What is Parvo and is your puppy at risk?

When you get a new puppy, it’s hard to focus on anything else. If their soft ears and juggernaut-like energy don’t overwhelm you, fantasies of introducing them to the park and your many friends just might.

Ruth Bader Ginsburg overseeing content creation

But somewhere in the excitement, if you’re lucky, someone will warn you about the lurking threat of parvovirus — a virus that has spread like wildfire during the past year.

Like the SARS-CoV-2 virus (the one responsible for COVID-19), canine parvovirus is responsible for a pandemic, only this one started in the 1980s and affects a wide range of animals, including dogs.

In July of 2020, BluePearl veterinary hospital in the San Francisco Bay Area reported a 70% increase in parvovirus cases among domestic dogs. What caused the spike in cases is unknown — most likely it’s some combination of an uptick in new pet adoptions, a low tolerance for the necessary isolation, and the temporary closing of veterinary clinics.

Regardless of the cause, the spike in cases is alarming. And, while parvovirus has been around for a long time, it’s not easy for new puppy parents to find consistent information about what it is, and how to avoid it.

In the hopes of preventing future cases and helping you enjoy those magical — albeit occasionally frustrating — early days with your pup, here’s what you need to know about canine parvovirus.

What is canine parvovirus (parvo)?

Canine parvovirus (parvo) is a type of virus that infects dogs, cats, and other canines. Infected animals may show no symptoms at all, but the virus is best known for causing diarrhea, intestinal bleeding, and sepsis. If left untreated, canine parvovirus can be lethal.

Given the right treatment, though, as much as 80% of infected dogs can survive the ordeal [1].

How do puppies get parvo?

Puppies can get parvo by swallowing dirt or feces that contain the virus. This is easy to do when they come into contact with an infected dog — especially because dogs tend to meet each other by sniffing their rear ends [2].

Ruth and her best friend, rolling around in the backyard

More likely, though, dogs become infected when they go to an area where infected animals may have recently pooped. This can be places like a park, a friend’s backyard, or a city sidewalk.

Similarly, the virus may be capable of traveling via fomites — crumb-like particles of dirt or other material. If you or another animal visit a place where canine parvovirus is in the environment, it’s possible that your shoes (or their paws) would pick up fomites containing the virus. If your dog chews or licks your shoes, it could ingest fomites containing the virus [2].

At the moment, it’s not known how much of the virus a dog would need to ingest to become infected.

Is parvo in your backyard?

Unfortunately, the answer is: Maybe.

Many believe that parvo can survive in the environment for a long period of time, possibly months or years. In reality, we don’t actually know how long the virus can live in soil, concrete, or other surfaces.

What we do know is based on two studies that were carried out in the 1980s, shortly after parvo was first discovered [3,4]. In the more detailed of the two studies, researchers left parvo infected feces in various environments and measured both the amount of virus in the samples and the virus’ ability to infect a dog after various lengths of time [3].

The results of this study were mixed. When indoors and kept at -4 degrees Fahrenheit (-20 C), the virus could endure for 12 months and retain its infective potential. At room temperature, it could only last 2 months. When outdoors, the virus only persisted for 5 months while in a space that was protected from sunlight and kept moist. Importantly, the virus that was kept outdoors was not found to be infectious.

What does this mean for your puppies risk of catching parvo?

We know from the 1980s’ studies that the virus can, at the very least, survive in the environment if given the right conditions. We also know that parvo has managed to spread into wild animals (having a devastating impact on wolves in Minnesota) [4–11].

The safest interpretation of this data is that your dog’s risk of becoming infected varies from place to place and depends on many factors.

A man narrowly avoids attack from Ruth on an SF beach

In places like cities — especially in San Francisco — where there are many animals, public places are high risk. You can’t know if an infected animal (either a dog or other urban animal) has recently defecated in the area. Given that we don’t yet know how long the virus lasts in these spaces, it’s safest to avoid them until your dog is fully vaccinated.

