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Veterinary Public Health Program
313 N Figueroa St. Rm 1127
Los Angeles, CA 90012
Tel (213) 288-7060
Fax (213) 481-2375
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H3N2 canine influenza in Los Angeles County


VETERINARIANS - Please report cases of Canine Influenza herepdf icon 12432

Download our Canine Influenza H3N2 handout - English Espaņol


Overview of Canine influenza H3N2

3 dogs

The canine influenza virus H3N2 (CIV H3N2) usually causes mild to moderate disease in dogs and on rare occasions can also infect cats. This strain of canine influenza was first found in the US in 2015 when it was detected in Chicago and spread to other parts of the country.


Infected dogs are contagious to other dogs 2 days before the start of clinical signs, and for at least 21 days or more afterward, even after they appear healthy. In August 2017, the Veterinary Public Health Program (VPH) learned from The College of Veterinary Medicine at the University of Wisconsin that some infected dogs may shed the virus for 30 days or more.  Transmission of influenza usually occurs through contact with infected respiratory secretions (e.g. coughing, sneezing) as well as from contamination of the environment (e.g. bedding, floors, bowls, collars, leashes). To date, there is no evidence that humans can become sick with canine influenza H3N2.


When CIV H3N2 cases occur locally, VPH's goal is to stop the spread of the virus to protect the animals of our county. The most effective tool in stopping the spread is home isolation of sick dogs for 28 days from the first day of illness and a 14 day quarantine for exposed dogs (to see if they will develop symptoms).  VPH strongly recommends that dogs be vaccinated against CIV H3N2 before they enter boarding kennels, dog day care, dog parks, or engage in dog group activities.  This vaccine is also advisable for dogs that may occasionally encounter other dogs.


Outbreak of Canine Influenza H3N2 cases in Los Angeles County


July 2021 - January 2022 - Outbreak in dogs throughout Los Angeles County

Between July 2021 and January 2022, 1344 total reported cases of CIV H3N2 in dogs in LA County were reported to Veterinary Public Health.  This was the largest outbreak of CIV H3N2 reported in LA County.  Of the cases reported with known exposure, 85% (972/1146) were associated with attending boarding kennels, dog daycare settings, or shelters.  The virus spread rapidly among dogs throughout LA County, affecting at least 68 congregate facilities and 2 animal shelters.  Each facility was contacted, either in person or via phone and email, and given recommendations on how to control the spread.  15% of the reported cases never visited a boarding or daycare facility but were exposed in settings including walks in their neighborhoods, dog parks, groomers, and veterinary clinics.  Sadly, 21 deaths were associated with this outbreak.   To stop the spread of the outbreak, pet owners and veterinarians were strongly encouraged to vaccinate dogs against CIV H3N2 and to isolate sick pets at home for 28 days from the first day of illness.  Pets exposed to confirmed or suspected cases were advised to be kept quarantined at home and observed for clinical signs for 14 days. 


Is it still recommended to have my dog vaccinated for Canine Influenza?

Yes.  It remains important that dogs are fully vaccinated against CIV H3N2 before they enter boarding kennels, dog daycare, dog parks, or engage in dog group activities.  This vaccination is also advisable for dogs that may occasionally encounter other dogs.  The importation of dogs and puppies from canine influenza endemic areas remains constant throughout the year.  Given how quickly the virus spreads and how long dogs are contagious to others, the risk for dogs in LA County to contract the disease will always be present.  Dogs are considered fully vaccinated when at least 14 days have passed since the last booster was administered.  The CIV H3N2 vaccine decreases the severity of clinical disease and viral shedding but does not prevent against infection.  Therefore, herd immunity in the dog community is important for outbreak control.


The epidemic curve for this outbreak with information about boarding/daycare status is below:

chart showing reported numbers of CIV H3N2 cases of dogs in LA County from July 2021 to February 2022



map showing reported numbers of cases of canine influenza in dogs in Los Angeles County from July to December 14, 2021



Pet owners

  • If your pet has symptoms of influenza, keep it away from other animals and contact your veterinarian.

