Parvovirus in Dogs
Parvovirus in dogs is a highly contagious acute viral infectious disease. This page takes a deeper look at parvovirus, such as how it is spread and the two forms of canine parvo.

Dog parvo, or canine parvovirus (CPV), is caused by a strain of parvovirus (CPV2) which was first described in the 70s. It is highly contagious and can bring on acute symptoms rapidly.

The virus tends to attack rapidly reproducing cells, such as the cells of the GI tract lining.

Parvovirus can affect dogs, wolves and foxes; but it cannot be spread from dogs to humans.

Although canine parvovirus can affect all dogs, puppies between weaning and up to six months of age are most vulnerable.

Once infected, a puppy has a 50-50 chance of survival, even with medical treatment. The critical period is the first four days of infection. If timely treatment and care is given to an infected puppy, and if the puppy can get past the first four days, he will probably live and become immune to the virus.

If left untreated, the puppy will die in 2 to 3 days.

Spreading of Parvovirus in Dogs

Unlike the distemper virus, the canine parvo virus is not enveloped in fat, making it extremely hardy in the environment and very hard to kill.

The parvovirus is spread by oral contact with the feces of infected dogs.

The virus is shed in extremely large amount in the stools and vomitus of infected dogs for up to several weeks after infection.

The parvovirus can also be passed from yard to yard by birds carrying the virus on their feet or by people carrying the virus on clothing or shoes.

Fecal matters containing the virus can also be carried on the infected dog’s hair and feet, as well as on contaminated crates.

As you can see, it is very easy for a dog to be exposed to the parvo virus, but not all dogs exposed to the virus will get infected.

Whether an individual dog gets infected or not depends primarily on several factors, such as:

  • the age, overall health, and breed of the dog;
  • the amount of virus that the dog has been exposed to;
  • whether the dog has been vaccinated against the disease, or whether he has previously been infected and is therefore immune to the virus.

Two Forms of Parvovirus in Dogs

There are two general strains of the parvovirus: intestinal and cardiac.

Intestinal Parvo

This form of parvovirus is the most common form of the dog parvo virus.

Dogs are infected through oral contact with the parvovirus that is found in contaminated feces or soil.

Once the dog has been exposed to the virus, it replicates in the lymphoid tissue in the throat, and then infects the bloodstream and attacks cells of the lining of the digestive tract, lymph nodes and bone marrow.

Cardiac Parvo

Cardiac parvovirus is more deadly but quite rare. It affects mostly neonatal puppies.

The cardiac strain attacks the heart and causes myocarditis (inflammation of the heart and damage of the heart muscle). It can kill rapidly with few or no symptoms.

Usually, a puppy with cardia parvo will have breathing difficulties, followed by congestive heart failure, and sudden death.

Symptoms of Parvovirus in Dogs

Signs and symptoms of parvo in dogs can be unspecific and can range from mild to serious depending on such factors as the dog’s age and health condition.

For example, many adult dogs may have been exposed to the parvo virus but they may not show any symptoms at all.

As mentioned above, there are two forms of canine parvovirus (intestinal and cardiac). Since intestinal parvo is the more common form, let’s look at the signs and symptoms of this form of parvo.

After an incubation period that lasts for an average of 4 to 5 days, the following acute parvo symptoms will show:


In intestinal parvo, the parvovirus attacks the cells in the dog’s intestinal wall, causing gastrointestinal problems such as vomiting.

Usually the infected puppy vomits uncontrollably and will continue to retch. Even as the stomach contents have been thrown up, the puppy will continue to vomit yellow bile.


Another GI tract problem and classic parvo symptom is profuse diarrhea, with very foul-smelling stool. Initially, the stool may contain yellowish or greenish mucus. Later on, the stool will become runny and dark-brown – an indication that the stool contains old, not fresh, blood.


Dehydration develops rapidly when the dog has recurrent diarrhea and vomiting. Dehydration can quickly cause shock and result in death. In fact, many dogs with parvo die of dehydration.


A dog with parvo may appear depressed. A normally active and playful dog may turn into a weak, lethargic, and depressed dog who does not want to play.

This depressive state is caused by low blood sugar and dehydration as a result of diarrhea and vomiting.


Some dogs with parvo do not develop a fever; whereas others may have a high fever of up to 106°F (41.1°C).

Abdominal Pain

In addition to diarrhea, some dogs with parvo may have severe abdominal pain (indicated by a tucked-up belly).

Appetite Loss

A dog sick with parvo will lose his appetite and show no interest in food.


Suspect parvovirus if your puppy has a sudden onset of vomiting and diarrhea. Take him to the vet immediately for diagnosis and treatment.

See Treating Parvo for more information.