Canine Influenza: Frequently asked questions by sheltering organizations
1. What is canine influenza?
Canine influenza is a highly contagious respiratory infection of dogs caused by a novel influenza A subtype H3N8 virus first discovered in 2004.
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2. Where does canine influenza occur?
Canine influenza has been documented in 30 states and the District of Columbia. Canine influenza virus (CIV) has been very prevalent in many communities in Colorado, Florida, New Jersey, New York, and Pennsylvania.
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3. What type of infection does CIV cause?
Similar to influenza viruses that infect other mammals, CIV causes an acute respiratory infection in dogs. It is one of several viruses and bacteria that are associated with canine infectious respiratory disease, or what’s commonly referred to as “kennel cough.” CIV infection can cause respiratory disease by itself or in conjunction with other respiratory pathogens such as distemper virus, respiratory coronavirus, parainfluenza virus, adenovirus, and Bordetella bronchiseptica. It is important to note that influenza virus is not related to parainfluenza virus, and vaccines containing parainfluenza virus do not induce cross-protective immunity to CIV.
Unlike human influenza, canine influenza is not a “seasonal” infection. Infections can occur year round.
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4. Who is susceptible to CIV infection?
Dogs of any breed, age or health status are susceptible to infection. Vaccination with DA2PP or the “kennel cough” vaccine for Bordetella does not provide any immunity to canine influenza.
Canine influenza outbreaks are most likely to occur in facilities where dogs are housed together and there is frequent introduction of new dogs into the resident population. Canine influenza outbreaks have impacted many sheltering facilities and organizations around the country since 2004, including open admission shelters, limited admission shelters, and foster homes or rescue/adoption groups in California, Colorado, Delaware, Florida, Georgia, Kentucky, New Jersey, New York, Pennsylvania, South Carolina, Utah, Virginia, and Wyoming. Many of these outbreaks have resulted in increased euthanasia due to the overwhelming number of sick dogs or the severity of illness.
CIV does not infect people, and there is no documentation that other species have become infected by exposure to dogs with canine influenza. However, ferrets are very susceptible to influenza virus infections in general and should be protected from exposure to dogs with canine influenza (and people with human influenza). We recommend that other species such as cats, birds, small mammals (rabbits and rodents), and pot-bellied pigs also be protected from exposure to infected dogs.
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5. How is canine influenza transmitted?
As with other respiratory pathogens, the most efficient transmission of CIV occurs by direct contact with infected dogs and by aerosols or very fine mists containing virus that are generated by coughing and sneezing dogs. The virus also contaminates kennel surfaces, food and water bowls, collars and leashes, and the hands and clothing of people who handle infected dogs. Influenza virus can remain viable on surfaces for up to 48 hours, on clothing for 24 hours, and on hands for 12 hours. In a shelter environment, CIV is mostly spread by aerosols that move throughout the kennel ward and by staff members that handle infected dogs, then handle other dogs without washing hands and changing clothes.
Important risk factors for introduction of CIV into a shelter population include 1) location in a community where the virus is prevalent, and 2) transfer of dogs from shelters where the virus is prevalent to other shelters, foster homes, or rescue adoption groups. The virus has also been transferred from infected dogs in shelters to pet dogs at home by staff carriage of virus on hands and clothing.
CIV is easily inactivated by washing hands, clothes and other items with soap and water. Quaternary ammonium disinfectants, bleach, or Trifectant will kill influenza viruses in the environment.
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6. What are the clinical signs of canine influenza?
Similar to other respiratory pathogens, CIV causes a transient fever, cough, sneezing, and nasal discharge. Persistent coughing is the primary clinical sign.
Virtually all exposed dogs become infected; about 80% develop a flu‐like illness, while another 20% do not become ill despite being infected. Once CIV is brought into a facility or foster home by an infected dog, all dogs in the facility or foster home should be considered exposed and likely will become infected, whether or not they develop clinical disease.
Influenza virus replicates in the respiratory tract from the nose to the lungs. Virus replication destroys the tissue barriers that normally protect the respiratory tract from bacterial infection, and it may take 3 to 4 weeks for these barriers to regenerate. Therefore, dogs infected with CIV are predisposed to secondary bacterial infections from the nose to the lungs, resulting in purulent nasal discharge, productive cough, and even pneumonia. In addition to secondary bacterial infections, there is an intense inflammatory response to CIV infection; this inflammation persists for several weeks and contributes to the persistence of the cough.
Fortunately, most dogs recover within 2 to 3 weeks without any further health complications.
While the overall mortality rate for canine influenza is low, the secondary pneumonia that occurs in some dogs can be life-threatening without proper treatment, usually in a hospital setting. There is no evidence for age or breed susceptibility for developing pneumonia.
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7. What is the incubation time and how long are dogs contagious?
The incubation period is the time from infection by a pathogen to onset of clinical disease. The incubation period for CIV is 2 to 4 days. Peak viral shedding from the upper respiratory tract starts during the incubation period; therefore, dogs are most contagious prior to showing obvious clinical signs. Dogs with subclinical infection also shed virus and are contagious.
