Parvovirus in Dogs
Canine parvovirus (CPV) is a single-stranded DNA virus that can infect unvaccinated dogs of any age. It has two main variants: canine parvovirus-1 (minute virus of canines) and canine parvovirus-2 (CPV-2). CPV-2 is the most virulent strain, and the primary cause of the severe puppy enteritis that accompanies parvovirus. CPV can affect domestic and undomesticated canine species, in addition to skunks and racoons.
Any unvaccinated dog can get infected by parvovirus, but there are specific breeds that are at higher risk of developing parvovirus.
These breeds include: Rottweilers, Doberman Pinscher, American Pit Bull Terriers, English Springer Spaniels, and German Shepherds.
Canine Parvovirus Evolution
The first of the canine parvoviruses, known as CPV-1, only presented a threat to puppies. Experts believe it mutated from the already well-known feline panleukopenia virus (FPV).
Around 1978, a new variant, CPV-2, emerged. No dogs had immunity against this new variant, which resulted in a CPV epidemic. By 1979, a second virus (CPV-2a) materialized, which was even more aggressive, followed by another variant (CPV-2c) in 2000. When CPV-2 first emerged in Europe, it presented itself through hemorrhagic enteritis (vomiting, bloody diarrhea) among dogs. The first case in the United States was confirmed in 2006, and CPV-2c infections are still prevalent throughout the country. Clinically, infections of different strains of CPV are identical and unable to be distinguished.
How Parvo Works
Vaccinated dams will transfer antibodies against parvovirus to their puppies in the first 24 hours of nursing. These antibodies help protect puppies for the first 6-8 weeks of life, but as the maternal antibodies fade, puppies become susceptible to CPV. If the dam is not vaccinated, puppies could become susceptible at any point.
Puppies and adult unvaccinated dogs contract parvovirus by fecal oral transmission. This means they must ingest the virus from infected fecal material in the environment. The virus can be spread in the environment, directly from infected dogs, or from people as fomites. CPV is highly resistant to heat, cold, and humidity, and can live for long periods of time in the environment. It has been noted to survive at room temperature up to two months, and outdoors for years.
Once exposed to the virus, the incubation period is 5-7 days before clinical signs develop. CPV spreads throughout the body after replication in the back of the throat, within the lymphatic tissue. This virus attacks rapidly dividing cells with a particular affinity for the gastrointestinal tract, bone marrow, and the myocardium (heart muscle tissue). Clinical signs develop based on which cells are being affected.
Symptoms of Parvovirus in Dogs
Clinical signs are predominately based on the gastrointestinal tract.
Signs associated with parvovirus include:
- Decreased appetite
- Diarrhea (which can be bloody)
Some puppies will develop myocarditis due to infection of the muscles of their heart. Ultimately, these puppies can develop congestive heart failure, since their hearts aren’t able to pump blood appropriately.
These puppies will show different clinical signs than puppies with gastrointestinal upset, including:
- Trouble breathing
- Blue or cyanotic mucous membranes
Diagnosis of Canine Parvovirus
Diagnosis of CPV is based on medical history, vaccination status, possible exposure, and clinical signs. All unvaccinated dogs that show gastrointestinal symptoms should be tested for parvovirus. The most common test for parvovirus is the snap ELISA bedside test that provides results in under 15 minutes. The ELISA test has antibodies against CPV and tests for the antigen of CPV to bind to the antibody. When this reaction occurs, the test changes color (pictured below).
The ELISA Test with a positive result.
Due to the new variants of CPV, including CPV-2 a, b, and c, the snap test may show a false negative. Based on clinical signs and vaccination history, a veterinarian may elect to recommend treatment for parvovirus without a positive snap test.
Additional recommended diagnostics include:
- Complete blood cell count (CBC). CPV affects the bone marrow, and decreases in WBC are very common.
- Chemistry panel. This evaluates internal organ function.
- Electrolyte panel. This helps determine if supplementation is needed.
- Fecal analysis. Evaluates for concurrent gastrointestinal parasites.
- Radiographs. Evaluates for other causes of vomiting, including foreign material ingestion or an intussusception.
Additional CPV specific testing includes PCR analysis, viral isolation, and antibody titer monitoring. These tests do not have an immediate turn around and treatment should be pursued while results are pending.
Treatment of Canine Parvovirus
Aggressive treatment is recommended for cases of CPV. Mortality without treatment is 10% in adult dogs and over 90% in puppies. Treatment of parvovirus with supportive care improves mortality and greater than 50% of puppies treated will survive. Treatment is focused on maintaining hydration and keeping up with large volume losses through the GI tract. Although CPV is a virus, preventing secondary bacterial infections with antibiotics is important in treatment. Due to gastrointestinal damage, bacteria can translocate into the bloodstream and cause wide spread sepsis. Managing nausea with antiemetics is important in therapy. Pain medication may also be needed based on GI discomfort.
A normal treatment plan typically includes:
- IV fluids
- Electrolyte supplementation
- Dextrose supplementation (if blood glucose is low)
- Antiemetics (to manage nausea)
- Pain medication if indicated
- Appetite stimulants
Nutritional therapy early in treatment has been shown to have earlier clinical improvement and increased weight gain in puppies suffering from CPV. Puppies that had a feeding tube and started to receive a liquid veterinary diet within the first 24 hours of hospitalization showed clinical improvement quicker and gained weight sooner than a hospitalized group without early feeding. Feeding tubes and early feeding are commonly recommended for parvo puppies, as they tend to not eat on their own when feeling sick.
Plasma or canine albumin transfusions may be needed for severe cases of CPV, related to protein loss from vomiting and diarrhea. Using serum from immunized dogs to transfer immunity has not been shown to be an effective treatment in CPV.
Oseltamivir (TamifluⓇ ) is an antiviral medication that has been experimentally used to treat puppies with CPV. Using oseltamivir early in the course of treatment has been shown to shorten hospitalization in some puppies with CPV. Starting this anti-viral late in the course of disease has not been shown to be beneficial. Availability of this medication often precludes usage, but may be recommended on a case-by-case basis.
Fecal Microbiota Transplant
A newer treatment that has shown to help in puppies with severe diarrhea secondary to CPV is fecal microbiota transplant. This has been done in human medicine to help treat clostridium difficile infections. It consists of transplanting a healthy dog’s GI bacteria into the puppy with CPV to resolve diarrhea. In one study, puppies with CPV had a quicker resolution of diarrhea when compared with puppies that did not receive the fecal transplant.
Outpatient vs. Inpatient Treatment
In 2017, the veterinary school at Colorado State University created an outpatient therapy plan for CPV and evaluated outpatient vs inpatient treatment options. While aggressive in-hospital treatment for CPV is always recommended, outpatient treatment may be a reasonable option for those who cannot afford multiple day in-hospital care. Survival to discharge was 90% for puppies treated with standard in-hospital treatment and 80% survival for puppies treated with less aggressive outpatient therapy. Outpatient therapy included subcutaneous fluid therapy instead of IV fluid therapy, subcutaneous antibiotic and antiemetic injections instead of IV injections, and syringe feeding of a veterinary recovery diet. If patients fail to respond with outpatient therapy, it is recommended that they be admitted to the hospital and given aggressive inpatient therapy.
Prevention of Parvovirus
Vaccination is the best preventative measure against CPV. All dogs should receive a full series of puppy vaccines and adult dogs should have their vaccines boostered to maintain full immunity against CPV. Any breeding dam should be fully vaccinated to ensure that they pass immunity on to their puppies. Puppies should be vaccinated starting at 6 weeks of age and then every 2-4 weeks until 16 weeks of age. At one year, they should receive a booster of their core vaccine and then every three years from then on. These recommendations are based on the 2017 AAHA vaccine recommendations.
Due to the virus’ prevalence and persistence in the environment, unvaccinated dogs should be kept isolated from other dogs and communal dog spaces until fully vaccinated. Any space that has been exposed to CPV should be fully disinfected with bleach or an accelerated hydrogen peroxide cleaner. All unvaccinated dogs should be kept away from environments that may have been exposed to CPV.