Key Facts about Canine Influenza (Dog Flu)
Questions & Answers
- What is canine influenza (dog flu)?
- Can canine influenza viruses infect people?
- Where did canine influenza viruses come from and how long have they been around?
- How does the issue of canine influenza apply to dogs imported into the US from other countries?
- What is CDC doing about canine influenza?
- What are signs of canine influenza in dogs?
- How serious is canine influenza in dogs?
Canine influenza (also known as dog flu) is a contagious respiratory disease in dogs caused by specific Type A influenza viruses known to infect dogs. These are called “canine influenza viruses.” No human infections with canine influenza have ever been reported. There are two different influenza A dog flu viruses: one is an H3N8 virus and the other is an H3N2 virus. Canine influenza A(H3N2) viruses are different from seasonal influenza A(H3N2) viruses that spread annually in people.
In general, canine influenza viruses are thought to pose a low threat to people. To date, there is no evidence of spread of canine influenza viruses from dogs to people and there has not been a single reported case of human infection with a canine influenza virus in the U.S. or worldwide. In 2016, CDC used the Influenza Risk Assessment Tool to evaluate the potential pandemic risk of canine influenza H3N2 viruses and found it to be low.
However, influenza viruses are constantly changing and it is possible that a canine influenza virus could change so that it could infect people and spread easily between people. Human infections with novel (new, non-human) influenza A viruses against which the human population has little immunity are concerning when they occur because of the potential that a pandemic could result. For this reason, the World Health Organization global surveillance system has led to detection of human infections by novel influenza A viruses of animal-origin (such as avian or swine influenza A viruses), but to date, no human infections with canine influenza A viruses have been identified.
Canine influenza H3N8 viruses originated in horses, spread to dogs, and can now spread between dogs. H3N8 equine influenza (horse flu) viruses have been known to exist in horses for more than 40 years. In 2004, cases of an unknown respiratory illness in dogs (initially greyhounds) were reported in the United States. An investigation showed that this respiratory illness was caused by equine influenza A(H3N8) viruses. Scientists believe this virus jumped species (from horses to dogs) and has adapted to cause illness in dogs and spread among dogs, especially those housed in kennels and shelters. This is now considered a dog-specific, or canine, H3N8 virus. In September 2005, this virus was identified by experts as a “newly emerging pathogen in the dog population” in the United States. It has now been detected in dogs across much of the United States.
Canine influenza H3N2 viruses originated in birds, spread to dogs, and can now spread between dogs. Transmission of H3N2 canine influenza viruses to cats from infected dogs has been reported also. Canine influenza A H3N2 viruses were first detected in dogs in South Korea in 2007, and also have been reported in dogs in China, Thailand, and Canada. H3N2 canine influenza viruses were first detected in the United States in April 2015, and has now been found in more than 30 states. To date, the H3N2 canine viruses reported in the U.S. have been almost genetically identical to canine H3N2 viruses previously reported only in Asia.
Both of these canine influenza viruses (H3N8 and H3N2), are now considered endemic in dogs in the United States. Additionally, at this time there is no evidence that canine influenza affects humans nor that it has pandemic potential. If there were evidence that canine influenza viruses were able to infect people with the potential for sustained human to human spread, CDC would execute its existing authorities to limit the introduction and/or spread of that pandemic strain either into or within the U.S.
CDC regulations require that dogs be healthy to enter the United States, thus dogs may be denied entry or further evaluated if they look like they are sick with a communicable disease such as canine influenza. CDC can require a veterinary examination at the owner’s expense for dogs that appear sick, or a necropsy (animal autopsy) for dogs that are dead upon arrival in the United States.
Multiple agencies may have regulatory authority over pets such as dogs and cats when they enter the United States. CDC works closely with other federal agencies to protect U.S. borders against diseases in humans that are carried by animals and animal products. The United States Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) Veterinary Services (VS) has animal health requirements related to bringing (importing) a pet dog to the United States from a foreign country.
Current CDC influenza virus regulations apply only to viruses with pandemic potential in people. However, CDC is doing a number of things to be prepared in the unlikely event that canine influenza becomes a threat to humans or to animals other than canines. First, CDC continues to conduct year-round surveillance for seasonal and novel influenza A viruses and all human infections with novel influenza A viruses are fully investigated. Human infection with a novel influenza A virus of animal origin is reportable to CDC; no human infections with canine influenza viruses have been reported to date. Second, CDC and USDA APHIS VS have existing collaborative protocols to work together in the event of outbreaks of novel influenza A viruses. These same protocols would be followed in the event of an outbreak of canine influenza with suspected human infections. Third, CDC conducted a risk assessment on the pandemic potential of canine H3N2 viruses using the Influenza Risk Assessment Tool, and found it to be low risk.
The signs of this illness in dogs are cough, runny nose, fever, lethargy, eye discharge, and reduced appetite, but not all dogs will show signs of illness. The severity of illness associated with canine flu in dogs can range from no signs to severe illness resulting in pneumonia and sometimes death.
Most dogs recover within 2 to 3 weeks. However, some dogs may develop secondary bacterial infections which may lead to more severe illness and pneumonia. Anyone with concerns about their pet’s health, or whose pet is showing signs of canine influenza, should contact their veterinarian.
The percentage of dogs infected with this disease that die is very small. Some dogs have asymptomatic infections (no signs of illness), while some have severe illness with infection. Severe illness is characterized by the onset of pneumonia.
Almost all dogs are susceptible to canine flu infection, and virus infection tends to spread among dogs housed in kennels and shelters. Canine flu is thought to spread mainly among dogs through respiratory droplets produced during coughing and sneezing from infected dogs, or through contact with contaminated surfaces. Therefore, dog owners whose dogs are coughing or showing other signs of respiratory disease should not expose their dog to other dogs or to cats. Clothing, equipment, surfaces, and hands should be cleaned and disinfected after exposure to dogs showing signs of respiratory disease.
Testing to confirm H3N8 and H3N2 canine influenza virus infection in dogs is available. Your veterinarian can tell you if testing is appropriate.
Treatment largely consists of supportive care which helps to keep the dog hydrated and comfortable while its body then mounts an immune response to the infection to facilitate recovery. In the milder form of the disease, this care may include medication to make your dog be more comfortable and fluids to ensure that your dog remains well-hydrated. Broad spectrum antibiotics may be prescribed by your veterinarian if a secondary bacterial infection is suspected.
Vaccines to protect dogs against both H3N8 and H3N2 canine flu are available in the United States. Your veterinarian can provide additional information about these vaccines and whether you should consider vaccinating your dog.
Consult your veterinarian to determine if an appointment is needed so the veterinarian can evaluate your dog and recommend an appropriate course of treatment.
More information on canine influenza in pet dogs can be found at the following links:
- Media Briefing on Canine Influenza. September 25, 2005.
- Update on Canine Influenza (Dog Flu) Outbreak Reported in Chicago Area. April 13, 2015.
- Influenza A Virus (H3N8) in Dogs with Respiratory Disease, Florida. Volume 14, Number 6 – June 2008.
- Canine influenza.