Evaluation of virus isolation, one-step real-time reverse transcription polymerase chain reaction assay, and two rapid influenza diagnostic tests for detecting canine Influenza A virus H3N8 shedding in dogs

Temperature-Sensitive Live-Attenuated Canine Influenza Virus H3N8 Vaccine

Canine influenza is a respiratory disease of dogs caused by canine influenza virus (CIV). CIV subtypes responsible for influenza in dogs include H3N8, which originated from the transfer of H3N8 equine influenza virus to dogs; and the H3N2 CIV, which is an avian-origin virus that adapted to infect dogs. Influenza infections are most effectively prevented through vaccination to reduce transmission and future infection. Currently, only inactivated influenza vaccines (IIVs) are available for the prevention of CIV in dogs. However, the efficacy of IIVs is suboptimal, and novel approaches are necessary for the prevention of disease caused by this canine respiratory pathogen. Using reverse genetics techniques, we have developed a live-attenuated CIV vaccine (LACIV) for the prevention of H3N8 CIV. The H3N8 LACIV replicates efficiently in canine cells at 33°C but is impaired at temperatures of 37 to 39°C and was attenuated compared to wild-type H3N8 CIV in vivo and ex vivo The LACIV was able to induce protection against H3N8 CIV challenge with a single intranasal inoculation in mice. Immunogenicity and protection efficacy were better than that observed with a commercial CIV H3N8 IIV but provided limited cross-reactive immunity and heterologous protection against H3N2 CIV. These results demonstrate the feasibility of implementing a LAIV approach for the prevention and control of H3N8 CIV in dogs and suggest the need for a new LAIV for the control of H3N2 CIV.

IMPORTANCE

Two influenza A virus subtypes has been reported in dogs in the last 16 years: the canine influenza viruses (CIV) H3N8 and H3N2 of equine and avian origins, respectively. To date, only inactivated influenza vaccines (IIVs) are available to prevent CIV infections. Here, we report the generation of a recombinant, temperature-sensitive H3N8 CIV as a live-attenuated influenza vaccine (LAIV), which was attenuated in mice and dog tracheal, explants compared to CIV H3N8 wild type. A single dose of H3N8 LACIV showed immunogenicity and protection against a homologous challenge that was better than that conferred with an H3N8 IIV, demonstrating the feasibility of implementing a LAIV approach for the improved control of H3N8 CIV infections in dogs.

A Multiplex RT-PCR Assay for Detection and Differentiation of Avian-Origin Canine H3N2, Equine-Origin H3N8, Human-Origin H3N2, and H1N1/2009 Canine Influenza Viruses

Virological and serological surveys have documented that H1N1/2009, avian-origin canine H3N2 (cH3N2), seasonal human-origin H3N2 (hH3N2), and equine-origin H3N8 influenza viruses are consistently circulating in dogs. In the present study, a multiplex reverse-transcriptase polymerase chain reaction (mRT-PCR) assay was developed for simultaneous detection and differentiation of these influenza viruses. Four primer sets were designed to target the hemagglutinin genes of H1N1/2009, cH3N2, hH3N2, and H3N8 canine influenza viruses (CIVs). This mRT-PCR assay demonstrated high specificity and sensitivity for the four CIV subtypes. Additionally, mRT-PCR results obtained from 420 clinical samples were consistent with those obtained by the conventional virus isolation method. Our mRT-PCR assay is reliable for clinical diagnosis and rapid identification of CIVs.

Canine influenza viruses with modified NS1 proteins for the development of live-attenuated vaccines

Canine Influenza Virus (CIV) H3N8 is the causative agent of canine influenza, a common and contagious respiratory disease of dogs. Currently, only inactivated influenza vaccines (IIVs) are available for the prevention of CIV H3N8. However, live-attenuated influenza vaccines (LAIVs) are known to provide better immunogenicity and protection efficacy than IIVs. Influenza NS1 is a virulence factor that offers an attractive target for the preparation of attenuated viruses as LAIVs. Here we generated recombinant H3N8 CIVs containing truncated or a deleted NS1 protein to test their potential as LAIVs. All recombinant viruses were attenuated in mice and showed reduced replication in cultured canine tracheal explants, but were able to confer complete protection against challenge with wild-type CIV H3N8 after a single intranasal immunization. Immunogenicity and protection efficacy was better than that observed with an IIV. This is the first description of a LAIV for the prevention of H3N8 CIV in dogs.

Development and application of multiplex PCR assays for detection of virus-induced respiratory disease complex in dogs

Canine infectious respiratory disease complex (CIRDC) viruses have been detected in dogs with respiratory illness. Canine influenza virus (CIV), canine parainfluenza virus (CPIV), canine distemper virus (CDV), canine respiratory coronavirus (CRCoV), canine adenovirus type 2 (CAdV-2) and canine herpesvirus 1 (CaHV-1), are all associated with the CIRDC. To allow diagnosis, two conventional multiplex polymerase chain reactions (PCR) were developed to simultaneously identify four RNA and two DNA viruses associated with CIRDC. The two multiplex PCR assays were then validated on 102 respiratory samples collected from 51 dogs with respiratory illness by sensitivity and specificity determination in comparison to conventional simplex PCR and a rapid three-antigen test kit. All six viruses were detected in either individual or multiple infections. The developed multiplex PCR assays had a >87% sensitivity and 100% specificity compared to their simplex counterpart. Compared to the three-antigen test kit, the multiplex PCR assays yielded 100% sensitivity and more than 83% specificity for detection of CAdV-2 and CDV, but not for CIV. Therefore, the developed multiplex PCR modalities were able to simultaneously diagnose a panel of CIRDC viruses and facilitated specimen collection through being suitable for use of nasal or oral samples.

