Taming canine disease outbreaks in shelters

January 31, 2023

Our Best Friends Network team is hearing from a lot of partners about canine disease outbreaks in shelters lately, so we sat down with Best Friends medical director Erin Katribe, DVM, to get her insight on preventing or managing distemper, parvo and canine influenza.  

Distemper, parvo and canine influenza are pretty common diseases affecting dogs in shelters; can you break down the difference between the three?  

All three of these are important infectious diseases in shelters, and they all have the potential to seriously impact lifesaving. There are some key differences, which will be important when we talk about management and prevention in shelters.

First, parvovirus is nearly exclusively a disease of young dogs and it’s spread through the feces. The virus is extremely hardy in the environment, meaning that without thorough disinfection, it can live for weeks or months in the soil or in contaminated indoor areas of the shelter.  

Distemper and canine influenza are both respiratory viruses that affect both puppies and adults. These two viruses can be spread through direct contact between infected dogs or by airborne spread. They are much shorter-lived in the environment than parvo, though contaminated equipment or staff transmitting virus on contaminated clothing or hands are important sources of infections in shelters.

All three carry a significant risk of serious illness in affected dogs, though influenza does not commonly cause severe disease. Distemper more frequently causes severe disease in young puppies, but adults often get more mild infections. This is contrary to popular belief, which has painted a grim picture for all affected dogs when that is simply not the case. A small percentage of distemper cases will develop neurological signs that can be severe or warrant euthanasia. Without treatment, parvo can absolutely be fatal in puppies, but with treatment, survival rates can be higher than 90%.  

Any shelter trying to reduce the spread of infectious disease should first focus on reducing crowding through such things as recruiting more fosters. What other elements are within shelters’ control that can limit or prevent the spread of disease?

Vaccination on intake is huge. That means vaccinating animals the second they walk in the door, if not before they enter the shelter because full protection for diseases like distemper can take weeks. Even though full protection takes weeks, though, we do start to get some degree of protection rapidly after the very first vaccine in some animals, which makes early vaccination so important.  One of the benefits of doing managed intake is that shelters can start vaccines in advance of animals coming in. They even have an opportunity to get a vaccine on board before those animals physically enter the shelter.

Shelters must also pay attention to the type of vaccines they’re using, as well as storing and handling those vaccines correctly. I recommend modified live vaccines for all diseases for which those are available. Regarding handling, I see shelters all the time that want to be efficient and mix up all of the distemper/parvo combo vaccines each morning for their anticipated intake that day. Unfortunately, those vaccines are no longer good within 30 minutes to an hour of mixing them up. It's no better than injecting water into those dogs.  

When we're talking about our most vulnerable populations, puppies and kittens, protection is really variable. We never know when our vaccines will take effect in those populations, so my advice is start early and vaccinate frequently. Handle all vulnerable animals with extra protection, like gloves, to prevent the spread of disease. Best of all, keep them out of the shelter and in foster care. Not only are there tons of socialization benefits, but that keeps them out of the most dangerous place in terms of infectious disease.

Of note regarding influenza is that while there is a canine vaccine available, because of the type of vaccine, any significant degree of protection always takes several weeks with no benefit early on (not until after the second dose). Most dogs are not residing in the shelter for that long; even if they are, their initial several weeks are spent unprotected. For this reason, canine influenza is not a vaccine we routinely recommend in shelter settings. Those resources could be better utilized getting dogs out through adoption or reducing other risk factors like population density that will have a much more direct impact on this disease in shelters.

What are some of the biggest issues you're seeing around cleaning, disinfecting, handling, etc.?

Oftentimes, shelters may not be using a product that is effective against the diseases that we're worried about. The labels on some disinfectants might say they are effective against some of our more stable viruses, like parvovirus, panleukopenia, and calicivirus, but independent research has shown they may not be. There are great resources online about which disinfectants are effective for specific pathogens; we have some info in our playbook on this topic as well. It’s not just choosing the right disinfectant, however; it’s about diluting it appropriately and allowing it to sit for the full contact time. Even at shelters that are using an effective product, I often see them just eyeballing the concentration when they mix up disinfectants, or they’re not allowing for the full five to 10 minutes of required contact time needed for disinfection.  

You also have to consider the role of fomites. Any object, piece of equipment, or even our bodies can get contaminated with a virus and then transmit it to another animal. Staff must be very careful about handling any of the most high-risk animals. That might mean using gloves and gowns or simply wrapping that animal in a blanket so we're not contaminating the front of our clothing or giving them anything that we might already have been contaminated with. Some diseases are extremely stable in the environment, like parvo, and can live for weeks or months on surfaces if not properly disinfected.