  • Symptoms of influenza may include: cough, fever, sneezing, discharge from the nose, lethargy, and/or loss of appetite.  Some dogs have no symptoms. 

  • Vaccinate dogs against CIV H3N2 before they enter boarding kennels, dog day care, dog parks, or engage in dog group activities.  This vaccination is also advisable for dogs that may occasionally encounter other dogs.

  • The CIV vaccine is two doses, given 3-4 weeks apart.  To provide time for immunity to develop, dogs should wait 2 weeks after receiving the second dose of the vaccine before entering facilities or having contact with other dogs.

  • Canine Influenza & Leptospirosis Vaccine Providers in Los Angeles County and Neighboring Counties

  • If your pet is sick, keep your pet at home for 28 days from the first day of illness - this will help to prevent your dog from spreading the disease to other dogs even after they are fully recovered.

  • If your pet is asymptomatic but was exposed to other sick pets, keep your pet at home for 14 days to monitor for symptoms and then contact your vet if they become ill.

  • To prevent spread of disease, do not let a sick pet share its food bowl, leash, toys, or other supplies with other pets

  • Wash your hands after touching your pet


Veterinarians/Animal workers

  • Do not allow coughing dogs into your common spaces in your practice (lobby, shared treatment room or kennel space, etc.).  Move them immediately into an exam room, or (if not hot outside), have the owner wait in the car with their coughing dog.

  • In any case with a coughing dog, ask about the health of the dogs that spend time near the coughing dog, to determine if there may be an outbreak.  Advise the owner to keep the coughing dog at home.

  • Dogs that interact with other dogs (e.g. boarding, daycare, dog park, groomer) should be vaccinated against CIV H3N2

  • Isolation and quarantine

    • Confirmed or suspected cases - home isolation for 28 days

    • Pets exposed to confirmed or suspected cases - home quarantine and observation for clinical signs for 14 days

  • Report any suspected or confirmed cases of influenza in dogs or cats to VPH using this reporting form.

  • If a case is suspected, use proper isolation measures to prevent infection via direct contact or fomites

  • Recommendations for disinfection and biosecurity available here.

  • Canine Influenza Posters for Veterinary Clinics


Archived Materials

These materials were used during the outbreak and may have outdated information as the outbreak has since ended.


More Information

Canine Influenza - Los Angeles County Department of Public Health

Canine influenza (Dog Flu) - Centers for Disease Control and Prevention (CDC)

Canine Influenza - American Veterinary Medical Association (AVMA)

Outbreak of Canine Influenza H3N2 in the San Francisco and Bay area in Northern California Jan-Feb 2018



Historic Canine Influenza H3N2 Cases in Los Angeles County


March 2018 - Single case in a dog imported from South Korea

In mid-March 2018, a group of 3 dogs were imported from South Korea. One of the 3 had ocular and nasal discharge, and tested PCR positive canine influenza H3N2. The sick dog was placed into 40 days of home isolation, and the 2 exposed dogs were placed in a 14 day home quarantine. An additional dog on the same flight was also quarantined at home for possible exposure.


January 2018 - Single case in a dog in the South Bay area

In late January 2018, a dog in the South Bay area became ill with cough, fever and loss of appetite. The dog tested PCR positive for canine influenza H3N2 by PCR. The source of the infection is unknown, and no evidence of an outbreak was found.


November 2017 - Single case in a dog in the San Fernando Valley

In early November 2017, a veterinarian in the San Fernando Valley area reported that a dog with moderate coughing and mild sneezing had tested positive for canine influenza H3N2 by PCR. The dog had been at a grooming facility during the week before illness, but had no other reported contact with dogs. The dog was placed in home isolation for 40 days, and an investigation was performed. Veterinary practices and animal-related businesses in the immediate area were contacted to find out if they were also seeing cases. There was no evidence of a larger outbreak.


August 2017 - Outbreak in 27 dogs in the San Gabriel Valley

In early August 2017, VPH was notified that a dog in the San Gabriel Valley tested positive for canine influenza H3N2 by PCR. The dog developed a mild cough in late July after boarding at a local kennel. The veterinarian had tested the dog for influenza 2 days later.


