No evidence of horizontal infection in horses kept in close contact with dogs experimentally infected with canine influenza A virus (H3N8)

doi:10.1186/1751-0147-54-25

Acta Vet Scand. 2012; 54(1): 25.

Published online 2012 April 16. doi: 10.1186/1751-0147-54-25

PMCID: PMC3416777

No evidence of horizontal infection in horses kept in close contact with dogs experimentally infected with canine influenza A virus (H3N8)

Takashi Yamanaka,¹ Manabu Nemoto,¹ Hiroshi Bannai,¹ Koji Tsujimura,¹ Takashi Kondo,¹ Tomio Matsumura,¹ Masanori Muranaka,¹ Takanori Ueno,¹ Yuta Kinoshita,¹ Hidekazu Niwa,¹ Kazuya IPJ Hidari,² and Takashi Suzuki²

¹Epizootic Research Center, Equine Research Institute, the Japan Racing Association, 1400-4 Shiba, Shimotsuke, Tochigi, 329-0412, Japan

²Department of Biochemistry, School of Pharmaceutical Sciences, Global COE Program, University of Shizuoka, 51-1 Yada, Suruga-ku, Shizuoka, 422-8526, Japan

Corresponding author.

Takashi Yamanaka: yamanaka/at/epizoo.equinst.go.jp; Manabu Nemoto: nemoto_manabu/at/epizoo.equinst.go.jp; Hiroshi Bannai: hiroshi_bannai/at/jra.go.jp; Koji Tsujimura: kotsuji/at/epizoo.equinst.go.jp; Takashi Kondo: kondo/at/epizoo.equinst.go.jp; Tomio Matsumura: tomats/at/epizoo.equinst.go.jp; Masanori Muranaka: masanori_muranaka/at/jra.go.jp; Takanori Ueno: takanori_ueno/at/jra.go.jp; Yuta Kinoshita: yuta_kinoshita/at/jra.go.jp; Hidekazu Niwa: niwa/at/epizoo.equinst.go.jp; Kazuya IPJ Hidari: hidari/at/u-shizuoka-ken.ac.jp; Takashi Suzuki: suzukit/at/u-shizuoka-ken.ac.jp

Received January 18, 2012; Accepted April 16, 2012.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Background

Since equine influenza A virus (H3N8) was transmitted to dogs in the United States in 2004, the causative virus, which is called canine influenza A virus (CIV), has become widespread in dogs. To date, it has remained unclear whether or not CIV-infected dogs could transmit CIV to horses. To address this, we tested whether or not close contact between horses and dogs experimentally infected with CIV would result in its interspecies transmission.

Methods

Three pairs of animals consisting of a dog inoculated with CIV (10^8.3 egg infectious dose₅₀/dog) and a healthy horse were kept together in individual stalls for 15 consecutive days. During the study, all the dogs and horses were clinically observed. Virus titres in nasal swab extracts and serological responses were also evaluated. In addition, all the animals were subjected to a gross pathological examination after euthanasia.

Results

All three dogs inoculated with CIV exhibited clinical signs including, pyrexia, cough, nasal discharge, virus shedding and seroconversion. Gross pathology revealed lung consolidations in all the dogs, and Streptococcus equi subsp. zooepidemicus was isolated from the lesions. Meanwhile, none of the paired horses showed any clinical signs, virus shedding or seroconversion. Moreover, gross pathology revealed no lesions in the respiratory tracts including the lungs of the horses.

Conclusions

These findings may indicate that a single dog infected with CIV is not sufficient to constitute a source of CIV infection in horses.

Keywords: Canine influenza, Dog, H3N8, Horse, Interspecies transmission

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