Canine parvovirus or CPV, is the infectious agent that causes canine parvoviral enteritis. This condition is often just known as ‘parvo’.
The virus cause acute, very severe enteritis (inflammation of the intestine) and primarily affects young dogs and puppies. However, any dog that is not immune can be infected.
CPV is shed in the faeces of infected dogs – often before they start showing clinical signs of disease, and for about 10 days after recovery. Infection is by nasal contact or ingestion of the virus.
CPV is an extremely robust viral particle, which survives extremely well in the environment. It can survive contact with many common detergents and disinfectants, and is resistant to changes in temperature. It can persist at room temperature for over 2 months, and significantly longer, even for several years, in a cooler outdoor environment. So, direct contact with an infected dog is not required; dogs can become infected by surviving viral particles in the environment.
Parvoviral enteritis presents in a similar way to other forms of gastrointestinal disease in dogs – with vomiting and diarrhoea. However, the severity of the condition is much more marked than most other causes. Affected dogs are often very lethargic and depressed, and sometimes even completely collapsed due to the severity of fluid loss. The diarrhoea they pass is very profuse and bloody. This diarrhoea is a dark brown due to digested blood being passed, rather than the traces of fresh red blood that are sometimes seen with mild enteritis affecting the large intestine. The diarrhoea has a marked foetid and unpleasant odour – even more so than most other forms of diarrhoea.
Infection with parvovirus also suppresses the white blood cell count. This means the body is then even less able to respond to any other infection, which can cause these very poorly pups to become even poorlier.
There is no specific treatment for parvoviral enteritis. Affected dogs require intravenous fluid support to replace water, protein and electrolytes being lost in diarrhoea. They also require antibiotics to prevent secondary infection due to immune suppression, pain relief and medications to control nausea and vomiting. They require extremely intensive nursing, as they can be some of the most vulnerable patients we deal with. Strict barrier nursing is also required to prevent the risk of any other vulnerable patients in the hospital becoming infected.
Disease caused by infection with CPV is extremely serious. The illness is very severe, compounded by the fact that may affected dogs are very young, and therefore far more vulnerable to dehydration and shock. Even with treatment, as many as half of affected dogs may not survive. Survival without intense medical treatment is even less likely.
Preventing infection by providing immunity is extremely important. In their first weeks of life, puppies are protected by immunity passed from their mother, both across the placenta and in the colostrum they drink after birth. Ensuring that the mother is vaccinated appropriately, she is in good health and able to produce enough milk for the puppies, and that all puppies feed quickly after birth will maximise the protection for the puppies in their first weeks.
Puppies should be raised in a clean, safe environment that ensures that they are not exposed to the risk of parvovirus infection. As the immunity from their mother starts to wane, they should be vaccinated against CPV. This is generally as a combination vaccine against CPV, distemper and infectious hepatitis. Generally, vaccintion is carried out from 8 weeks, with a second dose 2-4 weeks later. If puppies are considered to be at increased risk of infection, for example if CPV is known to be common in the area, or puppies were orphaned or not fed by their dam, vaccination can be started earlier, but it still has to finish after 10-12 weeks of age (depending on the vaccine) so extra doses may be required.
It is very important that, until they have received their second dose of CPV vaccine, puppies are not exposed to the risk of infection. They should not be allowed on the ground outside of controlled environments such as their own garden, particularly areas that see a lot of dog traffic such as parks or even the vet clinic. Contact with other dogs should also be limited to those who are up to date on their vaccinations.
Vaccination against CPV is a modified live vaccine. This means that the immune response generated is long lasting. After their puppy series, re-vaccination is recommended at 12 months of age. This is to mitigate against the small risk that the puppy did not respond to their first vaccinations adequately – for example if their immunity from their dam was persisting at that stage.
After this, vaccination against CPV is recommended every three years. This is because studies have shown that in a significant minority of dogs, immunity to at least one of the components of the vaccine starts to decline after this time. Manufacturers recommendations are established to make sure that all dogs remain protected, hence why vaccination is recommended every three years.
In many dogs, good immunity to CPV will still be present when re-vaccination is advised. There is no evidence that re-vaccinating a dog at this stage causes any harm. However, some owners prefer to monitor their dogs’ immunity and re-vaccinate only when it starts to wane. The only way to truly know when this occurs would be to ‘challenge’ the dog with the illness, which would be both impractical and highly unethical. A blood test, often called a titre test, can be used to gain an idea of whether the dog still has immunity against CPV. If this is an option you are interested in, we are happy to discuss it further.