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.
