Parvovirus (parvo) is a clinical condition caused by infection with canine parvovirus. It is extremely contagious and causes severe, often fatal disease in dogs. An infected dog sheds the virus for 1-2 weeks, but the virus can then remain active in the environment for several months and is resistant to many common detergents and disinfectants.
Routine vaccination against parvovirus is recommended for all dogs. Some dogs seem to be more vulnerable to parvovirus, especially black and tan breeds such as Rottweilers and Dobermans, and an additional puppy vaccine may be advisable in high-risk areas. Vaccination is not a guarantee of protection, as not every dog will produce a sufficient immune response to the vaccine. For this reason, vaccinated dogs can still contract parvovirus, though this is uncommon, and their chances of survival are better than in an unvaccinated dog.
Parvovirus attacks tissues with high cellular turnover such as the intestines, lymph nodes and bone marrow. Initially, affected animals may seem lethargic and lack appetite. They may vomit and will rapidly develop diarrhoea. In about 75% of cases, the diarrhoea is very bloody and has a distinctive smell.
Parvovirus prevents production of white blood cells in the bone marrow, which reduces the body’s ability to fight the infection. Diarrhoea can be passed in very large quantities and quickly leads to dehydration and collapsing. If damage to the intestines is severe, bacteria can enter the blood stream and cause a widespread infection known as septicaemia.
Parvovirus is suspected in any case with bloody diarrhoea, profuse diarrhoea in a young puppy, or vomiting and diarrhoea in an unvaccinated dog.
Parvovirus can be detected on a patient-side ELISA test performed on faeces, like a COVID-19 lateral flow test. Much like lateral flow tests, these are not 100% reliable, and a positive result relies on the virus being shed at the time the test is performed. In cases where the test is negative but there is a strong clinical suspicion, the ELISA may be repeated 24 hours later. A more sensitive test, known as a PCR, can be performed at an external lab. This test is much more reliable but can take up to 7 days to get a result, so the ELISA test is often used in the first instance.
Additional tests may be recommended to rule out other conditions that look like parvovirus. These could include general blood tests, imaging of the abdomen (such as ultrasound), or sending a faecal sample to the lab. Blood tests will also provide information about how the disease is affecting the dog, such as measurement of white blood cell count, detection of anaemia and monitoring of electrolytes.
Dogs with parvovirus need intensive care and will always need to stay at the vets, often for several days. Due to the highly infectious nature of the virus, patients will be housed in an isolation unit. Referral to a practice with suitable facilities may be advised.
Unfortunately, there is no treatment that is proven to cure parvovirus infection in dogs. Treatment consists of supportive care to help the body fight the infection, with or without antivirals. Typically, this involves:
Fluid therapy (drip)
Dogs with parvo lose large amounts of fluid in diarrhoea and often can’t keep water down. A drip is used to prevent dehydration and keep blood pressure stable.
Most dogs will not want to eat but require energy to fight infection. Assisted nutrition can be provided by mouth or straight into the stomach via a feeding tube.
There is one antiviral treatment (interferon) available that is licensed for treatment of canine parvovirus. It is given by intravenous (IV) injection once a day for three days. It is very expensive, but studies suggest it can increase survival rates.
Although parvo is a viral infection, damage to the intestines increases the risk of bacteria passing into the blood stream. Antibiotics are used to prevent development of sepsis.
Dogs with parvo are often given anti-nausea drugs, pain relief, and gastro-protectants. They may be given medication to help keep the intestines moving or to maintain blood pressure.
Prognosis for dogs with parvovirus is cautious, as it is considered a fatal disease. Dogs who have received a full vaccine course, and are older than 6 months, have a greater chance of recovery as they tend to be less severely affected. Very young puppies and those who are unvaccinated are unfortunately less likely to recover. Dogs that show a response to treatment within the first 3-4 days are more likely to continue to improve. For dogs who recover from parvovirus, the prognosis is excellent, however yearly vaccinations are still advised to maintain immunity.
Successful treatment of parvovirus is intensive, lengthy and expensive, with dogs often requiring a week or more in hospital. Where finances are limited, or no initial response to treatment is seen, euthanasia should be considered to prevent suffering.
Parvovirus is an extremely resilient virus, and there is a risk that new animals entering the house can become infected even many months later. Where possible, it is recommended to clean with a bleach solution (1 part bleach to 30 parts water), allowing 10-15 minutes contact time before thoroughly rinsing off. Food dishes and toys can be soaked in the bleach solution. Beds, toys and blankets should be put through the washing machine using hot water and bleach. Bleach should not be used on grass or soil but watering these areas combined with exposure to sunlight should reduce the viral load.
Essential annual vaccinations are included in The Healthy Pet Club membership.