Is Parvovirus Becoming More Common in British Dogs?

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Parvovirus – for those in the veterinary industry, the name of this virus causes dread. A dangerous, unpleasant and deadly virus of young dogs, Parvovirus outbreaks can send panic through a local area. Thankfully, though occasional outbreaks do occur overall cases remain rare. Despite this, Parvovirus seems to be on the minds of a lot of dog owners right now so today we will investigate whether Parvovirus is becoming more common in the UK and why this might be the case?

Canine Parvovirus Overview

Most dog owners will have heard of “Parvo” – but how much do you know about it?

What is Parvovirus?

Canine Parvovirus (CPV) is a virus that infects mainly dogs (though can infect foxes, wolves, cats and other mammals – it cannot infect humans). The original virus, CPV-2, was first identified in the 1970s. This variant split into CPV-2a and CPV-2b variants which have mostly replaced the original CPV-2 virus. More recently in 2000, a third variant, CPV-2c was identified which more significantly differs in its structure from the other two strains. There is also the rarer CPV-1 that causes similar disease. As of this article, there have not been any other reported strains identified. The closely related feline panleukopaenia virus (FPLV) infects only cats.

How Does it Spread?

Parvovirus is mainly spread via faecal-oral contamination. An animal infected with Parvovirus releases the virus into their faeces, which may then be directly ingested by another animal, or contaminate the environment. Dogs shed the virus from around 4-6 days after being infected, and shed for weeks even after the illness has passed. Some animals become infected and show no symptoms but still can infect other animals. The virus can also rarely spread from infected pregnant mothers to their unborn pups.

Once inside the body, the virus infects rapidly dividing cells in the lymph nodes, intestines and bone marrow, eventually killing the cells. This damage is what causes disease. Very young puppies are most vulnerable to disease if they did not receive any natural immunity from their mother (if she was unvaccinated for example), or once this maternal protection wears off around 6-14 weeks old. Adult dogs that have never been vaccinated are also more vulnerable to Parvovirus. There is also some evidence that purebred dogs are more susceptible to Parvovirus than other dogs, particularly Rottweilers and Dobermans. Having other diseases like intestinal parasites may make the disease worse.

What Symptoms Does it Cause?

The most common symptom associated with Parvovirus infections is profuse watery bloody diarrhoea, due to intestinal cells being destroyed. This damage allows secondary bacteria to enter the blood stream which can cause a massive immune response (Systemic Inflammatory Response Syndrome, SIRS). These conditions lead to anorexia, dehydration, vomiting, a temperature, increased heart and respiratory rate, depression, collapse and even death. Dogs can also be at risk of an intussusception, where the intestines roll in on themselves, leading to a dangerous blockage. In young dogs mortality rates can be as high as 90% if left untreated.

How Do Vets Diagnose Parvovirus?

Parvovirus can often be presumptively diagnosed based on its symptoms. However, Parvovirus must be distinguished from other diseases because Parvovirus can easily infect other dogs and precautions need to be put in place to prevent this.

The quickest way to diagnose Parvovirus is via a SNAP test in the clinic which takes a couple of minutes, and rapidly detects viral proteins from a rectal swab sample. However, depending how much virus the animal is shedding, only 56% of positive-cases are detected via this method, meaning it has a high false-negative rate (saying the dog is negative when actually they are positive). Repeating the test a few days later once the viral shedding has increased may help diagnosis. A more accurate test is detecting viral DNA in faeces via PCR. It has a much higher sensitivity (low false-negative rate) than the ELISA. However, this test can take a few days to run, and is not commonly found in first-opinion practices. The limitations of these tests mean that many vets must assume an animal with symptoms of Parvovirus is infected until proven otherwise, and start treatment immediately.

Other test results may give clues to diagnosis, but are not exclusively seen with Parvovirus alone. These include altered white blood cell counts (often low due to destruction, but can be increased due to secondary bacterial infection), low protein, low glucose and low platelets.

How is Parvovirus Treated?

Most cases of Parvovirus require intense treatment to fight the effects of the virus and secondary bacteria. This commonly includes intravenous fluid therapy to combat dehydration, antibiotics, anti-emetics to prevent vomiting, pain relief, and nutritional support. Throughout all of this, strict hygiene and barrier-nursing is required to prevent the virus spreading around the vet practice and to other animals. Hospitalisation can be needed for a few days up to two weeks. With hospitalisation, the survival rate can rise to as high as 90%.

Various new drugs and treatments are also in development that targets the virus itself, though few are commonly available yet. One notable drug is a monoclonal antibody (a very specific antibody) given early on in infection to improve survival rates; another is a drug that temporarily enhances the antiviral actions of the immune system

Can Parvovirus Be Prevented?

