17th Mar, 2020

Written by Dr Larry Kraizick – Bruma Lake Veterinary Clinic

Canine parvovirus is a viral disease that affects dogs. It was first reported in early 1978. Parvovirus is capable of causing two different sets of clinical problems. The first to be recognised, and the most common, is the “intestinal” form, which manifests with diarrhoea, often bloody vomiting, loss of appetite, depression, fever, and sometimes death.

The second syndrome, the “cardiac” form, occurs in very young pups and is almost unheard of these days. Any age, breed or sex of dog can be affected by parvovirus. However, infection with parvovirus does not automatically mean illness. Several factors such as age, environment, stress, parasites, and the general health status of each individual infected dog can affect the severity of illness.

It’s been reported that black and tan dogs such as Rottweilers and Dobermans, as well as Staffordshire Terriers, Pit Bull Terriers, German Shepherds, Huskies and Labradors, are more susceptible. The degree of illness can range from very mild and not apparent to very severe, often resulting in death. The disease is usually more severe in young dogs (less than one year of age) or very old dogs. Wild canids such as wolves and jackals are also susceptible.


The origin of this virus is unknown
The theory is that it originated by mutation from another parvovirus, probably the feline parvovirus (that’s why it’s sometimes called cat flu), or from another canid parvovirus. Since its first appearance in 1978, canine parvovirus has spread to every continent in the world, probably as the result of the hardy nature of the virus. It’s resistant to extremes of temperature (i.e. it survives freezing and extreme heat) and is unharmed by detergents, alcohol and common disinfectants.


DIRECT TRANSMISSION: This occurs when an infected dog comes in contact with a healthy dog. The virus is found in heavy concentration in the infected dog’s stool.

INDIRECT TRANSMISSION: Virus particles can be easily spread on shoes, clothing and other inanimate objects. Flies, fleas and animals, as well as people, can, therefore, act as mechanical sources of infection.


ORAL PHASE: The disease process begins with the oral ingestion of the virus. The virus initially invades the lymph glands of the throat (lymph nodes and tonsils), where it multiplies. Following multiplication in the lymph glands for one to two days, the virus then enters the bloodstream, which causes the VIREMIA phase (virus in the blood).

VIREMIA PHASE: This phase is characterised by massive amounts of virus in the dog's bloodstream, which in turn is spread to all parts of the body, such as the intestine, bone marrow, spleen, other lymph nodes, and the heart (in young pups less than six weeks of age).

As the infection spreads, the symptoms of the illness become apparent.

CONTAGIOUS STAGE: The final phase in the cycle is the contagious or “shedding” phase. As many as 30 billion parvovirus particles can be shed from the intestines of an infected dog in every ounce of their stool. The highest concentration of virus in the stool is seen when the infected dog is showing signs of illness. A dog can, however, be a source of infection to other dogs without having observable signs of illness. Shedding can occur for at least four weeks after a dog becomes infected with the virus. Chronic “carriers” are not known to exist as in other viral diseases. Parvovirus in the environment can infect susceptible dogs for many months once shed in the stool.


From infection to symptoms usually takes between three to seven days. Here are some of the symptoms and clinical signs you may see in this condition. Early, vigorous treatment of illness caused by canine parvovirus infection is imperative, since vomiting and diarrhoea can lead to dehydration and electrolyte imbalances in the blood and body.

Bacteria in the gut can cause a secondary infection with toxins moving into the blood, ENDOTOXAEMIA, and/or spread of bacteria into the blood causing systemic infection, SEPTICAEMIA. There’s also a chance of one part of the intestine telescoping into another – INTUSSECEPTION.

Cardiac Form (puppies less than six weeks old): This form is extremely rare, because most mothers have antibodies that they pass to the pups in their first milk. This usually provides protection during the first six weeks of life.

Intestinal Form (any age or dog affected, but more severe in puppies):

1.  Listless

2.  Loss of appetite

3.  Fever

4.  Vomiting

5.  Diarrhoea with or without blood (more serious if blood is present)

6.  Severe abdominal pain

7.  Weakness

8.  Collapse



1.  AGE: It’s unusual for dogs over one year old to develop parvo enteritis and very rare (although not impossible) for dogs over two years old to get this disease.

2.  SYMPTOMS: vary from mild to severe.

3.  PARVO SNAP TEST: a stool sample is used for this test. 

4.  BLOOD SMEAR: shows decreased white blood cells early on.

5.  ELECTRON MICROSCOPY: may be used to confirm, but is usually not necessary.

Part II and the treatment of parvo will be featured in April on our Health Matters page!