Vaccination often good for life
May 9, 2005
At first glance, it sounds like an epidemic.
Last year, 120 shelter dogs in Chicago died of canine distemper. The
usually fatal viral disorder also hit Los Angeles, Miami, Phoenix,
Atlanta, Dallas and Washington state.
Last month New York City's Animal Care & Control issued a press
release headlined "Protect Your Pets, New York" - followed by no less
than three exclamation points - urging owners to "fully immunize"
their animals. And just last week, shelter officials confirmed a
distemper case in a dog that had reportedly been vaccinated.
But before you speed-dial your vet to schedule a distemper booster,
listen to vet Ronald Schultz, chairman of pathobiological sciences at
the University of Wisconsin School of Veterinary Medicine at Madison,
who has been studying the efficacy of canine vaccines since the 1970s.
"The idea that outbreaks occurred as a result of owners inadequately
vaccinating their dogs really is not the case at all," says Schultz,
who was part of a task force studying the Chicago outbreak. "If a dog
was effectively vaccinated as a puppy, and very certainly if it was
ever vaccinated at a year old, it is immune for life."
Schultz adds that the majority of the sick Chicago dogs had never
been vaccinated. (Illness in vaccinated dogs was a "red herring," he
says: Either the dog was already infected when vaccinated, or was one
of those rare cases - one in every 5,000 dogs - that can't respond to
the distemper vaccine, "whether it is given monthly, daily or
hourly.") By contrast, he says, "the vaccinated pet population in
Chicago never had any problem."
Distemper was the leading cause of death among dogs until the 1950s,
when a vaccine was introduced. Until recently, it has been considered
an "old" disease - not quite eradicated, but generally under control,
with shelters normally seeing only a handful of cases.
Schultz notes that today, canine distemper is still prevalent among
wildlife, including raccoons, coyotes and foxes. That is likely how
the Chicago outbreak began, he adds: Vehicles used to transport stray
dogs had previously picked up infected raccoons, providing a point of
(Because the distemper cases in Chicago were new strains, there was
concern they might be resistant to vaccines, says John A. Lednicky,
assistant professor of pathology at Loyola University Medical Center
in Maywood, Ill. While testing by Schultz disproved this, Lednicky
notes the new strains are significant because "often, the symptoms
are just neurological," impeding diagnosis. Indeed, area vets
misdiagnosed dogs as epileptic that had this form of distemper.)
With the distemper vaccine, Schultz says, one jab'll do you -
provided the shot imparts immunity. That can be gauged with a titer,
a blood test that measures antibody levels.
Puppies are trickier. During their first weeks of life, they are
protected by maternal antibodies from their mother's colostrum.
Vaccinating too early can result in those antibodies interfering with
the vaccine, leaving the puppy more vulnerable than before.
And the age at which maternal immunity fades varies from puppy to
puppy. Schultz says that at 6 weeks, about half of puppies no longer
have maternal immunity; at 9 weeks, it's about 75 percent; and at 12
weeks, about 90 percent. Given those odds, he recommends keeping a
puppy relatively isolated until 12 weeks, then vaccinating. Several
weeks later, owners should titer, and, if the puppy has inadequate
antibody levels, revaccinate. (Titering earlier is ineffective
because it can't distinguish between passive maternal immunity and
active immunity from the vaccine.)
Ed Boks, executive director of the AC&C, says that, in shelters, mass
vaccination is crucial for avoiding outbreaks.
Schultz doesn't disagree but notes the significant difference between
never-vaccinated strays in a shelter and well-cared-for companions
that have already been vaccinated, perhaps multiple times. His
concern for the latter is not that they are at great risk for
distemper, but rather that overzealous owners - and vets - might
erroneously conclude that more is more.
"Veterinarians in general don't know much about vaccines, and they
know less about immunology," he says, adding that some still give
yearly "shots," even though research has shown that is an arbitrary
timetable. "And vaccine companies have really taken advantage of
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