Should shelters be relying on symptoms/signs to manage their population appropriately?

It is absolutely crucial to identify signs of infectious disease early and isolate those animals right away.  This prevents a single case of infectious disease from turning into a full-fledged outbreak.  

Unfortunately, though, that alone is not enough. Animals may come in looking healthy and become most contagious once they break with symptoms. Sometimes, however, they're contagious even before clinical signs start. That can be really, really scary. The bright, happy puppy who is bouncing off the walls at 8 a.m. can break with parvo at noon, and that means the puppy was contagious at 8 a.m. even though he seemed fine (and our staff and volunteers who were hugging all over him have now been spreading virus all over the shelter).  

This can also apply to distemper and influenza, although the healthy-appearing infected dog isn’t as overtly contagious to other dogs as he is when he’s coughing and sneezing; those coughs and sneezes propel large numbers of viral particles many, many feet away.  In this pre-clinical period, though, staff and fomite transmission are hugely important.  

Additionally, there are variances among symptoms for distemper. For example, it’s a myth and a misperception that distemper always causes neurological signs. That’s only true for about 10% of dogs. I often see shelters that don't recognize they have distemper until they have an entire shelter full of coughing, snotty dogs because they think they should be seeing more neurological signs. That's absolutely not the case. If you're a Southern shelter or in areas where this is endemic, I would say it's very likely that you have had it and just don't know if you're not testing.  

Regardless, once shelter staff or volunteers notice an animal who seems unwell, they need to remove those animals to isolation.  

Yes, they need to be isolated to protect the rest of the population from getting exposed. In the event that doesn't happen quickly enough, or if there has been a lot of exposure and we end up with a true outbreak situation, it’s essential to separate populations from one another based on a few other factors.  

First, are they showing clinical signs of disease? What testing results are either pending or completed that show which ones are positive? Dogs with distemper may start demonstrating clinical signs after 10 to 14 days. It can be longer, but most of the time it's two weeks or less. That means we have to wait two weeks and watch any of these exposed to dogs to see if they are going to break with clinical signs. This time frame is a bit shorter for parvo, which takes seven to 10 days, and for influenza, which takes a week or less.

Meanwhile, we have potentially unexposed dogs needing to enter the shelter's care and the worst thing we can do is just put them into that population of exposed dogs. If any of those exposed dogs break with clinical signs and we've put these new healthy dogs in that same room, that same building, that same population – they're all now exposed.  

It almost goes without saying that such separation can be really challenging depending on a shelter’s facilities. What are some of the strategies you use to compensate?

Whenever I manage outbreaks with shelters, I talk about what spaces they have to work with and advise them how to use every possible area. But there is a strong case for implementing limited admission. For example, at Pine Bluff Animal Control in Arkansas, a distemper outbreak meant we had to drastically reduce intake to true emergencies because there was no way to keep that unexposed new population separate from the exposed population.  

I oftentimes hear, “Well, we're an open intake shelter. We have these contracts, so we have to take in dogs.” If you don't have a way to separate new intakes, it's irresponsible to continue to take in animals at the same level and expose them to potentially fatal infectious diseases. And turning any dog away in such circumstances requires full transparency. Shelters must be honest with the public and contract-holders and say, “We do not have a way to safely take these animals; we are putting them at risk if we accept them.”  

Ok, and for those dogs currently in the population who are sick – but whom the shelter has decided to isolate and treat appropriately – what are the currently accepted standards of treating parvo, canine influenza, and distemper?  

One item of note is that all three of these diseases are viral and we do not have any direct treatment for them. All treatment is supportive or aimed at treating secondary bacterial infections. The virus simply has to run its course in an infected dog.  

For parvo, clinical signs typically consist of vomiting and diarrhea, and this can result in profound dehydration. This virus attacks the gastrointestinal tract and the bone marrow, resulting in compromise of the intestinal lining. Combined with a weakened immune system, bacteria that are normal in the GI tract can pass into the blood stream causing potentially fatal sepsis, or body-wide infection. Treatment typically consists of fluid therapy, anti-nausea medication, antibiotics to prevent secondary bacterial complications, and nutrition to help heal the intestinal tract.  

Influenza is characterized by coughing and upper respiratory signs; it rarely causes more severe disease, though it can progress to pneumonia, particularly when other respiratory viral or bacterial infections are present (and coinfections are common in shelters). As with general upper respiratory infections in shelters, antibiotics are often warranted. They will not treat influenza directly but may be effective against other bacterial co-infections or reduce the chances of a bacterial pneumonia.  

