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Parvovirus: What You Need To Know

Spring brings sunny, warm weather which means more dog owners will be hitting the walking trails, parks, and other venues to enjoy time with their canine family members. Exposure to other dogs or areas where other dogs frequent can put your dog at risk of contracting diseases such as Bordetella, Distemper, Parvovirus, and intestinal parasites. In this newsletter, we are going to focus on Parvovirus which is one of the most deadly viruses among puppies and younger dogs.

What causes ‘Parvo’?

‘Parvo’ is the term used to describe the disease caused by canine parvovirus type 2. This virus first emerged in Europe in 1976. By 1987, the parvovirus had caused a worldwide epidemic of myocarditis (heart disease) and gastroenteritis (inflammatory disease of the intestines). Scientist developed the first parvo vaccine in 1979. More than 30 years later, vaccinations for the parvovirus have greatly reduced the frequency in which dogs become infected with the deadly disease, but outbreaks do still occur among those dogs who are not vaccinated or are immunocompromised. It is also known that canine parvovirus type 2 can infect wild animals such as wolves, raccoons, skunks, and foxes. Parvovirus most often affects unvaccinated dogs less than one year of age. Puppies less than 5 months of age are the most severely affected.

How do dogs become infected with the parvovirus?

The parvovirus is shed in the feces of an infected dog. Shedding usually begins shortly before symptoms of the disease occur and can continue up to 14 days after symptoms resolve. Dogs become infected with parvovirus after ingesting infected feces or coming in contact with items or surfaces that are contaminated with infected feces such as toys and bedding. Direct contact with other dogs is not required to spread the virus. The virus is very hardy and can live for months in the environment. A 1:30 bleach solution will kill the parvovirus from indoor surfaces and items. Sunlight and rainwater will help decrease the amount of virus outdoors.

What happens to the body when a dog is infected with parvovirus?

The parvovirus enters the body through the mouth. It first infects the tonsils and lymph nodes, enters the blood stream, then moves to the bone marrow and intestines. In very young dogs, the heart may also be affected.

Lymph nodes

The virus initially replicates inside lymphocytes (a type of white blood cell) that are inside the lymph nodes. After a day or two, these infected lymphocytes are released into the blood stream. Many of these infected lymphocytes are eventually killed. This causes a decrease in these types of cells which are important in fighting off infections.

Bone Marrow

Like most viruses, the parvovirus thrives in rapidly dividing cells such as those in the bone marrow and the intestines. Once inside the bone marrow, the virus destroys young white blood cells that would normally mature into immune cells that help fight infections. The destruction of lymphocytes coupled with the destruction of young white blood cells weakens the immune system and makes it much easier for the virus to invade the rapidly dividing cells of the intestines.


The cells lining the intestines are constantly being shed and replaced by new cells. This intestinal lining aids in the absorption of nutrients, prevents fluid loss, and acts as a barrier to prevent bacteria from entering the blood stream. When the parvovirus invades these cells, it prevents old cells from being replaced with new cells. Eventually, the lining of the intestines breaks down. Nutrients can not be adequately absorbed, fluids are lost leading to diarrhea and dehydration, and bacteria can enter the blood stream. The bodies ability to fight these bacteria is greatly diminished because of the destruction of lymphocytes in the blood stream and white blood cells in the bone marrow.

That are the symptoms of parvovirus disease?

The incubation period of a disease is the time period between exposure and the development of clinical symptoms. The incubation period of the parvovirus is typically 3-5 days but can be as long as 14 days. Initial symptoms typically begin with lethargy and lack of appetite. These symptoms are followed by vomiting and diarrhea. The diarrhea is due to fluid loss through the compromised intestinal lining. Vomiting and diarrhea can quickly lead to severe dehydration. The diarrhea may or may not contain blood. Many dogs develop a fever. Blood work typically reveals a decrease in white blood cells.

How is parvovirus diagnosed?

A veterinarian will consider the dogs age, symptoms, and vaccination status when determining if a parvovirus test is needed. The most common test is the ELISA test which tests the feces for parvovirus. This test is simple and can be done at any veterinary clinic in 15 minutes. These test are very accurate but do occasionally result in a false negative or false positive. The veterinarian may have to rely on other methods to diagnosis such as more complex fecal tests or blood test. Blood test usually, but not always, reveal a very low white blood cell count.

How is parvovirus treated?

There is no treatment that kills the parvovirus. Parvovirus infections are treated with supportive care that includes intravenous fluids for dehydration caused by vomiting and diarrhea, intravenous antibiotics for bacterial infections caused by the compromised intestines, and medications to combat vomiting and diarrhea. Blood transfusions may be beneficial to replace white blood cells. Left untreated, parvovirus can result in death of the dog due to severe dehydration, electrolyte imbalances, and septicemia (infection of the blood). The disease is most severe in puppies less than five months of age and can be difficult to treat. Treatment is generally needed for at least three or more days.

How is parvovirus prevented?

Vaccinations are crucial in preventing dogs from becoming infected with the parvovirus. All puppies should be vaccinated against the parvovirus starting at 6-8 weeks of age. A booster vaccination should be given every 3-4 weeks after that until the dog is 16 weeks of age. Another vaccination should be administered at one year after the last booster and then every one to three years after that. Older dogs with unknown vaccine histories should receive at least two boosters 3-4 weeks apart, then one year later, then every one to three years after that. It is very important that puppies or dogs with unknown vaccine history be isolated from other dogs and areas where other dogs have been present until their vaccinations have been completed.

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