Avian Flu Diary: LA County Health Dept. Reporting Canine H3N2 Outbreak

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Yesterday marked the two-year anniversary of the announced arrival to North America of an Asian H3N2 canine influenza virus (see April 2015 Midwest Canine Influenza Outbreak Due To `New’ Korean H3N2 Virus).

We'd been tracking this emerging canine virus - first in South Korea, then in China - with considerable interest for several years.

Prior to 2004, dogs were thought largely immune to influenza A infection. All of that changed when an equine H3N8 virus mutated enough to adapt to a canine host, and began to spread among greyhounds in Florida more than a dozen years ago (see EID Journal article Influenza A Virus (H3N8) in Dogs with Respiratory Disease, Florida).

A 96% match to the equine H3N8 virus, this canine H3N2 was believed to have jumped directly from horses to dogs without any reassortment.

Since then canine H3N8 has been sporadically reported across much of the United States. It is considered a `canine specific’ virus, and there have been no reports of human infection.

A few years later (2007) we saw an avian H3N2 virus also adapting to dogs in Korea (see Transmission of Avian Influenza Virus (H3N2) to Dogs). Analysis showed that the HA and NA genes of the A/canine/Korea/01/2007 (H3N2) isolate were closely related to those identified in 2003 from chickens and doves in South Korea.

While the canine H3N8 virus has remained fairly stable over the last decade, the same can't be said for the Asian H3N2 virus. We've seen numerous reports coming out of China and Korea suggesting the canine H3N2 may be adapting to other hosts, and continues to reassort with other avian and human flu viruses. Including:

A Canine H3N2 Virus With PA Gene From Avian H9N2 - Korea

Canine H3N2 Reassortant With pH1N1 Matrix Gene

Virology J: Human-like H3N2 Influenza Viruses In Dogs - Guangxi, China

Interspecies Transmission Of Canine H3N2 In The Laboratory

And a year ago (April 2016) we also learned that dogs infected with Asian H3N2 shed the virus for 2 to 3 times longer than with H3N8 (see JAVMA: Prolonged Viral Shedding Of Canine H3N2), which may account for its rapid spread across the country.

Like canine H3N8, we've seen no evidence that this H3N2 virus currently poses a threat to human health. Like all flu viruses, however, it continues to evolve, and so there no guarantees that couldn't change over time.

In 2014, in Study: Dogs As Potential `Mixing Vessels’ For Influenza, we looked at a study in the Journal of Virology, that tested the ability of different influenza strains to infect, and replicate in, canine tracheal tissues. A press release from the American Society for Microbiology warned:

Evolution of Equine Influenza Led to Canine Offshoot Which Could Mix With Human Influenza

WASHINGTON, DC – June 19, 2014 – Equine influenza viruses from the early 2000s can easily infect the respiratory tracts of dogs, while those from the 1960s are only barely able to, according to research published ahead of print in the Journal of Virology. The research also suggests that canine and human influenza viruses can mix, and generate new influenza viruses.

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The CDC's Q&A on canine flu reads:

Can canine influenza viruses infect humans?

To date, there is no evidence of transmission 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.

However, influenza viruses are constantly changing and it is possible for a virus to change so that it could infect humans and spread easily between humans. Human infections with new influenza viruses (against which the human population has little immunity) are concerning when they occur. Such viruses could present pandemic influenza threats. For this reason, CDC and its partners are monitoring the canine influenza H3N8 and H3N2 viruses (as well as other animal influenza viruses) closely. In general, canine influenza viruses are considered to pose a low threat to humans.

All of which brings us to a press release from the Los Angeles County Health Department regarding a recent outbreak of the Asian H3N2 virus among dogs in their region.

H3N2 canine influenza in Los Angeles County, 2017

VETERINARIANS - Please report cases of Canine Influenza here

Download our H3N2 Canine Influenza handout - English Español

Update

As of April 7, there have been 34 sick dogs reported, including 5 confirmed by laboratory testing (PCR) and 29 suspected. The sick dogs, plus an additional 8 healthy but exposed dogs, are under quarantine or isolation in 10 locations around Los Angeles County. So far there are no cases reported outside of these locations.

Samples from the several dogs have been submitted to veterinary virologists in order to compare this virus to the H3N2 canine influenza virus that caused the outbreak in dogs in Chicago in 2015.

Background

In March 2017, H3N2 canine influenza was identified in dogs in Los Angeles (LA) County. Most of the dogs were imported from Asia and seen by a veterinarian upon arrival into LA County. The dogs showed signs consistent with influenza such as coughing, sneezing, fever and nasal discharge. A total of 27 dogs were sick with the disease and treated with supportive care. Final testing of two dog revealed a strain of canine influenza (H3N2) commonly found in Asia, further testing is pending. Most of the dogs have recovered.

H3N2 canine influenza usually causes mild 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 caused a large outbreak in the Chicago area that spread to other parts of the country. Infected dogs start shedding the the virus 2 days before the start of clinical signs, and for 21 days or longer afterward. 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 H3N2 canine influenza.

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As this virus if far more prevalent in Asia - particularly among farmed dogs (see China: Avian-Origin Canine H3N2 Prevalence In Farmed Dogs) - and continues to evolve, it is important to compare any recently imported viruses to those that arrived two years ago.

Interestingly, last summer, in PLoS One: Evidence of Subtype H3N8 Influenza Virus Infection among Pet Dogs in China, we saw signs of H3N8 infection in Asian dogs, although researchers weren't able to definitively say whether our North American canine H3N8 was imported into China, or if avian (or possibly equine) H3N8 jumped species barriers in China.

While we primarily monitor birds and swine for emerging flu viruses, we can't discount the possibility of being blindsided by a virus coming from another host species. Dogs and cats, being companion animals, are viewed as being in unique positions to serve as a bridge between novel viruses in the wild and humans.

Some previous dog and cat flu related blogs you might be interested in, include: