Canine Parvovirus - What Owners Should Know

What is parvo?

Canine parvovirus, or parvo, is a highly contagious and serious disease. It is caused by a virus that attacks the cells of the intestinal tract and bone marrow. It affects puppies, adult dogs, and wild canids (foxes, wolves, coyotes). In very young or unborn puppies, the virus can also cause damage to the heart. There are many variants of the parvovirus. All variants cause similar clinical signs, but shifts in variants within a particular region can lead to more severe disease for a period of time.

How is parvo spread?

Parvovirus is considered ubiquitous (present everywhere). This means that EVERY puppy or unvaccinated dog is at risk for the disease, even if they never leave the back yard. Higher risk environments include dog parks, groomers, shelters, and other areas where possibly unvaccinated dogs tend to congregate. The virus is very hardy and can survive in the environment for long periods of time. It is readily carried on shoes, clothing, car tires, etc to new areas. It can survive freezing during the winter and many household disinfectants are not able to kill it. Infected dogs shed the virus for at least 2 weeks after exposure. Shedding may begin 2-3 days before the dog starts showing symptoms. Large numbers of viruses are shed, contaminating the environment. Parvo can be transmitted by direct dog-to-dog contact, contact with infected feces, or contact with contaminated environments or people. Contaminated kennels, food/water bowls, leashes, collars, bedding, and clothing can also transmit the virus. For example, a person walking through the park where parvovirus particles are in the ground may carry the virus on their shoes back to their house and expose their puppy to the disease. Alternatively, birds may feed on the food in the bowl of an infected dog down the street, then fly into the yard of a puppy, exposing it to the virus.

What dogs are at risk?

All dogs are at risk. Puppies and unvaccinated adult dogs are at a much higher risk of being infected with parvo. Certain breeds, such as Pit Bulls, Rottweilers, Doberman Pinschers, and Labradors are especially susceptible to parvo.

What are the signs and symptoms of parvo? How does the disease progress?

After exposure, it takes 3-14 days (usually 5-7 days) for signs to develop. Common clinical signs of parvovirus infection include lethargy, loss of appetite, fever, vomiting, and diarrhea. The diarrhea is often severe and bloody. A puppy showing any of theses signs should be seen by a veterinarian immediately. Parvovirus attacks the tissue lining the intestinal tract, which is what causes bloody diarrhea. This also leads to a breakdown of the tissue barrier preventing intestinal bacteria from entering the blood stream. Vomiting and diarrhea, combined with not eating or drinking well, often leads to rapid, severe dehydration. The parvovirus simultaneously attacks the bone marrow, which is where the white blood cells that fight infection are produced. This leads to a decline in the animal’s white blood cells, so they are no longer able to fight off the bacterial infections arising from the compromised intestines. Sepsis, or infection throughout the blood stream, may result. Sepsis and dehydration may lead to death, often within 48-72 hours of onset of clinical signs.

How is parvo diagnosed and treated? What is the prognosis for parvo?

Parvovirus is often strongly suspected in puppies or unvaccinated adult dogs who show the clinical signs of the disease. Diagnosis is made with a fecal swab test that looks for parvovirus particles that are being shed in the dog’s feces. Sometimes very early in the course of the disease, the patient is not yet shedding the virus and the test will show a false negative result. In these cases, retesting after a few days may be needed to confirm the diagnosis of parvo.

There is no specific treatment available that directly kills the virus in infected dogs. Instead, treatment is aimed at stabilizing the patient until the dog’s immune system can fight off the virus. Fluids are given to treat and prevent dehydration. Broad spectrum antibiotics are used to fight the secondary bacterial infections and prevent sepsis. Anti-nausea medications, gastroprotectants, and nutritional support are also provided.

Ideally, parvo patients are hospitalized to receive aggressive treatment and have the best chance of a positive outcome. If hospitalization is not an option, outpatient care can be initiated (i.e. bringing the dog in daily for fluids and injections with good nursing care at home), but the prognosis is not as favorable. With aggressive treatment and hospitalization, the survival rate for parvovirus is 80-90%. Early recognition and diagnosis followed by aggressive treatment are very important to having the best chance at a successful outcome.

Parvo positive patients are highly contagious and should be isolated to help limit the spread of the disease. Proper cleaning and disinfection of areas where the infected dog is or has been is also important (see disinfection section below). Infected dogs shed the virus for 2-4 weeks, so proper sanitation, disinfection and isolation must continue during this time.

