Canine Parvovirus - Parvo in Dogs and Puppies

By J. E. Davidson

Canine parvovirus, also known as CPV-2 or parvo, is a highly contagious viral infection that can be lethal to dogs. It first appeared in the late ‘70's, probably a mutation of the feline distemper virus. Dogs had no natural immunity to the virus and vaccines were not yet available. Many dogs succumbed to the virus but modern veterinary vaccinations, treatment, and the natural antibodies most dogs have developed today make the disease less insidious, and when treatment is begun at the onset of symptoms many dogs will recover.

CPV-2 infection is characterized by severe vomiting and diarrhea, often containing blood. The feces have a telltale odor. The dog will be lethargic and feverish, have abdominal pain, and may refuse to eat. Dehydration and electrolyte imbalances will result from the loss of body fluids, and hypoglycemia from lack of eating may cause electrolyte imbalances (electrically-charged chemicals necessary for normal cell function). The main cause of death is from septicemia when toxins from the bacteria attacking the intestinal system are released into the circulatory system and travel throughout the dog’s body. Dehydration and electrolyte imbalances may also cause shock and eventually death.

Newborn puppies have a natural immunity to CPV-2 when they receive antibodies from their mother’s milk in their first 24 hours. This immunity gradually diminishes over the first two to five months of the puppy’s life. Vaccines given while the puppy still has a high level of natural immunity will be ineffective, and the puppy may have a period of several days or weeks, before vaccinations will be effective, when it is vulnerable to infection. Vaccinations are usually given in a series to lessen the puppy’s risk of infection during this window of susceptibility.

Many adult dogs who come in contact with the virus will show few if any symptoms but may become carriers of the disease. It is unusual for an adult dog who is current on his parvo vaccine and yearly boosters to contract the disease. Puppies less than six months old are the majority of parvo cases. Doberman Pinscher Dogs, Rottweiler Dogs, German Shepherd Dogs and other black and tan breeds seem to be more susceptible to the virus. Diagnosis is made by the dog’s age (usually less than six months), a physical exam and the symptoms present. Parvo symptoms resemble other diseases and are often misdiagnosed. Canine parvovirus is positively diagnosed through a lab test of the sick dog’s blood or feces. A dog showing signs of severe or bloody diarrhea and vomiting should be examined by a veterinarian as soon as possible. Early treatment is vital to the dog’s recovery.

The virus is eliminated in the dog’s feces and is transmitted when another dog orally contacts the virus. CPV-2 is hardy, resistant to high heat or freezing temperatures, and will live in the environment for five months or more. It will live on inanimate objects and can be brought into a home or yard on shoes, clothing, hands, visiting pets, or an automobile. It may also be transmitted by rodents and insects. Household bleach is the only chemical that is able to deactivate the virus.

When a dog comes in contact with the virus, it begins multiplying in the lymph tissue of the nose. The virus moves into the bone marrow where it inhibits the production of white blood cells which fight infection. In the small intestine, the virus attacks the villi, the small projections that absorb fluid and nutrients, and the lining of the intestines may slough off. Dogs with weakened immune systems or intestinal parasites are especially susceptible to intestinal system damage.

The incubation period of the virus is seven to ten days, and the dog will begin excreting the virus in his feces three days after exposure. Dogs suffering from CPV-2 should be isolated from other dogs and their quarters should be cleaned with a bleach solution of one-half cup bleach to a gallon of water. Any gowns or gloves used should be disposed of and shoes should be cleaned with the bleach solution. Treatment consists of replacing the fluids lost through vomiting and dehydration. Severe cases will be given an electrolyte solution intravenously, and milder cases may be given subcutaneous or oral fluids. Antibiotic therapy may be given to treat secondary bacterial infections, and drugs to control vomiting may be administered. If vomiting continues despite the drug treatment, blood transfusions may be needed to avoid an anemic condition. Prompt professional veterinary care is necessary; home treatment of canine parvovirus is very difficult and does not have a good prognosis. Any other dog in the household should be current on its parvo vaccine and kept away from the sick pet and any contaminated areas.

Parvo still continues to be a common illness that kills many puppies. Despite safe and effective modern vaccines, puppies still have several days or weeks when they may be at risk of infection. Avoid exposing your puppy to other dogs or their feces, or places where dogs congregate, such as dog parks and kennels, until the series of vaccinations is complete, and have the puppy examined by a vet at the first sign of symptoms so that prompt, lifesaving treatment may begin if necessary.

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