Background:
Parvovirus is a close relative of feline panleukopenia virus and in
fact, may have mutated from the feline form and infected the dog in
the late 1970’s. Extremely hardy, the virus survives for long
periods outside its host. The virus can live in the environment up
to 6 months and survives winter under a blanket of snow where the
temperature is usually around 25-28 degrees F. Extremely cold
temperatures prior to snow fall may kill the virus. Sodium
hypochlorite (bleach) is the only effective disinfecting agent. The
virus is transmitted by oral ingestion of viral-contaminated feces.
Upon ingestion by the new host it infects local lymph nodes, quickly
multiplies and then moves through the blood to the small intestine.
The virus attacks the lining of the intestines, interfering with
digestion and absorption of nutrients. Additionaly, the normal
bacterial flora of the small intestine which aid in digestion are
now exposed to ulcerated mucosa, providing a direct route into the
blood stream. Bacteria and toxins move into the bloodstream,
ultimately causing death. The incidence of the disease is highest in
young dogs whose immunity is not fully developed. Most dogs are
infected between the ages of 2-6 months, when maternal antibody
decreases below a protective level in the puppy.
Clinical
Signs:
In vaccinated adult dogs, an infection with parvovirus is usually
controlled by the dog’s own immune system prior to the development
of clinical signs. However, in young or unvaccinated dogs, infection
will cause frequent vomiting and very fluid diarrhea, often with
blood. Symptoms appear 5-6 day following infection.
Diagnosis:
Generally, diagnosis is based on the symptoms of the disease and
falling white blood cell counts. Good rapid diagnostic tests are
also available at veterinary clinics. Additionally, the virus can be
found in the feces by commercial labs using electron microscopy.
Treatment:
Treatment for the disease is primarily supportive. Aggressive
intravenous fluid therapy is given to combat dehydration.
Antibiotics are given intravenously to reduce secondary bacterial
infection. Food is withheld until vomiting has ceased. Many
veterinarians employ antiemetics to calm the stomach and aid in the
control of dehydration. Blood transfusions have been employed to
increase the level of globulins, red blood cells and serum protein
which are lost through diarrhea. Most recently, anti-toxins and
anti-parvo serum have been used. Early detection and aggressive
therapy are the key to survival in parvoviral infections. Parvovirus
is best prevented by vaccination. Modified live vaccines are
effective and safe. Immunity is stimulated with a set of four
vaccines, starting at 8 weeks of age and repeating every 3-4 weeks
until the puppy is sixteen weeks old. Some investigators have
suggested extending the protocol until 20-26 weeks because of the
persistence of maternal antibody in the puppy which neutralizes the
vaccine. Annual revaccination is highly recommended.
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