Multiplex RT-PCR detection of H3N2 influenza A virus in dogs

A multiplex RT-PCR (mRT-PCR) assay to detect H3N2 CIV genomic segments was developed as a rapid and cost-effective method. Its performance was evaluated with forty-six influenza A viruses from different hosts using three primer sets which amplify four segments of H3N2 CIV simultaneously. The mRT-PCR has been successful in detecting the viral segments, indicating that it can improve the speed of diagnosis for H3N2 CIV and its reassortants.

Evolution of the hemagglutinin gene of H3N8 canine influenza virus in dogs

With the widespread use of a recently developed canine influenza virus (CIV) H3N8 vaccine, continual molecular evaluation of circulating CIVs is necessary for monitoring antigenic drift. The aim of this project was to further describe the genetic evolution of CIV, as well as determine any genetic variation within potential antigenic regions that might result in antigenic drift. To this end, the hemagglutinin gene of 19 CIV isolates from dogs residing in Colorado, New York, and South Carolina humane shelters was sequenced and compared to CIV strains isolated during 2003–2012. Phylogenetic analysis suggests that CIV might be diverging into two geographically distinct lineages. Using a mixed-effects model for evolution and single likelihood ancestor counting methods, several amino acid sites were found to be undergoing selection pressure. Additionally, a total of six amino acid changes were observed in two possible antigenic sites for CIVs isolated from Colorado and New York humane shelters between 2009 and 2011. As CIV isolates might be diverging into geographically distinct lineages, further experiments are warranted to determine the extent of antigenic drift occurring within circulating CIV.

Rapid detection of equine influenza virus H3N8 subtype by insulated isothermal RT-PCR (iiRT-PCR) assay using the POCKIT™ Nucleic Acid Analyzer

Equine influenza (EI) is an acute, highly contagious viral respiratory disease of equids. Currently, equine influenza virus (EIV) subtype H3N8 continues to be the most important respiratory pathogen of horses in many countries around the world. The need to achieve a rapid diagnosis and to implement effective quarantine and movement restrictions is critical in controlling the spread of EIV. In this study, a novel, inexpensive and user-friendly assay based on an insulated isothermal RT-PCR (iiRT-PCR) method on the POCKIT™, a field-deployable device, was described and validated for point-of-need detection of EIV-H3N8 in clinical samples. The newly established iiRT-PCR assay targeting the EIV HA3 gene was evaluated for its sensitivity using in vitro transcribed (IVT) RNA, as well as ten-fold serial dilutions of RNA extracted from the prototype H3N8 strain A/equine/Miami/1/63. Inclusivity and exclusivity panels were tested for specificity evaluation. Published real-time RT-PCR (rRT-PCR) assays targeting the NP and HA3 genes were used as the reference standards for comparison of RNA extracted from field strains and from nasal swab samples collected from experimentally infected horses, respectively. Limit of detection with a 95% probability (LoD95%) was estimated to be 11copies of IVT RNA. Clinical sensitivity analysis using RNA prepared from serial dilutions of a prototype EIV (Miami 1/63/H3N8) showed that the iiRT-PCR assay was about 100-fold more sensitive than the rRT-PCR assay targeting the NP gene of EIV subtype H3N8. The iiRT-PCR assay identified accurately fifteen EIV H3N8 strains and two canine influenza virus (CIV) H3N8 strains, and did not cross-react with H6N2, H7N7, H1N1 subtypes or any other equine respiratory viral pathogens. Finally, 100% agreement was found between the iiRT-PCR assay and the universal influenza virus type A rRT-PCR assay in detecting the EIV A/equine/Kentucky/7/07 strain in 56 nasal swab samples collected from experimentally inoculated horses. Therefore, the EIV H3N8 subtype specific iiRT-PCR assay along with the portable POCKIT™ Nucleic Acid Analyzer provides a highly reliable, sensitive and specific on-site detection system of both equine and canine influenza viruses.

Epidemiology and ecology of H3N8 canine influenza viruses in US shelter dogs

BACKGROUND

H3N8 canine influenza virus (CIV) infection might contribute to increased duration of shelter stay for dogs. Greater understanding of factors contributing to CIV within shelters could help veterinarians identify control measures for CIV.

OBJECTIVES

To assess community to shelter dog CIV transmission, estimate true prevalence of CIV, and determine risk factors associated with CIV in humane shelters.

ANIMALS

5,160 dogs upon intake or discharge from 6 US humane shelters, December 2009 through January 2012.

METHODS

A cross-sectional study was performed with prospective convenience sampling of 40 dogs from each shelter monthly. Nasal swabs and serum samples were collected. Hemagglutination inhibition and real-time reverse transcriptase-polymerase chain reaction assays were performed for each nasal and serum sample. True prevalence was estimated by stochastic latent class analysis. Logistic regression was used to identify risk factors associated with CIV shedding and seropositivity.

RESULTS

Nasal swabs were positive from 4.4% of New York (NY), 4.7% of Colorado (CO), 3.2% of South Carolina, 1.2% of Florida, and 0% of California and Texas shelter dogs sampled. Seropositivity was the highest in the CO shelter dogs at 10%, and NY at 8.5%. Other shelters had 0% seropositivity. Information-theoretic analyses suggested that CIV shedding was associated with region, month, and year (model weight = 0.95) and comingling/cohousing (model weight = 0.92).

CONCLUSIONS AND CLINICAL IMPORTANCE

Community dogs are a likely source of CIV introduction into humane shelters and once CIV has become established, dog-to-dog transmission maintains the virus within a shelter.