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Veterinarian Technician August 2012 (Vol 33, No 8)

Canine Influenza: What You Should Know for Educating Clients

by Allison L. Smith, BS, CVT

    CETEST This course is approved for 1.0 CE credits

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    Canine influenza virus (CIV) is relatively new and causes a highly contagious respiratory infection. The first reported case of canine influenza was in 2004 at a greyhound racetrack in Florida.1–3 Since then, cases have been reported in 30 US states.1,2 CIV is thought to be a mutation of the equine influenza virus (H3N8).1,2 Although CIV was originally discovered in greyhounds, cases have since been reported in other purebred and mixed-breed dogs at various life stages.2

    CIV is spread through contact with respiratory secretions or contaminated surfaces and inhalation of airborne particles. The virus can be aerosolized for up to 20 feet.4 Fomites, such as bowls and toys, are a common way for the virus to spread in places where multiple dogs are housed. The virus can also be passed from an infected dog to a healthy dog on the clothing and shoes of staff members. If an infected dog coughs or sneezes, the virus can remain in the air for an extended time before settling on surfaces.2 The virus can remain infectious on surfaces for up to 48 hours and on clothing for up to 24 hours.1 Once a dog is infected with the virus, it takes approximately 2 to 4 days for the dog to begin exhibiting clinical signs.2,5 The optimal shedding time for the virus is often during the incubation period, before clinical signs develop.2,4 This means that a seemingly healthy dog can spread the disease to other dogs before the owner realizes that the dog is sick. Viral shedding drastically declines within the first 4 days that the patient exhibits clinical signs. However, viral shedding can continue for up to 10 days after clinical signs develop.1 In 20% to 25% of cases, dogs have not exhibited clinical signs while shedding the virus.1

    Clinical Signs

    Because CIV infection is relatively new, dogs have not developed natural immunity to it. Therefore, exposure to CIV results in clinical signs in 80% to 90% of dogs.1,2,5 Dogs infected with CIV can have general respiratory clinical signs, including lethargy, fever, nasal discharge, and coughing. In mild cases of infection, clear nasal discharge quickly changes to mucopurulent discharge.1,2 A dry, nonproductive cough or a soft, moist cough can also be seen. A low-grade fever (up to 104°F) may be seen in dogs with mild infection.1,2,5

    Some dogs may develop a more severe form of influenza that results in pneumonia. Dogs at risk for severe CIV infection can be very young, very old, already immunocompromised by another disease, and/or malnourished (poor body condition).4 Up to 20% of infected dogs develop severe CIV infection,2 resulting in a fever >104°F and an increased respiratory rate (i.e., >50 breaths/min).1,2 Even young, healthy dogs can develop severe influenza, and patients that exhibit the clinical signs can die if they are not treated quickly.


    A thorough patient history is important when dealing with a suspected case of influenza. Clinical signs, along with determining the patient’s exposure to other dogs, especially group housing, can alert veterinary staff to the possibility of exposure to influenza infection. Being aware of recent influenza outbreaks in the area is important when pursuing a diagnosis for a patient with respiratory signs. A complete blood count, a chemistry panel, and thoracic radiography are beneficial diagnostic tools. In patients with viral infection, leukopenia can be seen on a complete blood count, or leukocytosis may develop with secondary pneumonia.2,5 Thoracic radiographs can show a bronchointerstitial pattern and/or consolidation of lung lobes.2,5 If a secondary bacterial infection is present, culture and sensitivity testing of various areas in the respiratory tract can help determine appropriate antibiotic therapy.2,4 Viral culture for antemortem diagnosis is not recommended by the American Veterinary Medical Association. More definitive laboratory tests for influenza include serology, a polymerase chain reaction test, an antibody test, and an antigen test.1,2,4 These tests can detect CIV and rule out other respiratory illnesses. However, it takes time to obtain these results, and supportive care should be started quickly to alleviate clinical signs.


