Comparison of the Infectivity and Transmission of Contemporary Canine and Equine H3N8 Influenza Viruses in Dogs

Influenza A viruses circulating in dogs: A review of the scientific literature

Influenza A viruses (IAV) cause persistent epidemics and occasional human pandemics, leading to considerable economic losses. The ecology and epidemiology of IAV are very complex and the emergence of novel zoonotic pathogens is one of the greatest challenges in the healthcare. IAV are characterized by genetic and antigenic variability resulting from a combination of high mutation rates and a segmented genome that provides the ability to rapidly change and adapt to new hosts. In this context, available scientific evidence is of great importance for understanding the epidemiology and evolution of influenza viruses. The present review summarizes original research papers and IAV infections reported in dogs all over the world. Reports of interspecies transmission of equine influenza viruses H3N2 from birds to dogs, as well as double and triple reassortant strains resulting from reassortment of avian, human, and canine strains have amplified the genetic variety of canine influenza viruses. A total of 146 articles were deemed acceptable by PubMed and the Google Scholar database and were therefore included in this review. The largest number of research articles (n = 68) were published in Asia, followed by the Americas (n = 44), Europe (n = 31), Africa (n = 2), and Australia (n = 1). Publications are conventionally divided into three categories. The first category (largest group) included modern articles published from 2011 to the present (n = 93). The second group consisted of publications from 2000 to 2010 (n = 46). Single papers of 1919, 1931, 1963, 1972, 1975, and 1992 were also used, which was necessary to emphasize the history of the study of the ecology and evolution of the IAV circulating among various mammalian species. The largest number of publications occurred in 2010 (n = 18) and 2015 (n = 11), which is associated with IAV outbreaks observed at that time in the dog population in America, Europe, and Asia. In general, these findings raise concerns that dogs may mediate the adaptation of IAVs to zoonotic transmission and therefore serve as alternative hosts for genetic reassortment of these viruses. The global concern and significant threat to public health from the present coronavirus diseases 2019 pandemic confirms the necessity for active surveillance of zoonotic viral diseases with pandemic potential.

Canine and Feline Influenza

Influenza virus infections of carnivores-primarily in dogs and in large and small cats-have been repeatedly observed to be caused by a number of direct spillovers of avian viruses or in infections by human or swine viruses. In addition, there have also been prolonged epizootics of an H3N8 equine influenza virus in dogs starting around 1999, of an H3N2 avian influenza virus in domestic dog populations in Asia and in the United States that started around 2004, and an outbreak of an avian H7N2 influenza virus among cats in an animal shelter in the United States in 2016. The impact of influenza viruses in domesticated companion animals and their zoonotic or panzootic potential poses significant questions for veterinary and human health.

A Comprehensive Review on Equine Influenza Virus: Etiology, Epidemiology, Pathobiology, Advances in Developing Diagnostics, Vaccines, and Control Strategies

Among all the emerging and re-emerging animal diseases, influenza group is the prototype member associated with severe respiratory infections in wide host species. Wherein, Equine influenza (EI) is the main cause of respiratory illness in equines across globe and is caused by equine influenza A virus (EIV-A) which has impacted the equine industry internationally due to high morbidity and marginal morality. The virus transmits easily by direct contact and inhalation making its spread global and leaving only limited areas untouched. Hitherto reports confirm that this virus crosses the species barriers and found to affect canines and few other animal species (cat and camel). EIV is continuously evolving with changes at the amino acid level wreaking the control program a tedious task. Until now, no natural EI origin infections have been reported explicitly in humans. Recent advances in the diagnostics have led to efficient surveillance and rapid detection of EIV infections at the onset of outbreaks. Incessant surveillance programs will aid in opting a better control strategy for this virus by updating the circulating vaccine strains. Recurrent vaccination failures against this virus due to antigenic drift and shift have been disappointing, however better understanding of the virus pathogenesis would make it easier to design effective vaccines predominantly targeting the conserved epitopes (HA glycoprotein). Additionally, the cold adapted and canarypox vectored vaccines are proving effective in ceasing the severity of disease. Furthermore, better understanding of its genetics and molecular biology will help in estimating the rate of evolution and occurrence of pandemics in future. Here, we highlight the advances occurred in understanding the etiology, epidemiology and pathobiology of EIV and a special focus is on designing and developing effective diagnostics, vaccines and control strategies for mitigating the emerging menace by EIV.

Prolonged intermittent virus shedding during an outbreak of canine influenza A H3N2 virus infection in dogs in three Chicago area shelters: 16 cases (March to May 2015)

OBJECTIVE To estimate an appropriate isolation period for dogs infected with canine influenza A H3N2 virus on the basis of the duration of virus shedding. DESIGN Retrospective case series. ANIMALS 16 dogs, from 3 Chicago area shelters, naturally infected with canine influenza A H3N2 virus. PROCEDURES Medical records of 16 affected dogs were reviewed. Nasal swab specimens from each dog had been tested periodically for a minimum of 15 days following an initial positive real-time reverse transcriptase PCR (rRT-PCR) assay result for influenza A virus shedding. Amplicons were purified, quantified, and sequenced by the Sanger DNA sequencing technique. Virus isolation and sequence results of canine influenza A H3N2 virus from nasal swab specimens were obtained in conjunction with signalment, description of clinical signs, type of treatment, and outcome. RESULTS Viruses from each dog were identified as canine influenza A H3N2 virus on the basis of DNA sequencing. The interval between first and last positive rRT-PCR assay results ranged from 13 to 24 days, whereas the time interval from first reported clinical signs to last positive assay results ranged from 15 to 26 days. Isolation of canine influenza A H3N2 virus was successful in the late shedding period from nasal swab specimens of 4 dogs at 15 and 20 days after the first positive rRT-PCR assay result and 18 to 20 days after the first clinical signs. Clinical signs resolved for all dogs that remained in the shelters during the testing period. CONCLUSIONS AND CLINICAL RELEVANCE Dogs infected with H3N2 virus should be isolated for a period of ≥ 21 days following onset of illness. Even when resolution of clinical signs occurs sooner than 21 days, shedding of H3N2 virus may persist.

