Emergence of human-like H3N2 influenza viruses in pet dogs in Guangxi, China
© Chen et al.; licensee BioMed Central. 2015
Received: 13 July 2014
Accepted: 19 January 2015
Published: 3 February 2015
After the 1968 H3N2 pandemic emerged in humans, H3N2 influenza viruses continuously circulated and evolved in nature. An H3N2 variant was circulating in humans in the 1990s and subsequently introduced into the pig population in the 2000s. This virus gradually became the main subtype of swine influenza virus worldwide. However, there were no reports of infections in dogs with this virus.
In 2013, 35 nasal swabs from pet dogs were positive for Influenza A virus by RT-PCR. Two viruses were isolated and genetically characterized. In the phylogenetic trees of all gene segments, two H3N2 canine isolates clustered with Moscow/10/99 and most H3N2 swine influenza viruses. These results indicated that two H3N2 CIVs possessed high homology with human/swine influenza viruses, which at the same time exhibited some amino acid substitutions in NA, polymerase basic protein 1 (PB1), and nucleoprotein (NP), which probably were related to the interspecies transmission.
These two viruses share the highest homology with swine H3N2, Moscow/99-like viruses, which indicated that these viruses might originate from swine viruses.
Influenza A viruses circulate worldwide and are endemic in multiple species from birds to mammals . Historically, dogs have been infected with different subtypes of influenza viruses. After the interspecies transmission of influenza H3N8 viruses from horses to dogs was reported in 2005, avian-origin H5N1, H3N2, H5N2 and H9N2, pdm09 H1N1 human, and novel H3N1 influenza viruses with pdm/09 internal genes were also isolated from dogs [2-8]. Recently, a serological survey proved that dogs could be infected with human influenza viruses, and different subtypes of influenza viruses even coexist in dogs [9-11]. Infection of dogs with human H3N2 viruses has been reported [12-14], however, there was a lack of virological evidence about seasonal human H3N2 influenza viruses in dogs. Here, we present the results of genetic and phylogenetic characterization of H3N2 canine influenza viruses (CIVs) isolated in 2013 in Guangxi, China. Genetic analysis demonstrated that human-like H3N2 swine influenza viruses appeared in pet dogs. It provides further evidence that dogs can be regarded as intermediate hosts and can play an important role in influenza ecology.
Description of two H3N2 canine influenza viruses from Guangxi in 2013
gastroenteritis, diarrhea, Canine Parvovirus Virus (CPV) positive
Cough, sneeze, nasal discharge, low appetite, depression; body temperature:39.5°C
Sequence identity of genes of the two H3N2 CIVs isolated in Guangxi to related sequence in GenBank
Virus with highest identity
Identities a (%)
GenBank accession No.
Influenza virus lineage
Common amino acid changes compared to Moscow/10/99 strain b
T192I, V196A, V226I, K239N(L2)
S44P, V240I, L370S, V398I, I464L
E75D, R189K, G354R(L2), F512L(L1), M718L(L2)
E241D, F600L, T745A
M105I, I119T(L1), R195G(L1), 251I(L1), A251V(L1),D290N, K357R, A493T
M1: S275P; M2: G184R(L1), G199R(L1)
There were no deletions in the neuraminidase (NA) stalk region. However, S44P, V240I and V398I substitutions were found in the NA protein of both CIVs. Besides, substitution R189K in PB1 and A493T in NP genes were present in CIVs differed from swine or human influenza viruses (Table 2). Further experiments are required to explore whether these mutations will help human-like H3N2 viruses adapt to dogs.
A total of 315 canine blood samples were separated by centrifugation at 2000 rpm for 10 min and the supernatants were collected into Eppendorf tubes and stored at −20°C, for testing the antibody titer against H3N2 CIVs by hemagglutination inhibition (HI), as previously described . An HI titer ≧40 was considered positive. All tested samples were negative (data not shown). A previous serological survey showed only a 1.2% seropositive rate of human H3N2 influenza viruses in dogs . Ramirez-Martinez, et al. also reported that the seroprevalence of human influenza in dogs only reached 0.9% . All these results suggest that the number of dogs infected with H3N2 human influenza viruses seems to be limited, which means that human influenza viruses have not spread or established themselves in the canine population yet. However, dogs possess specific receptors for human (α2,6-NeuAcGal) and avian (α2,3-NeuAcGal) viruses [20,21], which implies that dogs can be regarded as intermediate hosts that can become co-infected with different subtypes of influenza viruses. Furthermore, pet dogs share the same environment with humans and are in close contact with their owners, therefore increasing the opportunities for pet dogs to be exposed to human influenza viruses.
Emergence of human-like H3N2 influenza viruses in pet dogs, with or without any clinical signs, raises further concerns about whether the viruses have crept into the dog population, and whether novel reassortant influenza viruses will emerge from infection of pet dogs that pose a potential threat to public health. Continued surveillance for influenza viruses in dogs will become essential.
We thank the anonymous reviewer for critical comments and suggestions. We also thank Professor Ashour Joseph for his valuable comments and guidelines. We thank all the Animal Clinics of Guangxi. The Project was sponsored by the Scientific Research Foundation of Guangxi University (Grant No. XJZ140236) and was founded by National agricultural technology system modernization (Grant No. nycytxgxcxtd-03-15-1).
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