Friday, November 9, 2012

Parvovirus; Think Outside the Box

By Dr. Beth Guerra

Quite a few years ago, I evaluated a one year old schnauzer for an acute onset of vomiting and diarrhea. He had no known medical problems and had not eaten anything unusual that could have caused his symptoms. The owner allowed me to do a complete workup, including x-rays and bloodwork. There were very few abnormalities except for a very low white blood cell count, which can indicate overwhelming infection or inadequate bone marrow response to infection. I was wracking my brains for a cause that would also explain his symptoms, when I noted in the chart that the owner had acquired him as a very young puppy and that he was not yet neutered.  When I asked why she had not neutered him, she said he had never visited a veterinarian. That set off a bell in my head, and I questioned her about vaccine status. She reported he had never had any vaccines or boosters and that the breeder did not mention that he was given any before she acquired him. I immediately set up a parvo test, and it was a strong positive.

Veterinarians tend to think of parvovirus as a disease of very young puppies, usually under 16 weeks of age. The general public knows of parvo as “the puppy killer” because it is highly contagious and often affects young dogs that are not fully developed and therefore have an immature immune system. What I had failed to think of in this case was that even though this dog was a year old, he had never been vaccinated and therefore was still at risk for contracting the virus. We just had another case present this week with a severe parvo infection who is 4 years old, but again, had not been fully vaccinated.  In our current case, he had a single puppy shot and not the full series needed to produce immunity.

Parvovirus is ubiquitous in the environment and very difficult to kill with normal disinfectants; prolonged contact with a bleach solution is required. It is highly contagious and can remain in the environment for many months. Transmission between animals is via oral exposure to feces containing the virus, however, objects such as bedding and toys can also transmit the virus. Infection can be widespread in environments such as pet stores or breeding facilities due to close contact between animals. Incubation within the body can be up to two weeks and the virus can continue to be shed in the feces after infection has resolved.

The virus targets specialized crypts in the intestinal lining where new cells are rapidly produced. These cells die off and the intestinal lining becomes more permeable, allowing for loss of vital blood proteins and electrolytes and also letting harmful bacteria into the bloodstream from the intestinal tract. 

Symptoms include vomiting, diarrhea (often bloody), inappetance, and abdominal pain. Septic shock or disseminated intravascular coagulation (widespread hemorrhage) can occur in severe cases. The virus can also destroy developing white blood cells. The drop in crucial white cells increases the risk of secondary bacterial infections.

Diagnosis is based on presenting symptoms, vaccine history, and test results, which can include a positive parvo test (fecal test that can be done in house), decreased white blood cell count, or low blood albumin. Some puppies also have intestinal parasites that are found on fecal exam. Therapy is supportive while the virus runs its course. Intravenous fluids, anti-emetics, and broad spectrum antibiotics are utilized to minimize secondary effects of the virus. Some animals receive transfusions of whole blood or plasma. Parvovirus can be rapidly fatal if left untreated and these cases usually require several days of hospitalization on the road to recovery. Puppies that develop severe sepsis or secondary infections, such as pneumonia, may succumb to the disease. However, studies have shown that chance of survival with aggressive treatment is over 90%.

Once infection has cleared, the puppy may have lifelong immunity, however, vaccines are the best prevention. Puppies usually receive a series of “combo” vaccines, which include distemper, parvovirus, adenovirus, and parainfluenza. Vaccines begin around 8 weeks of age and boosters are administered every few weeks until they are 16 weeks of age. Whether you obtain a puppy from a breeder, pet store, or friend, it is important to question them about the vaccination status up to that point. Infection with parvovirus can occur at any time between boosters, so it is important to have your puppy evaluated by a veterinarian and comply with the  FULL vaccine schedule.

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