Outside of cities, however, it may be different. If your yard has been protected from infected animals for years, is fairly dry, and it gets a lot of sunlight, there’s probably a low risk that your dog would find infectious parvo.

Urban wildlife and parvo

As mentioned earlier, canine parvovirus can infect more than dogs. Raccoons, coyotes, wolves, and foxes have all been found to carry canine parvoviruses, sometimes without symptoms [4–11].

Because of this, It’s possible that wildlife in a park (or night time visitors to your backyard) could transmit the virus to domestic animals — either through fomites or their own feces.

Whether the virus is able to transfer from urban wildlife to domestic dogs in a significant way, however, is not yet known.

What are the symptoms of parvo?

Parvo wreaks havoc on dogs’ digestive and immune systems. This causes a number of related symptoms that include [1,2]:

• Sluggishness
• Vomiting
• Loss of appetite
• Inability to keep water down
• Particularly foul smelling, mustard yellow diarrhea (possibly with blood in it)
• Fever
• Tenderness around the dog’s stomach

When parvo infects a dog, it goes after parts of the body where new cells are being made [12]. This is partly why puppies are hard hit by the virus — there are many new cells being made in a growing body.

Two of the hardest hit places in the dog’s body are its digestive tract and bone marrow, both of which have naturally high turnover of cells.

In the gut, parvo kills cells that line the gut barrier which leads to inflammation, vomiting, and diarrhea. Unfortunately, this also creates holes in the gut that allow bacteria — which are normally confined to the gut microbiome — into the bloodstream [12].

Usually when bacteria cross the gut barrier, they’re met with a strong response from immune cells. But, parvo also attacks the body’s immune system by infecting newly born or maturing immune cells( specifically in the thymus and the bone marrow)[12]. As the virus kills nascent immune cells, the body’s ability to mount a defense against invading bacteria is undercut.

With a compromised gut barrier and a weakened immune system, bacteria and other pathogens can invade the body with ease. Septic shock, a cytokine storm, and other lethal events may follow [1,2,12].

Preventing parvo

Fortunately, there are steps you can take to protect your dog.

Ruth in her comfortable swaddle

One of the most important steps is to get your puppy vaccinated. The World Small Animal Veterinary Association (WSAVA) considers parvo vaccination to be essential for puppies [13].

Vaccination usually takes place in repeated doses from the age of 6 to 16 weeks old [13]. There is a delay in the beginning because many puppies have inherited antibodies against parvo from their mothers. However, after 6 weeks, these antibodies decline and eventually go away. In order to keep your puppy immunized against parvo, it will need vaccines. (If the vaccine is given too early, the mother’s antibodies can prevent the vaccine from working.)

It is important to note, too, that young puppies may carry antibodies from their mother, but they are far from safety when it comes to parvo. Young puppies in particular need to be kept away from places where parvo may be.

This brings us to the second big step that you can take: Be extremely cautious in exposing your dog to the outside world. This means sanitizing your shoes and hands when coming into the puppy’s space.

It also means limiting what outdoors space you expose the puppy to. If you live in a city, it’s probably best to quarantine indoors until the dog is fully vaccinated. This is especially true in places like the San Francisco Bay Area, where parvo cases have been on the rise.

Socialization is important for young puppies. If you are going to arrange a playdate, make sure it’s with a dog who has been immunized (or a hygienic puppy), in a space that is sanitized, and that the incoming dog’s paws are cleaned (this is to avoid fomites being brought in).

Have fun and be safe

In those first few months, have fun with your dog and remember to laugh, even when they’re frustrating. Fear of parvo shouldn’t paralyze you, but you should take it seriously and whenever possible, er on the side of caution. (And please, pick up your dog’s poop—it’s hard to know if they’re carrying any viruses that can spread through feces; picking up the poo will help protect other dogs and wildlife).

I hope this is helpful for you, and follow me for content like this. Future posts will take a more narrative approach and explore related topics, such as parvo in wild animals.

