Virulence of a novel reassortant canine H3N2 influenza virus in ferret, dog and mouse models

The inactivated vaccine of reassortant H3N2 canine influenza virus based on internal gene cassette from PR8 is safe and effective

Canine influenza (CI) is a contagious respiratory disease in dogs, which poses a threat to canine health. A safe, high-yield vaccine seed virus is critical for CI vaccine development. We developed a PR8-based reassortant H3N2 canine influenza virus (RT CIV) using the reverse genetic method and evaluated its yield in canine kidney epithelial (MDCK) cells, Vero cells, and specific pathogen-free (SPF) chicken embryos. Mice and dogs were infected with RT CIV, and the pathogenicity was evaluated. The viral titers of RT CIV increased in MDCK cells, Vero cells, and SPF chicken embryos; the HA yield in SPF chicken embryos increased 4-fold. However, RT CIV was not lethal to mice, and it showed similar virulence as wild-type CIV. RT CIV also showed minimal pathogenicity in dogs, which manifested as mild fever and rhinorrhea for the first two days post-infection. Thus, RT CIV carrying the internal gene cassette from PR8 showed almost no pathogenicity in dogs. And the reassortant virus inactivated vaccine could provide complete protection against H3N2 CIV. To our knowledge, this is the first report on the pathogenicity of PR8-based reassortant H3N2 CIV in dogs. These studies are relevant for developing a high-yield and safe CI vaccine.

Comparison of Pathogenicity of Different Infectious Doses of H3N2 Canine Influenza Virus in Dogs

The canine influenza virus (CIV) outbreaks have raised concerns as they pose a threat to the health of dogs. The successful construction of a canine influenza (CI) infection model is essential to study the CIV. Here we investigated the pathogenicity of different infectious doses of H3N2 CIV in Beagle dogs. Thirty-seven healthy Beagle dogs were used in the experiment and were infected with 10³, 10⁴, 10⁵, and 10⁶ 50% egg-infectious doses (EID₅₀). Compared to the dogs in the other three groups, those in the 10⁶ EID₅₀ group presented with obvious clinical symptoms, high virus titer, and typical pathological changes. Considering the ensemble of clinical scores, body temperature, virus shedding, lung lesions, pathological section scores, and visceral virus titers, we determined that 10⁶ EID₅₀ is the minimum infectious dose for the Beagle infection model. The other three infectious doses had almost no clinical symptoms. These results indicate that 10⁶ EID₅₀ is the minimum infectious dose of H3N2 CIV that can cause obvious clinical manifestations and pathological changes associated with CI in Beagle dogs. The theoretical framework developed in this research will guide the establishment of an infection model of CIV for future research.

H3N8 and H3N2 Canine Influenza Viruses: Understanding These New Viruses in Dogs

Two different influenza A viruses have infected and spread among dogs since 2000, and both have been widespread in dogs in North America. The H3N8 canine influenza virus arose in the United States as a variant of equine influenza virus. The H3N2 canine influenza virus arose in Asia by transfer of an avian influenza virus to dogs. Both viruses cause mild respiratory disease and are associated with outbreaks in densely housed dogs or those with frequent connections to other dogs. The 2 canine influenza viruses each caused widespread epidemics over at least several years that were associated with localized outbreaks.

Comparison of the virulence of three H3N2 canine influenza virus isolates from Korea and China in mouse and Guinea pig models

Background

Avian-origin H3N2 canine influenza virus (CIV) has been the most common subtype in Korea and China since 2007. Here, we compared the pathogenicity and transmissibility of three H3N2 CIV strains [Chinese CIV (JS/10), Korean CIV (KR/07), and Korean recombinant CIV between the classic H3N2 CIV and the pandemic H1N1 virus (MV/12)] in BALB/c mouse and guinea pig models. The pandemic H1N1 (CA/09) strain served as the control.

Results

BALB/c mice infected with H1N1 had high mortality and obvious body weight loss, whereas no overt disease symptoms were observed in mice inoculated with H3N2 CIV strains. The viral titers were higher in the group MV/12 than those in groups JS/10 and KR/07, while the mice infected with JS/10 showed higher viral titers in all tissues (except for the lung) than the mice infected with KR/07. The data obtained in guinea pigs also demonstrated that group MV/12 presented the highest loads in most of the tissues, followed by group JS/10 and KR/07. Also, direct contact transmissions of all the three CIV strains could be observed in guinea pigs, and for the inoculated and the contact groups, the viral titer of group MV/12 and KR/07 was higher than that of group JS/10 in nasal swabs. These findings indicated that the matrix (M) gene obtained from the pandemic H1N1 may enhance viral replication of classic H3N2 CIV; JS/10 has stronger viral replication ability in tissues as compared to KR/07, whereas KR/07 infected guinea pigs have more viral shedding than JS/10 infected guinea pigs.

Conclusions

There exists a discrepancy in pathobiology among CIV isolates. Reverse genetics regarding the genomes of CIV isolates will be helpful to further explain the virus characteristics.

Evaluation of protective efficacy of three novel H3N2 canine influenza vaccines

Canine influenza virus (CIV) has the potential risk to spread in different areas and dog types. Thus, there is a growing need to develop an effective vaccine to control CIV disease. Here, we developed three vaccine candidates: 1) a recombinant pVAX1 vector expressing H3N2 CIV hemagglutinin (pVAX1-HA); 2) a live attenuated canine adenovirus type 2 expressing H3N2 CIV hemagglutinin (rCAV2-HA); and 3) an inactivated H3N2 CIV (A/canine/Guangdong/01/2006 (H3N2)). Mice received an initial intramuscular immunization that followed two booster injections at 2 and 4 weeks post-vaccination (wpv). The splenic lymphocytes were collected to assess the immune responses at 6 wpv. The protective efficacy was evaluated by challenging H3N2 CIV after vaccination (at 6 wpv). Our results demonstrated that all three vaccine candidates elicited cytokine and antibody responses in mice. The rCAV2-HA vaccine and the inactivated vaccine generated efficient protective efficacy in mice, whereas limited protection was provided by the pVAX1-HA DNA vaccine. Therefore, both the rCAV2-HA live recombinant virus and the inactivated CIV could be used as potential novel vaccines against H3N2CIV. This study provides guidance for choosing the most appropriate vaccine for the prevention and control of CIV disease.

Influenza virus vaccine for neglected hosts: horses and dogs

This study provides information regarding vaccine research and the epidemiology of influenza virus in neglected hosts (horses and dogs). Equine influenza virus (EIV) causes a highly contagious disease in horses and other equids, and outbreaks have occurred worldwide. EIV has resulted in costly damage to the horse industry and has the ability of cross the host species barrier from horses to dogs. Canine influenza is a virus of equine or avian origin and infects companion animals that live in close contact with humans; this results in possible exposure to the seasonal epizootic influenza virus. There have been case reports of genetic reassortment between human and canine influenza viruses, which results in high virulence and the ability of transmission to ferrets. This emphasizes the need for vaccine research on neglected hosts to update knowledge on current strains and to advance technology for controlling influenza outbreaks for public health.