Updated November 10, 2022 – In August 2022, reports of a serious illness affecting dogs in northern Michigan swept the country. After an intensive investigation by state veterinarians, canine parvovirus was found to be the cause of the outbreak. Additional research revealed the outbreak occurred in dogs that didn’t have a complete vaccination against the disease.
Canine parvovirus made its first appearance in 1978, when a deadly intestinal disease began spreading like wildfire among dogs, regardless of age, breed or sex. Veterinary researchers at that time quickly mobilized to look for a cause and soon identified the culprit - a tiny intestinal virus that likely arose from a mutation in the feline panleukopenia virus.
An effective vaccine was soon developed and continually refined over the next 10 years. But, as the recent outbreak in Michigan demonstrated, the virus is still very much with us and remains a major cause of death in young dogs. It’s important for owners to keep up to date on the latest information about canine parvovirus and what can be done to protect your dogs from this terrible disease.
Canine parvovirus belongs to a large family of viruses know as parvoviruses, which are some of the smallest of all the known viruses. Many different types of animals from insects to mammals, including humans, can be infected by parvoviruses. However, the viruses tend to be species-specific. Feline panleukopenia virus is a well-known member of this very large family of very small viruses.
How It Spreads
Canine parvovirus is shed in the feces and vomitus of infected dogs. The virus is hardy and can survive in the environment for up to one year. Dogs are infected when they encounter the virus either in infected stool, in the environment (which includes objects such as toys, shoes and bowls) or in the vomit of infected dogs.
The incubation period for the virus is one to two weeks, although there are scattered reports of incubation periods as short as four days. Infected dogs can shed virus for a few days before they become sick and for an additional seven days after they start showing signs of infection.
Canine parvovirus needs rapidly dividing cells for growth, so once the virus enters the body it heads for tissues with rapid cell division and turnover, including the cells lining the intestinal tract, the bone marrow and heart muscle.
Viral invasion causes massive cell destruction and accounts for the most common signs we see in dogs infected with canine parvovirus – diarrhea, vomiting and low white blood cell counts. The destruction of the intestinal cells also makes it easier for the bacteria that live in the gut to enter the bloodstream, resulting in a serious condition known as sepsis. The lack of white blood cells to fight the infection compounds the problem. The disease can spiral out of control, resulting in death.
Diagnosis of parvovirus infection is fairly straightforward. Bloody diarrhea and vomiting in a young pup that is lethargic and not eating are classic signs of the disease. Low white blood cell counts are a good clue pointing toward the diagnosis, especially when coupled with vaccination history.
There are several tests used to confirm the diagnosis and almost all involve detecting the virus in feces. Although there are a few tests that can detect virus in the blood or via an oral swab, fecal tests are by far the most common.
Virus particles can be detected in the feces of infected dogs around three days after infection, and, on average, peak virus shedding occurs four to seven days after infection. There are several quick in-house tests that are very helpful for rapid diagnosis, although occasionally these can miss a case of parvoviral disease. On the other hand, false positive results of these in-house methods are uncommon.
As a backup, some tests are available through large diagnostic laboratories that can help make a diagnosis, especially in ambiguous cases. In most cases, veterinarians will start with a rapid in-house test and then confirm with additional testing.
A common question voiced by owners centers around interference with fecal testing in a recently vaccinated dog. False-positive fecal test results can occur if the test is done within 10 days of vaccination. However, if a pup is sick with signs compatible with parvovirus infection, a positive fecal test in a recently vaccinated puppy is most consistent with true infection.
The opposite situation, a false-negative result in a dog with parvovirus infection, can also occur but is uncommon. False-negative results typically occur when a dog is presented early in the course of the disease and simply isn’t shedding enough virus to be detected by rapid in-house testing. Additional, more sophisticated testing at a large clinical laboratory can help make a more definitive diagnosis in this rare situation.
Treatment and Recovery
Canine parvovirus infections are treatable but can be costly. Estimated survival rates range from 9% in untreated puppies to greater than 90% in puppies treated aggressively in specialty or teaching hospitals. Experts feel that if a patient survives the first three or four days of treatment, chances are good they’ll make a complete recovery.
New studies show encouraging survival rates in dogs treated at home, with survival rates of 75% to 80% reported with dedicated home therapy strategies. Many of these studies reported initial treatment in hospital followed by therapy at home. However, strict isolation protocols and hygiene need to be maintained by owners who have other dogs in the household. The good news is these strategies are helpful when finances are a concern.
Treatment for dogs with parvoviral enteritis mainly consists of supporting the patient while the immune system eliminates the virus. Fluid therapy is a cornerstone of treatment since dehydration is a major problem due to fluid losses from the gastrointestinal tract.
Other therapies shown to be of benefit include the judicious use of antibiotics, medications to control vomiting, and nutritional support administered as soon as possible.
Newer therapies include closer attention to and treatment of abdominal pain as a way to help keep patients comfortable. An intriguing therapy receiving a lot of attention in the veterinary world is the use of fecal transplantation, which showed promise in one study. Probiotic administration also is under investigation, but the jury is still out on whether probiotics improve survival or not.
Although most dogs have no life-long effects after recovery, one recent study looking at survivors of infection found that almost one-half suffered from some chronic gastrointestinal signs later in life (as reported by their owners). The authors couldn’t draw any conclusion regarding why these dogs might have a predisposition to gastrointestinal issues. More investigation is needed to determine what link, if any, exists between a past infection and long-term problems.
Vaccination remains effective at preventing infection. In addition, dogs that survive natural infection likely develop livelong immunity. Other measures to prevent exposure to parvovirus include keeping young dogs isolated until they finish their puppy vaccinations, keeping young dogs in clean environments and making sure puppies and adult dogs with unknown vaccination status complete a full series of vaccination against parvovirus.
How We Are Helping
Morris Animal Foundation played a pivotal role in providing funding to researchers on the front lines of the initial canine parvovirus outbreak and we’re proud of our contribution to help save the lives of millions of dogs around the world.
The Foundation joined with others when the desperate call went out from veterinary scientists to provide research money to explore the cause of this deadly disease. This funding propelled researchers at the Baker Institute for Animal Health at Cornell University to not only identify the canine parvovirus responsible for the outbreak but also create the first effective vaccine.
We’re continuing that tradition with a recently funded project at Cornell University that will be one of the most comprehensive studies of changes in parvovirus ever undertaken. Drawing on their expertise and samples accumulated over the last 42 years, the team will gauge whether commonly used vaccines can still neutralize the current parvovirus strains circulating in the canine population. Additionally, the researchers will study the types of antibodies used to neutralize the virus as a first step toward the development of novel treatments for this terrible disease.