    Other than supportive care, there is no specific treatment for canine influenza. Antibiotics can be used to prevent or treat secondary bacterial infection.4 The antibiotic choice should be based on culture and sensitivity testing results.2 For patients that develop pneumonia, hospitalization is usually required along with appropriate isolation procedures. These patients often benefit from intravenous fluids, oxygen therapy, and nebulization. Caution should be used when administering antitussives. In patients with a productive cough, antitussives are contraindicated.2,3 The length of treatment depends on the severity of the illness. A cough can persist for 10 to 21 days, even with medical treatment.1


    Nobivac Canine Flu H3N8 (Merck Animal Health) and Vanguard CIV (Pfizer Animal Health), which are killed virus vaccines that protect against the H3N8 virus, have been approved by the US Department of Agriculture for vaccination against CIV. For Nobivac Canine Flu H3N8, two doses given 2 to 4 weeks apart have been shown to produce a fivefold increase in a dog’s immunity to the virus2; after the initial vaccination series, a booster is administered annually. Vanguard CIV requires two doses that are administered 3 weeks apart, and a booster is administered annually. Dogs vaccinated with Vanguard CIV that contract the virus have a shorter viral shedding period: an average of 0.4 days compared with an average of 5.2 days in unvaccinated dogs.6 Vaccinated dogs that become infected with CIV develop clinical signs that are less severe than those seen in unvaccinated dogs.2,4

    Veterinary practices should perform risk assessments of all canine patients to determine whether vaccination is appropriate. Dogs that should be vaccinated against CIV include those that go to kennels, grooming or daycare facilities, or shows or those that are exposed to dogs that have recently been group housed.

    It is important to practice good hygiene and isolation procedures to prevent the spread of CIV between dogs. People should wash their hands with soap and water before and after handing infected dogs or coming into contact with their saliva, urine, feces, or blood. Wearing a gown while handling an infected dog or changing clothes afterward can help prevent transmission of the virus to a healthy dog.1 In addition, all surfaces and objects that an infected patient has contact with should be cleaned.


    Although CIV was originally transmitted to dogs from horses, there is no evidence that it can be spread to humans.1 According to the Centers for Disease Control and Prevention, there have been no reported cases of transmission of the H3N8 strain of influenza from dogs to humans.7

    It is important to know what (1) signs to look for in CIV-infected dogs and (2) precautions to take to limit the spread of disease. Veterinary professionals are responsible for educating clients about CIV infection to help prevent, recognize, and treat it.

    Downloadable PDF

    1. American Veterinary Medical Association. Control of canine influenza in dogs: questions, answers, and interim guidelines. AVMA Public Health. Available at http://www.avma.org/public_health/influenza/canine_guidelines.asp. Accessed April 2012.

    2. Intervet/Schering-Plough Animal Health. Canine influenza (dog flu) is an important illness that poses an emerging threat to all dogs. Available at http://www.doginfluenza.com/professionals/Overview.asp. Accessed April 2012.

    3. Miller L, Hurley K. Infectious Disease Management in Animal Shelters. Ames, IA: Wiley-Blackwell Publishing; 2009:173-180.

    4. King L. Infectious respiratory disease in dogs. Paper presented at: University of Pennsylvania School of Veterinary Medicine; March 2, 2011; Philadelphia, PA.

    5. Tilley L, Smith F Jr. Canine influenza. Blackwell’s Five-Minute Veterinary Consult: Canine and Feline. 4th ed. Ames, IA: Blackwell Publishing; 2007:198-199.

    6. Pfizer Animal Health. An Emerging Pathogen: Canine Influenza. December 2010.

    7. Centers for Disease Control and Prevention. Key facts about canine influenza (dog flu). http://www.cdc.gov/flu/canine. Accessed May 2012.

    References »

    NEXT: Cardiopulmonary Resuscitation: Administering Fluids, Oxygen, and Drugs

    CETEST This course is approved for 1.0 CE credits

    Start Test


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