After a particularly long and snowy winter for many parts of the country, warm weather is finally here! Unfortunately, the onset of warmer weather also brings with it something we don’t welcome – an uptick in cases of canine parvovirus.
The disease known as “parvo” is caused by a virus – specifically, canine parvovirus type 2, which first appeared in dogs in Europe, Asia, Australia, and the U.S. around 1976. Within 2 years, this virus was worldwide and spreading rapidly, causing an epidemic of severe gastrointestinal illness and killing thousands of dogs.
Researchers determined the virus was a strain of the feline panleukopenia virus that had undergone several mutations, which allowed it to cross over into the dog population. Scientists quickly began working to develop a vaccine, and in 1979, the first vaccination against parvo was developed at Cornell University.
Parvo most often strikes puppies and adolescent dogs aged 6 to 20 weeks, but older dogs can also be affected. Not every dog who is exposed becomes infected. Whether a dog becomes sick depends on the strength of his immune system – but if his immune system is compromised or not fully developed, a specific sequence of events happens as the virus attacks his body.
What Happens In A Dog Infected With Parvo?
After a dog is exposed to parvovirus, there is an incubation period of 3-7 days before the first symptoms appear. During that time, the virus begins attacking his tonsils (lymph nodes in the throat). Once inside the lymph nodes, the virus invades specialized white blood cells called lymphocytes and begins replicating itself. These viral copies then hitch a ride inside the lymphocytes and begin circulating throughout the dog’s entire body via his bloodstream.
Once in the blood, parvovirus targets rapidly-dividing cells such as those in the bone marrow and the cells lining the walls of the small intestine. In bone marrow, the virus destroys the young cells of the immune system, weakening the body’s ability to protect itself and making it easier for the virus to set up shop where it can do the most damage – in the gastrointestinal tract.
Once inside the GI tract, parvovirus begins to destroy the small intestine’s epithelium, which is the lining that helps absorb nutrients from food and creates a barrier against fluid loss and invasion of bacteria from other parts of the body. Eventually the dog’s epithelium becomes so damaged that it begins to break down, and bacteria normally confined to the gut begin to leak out and enter his bloodstream, creating the potential for body-wide infection (septicemia).
As the intestinal epithelium is destroyed, it begins to slough off and cause severe watery, bloody diarrhea, leading to dehydration and electrolyte loss. To make matters worse, by this time the dog’s body is left almost defenseless against the virus because the lymphocytes (which are part of the immune system) that were invaded during the incubation period are ultimately killed off, and his body is hampered from creating new ones due to the virus’s invasion of his bone marrow.
Symptoms of Parvovirus Infection
The first noticeable symptom in a dog with parvovirus is usually lethargy. He may appear depressed, weak, and uninterested in food or play. This stage may be followed by the onset of high fever, vomiting, and severe bloody diarrhea that has a very distinctive, acrid odor.
The odor of parvo diarrhea is unlike anything you’ve ever smelled before, and once you experience it, you will never forget it. In clinical practice, many times we knew if a puppy was infected with parvo just from that smell alone.
Diagnosis of Parvovirus Infection
The most common way to confirm the presence of parvo is by performing a fecal ELISA test. “ELISA” stands for “Enzyme-Linked Immunosorbent Assay”, which is a technology similar to that used in home pregnancy tests. This test can be run by a veterinarian in the clinic in under 15 minutes.
The second half of the parvo diagnosis is a simple blood test. Since parvovirus invades and destroys lymphocytes and bone marrow, it often causes a low white blood cell count. If the fecal ELISA test is positive for parvo and the white cell count is low, you can be fairly certain that the patient is suffering from parvovirus infection.
Treatment For Parvovirus
There is no cure for parvo. Treatment consists mainly of supportive therapy meant to keep the infected dog stable so that his body can eventually fight off the virus on its own.
- Intravenous (IV) fluids to counteract dehydration and electrolyte loss
- Medications to control vomiting, diarrhea and nausea
- Pain medication
- Antibiotics to prevent potentially fatal body-wide bacterial infection
Additionally, blood transfusions may be used in severe cases to boost low white blood cell counts. Blood plasma transfusions may also be given (in addition to the whole blood transfusion) to combat low blood protein resulting from severe diarrhea and vomiting.
All dogs with parvo need to be admitted to the hospital for at least 3-4 days; many dogs stay longer. Since parvo is extremely contagious, patients must be isolated and kept away from other hospitalized patients. While undergoing treatment, patients are completely dependent on IV’s for fluids and nutrition, as they are unable to eat or drink (taking anything by mouth only makes the diarrhea worse).
Age plays a major role in how successful treatment for parvo will be. Extremely young, old, or debilitated dogs are often not able to withstand the overwhelming infection that parvo causes. In most cases, puppies who have not improved by the third or fourth day of treatment usually have a poor prognosis.
