Parvovirus in Dogs

Laurie Anne Walden, DVM

Photo by C. E. Price

Canine parvovirus is highly contagious among dogs. Infection causes severe illness and is often fatal in dogs that do not receive intensive treatment.
 
Risk Factors
Parvovirus infection is most common in puppies that have not yet completed their initial vaccination series and in adult dogs that are not fully vaccinated against parvovirus. A recent outbreak of parvovirus in Michigan highlighted how quickly the virus can spread, especially in dogs in group housing like animal shelters. All dogs are at risk of infection, but whether a dog becomes ill depends on the dog’s level of immunity to the virus.
 
Transmission
Canine parvovirus type 2 (the version responsible for illness) infects domestic dogs and some wild animals, such as foxes, coyotes, wolves, and raccoons. The virus is shed in feces and resists drying, heat, and cold, so it stays in the environment for a long time.
 
Dogs are infected by ingesting even a tiny amount of feces that contains parvovirus. Dogs can be infected by contact with an infected dog or with contaminated feces, surfaces, or objects. People who have handled infected dogs or contaminated objects can carry the virus on their hands or clothes and infect other dogs. Wild animals might be a source of environmental spread of parvovirus. Animals that have no symptoms can be carriers.
 
Effects on the Body and Signs of Infection
Canine parvovirus targets the lining of the small intestine, bone marrow, heart, and other organs. Destruction of the intestinal lining causes vomiting, bloody diarrhea, dehydration, loss of barrier protection against bacteria, and inability to absorb nutrients. Some infected animals develop intussusception, a potentially life-threatening condition in which a section of intestine folds into itself like a telescope. White blood cells (part of the immune system) are produced in the bone marrow, so infected animals have low white blood cell counts and impaired immune function. Because of decreased intestinal barrier protection and immune function, infected animals are at risk of septic shock caused by bacterial infection. Young puppies sometimes develop myocarditis, or inflammation of the heart muscle.
 
These are some of the signs of parvovirus infection:

• Low appetite
• Low energy
• Vomiting
• Diarrhea, usually bloody and severe
• Painful belly

 
Death can occur within 3 days after symptoms begin.
 
Diagnosis
Parvovirus infection is often suspected on the basis of the patient’s symptoms, age, and vaccination history. Tests of fecal samples confirm the infection. A rapid test at a veterinary clinic is convenient but sometimes returns a false result, which can delay the diagnosis (this was the case with the outbreak in Michigan). A polymerase chain reaction (PCR) test at a diagnostic laboratory is accurate but takes longer. A blood test showing a low white blood cell count supports a diagnosis of parvovirus, especially in a sick puppy still awaiting a PCR test result.
 
Dogs with parvovirus infection usually also receive other tests, such as x-ray imaging or ultrasound of the belly.
 
Treatment
For most dogs with parvovirus infection, the best chance for recovery is hospitalization for intensive care very soon after symptoms start. No antiviral drug that kills parvovirus is currently available, so treatment consists of measures to reverse dehydration, minimize vomiting and diarrhea, prevent bacterial infection, reduce pain, and restore nutrition. Intensive care for parvovirus infection can be expensive.
 
Prognosis
Most dogs that receive prompt intensive treatment in the hospital survive. Most dogs that are not treated die. For dogs whose owners can’t afford hospitalization, the success of outpatient treatment depends on the individual dog (illness severity and immune status), type of treatment, and ability of the owners to provide care at home.
 
Prevention
The parvovirus vaccine is effective and is one of the core vaccines recommended for all dogs. This vaccine is part of the initial series of puppy vaccines. Puppies need to receive the entire initial vaccine series to have the best chance of being protected. The current recommendation is for puppies to be vaccinated every 2 to 4 weeks from the ages of about 6 weeks to at least 16 weeks. The vaccine is given again 1 year later and then every 3 years throughout the dog’s life. Some dogs never mount an immune response to vaccination (this is not common). Vaccinating all dogs helps keep puppies and vulnerable adult dogs safe.
 
Limiting a puppy’s exposure to other dogs and to places where other dogs gather reduces the risk of infection. However, this approach can hinder a puppy’s social and emotional development. In general, puppy classes and establishments that have protocols to reduce disease transmission (like requiring vaccines, proper disinfection and hygiene, and isolation of sick dogs) are relatively safe, especially when weighed against the risk of behavior problems in puppies that are not socialized. Exposure to dogs of unknown vaccination and health status, as in dog parks, is riskier. Ask your veterinarian about safe activities for your puppy, and keep your puppy away from sick dogs and other dogs’ feces.
 
For More Information

• American Veterinary Medical Association: https://www.avma.org/resources-tools/pet-owners/petcare/canine-parvovirus
• Cornell University College of Veterinary Medicine: https://www.vet.cornell.edu/departments-centers-and-institutes/baker-institute/our-research/canine-parvovirus

 
Public domain photo by C. E. Price

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