Equine and Canine Influenza H3N8 Viruses Show Minimal Biological Differences Despite Phylogenetic Divergence

The A/H3N8 canine influenza virus (CIV) emerged from A/H3N8 equine influenza virus (EIV) around the year 2000 through the transfer of a single virus from horses to dogs. We defined and compared the biological properties of EIV and CIV by examining their genetic variation, infection, and growth in different cell cultures, receptor specificity, hemagglutinin (HA) cleavage, and infection and growth in horse and dog tracheal explant cultures. Comparison of sequences of viruses from horses and dogs revealed mutations that may be linked to host adaptation and tropism. We prepared infectious clones of representative EIV and CIV strains that were similar to the consensus sequences of viruses from each host. The rescued viruses, including HA and neuraminidase (NA) double reassortants, exhibited similar degrees of long-term growth in MDCK cells. Different host cells showed various levels of susceptibility to infection, but no differences in infectivity were seen when comparing viruses. All viruses preferred α2-3- over α2-6-linked sialic acids for infections, and glycan microarray analysis showed that EIV and CIV HA-Fc fusion proteins bound only to α2-3-linked sialic acids. Cleavage assays showed that EIV and CIV HA proteins required trypsin for efficient cleavage, and no differences in cleavage efficiency were seen. Inoculation of the viruses into tracheal explants revealed similar levels of infection and replication by each virus in dog trachea, although EIV was more infectious in horse trachea than CIV.

IMPORTANCE

Influenza A viruses can cross species barriers and cause severe disease in their new hosts. Infections with highly pathogenic avian H5N1 virus and, more recently, avian H7N9 virus have resulted in high rates of lethality in humans. Unfortunately, our current understanding of how influenza viruses jump species barriers is limited. Our aim was to provide an overview and biological characterization of H3N8 equine and canine influenza viruses using various experimental approaches, since the canine virus emerged from horses approximately 15 years ago. We showed that although there were numerous genetic differences between the equine and canine viruses, this variation did not result in dramatic biological differences between the viruses from the two hosts, and the viruses appeared phenotypically equivalent in most assays we conducted. These findings suggest that the cross-species transmission and adaptation of influenza viruses may be mediated by subtle changes in virus biology.

Influenza virus reservoirs and intermediate hosts: dogs, horses, and new possibilities for influenza virus exposure of humans

Influenza A virus (IAV) infections in hosts outside the main aquatic bird reservoirs occur periodically. Although most such cross-species transmission events result in limited onward transmission in the new host, sustained influenza outbreaks have occurred in poultry and in a number of mammalian species, including humans, pigs, horses, seals, and mink. Recently, two distinct strains of IAV have emerged in domestic dogs, with each circulating widely for several years. Here, we briefly outline what is known about the role of intermediate hosts in influenza emergence, summarize our knowledge of the new canine influenza viruses (CIVs) and how they provide key new information on the process of host adaptation, and assess the risk these viruses pose to human populations.

A live attenuated equine H3N8 influenza vaccine is highly immunogenic and efficacious in mice and ferrets

Equine influenza viruses (EIV) are responsible for rapidly spreading outbreaks of respiratory disease in horses. Although natural infections of humans with EIV have not been reported, experimental inoculation of humans with these viruses can lead to a productive infection and elicit a neutralizing antibody response. Moreover, EIV have crossed the species barrier to infect dogs, pigs, and camels and therefore may also pose a threat to humans. Based on serologic cross-reactivity of H3N8 EIV from different lineages and sublineages, A/equine/Georgia/1/1981 (eq/GA/81) was selected to produce a live attenuated candidate vaccine by reverse genetics with the hemagglutinin and neuraminidase genes of the eq/GA/81 wild-type (wt) virus and the six internal protein genes of the cold-adapted (ca) A/Ann Arbor/6/60 (H2N2) vaccine donor virus, which is the backbone of the licensed seasonal live attenuated influenza vaccine. In both mice and ferrets, intranasal administration of a single dose of the eq/GA/81 ca vaccine virus induced neutralizing antibodies and conferred complete protection from homologous wt virus challenge in the upper respiratory tract. One dose of the eq/GA/81 ca vaccine also induced neutralizing antibodies and conferred complete protection in mice and nearly complete protection in ferrets upon heterologous challenge with the H3N8 (eq/Newmarket/03) wt virus. These data support further evaluation of the eq/GA/81 ca vaccine in humans for use in the event of transmission of an equine H3N8 influenza virus to humans.

IMPORTANCE

Equine influenza viruses have crossed the species barrier to infect other mammals such as dogs, pigs, and camels and therefore may also pose a threat to humans. We believe that it is important to develop vaccines against equine influenza viruses in the event that an EIV evolves, adapts, and spreads in humans, causing disease. We generated a live attenuated H3N8 vaccine candidate and demonstrated that the vaccine was immunogenic and protected mice and ferrets against homologous and heterologous EIV.

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.

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.