.9-478.5, respectively). Upon proportional odds modeling, having worked as an equine veterinarian (OR. =. 14.0; 95% CI. =. 2.6-75.9), having a history of smoking (OR. =. 3.1; 95% CI. =. 1.2-7.7), and receipt of seasonal influenza vaccine between 2000 and 2005 (OR. =. 2.3; 95% CI. =. 1.1-5.0) were important independent risk factors for elevations in MN assay. Conclusions: While we cannot rule out confounding exposures, these data support the premise that occupational exposure to EIV may lead to human infection.

Original languageEnglish
Pages (from-to)78-83
Number of pages6
JournalJournal of Clinical Virology
StatePublished - Jun 1 2015

Bibliographical note

Funding Information:
This work was supported by US Department of Defense Armed Forces Health Surveillanc Center’s Global Emerging Infections Surveillance and Response Program.

Funding Information:
We thank colleagues at the Centers for Disease Control and Prevention, Atlanta, GA for providing human viruses; Dr. Keith Soring, Iowa State Regulatory Veterinarian, for arranging access to Prairie Meadows Racetrack and Casino; David Halverson of the Iowa Equestrian Center for allowing enrollment during horse shows; and Dr. Peggy Miller of the Iowa Horse Council for allowing enrollment at the 2005 Iowa Horse Fair. We thank Debbie Wellman, Sharon Setterquist, and Norma Miller, formerly of the University of Iowa, for their technical assistance with the laboratory research. We thank BEI Resources for producing the recombinant neuraminidase subtype 8. This work was supported by US Department of Defense Armed Forces Health Surveillance Center’s Global Emerging Infections Surveillance and Response Program (Dr. Gray, principal investigator).

Publisher Copyright:
© 2015 Elsevier B.V.


  • Equine influenza virus
  • H3N8 subtype
  • Occupational exposure
  • Seroepidemiologic study
  • Veterinarians

ASJC Scopus subject areas

  • Virology
  • Infectious Diseases


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