Virus shedding decreases substantially after the incubation period, but continues for 7 to 10 days. Once virus shedding ceases, the dog is no longer contagious. Therefore, it is unlikely that dogs pose a significant infectious risk by 10 days after onset of clinical signs.
Knowledge of the virus shedding times is important to selection of diagnostic tests and to management of an outbreak.
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8. How is canine influenza diagnosed?
Canine influenza cannot be diagnosed by clinical signs because all of the other respiratory pathogens cause similar signs of coughing, sneezing, and nasal discharge. Many sheltering organizations believe that they have canine influenza, when in fact, the dogs are infected with other respiratory pathogens.
The best approach for diagnosis of canine influenza is collection of nasal swabs and serum samples. The swabs are used for detection of virus in dogs at the time they start coughing, and serum samples for detection of CIV‐specific antibodies in dogs that have been ill for more than 7 days. For dogs that have been ill for less than 4 days, veterinarians can collect nasal and pharyngeal swabs for submission to a diagnostic laboratory that offers a validated PCR test for CIV (Animal Health Diagnostic Laboratory at Cornell University, IDEXX RealPCR™ CRD Panel). The PCR tests are very sensitive in detecting virus, but the swabs must be collected during the period of high virus shedding (first 4 to 5 days of infection only). Positive PCR results are most likely correct, but negative results may be “falsely negative” due to swab collection when virus shedding has significantly decreased. In a population of dogs such as in a shelter or foster home, swabs should be collected from sick dogs as well as dogs that have been exposed but are not yet sick. This increases the probability of virus detection.
Serology is the most accurate and reliable diagnostic test for diagnosis of canine influenza in dogs that have been ill for more than 7 days and for confirmation of CIV infection in cases where the PCR test is negative but the index of suspicion is high. Paired acute (sick for <7 days) and convalescent (10 to 14 days later) serum samples are preferred for diagnosis of recent active infection based on seroconversion. Serum samples can be submitted to the Animal Health Diagnostic Laboratory at Cornell University, or the University of Florida College of Veterinary Medicine.
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9. How is canine influenza treated?
Since canine influenza is a viral infection, treatment consists mainly of supportive care based on clinical signs and laboratory tests. Although there is no specific antiviral treatment for canine influenza at this time, a variety of secondary bacterial infections may play a significant role, and antibiotics are indicated for dogs with fever, productive cough, and purulent nasal discharge. Nasal discharge usually responds within days to treatment with a broad spectrum bactericidal antibiotic, but cough may persist for 14 to 30 days. Antitussives (cough suppressants) are not very effective in reducing the frequency and duration of coughing, and should not be used on dogs with productive cough.
Dogs that develop pneumonia based on clinical signs and chest radiographs often require hospitalization for intravenous fluids and parenteral antibiotics. Ideally, a tracheal wash or bronchoalveolar lavage for bacterial culture and antibiotic sensitivity testing should be performed to target the choice of antibiotic. For dogs in which cultures are not performed, empirical treatment with a broad spectrum combination of bactericidal antibiotics to provide 4‐quadrant (gram positive, gram negative, aerobic, anaerobic) coverage has worked well. For more severe cases of pneumonia, oxygen supplementation and nebulization with coupage have been very beneficial.
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10. How can a canine influenza outbreak be managed?
The most important factor contributing to transmission of CIV within a facility is the failure to promptly remove sick dogs from the general population. The magnitude of canine influenza outbreaks has been amplified in those shelters that leave sick dogs in the population and treat them with doxycycline based on the assumption they have “kennel cough” due to Bordetella.
The cornerstones of influenza management strategies are to reduce virus transmission between dogs and reduce virus load in the environment. The overarching goal is to effectively create a break between sick and exposed dogs in the facility or foster home and the unexposed dogs that will be entering. Since most dogs fully recover from canine influenza, it meets the definition of a treatable-rehabilatable disease based on the Asilomar Accords. To reduce virus transmission and virus load in the environment, sick dogs should be promptly isolated in a separate physically enclosed area, and exposed dogs quarantined from newly admitted or unexposed dogs. Staff should care for unexposed dogs first, followed by the quarantined dogs, then the sick dogs in isolation. Staff should wear protective clothing and gloves to care for the quarantined and isolated dogs, including protective footwear such as rubber boots (not booties) to cover the lower leg. Footbaths are not very effective and may provide a false sense of security. Hands should be washed with soap and water after removing gloves.
Each sick or exposed dog should be isolated or quarantined for 14 days to allow for cessation of virus shedding. Following this period, they should not be an infectious risk and can be moved forward in their pathway to adoption.
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11. Is there a vaccine for canine influenza?
The cornerstone for prevention of influenza viral diseases includes reducing the number of susceptible individuals and increasing community immunity. This is best achieved by vaccination. In May 2009, the USDA approved the conditional licensure of the first canine influenza vaccine, developed by Intervet/Schering Plough Animal Health Corporation.
For more information about the vaccine, please see the FAQ for veterinarians.
For more details about canine influenza in shelters, please see Chapter 11 (“Canine Influenza”) in the new book entitled Infectious Disease Management in Animal Shelters, edited by Drs. Lila Miller and Kate Hurley and published by Wiley-Blackwell.