Killer disease returns to stalk dogs
By Peter Gorner
Tribune science reporter
Published February 6, 2005
History's biggest killer of dogs, canine distemper, appears to be breaking
out again, alarming experts who thought vaccinations had vanquished it in
the United States.
In the last year, epidemics of the incurable disease have been reported in
Los Angeles, Phoenix, Atlanta, Dallas, Miami and Washington state. A
distemper episode last year killed at least 120 dogs and halted adoptions in
shelters throughout the Chicago area before it was brought under control.
And the virus, while quieter now in Chicago, still poses a threat. "We're
still receiving some animals straight from the street that are sick with
active distemper," said Marek Dygas, chief veterinarian for the Chicago
Department of Animal Care and Control.
Not only is distemper devastating to dogs--commonly resulting in vomiting,
seizures, paralysis and death--but the highly contagious infection also can
spread to wildlife with shattering impact.
Its presence also might be a harbinger of other outbreaks, because owners
who don't vaccinate their dogs against distemper are unlikely to protect
them against other diseases--including rabies, which can spread to people.
Experts urge pet owners to ensure puppies and adult dogs are vaccinated.
"This is an absolutely horrific disease. Get your dog immunized," said
Ronald D. Schultz, a veterinary immunologist.
The incident at the city's municipal shelter, which normally sees only a
handful of distemper cases a year and saw none the previous year, was of so
much concern that a task force of academic scientists, veterinarians and
infectious disease specialists was formed to look into why so many dogs were
infected.
The scientists assumed that many animals brought to the shelter--often
strays or abandoned fighting dogs--had not been vaccinated.
"We see distemper in shelters throughout the country," said Schultz, a key
task force member. "It doesn't exist as a significant disease for the
average pet dog anymore, because if you vaccinate the dog as a puppy, you've
[usually] got lifetime immunity."
But testing showed the percentage of unvaccinated dogs was even higher than
expected. And the team remains concerned that lack of shots doesn't tell the
whole story.
The scientists worry that the virus has survived so long in this area
because a new, vaccine-resistant strain of neurologic distemper is
circulating. Maybe another virus is infecting animals, making them more
susceptible to distemper. The task force still regularly meets, and the
scientific quest for answers continues.
Canine distemper virus is a deadly sibling of measles that attacks the
respiratory, gastrointestinal and nervous systems. Until the 1950s, it was
the most feared disease of dogs.
"Before effective vaccines were developed, half of all litters--50 percent
of all puppies in the U.S.--were dying from distemper," said Schultz,
chairman of pathobiological sciences at the University of
Wisconsin-Madison's School of Veterinary Medicine.
Dogs can contract distemper by exposure to viral particles from infected
pets or wildlife that serve as reservoirs for the virus, such as foxes,
wolves, coyotes, raccoons and skunks.
Unvaccinated puppies under 4 months are the most susceptible. Classic signs
include coughing and sneezing, followed by a thick greenish discharge from
the eyes and nose. Depression, lack of appetite, vomiting and diarrhea are
common.
In advanced stages, the virus migrates from the face to the brain, causing
"bubble gum" seizures where the dog seems to be chewing on air. These can
progress to grand mal seizures and paralysis. There is no cure.
"We could only alleviate a sick animal's suffering by euthanasia," Dygas
said.
In recent decades, vaccination strategies have become so successful that
experts in dog distemper are a vanishing breed.
"Most of us are either retired or dead," Schultz noted wryly. "Younger
veterinarians--including some being quoted as experts--may have never seen
an active case of distemper. But if you have, you never forget it."
Dygas, who has worked in countries where distemper is less rare, detected
trouble at the shelter after a dog that had been adopted in April was
returned when it started showing neurological symptoms. He ordered a
distemper test, in addition to a postmortem rabies test.
Soon Dygas found Schultz, and they teamed up with virologist John Lednicky,
director of molecular virology at Loyola University Medical Center, to
address a flare-up of distemper. One of the first things they did was test
blood samples for antibodies to see how many shelter animals had been
vaccinated.
"Whenever something like this happens, it's usually a failure to effectively
vaccinate," Schultz said.
