Canine Parvovirus

Dr Gemma Gaitskell (BVetMed MSc MRCVS, Royal Veterinary College, London)

 

Canine parvovirus is a highly contagious disease which tends to affect puppies or older dogs with a weakened immunity or those which are incompletely vaccinated. It can cause very nasty clinical signs and be fatal. Canine parvovirus is found around the world, but fortunately, vaccination against the virus provides effective protection.

What is Parvovirus?

As the name suggests canine parvovirus (CPV) is a type of virus belonging to the Parvoviridae family. Canine parvovirus is a single-stranded DNA virus, which is extremely tough, and resistant to high temperatures and drying. It can also survive in the environment for long periods of time; possibly even for years. Survival times for the virus are higher at lower temperatures, especially if it is not exposed to light and the environment is sufficiently humid. Many detergents and disinfectants are ineffective against it.

Parvovirus is spread orally and survives in the digestive tracts of dogs. It requires cells that are dividing to in order to duplicate. Canine parvovirus specifically targets lymphoid tissue (tissues which are involved in the production of cells needed for an immune response) in the body and then in the later stages of infection the bone marrow. It is highly contagious.

Canine parvovirus is found around the world and there are different strains of the virus that vary depending on geographical location. The two types of parvovirus that infect dogs are CPV-1 and CPV-2.

• CPV-1 is an avirulent and endemic in the dog population.
• CPV-2 first emerged towards the end of the 1970’s in Australia. It is very closely related to the feline form of the virus. There are different variants of CPV-2 known as CPV-2 a, b and c. The c variant is the latest to emerge.

There are many different types of parvovirus that are specific to the species which the infect. The clinical signs they cause vary depending on the type and species that is affected. Where canine parvovirus is concerned it is thought that cats may be able to carry the virus acting as a source of infection.

How do Dogs Get Parvovirus?

Parvovirus is transmitted orally and spread through the faeces of dogs and cats and can also be found in the environment. It is extremely resistant and survives in the environment for prolonged periods of time, so it is more common for dogs to be infected in this way than by coming into contact directly with an infected dog.

Dogs infected with canine parvovirus often start to spread the virus in their faeces even before they show any symptoms of the disease and this contributes further to the spread of the virus. The risk of infection is greater in multi dog households or environments where there are large dog populations concentrated together, such as boarding kennels or breeding kennels.

When are Puppies at Risk from Parvovirus?

Most puppies are initially protected by the antibodies they receive from their mother’s colostrum for the first few weeks of their lives. However, after this period, their level of immunity then begins to go down and this is a window for infection either before, or in the absence of vaccination. Their susceptibility to the virus can also be increased by other factors such as stress, which can be caused by many aspects in the way a puppy is cared for, such as poor nutrition, weaning, and overcrowding amongst other things, intestinal parasites and other infections.

There is some evidence to suggest that there are certain breeds which may be more susceptible to canine parvovirus. These breeds include English Springer Spaniels, German Shepherds, Rottweilers, American Pit Bull Terriers and Dobermans.

Can Older Dogs Get Parvovirus?

Although less common, older dogs which are unvaccinated, incompletely vaccinated or have a weakened immunity due other illness and disease can become infected with canine parvovirus. Uncastrated male dogs older than 6 months of age also appear to be at a greater risk of developing clinical signs of canine parvovirus than unspayed females.

Symptoms of Parvovirus in Dogs

The severity of the symptoms of parvovirus can depend on the strain of the virus that a dog has contracted. These symptoms usually develop within 5-7 days of infection, but in some cases can take as long as 12-14 days to develop and become apparent. Clinical signs can range from mild diarrhoea and vague, unspecific signs to more severe and obvious signs. Some of these include:

• High temperature, tiredness and unwillingness to eat
• Vomiting and severe diarrhoea, caused damage to the intestinal lining as a result of the severe inflammatory reaction caused by the virus
• Bloody diarrhoea as a result of secondary bacterial infection caused by the damage to the intestine
• Abdominal pain
• Collapse
• Severe dehydration largely caused by the vomiting and diarrhoea

In very young puppies which do not have any immunity, or that are infected before they are born, parvovirus can also affect the heart, causing myocarditis. The syndrome is often known as ‘fading puppy syndrome’. However, this is now much less common, as most puppies receive some level of immunity from their mothers.

Care should be taken with dogs which have recovered from canine parvovirus as even once they have recovered it is possible that the virus may still be excreted in their faeces for up to 8 weeks afterwards although generally this period lasts for around 10 days.

Preventing Parvovirus in Dogs

Vaccination is the mainstay of prevention against canine parvovirus in dogs. Vaccination is very effective at providing immunity against the virus and preventing dogs from developing the clinical signs associated with it. Puppies should be kept away from environments where it is likely that they may pick up the infection before they are vaccinated either from other dogs or from their surroundings.

Puppies should first be vaccinated at:

• 6-8 weeks old
• Followed by, 10-12 weeks old
• And, again at 14-16 weeks

At a year, old dogs should be given a booster vaccination and then this should be repeated every 3 years. If a dog has had the initial course of canine parvovirus vaccines but misses a booster it is not necessary to restart the whole course of vaccinations. A single booster should be sufficient to restore adequate levels of immunity.

If canine parvovirus infection is suspected or confirmed in a dog it should be isolated immediately from other dogs to try and prevent the spread of this highly contagious disease. It is important to seek veterinary advice as soon as possible if your dog shows any of the signs associated with the virus so that aggressive supportive treatment can be provided. Veterinary practices should have facilities where dogs can be cared for in isolation without risking infection of any other patients.

There are strict procedures which veterinarians and nurses will follow to ensure the virus is not spread on clothes or shoes or by being left in the environment at a veterinary practise. If your dog is diagnosed with canine parvovirus your vet will be able to provide guidance on how to best disinfect your home and garden to ensure that you reduce the risk as much as possible of any virus being left to survive in the environment.

Can Parvovirus in Dogs Be Treated?

Dogs can recover from canine parvovirus infection, but the treatment is aimed at improving and relieving the clinical signs caused by the virus and alleviating the adverse effects of the symptoms as much as possible. The types of treatments which may be used include the use of fluids and electrolytes to combat the effects of dehydration and electrolyte imbalances caused by the vomiting and diarrhoea, in addition to antibiotics to try and minimise the possible damage caused by secondary bacterial infections. This treatment needs to be intensive to provide the best chances of recovery.

Canine parvovirus infection can lead to many secondary complications. Usually puppies which survive the first 4 days of the illness go on to make a full recovery. Although canine parvovirus is a very serious disease which causes nasty clinical signs it has a relatively low mortality rate. When dogs affected by canine parvovirus are given appropriate treatment and supportive care the overall survival rate is 68-92%. Dogs which manage to recover from canine parvovirus infection should be left with immunity.

The Importance of Vaccination Against Parvovirus

Vaccination is an essential tool to protect dogs from the severe illness that canine parvovirus can cause. It is an extremely effective and simple means of preventing the spread and devastating clinical signs that the virus can cause.