Little evidence of human infection with equine influenza during the 2007 epizootic, Queensland, Australia

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Abstract

Background

Equine influenza virus (EIV) is considered enzootic in Europe (except Iceland), Asia, North Africa, and North and South America. When EIV outbreaks occur they may severely impact the equine and tourist industries. Australia faced its first EIV outbreak beginning in August of 2007. The outbreak was concentrated in New South Wales and Queensland, with more than 1400 confirmed EIV infections in horses during the first month. Rapid response from the equine industry and the federal government was successful and Australia was declared free from EIV by the end of 2007.

Objectives

This cross-sectional study was designed to examine associations between exposure to EIV-infected horses and evidence of EIV infection in humans.

Study design

Employing informed consent, between October 2007 and April 2008, 100 subjects (89 with horse exposures and 11 non-exposed) were enrolled during equine events and at the University of the Sunshine Coast. All subjects provided a blood sample and were asked to complete an online questionnaire including health history, animal exposure and demographic information. Sera samples were tested for the presence of antibodies against two H3N8 EIV strains using microneutralization, hemagglutination inhibition, and enzyme-linked lectin assays.

Results

Evidence for H3N8 infection was sparse, with only 9 study participants having any indication of H3N8 infection and the seroreactivity seen was low and easily explained by cross-reactions against human influenza strains or vaccines.

Conclusions

These data provide little evidence to support the premise that EIV infections occurred among humans exposed to EIV-infected horses during the 2007 Australian epizootic.

Section snippets

Background

In the 1800s, when horses were central to transportation and commerce, equine influenza virus (EIV) epizootics brought national economic calamity in North and Central America [1]. Historical reports from Australia and New Zealand during the early 1900s report thousands of horses falling ill, severely impacting mounted forces during battle [2]. Today EIV epizootics continue to sporadically occur, however, their impact is more focused upon horse racing and tourism industries. Australia's horse

Objectives

As was observed in the 1800s [7] and experimentally proven through challenge studies in the 1960s [8], [9], [10], humans are readily infected with EIV. While some persons asymptomatically seroconvert, others develop classical influenza-like signs and symptoms. The goal of this study was to look for evidence that humans exposed to EIV infected horses in Queensland during the 2007 Australian epizootic were infected and if possible, to identify risk factors for those infections.

Study design

Permission for this cross-sectional study was granted by the Human Research Ethics Committees at the University of the Sunshine Coast in South East Queensland, Australia and at the University of Iowa, Iowa City, IA, USA. Potential participants were contacted between October 2007 and April 2008 throughout the enrollment target areas. Methods of contact included email messages, and attending Pony Club Association meetings and local public health information sessions.

Results

Blood samples were collected from 100 adults with variable levels of equine exposure between October 2007 and April 2008. Participants were recruited and blood collected while attending Pony Club Association meetings in South East Queensland, as well as at the University of the Sunshine Coast. Among the 100 participants, 64 completed the online questionnaire. Of those who completed the questionnaire, 53 (82.8%) had variable levels of direct equine exposure, 42 reported contact with horses in

Discussion

The 2007 Australian EIV outbreak caused significant economic and social hardship [5]. The outbreak was blamed in part upon complacency in EIV vaccine use [19] as EIV had not been previously detected in Australia. The epizootic presented a unique opportunity to examine the evidence for human EIV infection as EIV movement between horses was apparent and there was also evidence the EIV infected dogs exposed to sick horses [20], [21], [22].

Transmission of EIV to humans under natural conditions has

Funding

This research was supported by multiple grants from the US Department of Defense Armed Forces Health Surveillance Center's Global Emerging Infections Surveillance and Response Program (Dr. Gray, principal investigator) and an ARRA supplement grant from the National Institute of Allergy and Infectious Diseases (R01 AI068803-Dr. Gray).

Competing interests

The authors have no conflicts of interest or competing interests to declare.

Ethical approval

This study was approved by institutional review boards at the University of Iowa and at the University of the Sunshine Coast.

Acknowledgements

We thank Dwight Ferguson, Ana W. Capuano, Kerry R. Leedom, Whitney S. Krueger, and Sharon F. Setterquist of the University of Iowa's College of Public Health and Elizabeth Findlay, Deborah Hitchen-Holmes, Jamie Peetz, Nick Prass, and Scott Burnell of the University of the Sunshine Coast for their research support; Dr. Thomas M. Chambers from the University of Kentucky, Dr. Batsukh Zayat of Mongolia's Veterinary Medical Institute, and Dr. Y. Sakoda from Japan's Hokkaido University for sharing

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