When treating parvo, time is of the essence. The sooner a dog receives treatment, the better his chance for survival.
What Makes Parvo Such a Dangerous Disease?
So what is it that makes parvovirus so much more dangerous than other viral infections or diseases?
Parvo is extremely contagious.
It can be spread by direct contact with an infected dog, on surfaces (grass, floors, kennels), via fomites (bowls, bedding, collars, leashes, toys), and by people (on hands, shoes, and clothing).
There are extended periods of viral shedding with parvo.
An infected dog can shed virus in his stool for several days before symptoms appear, and for months after recovery from clinical signs, increasing the chance that other dogs might unknowingly be infected.
Initial signs are easily confused with simple GI distress.
This may cause guardians to delay treatment until the dog is dangerously ill.
Parvovirus is very hardy and can live in the environment for up to a year or longer.
The virus is resistant to heat, cold, humidity, and dryness. The only way to kill it is with 5% sodium hypochlorite household bleach mixed with water in a 1:32 solution (1/2 cup bleach mixed with a gallon of water).
The illness it causes is particularly severe.
Parvo attacks multiple systems in the body; it destroys the inner lining of the intestine, leaving the dog unable to absorb nutrients, and cripples his immune system, leaving him vulnerable to secondary infections.
Parvo also has a cardiac component.
Although less common than the intestinal form, the cardiac form of parvo shows up in puppies under 8 weeks of age who are usually infected by a mother with parvo while they are still in the womb. The virus attacks the puppies’ hearts, leading to myocarditis (inflammation of the heart muscle), irregular heartbeat, respiratory failure, and in almost all cases, death.
Parvo can cause death very quickly.
It’s not unusual for a dog to go from seemingly normal to “crashing” within 48-72 hours, which is a very short window of time to seek treatment.
There is no cure for parvo.
Supportive therapy is the only treatment available while the dog’s body recovers on its own. Though up to 85-95% of treated dogs survive a parvovirus infection, hospital intensive care admission and treatment is required for up to a week, and it’s expensive.
Parvo has a high mortality rate.
Left untreated, the mortality rate for parvo is over 90%.
Parvo can cause long-term or permanent damage.
If a dog survives infection, the virus can cause damage to his digestive system, making it harder for him to absorb nutrients from food. Parvo can also cause long-term kidney and/or liver damage and a weakened immune system, making the dog more susceptible to other diseases.
Parvo can create life-threatening complications.
If the symptoms of the virus weren’t bad enough, parvo can also create a complication called “intussusception”, where the intestine telescopes in on itself and causes a bowel obstruction. This condition requires immediate corrective surgery.
Prevention of Parvovirus Infection
The only way to truly protect your dog against canine parvovirus is through vaccination. The vaccine is administered to puppies and adult dogs as part of a combination vaccine that also protects against several other diseases.
In puppies, the shots are given every 3-4 weeks from the time the puppy is 6 weeks old until the age of about 16 weeks. A booster vaccination is recommended one year later, with boosters every 1-3 years after that. For adult dogs, vaccines may be given less frequently if a titer test (which determines the level of antibodies against parvo present in the blood) is run and it’s determined that the dog has a sufficient level of antibodies.
The good news is that, to date, research has found the currently available vaccines protect against all known strains of parvovirus, and a single vaccine can begin to offer protection within 3-5 days of being given. However, it’s important to remember that until a puppy has received the entire series of shots, he is not fully protected, and should be kept away from places where young puppies or dogs congregate (including pet stores, dog parks, doggie day cares, groomers, etc.) Any socialization with other dogs should be limited to healthy dogs with a well-known vaccination status.
There are other methods to help reduce or eliminate the spread of parvovirus. Any dog who has been infected should be kept away from other dogs for at least 4-6 weeks, and his environment should be thoroughly disinfected with bleach solution (as previously described). Grass and dirt can also be disinfected with bleach solution – yes, it will kill the grass, but it’s probably better to have a temporarily unsightly yard than risk infection of other dogs (or any puppies that you bring home in the future).
Regarding new puppies, the advised waiting period for bringing a new puppy into an area occupied by a dog previously infected with parvo is 6 months – and the puppy should have ALL vaccinations in the series prior to coming into the environment to ensure that he is properly protected.
Parvovirus: Easier To Prevent Than Treat
Thirty-plus years after its first appearance, parvovirus strikes puppies and dogs far less frequently, but outbreaks of this disease still occur every year. The most important thing to remember is that parvovirus is preventable. Vaccination against parvo should not be considered an option – it’s a must.
With proper vaccination, responsible guardianship, diligent hygiene and sanitation practices, and good veterinary care, occurrences of this devastating and potentially fatal disease can be reduced – and hopefully one day, eliminated.
You can download a shareable PDF brochure on parvovirus from the American Veterinary Medical Association.
Have you ever had a dog or puppy with parvo, or known anyone who has? Please tell us about it in the comments below!