Canine Influenza

Canine influenza (CI) is a respiratory infectious disease resulting from the canine influenza virus (CIV). The origin of this condition traces back to 1999 when the H3N8 equine influenza virus was initially identified in dogs. Subsequently, since 2004, H3N2 avian influenza viruses have persisted among domestic dogs in both Asia and North America. Presently, these two CIV subtypes, H3N8 and H3N2, are the most prevalent and globally circulating strains. These viral strains have become a cause for concern in the dog population, leading to outbreaks and sporadic cases globally. It is of utmost importance to promptly develop effective diagnostic techniques and tools, as well as secure vaccines for maximum protection. As an advanced animal disease diagnostic company, BioVenic has assumed corresponding responsibilities.

Etiology

CIV belongs to the family Orthomyxoviridae and the genus A influenza virus. It is a single-stranded negative-sense RNA virus. Like all IAVs, its genome is divided into basic polymerase 1 (PB1) and basic polymerase 2 (PB2), acidic polymerase (PA), hemagglutinin (HA), neuraminidase (NA), matrix protein (M), and nonstructural protein (NS) 8 fragments.

Fig. 1 Diagram of the evolution of avian influenza viruses in hosts.¹

Geographical Distribution

H3N8 was first discovered to infect dogs in the U.S. in 2004, and related cases were subsequently reported in Thailand, China, South Korea, and other countries. H3N2 was first discovered in South Korea in 2007. Since then, this subtype has been prevalent in China, Thailand, and other regions, and was isolated from a sick dog in the United States in 2015. CI is becoming a noteworthy animal health problem in the U.S.

Dogs have varying degrees of susceptibility to influenza viruses from other hosts, including birds and mammals. Although biological and ecological barriers can reduce the spread of viruses, outbreaks or epidemics are still possible in densely populated populations with frequent contact.

Fig. 2 Avian influenza viruses are capable of infecting different hosts.²

Transmission

H3N8 and H3N2 CIVs require relatively close contact to spread, so long-term infection generally does not occur in domestic dogs, but may continue to spread in large animal shelters, kennels, or meat dog farms.

Risk Factors

Several factors can increase the risk of CPIV infection, such as:

• Dogs that are housed in crowded environments, such as kennels, shelters, or doggy daycares, have an increased risk of exposure.
• Additionally, dogs with a compromised immune system, such as those suffering from other illnesses or recovering from surgery, are more susceptible to the virus.

Public Health Risk

So far, there have been no reports of CIV infection in humans. Nevertheless, in recent years, influenza viruses of different origins and subtypes have continuously invaded dogs, and a variety of reassortant viruses have been produced in dogs. The role of pet dogs as an intermediate host and a "mixing container" is bound to make them play an important role in the ecological cycle of influenza viruses and pose a potential threat to human public health.

Pathogenesis

The PB2, PB1, HA, NP, NS, and M genes of influenza A play an important role in adapting to mammalian hosts, especially the PA, M, and NS genes, which can enhance the virulence and spread of recombinant viruses. The NS1 protein suppresses host innate immune defenses, allowing CIV to replicate in dog respiratory epithelial cells, resulting in characteristic clinical signs and symptoms.

Signs and Symptoms

The incubation period of CI is 2-5 days. 80% of sick dogs have a cough, sneeze, and runny nose as the main symptoms, and occasionally cause elevated body temperature. The cough lasts for 10-21 days, and the initial manifestation is a mild wet cough, and some individuals may also have a dry cough.

Diagnosis

Diagnosis mainly follows laboratory methods, mainly virus isolation, immunology, and molecular biology methods, among which virus isolation is the gold standard for detecting CIV. The diagnostic kits and solution development services we provide cover the following laboratory technologies.

• Immunodiagnostics
  
  • HA-HI: The HA-HI assay utilizes the property of CIV HA protein to agglutinate red blood cells to detect pathogens or corresponding antibodies.
  • ELISA: ELISA detection technology mainly uses the NP gene to diagnose CIV infection, and it is only practical in the case of CI outbreaks in dogs.
• Molecular Diagnostics
  Most molecular biology methods directly detect pathogens, and the NP and M gene segments are relatively conserved, which are often used to distinguish the genus specificity of CIV.
  
  • PCR
  • qPCR
  • RT-LAMP
  • Microarray

Treatment

• CI has a higher morbidity rate but a lower mortality rate. Most of the affected dogs can recover by themselves, but the duration is longer.
• Dogs with fever should be given antipyretic drugs or cold compresses in time.
• Secondary infection can be treated with broad-spectrum antibiotics, the effect is good, and the duration of symptoms can be significantly shortened.
• Dogs with severe symptoms can receive antiviral and supportive care to aid in their recovery.
• Except for some dogs with severe clinical symptoms that need targeted treatment, most dogs have a good prognosis.

Prevention and Control

Inactivated vaccines against H3N2 and H3N8 have been approved in the United States. Therefore, in the United States, we recommend prior immunization with the CIV vaccine to prevent the disease.

However, under the immune pressure of the vaccine, the CIV will mutate rapidly, so it is very important to formulate a reasonable prevention and control strategy, such as:

• Improve the breeding environment and keep the environment constant temperature.
• The survival ability of CIV in the environment is weak, hence disinfectants can be utilized to clean the surroundings and equipment.
• Dogs with respiratory symptoms or exposed to the virus should be isolated in time to cut off the aerosol transmission route.
• Dogs that are kept alone should not be taken to public places to avoid the spread of CIV.

BioVenic has made tremendous achievements in the diagnosis and prevention of CIV. We will help you mitigate the impact of CI and protect canine health by providing comprehensive CIV diagnostic kits and advanced vaccine development services. If you need our technical support, please feel free to contact us.

References

1. Chen, Ying, et al. "Emergence and evolution of novel reassortant influenza A viruses in canines in Southern China." MBio 9.3 (2018): 10-1128.
2. Joseph, Udayan, et al. "The ecology and adaptive evolution of influenza A interspecies transmission." Influenza and other respiratory viruses 11.1 (2017): 74-84.