References

(There were many more not listed here, but these should get you the information you’re looking for.)

1. Horecka, Kevin et al. “A Decade of Treatment of Canine Parvovirus in an Animal Shelter: A Retrospective Study.” Animals : an open access journal from MDPI vol. 10,6 939. 29 May. 2020, doi:10.3390/ani10060939
2. Nandi, S, and Manoj Kumar. “Canine parvovirus: current perspective.” Indian journal of virology : an official organ of Indian Virological Society vol. 21,1 (2010): 31–44. doi:10.1007/s13337–010–0007-y
3. EJ;, Gordon JC;Angrick. “Canine Parvovirus: Environmental Effects on Infectivity.” American Journal of Veterinary Research, U.S. National Library of Medicine, pubmed.ncbi.nlm.nih.gov/3017161/. — NOTE: This paper is unavailable in electronic copy. I had to base my understanding of this paper on the abstract.
4. Muneer, Mohammad A., et al. “Detection of Parvoviruses in Wolf Feces by Electron Microscopy.” Journal of Wildlife Diseases, vol. 24, no. 1, 1988, pp. 170–172., doi:10.7589/0090–3558–24.1.170.
5. Allison, Andrew B et al. “Frequent cross-species transmission of parvoviruses among diverse carnivore hosts.” Journal of virology vol. 87,4 (2013): 2342–7. doi:10.1128/JVI.02428–12
6. Kelman, Mark et al. “Phylogenetic and Geospatial Evidence of Canine Parvovirus Transmission between Wild Dogs and Domestic Dogs at the Urban Fringe in Australia.” Viruses vol. 12,6 663. 19 Jun. 2020, doi:10.3390/v12060663
7. Calatayud, Olga et al. “Carnivore Parvovirus Ecology in the Serengeti Ecosystem: Vaccine Strains Circulating and New Host Species Identified.” Journal of virology vol. 93,13 e02220–18. 14 Jun. 2019, doi:10.1128/JVI.02220–18
8. Duarte, Margarida D et al. “Snapshot of viral infections in wild carnivores reveals ubiquity of parvovirus and susceptibility of Egyptian mongoose to feline panleukopenia virus.” PloS one vol. 8,3 (2013): e59399. doi:10.1371/journal.pone.0059399
9. Mech, L. David, et al. “DEMOGRAPHIC EFFECTS OF CANINE PARVOVIRUS ON A FREE-RANGING WOLF POPULATION OVER 30 YEARS.” Journal of Wildlife Diseases, vol. 44, no. 4, 2008, pp. 824–836., doi:10.7589/0090–3558–44.4.824.
10. Voorhees, Ian E H et al. “Limited Intrahost Diversity and Background Evolution Accompany 40 Years of Canine Parvovirus Host Adaptation and Spread.” Journal of virology vol. 94,1 e01162–19. 12 Dec. 2019, doi:10.1128/JVI.01162–19
11. Spera, Caroline Giuseppa, et al. “Canine Parvovirus 2b in Fecal Samples of Asymptomatic Free-Living South American Coatis (Nasua Nasua, Linnaeus, 1766).” Brazilian Journal of Microbiology, vol. 51, no. 3, 2020, pp. 1399–1403., doi:10.1007/s42770–020–00293–2.
12. Sykes, Jane E. Canine and Feline Infectious Diseases. Elsevier/Saunders, 2014.
13. Day, M J et al. “WSAVA Guidelines for the vaccination of dogs and cats.” The Journal of small animal practice vol. 57,1 (2016): E1-E45. doi:10.1111/jsap.2_12431
14. Wilson, Stephen, et al. “Influence of Maternally-Derived Antibodies in 6-Week Old Dogs for the Efficacy of a New Vaccine to Protect Dogs against Virulent Challenge with Canine Distemper Virus, Adenovirus or Parvovirus.” Trials in Vaccinology, vol. 3, 2014, pp. 107–113., doi:10.1016/j.trivac.2014.06.001.