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Canine Influenza Is Here to Stay

Dog flu is real -- but it's important not to panic. Here's what you need to know.

Dr. Eric Barchas  |  Feb 9th 2016


Several weeks ago, I treated a very sick puppy. She recently had been adopted from a shelter, and had been noted to cough intermittently on the day of adoption. Since that time, the coughing had grown worse, and the dog became progressively lethargic. She ceased to consume food and water, and she had no interest in playing or going for walks.

An examination determined that the puppy was in bad shape. She was extremely lethargic and dehydrated. She had a significant fever. She frequently coughed, and she produced clear fluid from her nose and mouth when she coughed. When I palpated her windpipe, she began to cough, hard.

Based on her history and the findings of my exam, there was a high likelihood that she had a contagious disease. The owners were worried; their other dog had been exposed to the puppy. Would the other dog get this sick, too?

Photo of Dr. Eric Barchas by Liz Acosta.

Photo of Dr. Eric Barchas by Liz Acosta.

Another question was left unasked. It is a human instinct — and not our most admirable instinct in my opinion — to try to find someone (other than oneself) to blame for every unfortunate event that occurs in life. Perhaps the owners of the puppy were mature enough not to even wonder whether the puppy’s sickness was the fault of the shelter. At the very least, they did not ask.

So, let’s answer the second question first. Was this situation the fault of the shelter? Absolutely not. I am very familiar with the shelter in question, and it is one of the best-run facilities anywhere. However, the conditions a puppy experiences in any shelter — even the best — make her especially susceptible to respiratory pathogens.

The puppy had been a stray. Prenatal care likely was nil. The neonatal care, if any, that she received also no doubt was subpar. She became separated from her mother at a young age. She wound up in a shelter. The poor prenatal and neonatal care made her weak. The stress of her (up to now) unfortunate life made her even weaker. She became the perfect target for an opportunistic pathogen. Shelters, and the world, are full of opportunistic pathogens. Sometimes these things just happen, and they’re nobody’s fault.

Would the other dog in the house get that sick, too? Almost certainly not. However, there was potential for him to catch the bug. It would depend upon what pathogen was sickening the puppy. The other dog likely had been vaccinated against the worst thing it could be: canine distemper virus. Many other possible pathogens, such as canine influenza and any of the myriad viruses and bacteria implicated in canine infectious respiratory disease (CIRD, known colloquially as kennel cough) could infect him. However, since he was healthy and well cared for, he likely would not face a life-threatening situation such as the one confronting the puppy.

Of the many possible causes for the puppy’s symptoms, I was most worried about canine influenza. It can strike hard and fast, and it is extremely contagious. If the puppy had influenza, she was at risk of death from secondary pneumonia. What’s more, she could pose a risk to the other patients in the hospital.

Canine influenza has only been a known disease since 2004. The original canine influenza started as an equine virus that mutated and infected dogs. This virus, called H3N8, caused a large outbreak at the time that it came on the scene.

Sleeping puppy by Shutterstock.

Sleeping puppy by Shutterstock.

In 2015, a second strain of canine influenza, H3N2, started an outbreak in the midwestern United States. This strain is believed to have originated in Asia; it is genetically similar to a variant of influenza found in China and Korea. Some have speculated that it may have been brought into the USA by a dog rescued from a meat farm in South Korea. The extent of the outbreak currently is unknown, and with the ease of travel we enjoy today, there are concerns that the virus could rear its head anywhere at any time. Furthermore, it has been recently discovered that H3N2 is shed by dogs for much longer than other variants. This means that they may spread the disease for weeks after they no longer have symptoms. This was the type of influenza I worried about in the puppy.

Dogs may become infected with a third type of influenza virus as well: the dreaded “swine flu.” This variant, H1N1, is a human (and porcine) influenza virus, and it may be possible for dogs to catch it from their owners. However, dogs do not appear capable of spreading the virus to humans or other dogs.

Vaccines are available for both H3N8 and H3N2. The H3N2 vaccine is very new and, although field studies have shown it to be safe, it has not yet been truly battle tested for efficacy. All respiratory disease vaccines, including those for both canine influenza variants, do not prevent infection with the virus. At best, they reduce the severity and duration of the symptoms. What’s more, vaccinated dogs can still shed the virus and therefore spread the disease.

Canine influenza, unlike human influenza, does not appear to be seasonal. Infection rates are similar year-round.

A recent study calculated the mortality rate of influenza in dogs at 0.5 percent — on average, five out of every thousand infected dogs die. In general, only the most vulnerable individuals, such as the puppy in question, face a significant chance of mortality. Symptoms of influenza include coughing, lethargy, fever, and poor appetite. Some dogs with influenza become very sick; most have mild to moderate symptoms; some become infected and shed the virus without suffering any symptoms whatsoever.

Two technicians and I gowned up and began to implement our sanitation and isolation protocol to protect other patients from possible influenza. Blood tests did not show any significant problems. X-rays were compatible with early pneumonia. A DNA sample was collected from the back of the puppy’s throat to test for a number of the most common respiratory pathogens in dogs.

I am happy to report that the puppy rapidly rebounded with fluid and antibiotic therapy. The DNA test showed that she did not have influenza; rather, she had suffered an opportunistic pneumonia from a pathogen that usually only causes mild coughing. Her prognosis is excellent in her loving new home.

Although we dodged a bullet with the puppy, canine influenza is here to stay. How should dog owners respond? As with any scary situation, it is important not to panic. Remember that most healthy dogs do not become morbidly ill from the disease. If your dog is at high risk of infection (such as dogs that are exposed to lots of other dogs in their everyday life), or is at high risk of complications from infection (elderly dogs and dogs with other heart or respiratory problems are at special risk), then the vaccines might be appropriate.

As I have said countless times on Dogster, the best solution is to find a good vet who will talk about your dog and her lifestyle in order to make specific recommendations.

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