What is parvovirus?
Canine parvovirus (CPV) infection, also known as parvo, is a disease that mostly affects young or unvaccinated dogs. It causes vomiting, diarrhea (sometimes bloody), depression, and anorexia. The disease is potentially fatal.
The most significant canine parvovirus strains are CPV-2, CPV-2a, CPV-2b, and CPV-2c. These strains all cause the same disease, and vaccines protect against all strains.
CPV-2b and CPV-2c are associated with the most severe disease, and are the main strains found in North America. Fortunately, diagnostic tests for parvovirus detect all strains of the virus.
How does a dog become infected with parvovirus?
The primary source of parvovirus is the feces of infected dogs. The dog begins to shed the virus in the feces just before clinical signs develop, and shedding continues for about 14 days after clinical signs resolve. Susceptible dogs become infected by ingesting the virus. After ingestion, the virus enters the tonsils or lymph nodes, where it invades lymphocytes (a type of white blood cell), which then carry it in the bloodstream to many areas of the body, most notably the bone marrow and the lining of the intestine.
Unlike most other viruses, parvovirus is stable in the environment and is resistant to heat, detergents, alcohol, and many disinfectants. A 1:30 bleach solution destroys the infective virus after a minimum of 10 minutes' contact time. Infective CPV has been recovered from surfaces contaminated with dog feces even after three months at room temperature.
"Direct contact between dogs is not required to spread the virus."
Due to its environmental stability, parvovirus is easily transmitted via the hair or feet of infected dogs, or on shoes, clothes, and other objects contaminated by infected feces. Direct contact between dogs is not required to spread the virus. Dogs infected with the virus who show clinical signs will usually become ill within three to seven days of exposure.
What are the clinical signs of parvovirus?
The clinical signs of parvovirus can vary but generally include severe vomiting and diarrhea. The diarrhea often has a powerful smell, may contain a lot of mucus, and may or may not contain blood. Additionally, affected dogs often exhibit a lack of appetite, marked listlessness and depression, and fever. It is important to note that many dogs may not show every clinical sign, but vomiting and diarrhea are the most common and consistent signs; vomiting usually begins first.
Parvovirus may affect dogs of all ages but is most common in unvaccinated dogs less than one year of age. Young puppies under five months of age are usually the most severely affected and difficult to treat. Any unvaccinated puppy showing severe vomiting or diarrhea should be tested for parvovirus.
How is parvovirus diagnosed?
The clinical signs of parvovirus can look like many other diseases that cause vomiting and diarrhea, so diagnosing parvovirus is often challenging. Confirmation of parvovirus infection requires detection of CPV in the stool or CPV antibodies in the blood serum.
There is a simple in-clinic test for parvovirus that screens for this disease. Occasionally, a dog will have parvovirus but test negative for virus in the stool. Fortunately, this is an uncommon occurrence. A tentative diagnosis is often based on a reduced white blood cell count (leukopenia) and clinical signs. However, some clinically ill dogs may not have a low white blood cell count. If further confirmation of infection is needed, stool or blood can be submitted to a veterinary laboratory for additional tests.
How is parvovirus treated?
Treatment for parvovirus includes neutralizing the virus and treating the damage done prior to diagnosis. Canine parvovirus monoclonal antibody therapy (CPMA) prevents parvovirus from infecting cells and causing damage, much like a dog’s own antibodies. It can reduce the clinical signs of the virus but doesn’t address the damage already done by the infection.
The virus causes loss of the lining of the intestinal tract and weakens the immune system by affecting white blood cell numbers. The intestinal damage results in severe dehydration (water loss), electrolyte (sodium and potassium) imbalances, and infection in the bloodstream (septicemia). Septicemia occurs when the bacteria that normally live in the intestinal tract enter the bloodstream; if septicemia develops, the dog is more likely to die. Parvovirus can also cause inflammation of the heart muscle (myocarditis) and can cause neurological disease. Fortunately, this scenario is less common.
A critical part of parvovirus treatment is correcting dehydration and electrolyte imbalances, with the administration of intravenous fluids that contain electrolytes. In severe cases, plasma transfusions may be given. Antibiotics and anti-inflammatory drugs are given to prevent or control septicemia. Anti-nausea drugs are used to inhibit the vomiting that perpetuates the problems.
What is the prognosis?
Most dogs with parvovirus recover if aggressive treatment is used and if therapy is started before severe septicemia and dehydration occur. For reasons not fully understood, some breeds, notably the rottweiler, Doberman pinscher, Labrador retriever, American Staffordshire terrier, and Arctic sled breeds, have much higher fatality rates than other breeds. In most cases, puppies that have not improved by the third or fourth day of treatment have a poor prognosis.
Can parvovirus be prevented?
Vaccination is the best way to protect your dog against parvovirus. Puppies receive a parvovirus vaccination as part of their multiple-agent vaccine series. It is recommended that this vaccine be given at 8 weeks, 12 weeks, and 16 weeks of age.
In some high-risk situations, veterinarians will give the vaccine at two-week intervals, with an additional booster administered at 18 to 22 weeks of age. After the initial series of vaccinations, boosters will be required regularly. If an approved three-year parvovirus vaccine is used, the next booster vaccine will be routinely administered in three years.
Dogs in high-exposure situations (e.g., kennels, dog shows, field trials) may be better protected with a booster every year. Breeding dogs should be up-to-date on their parvo vaccination before breeding, and you may be able to give a pregnant female dog a parvovirus vaccine one week before whelping to transfer higher levels of protective antibodies to the puppies. Talk to your veterinarian about the vaccination schedule that best fits your pet’s lifestyle.
Is there a way to kill the virus in the environment?
Parvovirus is highly stable in the environment, which means it is necessary to disinfect contaminated areas properly. Use a solution of 3/4 cup of chlorine bleach in one gallon of water (133 ml: 4 liters) to disinfect food and water bowls and other contaminated items. Chlorine bleach must be used, because most disinfectants will not kill canine parvovirus – even those that claim to be effective against viruses.
Does parvovirus pose a health risk to my cats or me?
Currently, no evidence indicates that parvovirus is transmissible to humans. CPV2b and CPV2c can infect cats, but infection usually causes less severe signs in cats.
