Parvovirus, Dogs and Vaccination

I had started my first job with a veterinarian in the late 1970s when the parvovirus outbreak occurred.  Scores of dogs were admitted with bloody diarrhea, the smell of which could literally choke you.  If memory serves, it took about nine months for the outbreak to run its course, and those were not happy days for veterinary technicians, I assure you.  Almost all the dogs recovered, and life went on.

Of course, such a canine health crisis did not go unnoticed by the drug companies, who naturally came up with a vaccine for the disease.  Its sudden appearance spurred research into its source, which seems to be feline panleukopenia, which somehow morphed into a canine virus.  There is a theory that this mutation occurred in the laboratory, most likely while producing panleukopenia vaccines.

Symptoms of "parvo" are, besides the bloody diarrhea, vomiting, dehydration, fever, lethargy and anorexia (no appetite).  The treatment is still supportive, consisting mostly of fluid administration until the disease runs its course.  The vomitus and feces can carry the virus, so scrupulous clean-up is a must.

Canine parvovirus vaccines seem to vary widely in their efficacy.  As I recall from my vet tech days, dogs were initially inoculated with the feline panleukopenia (distemper) vaccine, which was thought to be similar enough to induce immunity.  Wrong!  After experimenting with killed virus, a modified live version came out that instilled a limited immune response.  By this time, however, the disease had mutated into two distinct strains, so the vaccine lost efficacy after a time.

Parvovirus vaccines don't work well on young pups.  Otherwise, in adults, protection lasts approximately 5 years; due to the modified-live aspect of the vaccine, though, more side effects can occur.  Intestinal as well heart problems have been reported in inoculated dogs, and side effects are exacerbated when given in tandem with other vaccines.  Since parvoviruses depress the immune system, the list of health problems that could conceivably occur with repeated vaccination seems endless.

What to do?  If you really need to inoculate your dog against this disease, it seems prudent to wait until he's older than 16 weeks, give the parvovirus shot separate from all others, and don't inoculate again until at least 5 years.  This should give your dog protection without unduly taxing his immune system.

Next up:  Canine distemper.
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Rabies Vaccination

Rabies affects all warm-blooded animals.  It is only considered a threat in some and not others, however.  For example, mice and squirrels can contract rabies; their size and the speed with which the disease kills them however, keep them from being much of a public health problem.  Where they present a problem is when a cat comes into contact with them, setting the stage for infection.  Cats and dogs, infected by wild animals like foxes, coyotes, racoons, skunks and even fisher cats (though most don't survive that encounter!) are the main concern of public health officials, both because they live in close proximity with humans and also because we are in a position to control their health care, including inoculating them against disease.

The rabies vaccine, first developed by Louis Pasteur, was used on a human bitten by a rabid dog circa 1885.  The boy survived.  Until about 1920, the vaccine was only used on humans.  A killed-virus vaccine was then developed for use on animals.  Generally, inactivated virus vaccines are used on dogs and cats today.

The efficacy of the rabies vaccine is unclear.  Some studies have shown the vaccine to induce the paralytic type of rabies in cats receiving the vaccine.  Catherine Diodati, author of Vaccine Guide for Dogs and Cats,
relates the experience of Pennsylvania in the late 1980s.  Rabies vaccinations were legislated for cats in 1987, despite no increase in rabies cases.  What did increase, however, were the cases of negative reactions at the injection site, including cases of fibrosarcoma.  When researchers examined the tumors, they found traces of aluminum, which was used in the vaccines.  Of course, they couldn't prove that the tumors were caused by the rabies shots; she notes, however, that the cases of fibrosarcoma in Pennsylvania outnumbered the number of nation-wide rabies cases in 1991 alone.

For cats, the risk of health problems due to inoculation are probably greater than that of contracting rabies.  Since these vaccines are usually administered  along with two or three others in one shot, the risk of complications increases.  From a public health point of view, vaccination doesn't always alleviate the risk of humans contracting rabies from a cat that has been bitten by a rabid animal.  Just handling the cat can allow infected saliva to enter wounds or breaks in the skin; the idea of rabies seldom enters the minds of concerned owners who see Tom limping home after a rumble, wounded and needing care.

Can you guess what the solution is?  Keep your cats indoors!

Happy Labor Day, when we remember all those who came before us, fighting for the 8-hour day, child labor laws and work place health and safety legislation.
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