The same is true for distemper as for influenza in terms of antibiotics, although distemper also can impact the gastrointestinal tract and the neurological system in some cases. GI signs are treated symptomatically as in parvo, and neurological signs may or may not require treatment depending on severity. Neurological signs can vary from mild, intermittent muscle twitches all the way to severe, long-lasting seizures that do not respond to treatment with anticonvulsant medications. Neurological signs are not common, though, and only occur in about 10% of infected dogs. If severe pneumonia does develop, these dogs may require oxygen therapy, but similar to neurological disease, this is not common.  

While some of the more severe cases of parvo and distemper may be challenging to manage for shelters without extensive hospitals, I would highlight that the less severe cases are absolutely within reach of many shelters’ medical programs. I have implemented parvo treatment wards, including intravenous therapy, in shelters with very limited veterinarian bandwidth, as have other organizations.  

Finally, I think shelters want to know what the role of euthanasia should be in managing these populations.

I was taught in vet school two things about distemper that are absolutely false. One of those is that we don’t have a really effective vaccine, so we were never going to see distemper, and that is absolutely false. I see it all the time. The other thing was that distemper is a death sentence, so if we saw it, we should just euthanize immediately. That’s also absolutely not the case. Many adult dogs (and some puppies) will only get distemper symptoms similar in severity to those in your run-of-the-mill kennel cough; as long as we can hang on to them safely without risking the rest of the population, then why wouldn’t we try to save them?  

Euthanasia, though, is warranted in some cases. For many shelters, this is when there isn’t a safe place to hold them, and fosters are not available. In other situations, euthanasia is absolutely appropriate when disease is so severe it’s not manageable, and euthanasia in those cases is truly to alleviate suffering.  For distemper, this might be for severe pneumonia or for unmanageable seizures. This is uncommon with influenza, although pneumonia is possible. In parvo puppies, it’s when they have overwhelming sepsis that isn’t responding to treatment.  

Even if a shelter is unable to hold on to individual dogs that contract distemper because they can’t hold onto them safely without risking the rest of the population, under no circumstances do I support euthanizing not just the sick animals but all the animals in the shelter. That used to be the approach to infectious diseases. No more.  

Unfortunately, there will often be the need to make some euthanasia decisions. While that is really hard, it's not a wrong decision when we think about risking the rest of the population. If a shelter can’t hang on to distemper-positive dogs for the entire contagious period without risking spread to others, for example, euthanasia may be the best option. But I would encourage any shelter going through an outbreak not to think they have to euthanize all of their positive dogs. Pine Bluff was a great example of that. They didn’t have the resources or the foster base to be able to hang on to all their distemper dogs, but they were willing and able to find fosters for a number of them.

Also, don’t think that distemper dogs have to go into homes with no other dogs. Your other dogs must be fully vaccinated, but the vaccine is highly effective, and we can place positive dogs in homes with other fully vaccinated, adult dogs. I’m a veterinarian and I feel completely comfortable putting distemper-positive dogs in my home and in foster homes with vaccinated dogs. I would not place positive dogs into homes where there are puppies or immunocompromised dogs, however.  

Early outbreaks of influenza resulted in more serious disease than the typical outbreaks we see today.  For this reason, euthanasia is rarely warranted.  In my experience, by the time an influenza outbreak has been identified, most dogs are already exposed or sick, and so euthanasia of all sick dogs would effectively mean euthanasia of the whole population.  In those situations, we simply wait it out and let the virus run its course through the population.  Most dogs will recover without complication.  In the event we identify this pathogen early, we can attempt to separate exposed from unexposed and prevent spread, but it can be difficult in crowded shelter settings.

To wrap it up, if you could impart one piece of information to shelters that are in the midst of a canine disease outbreak, what would you say?

I actually have a few pieces of advice. First, I want shelters that do find themselves in a distemper outbreak situation to consider that even if they can't save all the positive dogs, can they save at least some of them? That’s where progress starts.  

Yes, it’s challenging to find fosters who are comfortable with distemper dogs in their homes. I would also encourage any organization going through an outbreak to invite volunteers and public into the shelter. The most success I've had finding fosters for infectious diseases, including distemper, but also for issues like ringworm, is when the shelters have been able to invite people outside of staff to care for those animals. Those volunteers see that these diseases are not scary, and this can open the door to them considering fostering those populations.

Finally, shelters should be asking for help from experts.  Managing an outbreak can be really daunting and scary and every outbreak is different. If shelters find themselves in such a situation, reach out for help. That's part of what I do in my role, and many shelter medicine academic programs do so as well.  We can help manage your specific outbreak in your shelter and community with the available resources in a way that will save the most lives and achieve the quickest resolution. Managing an outbreak is very different than managing an individual case of disease, and so finding someone with additional training in shelter medicine is crucial.  

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