Parvovirus in dogs: Causes and signs

One of the smallest of the DNA viruses the parvovirus causes infection in animals and man. Canine parvovirus (CPV) causes a highly contagious enteric infection in dogs. The severity of the infection depends on the age of the dog and its breed. Certain breeds such as Rottweilers, American Pit Bull Terriers, Doberman Pinschers and German Shepherds are more prone to infection while other like Toy Poodles and Cocker Spaniels are less so. Older dogs suffer a mild, often asymptomatic, illness while dogs under the age of six months suffer severe infection. In puppies less than 12 weeks the consequences of infection are particularly severe.

The type of parvovirus causing the majority of infections changes over time. Up until 1980, CPV-2 caused most infections. In 1980, an emerging strain CPV-2a replaced this as the most common strain. Strain CPV-2b (first identified in 1986) replaced CPV-2a as the dominant strain and remains the most common strain found in infected dogs. Recently however another new strain appeared - CPV-2c.

A dog catches the infection from contact with another infected dog or from surfaces contaminate by feces or vomit from an infected dog. The virus remains viable in the environment on floors bedding and feeding containers for several months.

Before the introduction of an effective vaccination program neonatal puppies under the age of eight weeks suffered from a frequently fatal form of CPV infection when the virus infected their hearts causing myocarditis. Puppies born to vaccinated bitches have protection during this vulnerable period from maternal antibodies so this form of CPV infection is rare. Enteritis is most common in dogs between the ages of 6 to 20 weeks and 85% of cases of CPV occur in dogs under one year old.

The first tissue infected in a dog is the lymphoid tissue of the oro-pharynx from here the virus spreads via the blood stream to the ileum and jejunum where it infects the crypt cells lining the small intestine. An incubation period of between three to eight days occurs between the dog contracting the virus and the start of signs on infection. The start of signs of CPV infection is abrupt with the dog exhibiting lethargy, loss of appetite, fever, vomiting, and diarrhea.

A dog with CPV gastroenteritis frequently requires rehydration. A dog that is not vomiting and is not to severely dehydrated, may take oral rehydration therapy. Other dogs require intravenous therapy using lactated Ringer’s and 5% dextrose with additional potassium chloride.

Most dogs recover from the infection providing they receive some supportive therapy. Unfortunately, some dogs do not and may die within the first few hours of exhibiting signs of infection. A dog surviving the first two days of symptomatic infection usually recovers. A bland diet for a couple of weeks before reintroducing the animal to its normal food aids recovery.