Viral Enteritis
May, 1997
Last year, 2 of my articles dealt with intestinal disease in
dogs, caused by Parvovirus and Coronavirus. Recently, several
readers have asked questions not answered in those discussions.
This month, I'll cover a few of these topics.
In general, treatment for any canine viral infection involves
treating signs and symptoms only, because there is no effective
and readily available anti-viral medication. Probably the most
important aspect of treating viral enteritis is replacement of
fluids and electrolytes lost through diarrhea and vomiting, to
prevent or reverse dehydration. If signs are mild (which is not
unusual for coronavirus), this may be accomplished at home by
offering an electrolyte solution such a Pedialyte or Gatorade. If
this is not possible due to severe vomiting or lack of appetite
(which is common with parvovirus), lactated Ringer's solution is
administered in the hospital, either under the skin on the dog's
back or intravenously.
If signs are mild enough to treat at home, intestinal
"rest" can be accomplished by withholding food for 1-2
days before introduction of a bland diet. Strained chicken,
boiled chicken and rice, or a prescription diet work well for
this purpose. For hospitalized cases, intravenous catheter
placement allows for replacement of fluid, plasma or blood, as
well as other things that tend to be deficient, such as glucose
or potassium. Medications can be given to treat vomiting or
diarrhea, usually by injection. Due to the possibility of
endotoxic shock (caused by intestinal bacteria escaping into the
bloodstream), antibiotics are frequently given. Other drugs that
can combat endotoxemia include cortisone, flunixin meglumine
(Banamine) or Septi-Serum, an equine-origin antiserum rich in
antibodies. Puppies that respond to treatment usually show
improvement in the first 3-5 days.
Questions periodically arise regarding development of new and
more dangerous strains of parvovirus in dogs. Many cases are
suddenly seen in one geographical area, or many seem to die too
rapidly from the disease. Undoubtedly, mutations do occur, some
of which would increase the disease-causing ability of the virus.
However, a highly virulent virus that kills its host (and its
only means of replication) too rapidly, would not fare as well
over time as a virus that causes a lower mortality rate. It is
also unlikely that such a mutation would evade antibodies
stimulated by vaccination, because most parvovirus vaccines
contain whole live viruses and most mutations would involve
changing only a small part of the virus - 1 or 2 surface
proteins. The new strain would still have many similarities to
the old strain - most of its surface proteins would be unchanged.
These surface proteins are the targets that antibodies use to
neutralize a virus.
I mentioned in the previous article on parvovirus that puppies
who are already vaccinated sometimes contract the disease.
Antibodies they receive from their mother can interfere with a
good vaccine response, even at levels too low to be protective.
This is why all properly vaccinated puppies have a "window
of susceptibility" - a time period during which they are
able to catch the disease. However, use of recently developed
"high-titer" vaccines can narrow this window of
susceptibility and they're only a little more expensive than the
more commonly used vaccines.