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 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 also been reported. 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 the virus 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. The virus is highly contagious and can be transmitted via airborne droplets produced from coughing and sneezing, as well as via contaminated surfaces, hands and clothing.
Several other diseases can produce the same clinical signs as canine influenza, including kennel cough (caused by Bordetella bronchiseptica), parainfluenza, andenovirus and canine herpes virus.
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.
The signs of this illness in dogs are coughing, 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.
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, along with 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.
Keep your dog indoors and away from other dogs to prevent the spread of the disease.
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.
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