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Parvovirus in dogs

Parvovirus causes perhaps the most severe gastroenteritis in dogs, with a high fatality rate, but is entirely preventable by vaccination.

Parvovirus kills dogs because of severe gastroenteritis with vomiting, bloody diarrhoea, profound dehyrdration, shock and septicaemia. It is highly contagious and the virus remains infective in the environment of up to a year. Vaccination is essentially 100% effective – puppies need a course of vaccinations from 6 weeks of age and adult dogs need regular boosters. Vaccination is cheap protection against this horrible disease which causes terrible suffering for dogs and very expensive treatment for owners.

The name means “small poison(ous particle)”, but this tiny virus causes big problems. Parvovirus in dogs is rightly to be feared. It causes a very severe gastro-enteritis with a high fatality rate. The initial symptom is generally vomiting, combined with lethargy and failure to eat; diarrhoea, which is usually bloody, rapidly follows.  Untreated, most dogs die in a few days from dehydration and septicaemia. They suffer with abdominal pain, and the intractable vomiting and diarrhoea cause profound dehydration and shock, followed by death.

Parvovirus causes much more severe and long lasting diarrhoea than other viruses because it attacks the cells from which the lining of the gut grows. Most other viruses just attack the most superficial cells, and these are rapidly replaced.  It takes a number of days for the gut to grow a new lining after damage by parvovirus.

Treatment is successful in up to 90% of cases, and recovered dogs are normal and suffer no long term effects. It involves intensive care with intravenous fluids, antibiotics, anti-vomiting drugs, and sometimes plasma or a blood transfusion. Regular blood tests are needed to ensure maintenance of the electrolyte balance. Nowadays we start to feed these dogs early, instead of “nil by mouth” for extended periods. The dogs must be nursed in isolation because they are highly infectious to other (unvaccinated) dogs. This all makes treatment expensive, but it is certainly worthwhile for many dogs.

The virus is highly infective, liberated in very large numbers from the gut, and long lasting. Infection is by contact with infected faecal material. The virus can survive in the environment for months to years, although it is inactivated by sunlight and some disinfectants (such as bleach). It is clearly impossible to effectively disinfect a contaminated house yard, and very difficult even with concrete dog pens. Dogs can carry the virus on the coat for extended periods. We can easily transfer the virus on our skin and clothes

The incubation period is 4-14 days. Dogs start passing the virus about 3-4 days after exposure, generally before symptoms develop. They excrete the virus for 7-10 days – most dogs have stopped excreting the virus by the time they recover from the diarrhoea.

Vaccination is highly protective –almost all dogs which develop parvovirus are unvaccinated or inadequately vaccinated puppies. Puppies less than 6 weeks of age are protected by antibodies absorbed from their mother’s first milk (colostrum) in the first 24 hours of life. This protection interferes with vaccination, and wanes from around 6 to 12 (to 16) weeks. This is why we vaccinate puppies a number of times starting at 6 weeks of age. The best, modern, vaccines can “overcome” this maternal immunity at 10 weeks of age at the latest. Older vaccines needed more doses and a final, 16 week dose. Although modern vaccines are more expensive, they are more rapidly protective. This also means that puppies can get out and socialise earlier (from about 12 weeks).

As with many other infections, physical cleaning (removal of “fomites”) is critical – most disinfectants work poorly in the face of physical residues of vomit or faeces (etc). People in contact with suspect parvo cases should wash thoroughly with soap and water, and change their clothes before touching other (at risk) dogs. Clothes should then be laundered (hot water if possible) and dried in sunlight. Specific anti-parvovirus disinfectants are generally too aggressive for skin, so cleaning is the basis of care. Parvovirus cases should be nursed using disposable gowns, overshoes and gloves – these must not leave the isolation area.

Dogs which are “up to date” with their vaccinations are at virtually no risk. Note that many modern vaccines only need a “parvo” dose every three years, but check with your vet! Canine parvovirus cannot be spread to other species, although there are parvoviruses of cats (feline enteritis), pigs (reproductive disease) and humans – the fascinating “slapped face” disease (erythema infectiosum), typically in pre-school aged children.