Task force members said they were shocked to find that 65 percent of the
dogs entering the shelter had no evidence of vaccinations--not only against
distemper, but also against rabies. A 30 percent figure is more typical,
Schultz said.
Dygas said most of the infected dogs have been mixed-breed Rottweilers and
pit bulls.
"They had been owned and then released on the street. They never saw a
veterinarian before," he said. "When those animals were brought here, they
already were in bad condition. They didn't have proper nutrition. Their
immune system was not prepared to fight any kind of contagious disease."
Lednicky and his colleagues at the Conservation Medicine Center, a
collaboration among Loyola, the University of Illinois College of Veterinary
Medicine and Brookfield Zoo, have been studying dog distemper in
Chicago-area raccoons for more than eight years. Their research revealed
that the primary symptoms were neurological and that sick raccoons can
infect dogs and, in some cases, zoo animals.
"That's a big concern," Lednicky said. "When a virus starts cycling back and
forth among species, the rate of mutation can be speeded up. It was possible
that modern distemper vaccines no longer would work."
To test that possibility, Lednicky used high-tech molecular techniques to
isolate and sequence three strains of distemper virus from dogs that were
dying at the shelter. He drove the samples up to Madison, where Schultz
exposed vaccinated Wisconsin lab dogs to each viral isolate. The dogs
shrugged off the challenges, indicating the three current vaccines still
worked.
But Lednicky discovered an unusual strain of distemper virus circulating in
this area, one closely related to a strain that primarily attacks the
nervous system, causing acute and progressive inflammation of the brain and
spinal cord. That could account for the neurological symptoms seen here in
dogs and wildlife, he believes.
Researchers in Switzerland, who discovered the strain, have determined it to
be much more virulent than commonly studied distemper viruses. Recently the
Swiss asked Lednicky and Schultz to collaborate on further research.
As he pieces together the puzzle, Lednicky still worries the dog disease
might be masking something more dangerous.
"Is there a virus going around, similar to SARS, that is affecting animals
and making them more susceptible to distemper? Can it spread to humans?
Those are the questions I'm asking," he said.
The task force scientists credit the city's Animal Care and Control
Department for recognizing there was a problem and seeking outside advice.
But controlling an airborne disease in a large facility that processes and
houses 26,000 animals each year proved to be arduous.
"What was happening early on--when the outbreak first occurred--was like
pouring gasoline on a fire," Schultz said. "Every time they brought in a
new, susceptible animal, it became infected immediately because of all the
infection that was in the shelter."
Once the scientists increased awareness, Animal Care and Control began
vaccinating every arriving dog. A 30-day moratorium on adoptions was
instituted. Staff members donned disposable garments and sanitized their
shoes before moving in and out of areas where animals were housed. A new
quarantine protocol went into effect.
The epidemic eventually seemed to burn itself out, and the shelter restarted
its adoption program. Dygas said the shelter now has no positive cases in
the facility, at 2751 S. Western Ave.
Recently, shelter volunteers severely criticized the facility over hygiene
issues and a slow response to the distemper epidemic. The director at the
time of the outbreak, Nikki Proutsos, no longer works there.
Veterinarians in the area reported 27 confirmed cases outside the shelter
last fall, but only one case since October, said Patricia Montgomery,
executive director of the Chicago Veterinary Medical Association.
The task force scientists said Chicago should follow the lead of other
cities in the U.S. that offer free distemper and rabies vaccinations for
dogs as part of a public health program.
The Chicago Department of Public Health has no plans to sponsor such a
program, said spokesman Tim Hadac, adding that "once Animal Care and Control
gets a new director, we will doubtless touch base on any number of issues
that affect both our agencies."
But such a program not only would be more humane to pets, but also would
help protect wildlife, the scientists said.
Lednicky said he also is concerned because, as with West Nile virus,
wildlife often is a bellwether of emerging human public health problems.
"Our studies were tantamount to a random sample of stray dogs in Chicago and
suburbs--dogs most likely to come in contact with wildlife," Lednicky said.
"And that really scares me."
Link: http://www.chicagotribune.com/featur...ck=1&cset=true
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