VPH worked closely with the boarding facility to contact owners of dogs that were present during the second half of July 2017. At least 26 other dogs developed respiratory-like illness. Only three of these 26 dogs were tested for canine influenza by PCR, and all three were negative. Note that a negative PCR test does not rule out infection, since infected dogs can shed the virus intermittently. During this investigation, VPH learned from the University of Wisconsin that dogs infected with this virus may potentially be contagious for 30 days or longer (unpublished data). Therefore, dogs that had been ill were placed under home quarantine for 40 days after the onset of illness. Healthy animals that had been exposed to the sick dogs were quarantined at their homes for 14 days after last potential exposure. All of the sick dogs recovered and the outbreak resolved. The source of this outbreak was unknown. No direct link was found with the single case in May imported from Asia, however, since they both occurred in the San Gabriel Valley, it is possible that they may have been connected.


May 2017 - Single case in a ill dog imported from Asia to the San Gabriel Valley

In May 2017, a single dog imported from Asia was found to have fever and pneumonia soon after arrival. The dog was taken to two veterinary practices in the San Gabriel Valley area of Los Angeles County. It was kept at home until it appeared healthy, but was not isolated for 40 days. After it appeared healthy, it was taken to local dog parks. This case was not reported until August 2017, three months after the dog's illness.


April 2017 - Single case in a dog from San Bernardino County

In April 2017 VPH was notified of a single dog that had tested positive for canine influenza H3N2. The dog had been ill very early in March when it was brought from San Bernardino County into Los Angeles County. The dog had been kept in isolation for 2 weeks before being placed in a facility with a large group of dogs. VPH worked closely with the large facility to check for further spread of the virus. Very few dogs in the facility were coughing, suggesting that influenza was unlikely to have been on site. With the help of the College of Veterinary Medicine at the University of Wisconsin, VPH performed PCR testing on 10 of the 91 dogs in the facility for influenza - all 10 were negative.  Sixty-nine of the 79 dogs that had been in the facility in March and April were located. Most were healthy, but 14 had developed some coughing. Three of the 14 were serologically tested for exposure to canine influenza H3N2 and were negative, showing they had not been exposed to the virus. 


The Veterinary Public Health Unit of the San Bernardino County Department of Public Health assisted in the investigation by visiting two locations where the sick dog had spent time in that county, and found no evidence of any respiratory outbreaks in dogs.


March 2017 - Outbreak in 35 dogs, most imported from Asia

In March 2017, a local veterinarian reported a potential outbreak of canine influenza H3N2 in dogs imported from Asia. The dogs showed signs consistent with influenza such as coughing, sneezing, fever and nasal discharge. During the initial investigation, laboratory testing by polymerase chain reaction (PCR) confirmed the virus in two dogs.


After a prolonged investigation, a total of 52 dogs exposed to the virus were identified, including 35 sick animals. Of the 35 sick dogs, the virus was confirmed by PCR in 6 dogs and suspected in the other 29 dogs. A total of 62 dogs were placed under quarantine or isolation in 17 locations. The 62 dogs included the 35 sick dogs, plus 17 that were exposed but did not become sick, plus 10 that were living with the exposed but healthy dogs. It is likely that home quarantine played a significant role in helping to limit the size of the outbreak.


Two sick dogs died, however both had been suffering from other unrelated illnesses. Ultimately, all of the other sick dogs have recovered and were released from isolation. The College of Veterinary Medicine at the University of Wisconsin provided assistance by testing samples from several dogs. Samples were submitted to veterinary virologists in order to compare this virus to the canine influenza H3N2 virus that caused a large outbreak in the Chicago area in 2015.



Last updated: July 19, 2022

Public Health has made reasonable efforts to provide accurate translation. However, no computerized translation is perfect and is not intended to replace traditional translation methods. If questions arise concerning the accuracy of the information, please refer to the English edition of the website, which is the official version.
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