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PLoS Pathog. 2019 Feb 7;15(2):e1007531. doi: 10.1371/journal.ppat.1007531. eCollection 2019 Feb.

Absence of adaptive evolution is the main barrier against influenza emergence in horses in Asia despite frequent virus interspecies transmission from wild birds.

Author information

1
MRC-University of Glasgow Centre for Virus Research, Glasgow, United Kingdom.
2
State Central Veterinary Laboratory, Transboundary Animal Disease Laboratory, Avian Influenza Section, Ulaanbaatar, Mongolia.
3
Project Group Epidemiology of Highly Pathogenic Microorganisms, Robert Koch Institute, Berlin, Germany.
4
Departamento de Microbiología e Inmunología, Facultad de Medicina Veterinaria y Zootecnia, Universidad Nacional Autónoma de México, Ciudad de Mexico, México.
5
Animal Health Trust, Lanwades Park, Kentford, Newmarket, Suffolk, United Kingdom.
6
Wildlife Conservation Society, Bronx, NY, United States of America.
7
School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region, China.
8
Laboratory Animal Unit, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region, China.
9
Weipers Centre Equine Hospital, School of Veterinary Medicine, University of Glasgow, Glasgow, United Kingdom.
10
Boyd Orr Centre for Population and Ecosystem Health, Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom.
11
Department of Population Medicine and Diagnostic Science, College of Veterinary Medicine, Cornell University, Ithaca, NY, United States of America.

Abstract

Virus ecology and evolution play a central role in disease emergence. However, their relative roles will vary depending on the viruses and ecosystems involved. We combined field studies, phylogenetics and experimental infections to document with unprecedented detail the stages that precede initial outbreaks during viral emergence in nature. Using serological surveys we showed that in the absence of large-scale outbreaks, horses in Mongolia are routinely exposed to and infected by avian influenza viruses (AIVs) circulating among wild birds. Some of those AIVs are genetically related to an avian-origin virus that caused an epizootic in horses in 1989. Experimental infections showed that most AIVs replicate in the equine respiratory tract without causing lesions, explaining the absence of outbreaks of disease. Our results show that AIVs infect horses but do not spread, or they infect and spread but do not cause disease. Thus, the failure of AIVs to evolve greater transmissibility and to cause disease in horses is in this case the main barrier preventing disease emergence.

PMID:
30731004
DOI:
10.1371/journal.ppat.1007531
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Conflict of interest statement

The authors have declared that no competing interests exist.

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