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

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.

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.

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.

Mutation W222L at the Receptor Binding Site of Hemagglutinin Could Facilitate Viral Adaption from Equine Influenza A(H3N8) Virus to Dogs

An outbreak of respiratory disease caused by the equine-origin influenza A(H3N8) virus was first detected in dogs in 2004 and since then has been enzootic among dogs. Currently, the molecular mechanisms underlying host adaption of this virus from horses to dogs is unknown. Here, we have applied quantitative binding, growth kinetics, and immunofluorescence analyses to elucidate these mechanisms. Our findings suggest that a substitution of W222L in the hemagglutinin of the equine-origin A(H3N8) virus facilitated its host adaption to dogs. This mutation increased binding avidity of the virus specifically to receptor glycans with N-glycolylneuraminic acid (Neu5Gc) and sialyl Lewis X (SLe^X) motifs. We have demonstrated these motifs are abundantly located in the submucosal glands of dog trachea. Our findings also suggest that in addition to the type of glycosidic linkage (e.g., α2,3-linkage or α2,6-linkage), the type of sialic acid (Neu5Gc or 5-N-acetyl neuraminic acid) and the glycan substructure (e.g., SLe^X) also play an important role in host tropism of influenza A viruses.IMPORTANCE Influenza A viruses (IAVs) cause a significant burden on human and animal health, and mechanisms for interspecies transmission of IAVs are far from being understood. Findings from this study suggest that an equine-origin A(H3N8) IAV with mutation W222L at its hemagglutinin increased binding to canine-specific receptors with sialyl Lewis X and Neu5Gc motifs and, thereby, may have facilitated viral adaption from horses to dogs. These findings suggest that in addition to the glycosidic linkage (e.g., α2,3-linked and α2,6-linked), the substructure in the receptor saccharides (e.g., sialyl Lewis X and Neu5Gc) could present an interspecies transmission barrier for IAVs and drive viral mutations to overcome such barriers.

Streptococcal infections in cats: ABCD guidelines on prevention and management

OVERVIEW

Streptococcus canis is most prevalent in cats, but recently S equi subsp zooepidemicus has been recognised as an emerging feline pathogen.

S CANIS INFECTION

S canis is considered part of the commensal mucosal microflora of the oral cavity, upper respiratory tract, genital organs and perianal region in cats. The prevalence of infection is higher in cats housed in groups; and, for example, there may be a high rate of vaginal carriage in young queens in breeding catteries. A wide spectrum of clinical disease is seen, encompassing neonatal septicaemia, upper respiratory tract disease, abscesses, pneumonia, osteomyelitis, polyarthritis, urogenital infections, septicaemia, sinusitis and meningitis.

S EQUI SUBSP ZOOEPIDEMICUS INFECTION

S equi subsp zooepidemicus is found in a wide range of species including cats. It was traditionally assumed that this bacterium played no role in disease of cats, but it is now considered a cause of respiratory disease with bronchopneumonia and pneumonia, as well as meningoencephalitis, often with a fatal course. Close confinement of cats, such as in shelters, appears to be a major risk factor. As horses are common carriers of this bacterium, contact with horses is a potential source of infection. Additionally, the possibility of indirect transmission needs to be considered.

DIAGNOSIS

Streptococci can be detected by conventional culture techniques from swabs, bronchoalveolar lavage fluid or organ samples. Also real-time PCR can be used, and is more sensitive than culture.

TREATMENT

In suspected cases, treatment with broad-spectrum antibiotics should be initiated as soon as possible and, if appropriate, adapted to the results of culture and sensitivity tests.

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.

Experimental infection of dogs with H6N1 avian influenza A virus

H6N1 avian influenza A viruses, which have spread across North America, Europe and Asia, have been shown to be infectious not only for birds but also for mammals. Because humans lack immunity to H6N1 avian influenza A viruses, the emergence of these viruses in humans would probably cause a pandemic. Replication of H6N1 avian influenza A viruses in dogs may facilitate their adaptation in humans because dogs are often in close contact with humans. However, the susceptibility of dogs to these viruses is unknown. To address this question, we infected beagles intranasally (i.n.) with an H6N1 avian influenza A virus that was isolated from a mallard. Inoculation of this virus into beagles resulted in the virus being detectable in the lung and seroconversion with no clinical signs except for a fever at 1 day post-inoculation (dpi). In addition, the virus was transiently shed from the nose and in the feces of the infected beagles. Our results suggest that dogs can be subclinically infected with H6N1 avian influenza A viruses, which, like H7N9, have low pathogenicity in birds and may serve as an intermediate host to transfer this virus to humans. Certain actions may be taken to prevent the potential transmission of these viruses, including the development of H6N1 avian influenza vaccines for prevention.

Replication and immunogenicity of swine, equine, and avian h3 subtype influenza viruses in mice and ferrets

Since it is difficult to predict which influenza virus subtype will cause an influenza pandemic, it is important to prepare influenza virus vaccines against different subtypes and evaluate the safety and immunogenicity of candidate vaccines in preclinical and clinical studies prior to a pandemic. In addition to infecting humans, H3 influenza viruses commonly infect pigs, horses, and avian species. We selected 11 swine, equine, and avian H3 influenza viruses and evaluated their kinetics of replication and ability to induce a broadly cross-reactive antibody response in mice and ferrets. The swine and equine viruses replicated well in the upper respiratory tract of mice. With the exception of one avian virus that replicated poorly in the lower respiratory tract, all of the viruses replicated in mouse lungs. In ferrets, all of the viruses replicated well in the upper respiratory tract, but the equine viruses replicated poorly in the lungs. Extrapulmonary spread was not observed in either mice or ferrets. No single virus elicited antibodies that cross-reacted with viruses from all three animal sources. Avian and equine H3 viruses elicited broadly cross-reactive antibodies against heterologous viruses isolated from the same or other species, but the swine viruses did not. We selected an equine and an avian H3 influenza virus for further development as vaccines.

Equine influenza--a global perspective

To date, equine influenza outbreaks have been reported all over the world with the exception of a small number of island nations including New Zealand and Iceland. Influenza is endemic in Europe and North America and is considered to be of potentially major economic significance to the equine industry worldwide. The importation of subclinically infected vaccinated horses, and inadequate quarantine procedures have resulted in several major outbreaks in susceptible populations for example, in Australia (2007) when more than 76,000 horses on over 10,000 properties were reported as infected. This review summarises the current understanding of, and recent research on, equine influenza, including epidemiology, pathogenesis, clinical characteristics, laboratory diagnosis, management and prevention. Recent advances in diagnostic techniques are discussed as are the merits of different vaccination regimes.

Engineering H5N1 avian influenza viruses to study human adaptation

Two studies of H5N1 avian influenza viruses that had been genetically engineered to render them transmissible between ferrets have proved highly controversial. Divergent opinions exist about the importance of these studies of influenza transmission and about potential 'dual use' research implications. No consensus has developed yet about how to balance these concerns. After not recommending immediate full publication of earlier, less complete versions of the studies, the United States National Science Advisory Board for Biosecurity subsequently recommended full publication of more complete manuscripts; however, controversy about this and similar research remains.