Thankfully, yes, the majority of dogs can be protected from Parvovirus with a very effective vaccine. It is recommended that all puppies receive a vaccination from 6-8 weeks of age, then again around 10-12 weeks old. Some vets recommend a subsequent injection around 16 weeks of age. The immunity can then be maintained by a booster vaccine at 6-12 months old, and then is every three years subsequently. The most common type of vaccine is a modified live virus vaccine, meaning there is virus present in the vaccine that has been modified to not cause disease, but still create an immune response. Remember that vaccinating your puppy not only protects them, but other dogs too, especially those that cannot be vaccinated due to medical reasons.

Some, probably most, dogs will retain some immunity longer than 3 years, so titre tests are available to determine if an individual dog is one with a longer “immune memory”. However, reliable titre tests are often as expensive as, or even more than, the cost of a booster vaccine. – Ed.

Is Parvovirus Becoming More Common in the UK?

Thanks to widespread vaccination, Parvovirus is much less common in the UK than it used to be. But are cases on the rise? Anecdotally, this author has found Parvovirus brought up more frequently by owners worried their dog has the disease over the last few months. Why might this be? Is there truth to the claim?

Understanding of the Disease

We believe that a lot of the reason why Parvovirus concerns owners is a lack of understanding of the disease. This isn’t unreasonable – the disease is not that common and most owners are not medically trained. However, this author has found many owners of dogs with mild cases of diarrhoea, with or without blood, ask if Parvovirus is a possibility. In almost all cases this is unlikely, given the symptoms are mild, but this author believes it reflects only a surface level understanding of the disease; owners may be aware Parvovirus causes diarrhoea with blood, thus any appearance of these symptoms could be Parvovirus in their minds. Educating owners, such as with articles like this, may help minimise these fears.

The Media and Perception

It is likely that, as with many negative stories, the media amplifies the perceived incidence of Parvovirus. A quick Google search for ‘UK Parvovirus’ reveals dozens of local news stories from recent years detailing cases of Parvovirus in an area, often with a comment from local vets about the disease. Now while we are sure that the media has the public’s best intentions at heart, and want to inform pet owners so they can take precautions, it is quite easy for a person to stumble on multiple articles in quick succession (especially as online algorithms tend to pages forward related to those a person has previously shown interest in), meaning they might believe the numbers of cases of Parvovirus to be higher. Combined with people sharing these stories on social media, or even sharing their own stories if their pet had Parvovirus (or even an unrelated disease), and what is actually a handful of cases spread over half a decade looks more like widespread outbreaks.

As with all media, read past the headline and ask yourself where is the article from, when was it posted, and what does the article want you to think.

A New Strain?

Another rumour this author has heard more than once is regarding a new strain of Parvovirus that evades vaccines, meaning even dogs vaccinated against Parvovirus may be vulnerable to infection. We couldn’t find any evidence of this, and all sources maintain the above variants of CPV are the only ones currently known. CPV-2c is the newest strain, formally identified in Italy in 2000 (though samples from 1996 in Germany were also confirmed to be CPV-2c after this) – it has been proposed that this strain may cause more severe disease in dogs.

It was thus concerning when reports came out of dogs falling victim to this strain of Parvovirus despite being vaccinated. The biggest worry was that the vaccine used in these dogs was not as effective against CPV-2c. However, there is not conclusive evidence for this yet. Studies have shown in perfect laboratory conditions that the vaccines do protect dogs against CPV-2c but there aren’t any studies long-term in real-world settings. Nevertheless, the consensus from researchers and vaccine manufacturers is that normal Parvovirus vaccines do protect adequately against CVP-2c. Any individual cases of dogs getting ill from Parvovirus despite vaccination may be down to vaccinating them too early for it to be effective, or in older dogs with weakened immune systems. For UK readers, CVP-2c is the least common strain of Parvovirus in the country too, so that is lower down the list of concerns for us.

Actual Numbers and Vaccination Rates

It is hard to get concrete numbers of Parvovirus cases in the UK, as cases are not always reported. The most recent numbers we could find were from an emergency vets reporting a 129% increase in the number of cases during the first 3 months of 2021. However, these dates are critical, as they fall right in the middle of the COVID-19 pandemic, where the number of puppies being bred and sold were skyrocketing, while the numbers of owners visiting their vet for routine appointments (including vaccinations) had plummeted. These factors combined to create a population of young dogs with little to no protection against Parvovirus, leading to increased numbers of cases. We haven’t been able to find any concrete numbers, but we suspect that these case numbers have dropped now that owners are able to get their dogs vaccinated more easily after the return to normality.

But this does raise an interesting point that vaccination rates are likely correlated with the numbers of Parvovirus cases. Unfortunately, vaccine hesitancy, the reluctance of someone to have a vaccine, is increasing both in animals as it is in humans. We believe that if there is any real increase in the numbers of Parvovirus cases, this is likely to correlate with the reduced uptake of vaccinations in dogs. We hope we have so far explained why vaccination is so important to dogs, but we wanted to investigate this further in my next article discussing vaccine hesitancy.