After recovery, puppies are often sent home on antibiotics and other medications. It is important that these be given as directed. It is normal for a recovering puppy to have mild diarrhea or not pass any stool for several days as the intestines heal. Diarrhea should resolve after 3-5 days and the puppy should be active and eating without any vomiting. If this is not the case, the puppy should be taken back to the veterinarian for a check-up. Feed small, frequent meals to avoid gorging and GI upset. A special diet or home cooked food (i.e. boiled chicken and rice or fat free cottage cheese and pasta) may have been recommended. Feed this diet for 3-5 days, then begin transitioning back to your regular puppy food. Once the puppy is fully recovered, its vaccination series should be resumed to help protect it from distemper and other diseases.

How is parvo prevented?

Vaccination and minimizing exposure to the virus are critical steps to prevent parvo.

Vaccination against parvovirus is very, very important. Most puppy vaccines also protect against distemper and other serious diseases. If a puppy’s mother was current on her parvo vaccine when she gave birth, the puppy has some immunity from mom early in life. However, this immunity may wear off before the puppy’s own immune system is mature enough to fight off infection. If the puppy is exposed to parvo during this gap in immunity, it may become ill with the disease. In order to protect puppies against parvo and other diseases, a series of vaccines should be given. Vaccines should be administered every 3-4 weeks, starting at 6-8 weeks of age and ending at 16 weeks of age. If a puppy or dog is 16 weeks of age or older and has an incomplete or unknown vaccine history, 2 vaccines should be given 3-4 weeks apart. After this, revaccination should occur every 1-3 years depending on the recommendations of your veterinarian. “Feed store” and other over-the-counter or internet vaccines should be avoided as variability in storage conditions often cause the vaccines to be ineffective. It takes 3-5 days after vaccination for the dog to begin developing immunity.

Until a puppy has received its entire vaccine series, or until an adult dog is up to date on vaccines, their exposure to parvovirus should be minimized as much as possible. Avoid areas where dogs congregate, such as parks, groomers, pet stores, etc. Make sure when boarding or taking your pet for training classes that the establishment is responsibly run and all dogs are required to be current on their parvo vaccines. Use caution when having “play dates” or taking your puppy to visit other dogs and households. Use caution when walking your puppy. Be especially careful not to let the puppy come in contact with fecal material (poop) while walking or playing outdoors. Avoid contact with dogs that are lethargic, vomiting or have diarrhea. Also avoid dogs that have had recent contact with ill dogs. People who are in contact with sick or exposed dogs should avoid handling puppies or unvaccinated adult dogs, or at least wash their hands and change their closes beforehand.

While vaccines are one of the best ways to prevent parvo, they are not infallible. Reasons why a puppy may contract parvo despite being vaccinated include:

- vaccines not given during the appropriate time frame, leading to gaps in immunity

- vaccines being ineffective due to improper storage or administration

- the puppy was exposured to parvo prior to vaccination or during the 3-5 days after vaccination when immunity has not yet developed

- the puppy’s immune system did not respond to the vaccine (this is caused by a genetic anomaly and is primarily found in Pit Bulls, Rottweilers, Doberman Pinschers, and Labradors, though any breed of dog may be affected)

- while today’s parvo vaccines are very, very good, no vaccine is 100% effective.

Therefore, vaccination does not preclude the need to limit a puppy’s exposure to environments or individuals that may be contaminated with the virus.

How can I disinfect for parvo? How long before its safe to introduce a new puppy?

Indoors: Inside, the virus becomes inactive after 1 month. So, wait at least 30 days after the infected dog is no longer shedding the virus (2 to 4 weeks) before introducing a new puppy.

Outdoors: During the winter, the virus is frozen and protected. If the environment was contaminated right before or during winter, wait until after the ground has thawed before applying the following time periods. Shaded areas are considered contaminated for 7 months. Areas with good sunlight exposure are contaminated for 5 months.

Disinfection: Despite label claims on disinfectants, parvovirus remains almost impossible to completely remove from the environment. The goal of cleaning and disinfection is to reduce (not eliminate) the number of active viruses in the environment. The best disinfectant against parvo and other viruses is BLEACH. Mix 1 part bleach with 30 parts water (1/2 cup bleach per gallon of water). This mixture can be applied to bowls, floors, hard surfaces (including walls), toys, bedding, and any other fabric for which potential color change is not important. Wait at least 10 minutes after applying bleach mixture before wiping or rinsing. A steam cleaner can also be used to disinfect carpets and other fabrics. Yards can be watered down to help dilute the virus. The waiting times described above are still recommended before introducing a new puppy to the environment.

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