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What does Flopsy Bunny have in common with a Gambian
giant pouched rat?
Both — without even trying — can make you sick as a
Zoonoses (zo-uh-NO-seez) are communicable diseases that move from
animals to humans — sometimes directly, and sometimes via
an intermediate vector such as the flea.
The zoonotic bestiary includes many vectors, including pig, bat,
oyster and tick. The most urgent instance involves wild swans,
ducks and geese: the H5N1 influenza virus, or "bird flu," has now
spread to birds on the African continent. Then there are fad pets
(say, Paris Hilton's kinkajou, whose natural habitat isn't the
|Harvard Medical School’s
Dr. Arnold Weinberg showed how zoonoses can be triggered by
Zoonoses, known and described since antiquity, are now being battled
in a global context by (among others) the folks in conservation
medicine. Conservation medicine, an emerging specialty, integrates
three different fields: animal health, human health and ecosystem
health. It works to improve all three by using interdisciplinary
teams of veterinarians, physicians, ecologists, public health and
Conservation medicine has arisen in response to unprecedented
levels of disease in many species — including humans — and
it addresses the environmental causes of health problems.
In his Great Teachers Lecture "Zoonoses: Where the Wild Things
Are" on Mar. 8, Dr. Arnold Weinberg, professor of medicine at Harvard
Medical School, showed how zoonoses can be triggered and exacerbated
by anthropogenic change — war, chemical pollution, global
trade, wilderness encroachment and the warming of the earth's oceans.
To illustrate how animals suffer disease within their own kingdom,
Weinberg showed a Gary Larson ("The Far Side") cartoon: A wolf
pack is being exhorted by its leader, who's scoped out a farmyard
enclosure of pigs. "I say we do it!" says alpha wolf. "And trichinosis
Trichinosis is a disease caused by eating undercooked pork containing
"Animals have their own appetites," Weinberg said. "We are part
of a large family that is very diverse." As in any family, the
relationships are complex.
In evidence, he showed a slide of imported discarded tires. Mountains
of them piled up in Houston. These lent the Asian tiger mosquito
space to breed, hitchhike and eventually cause an outbreak of Eastern
The zoonotic scale is huge and its dissemination various. "Of
1,400 known pathogens," Weinberg said, "around 800 originate in
non-human sources, and 200 are competent enough to be involved
in human disease." Disease can spread on three levels — wild,
domestic and human. In the wild, disease can loop from deer to
tick and back. It can shift from wild to domestic — meadow
mice to homes. And it can go from domestic to human, in the classic
example of rabies transmission — dog bites man.
Distribution depends on several factors: arthropod vectors and
reservoirs; animal and aquatic hosts; migration patterns; global
trade; and climatic conditions such as global warming. Weinberg
explained: "Water temperature must be over 20 degrees Centigrade
[>70 degrees Fahrenheit] for Vibrio parahaemolyticus to
reproduce and get into bivalves," he said. "Diseases that used
to be found only in warmer waters are now found in the North Sea
and the North Atlantic." Cape Cod's oysters are therefore no longer
free from this family of bacteria, which causes gastrointestinal
disease, skin infections and septicemia.
Other factors include human activities: importing untreated animal
hides and skins; travel (especially of the adventurous sort); exotic
pets; and bioterror. Mechanisms of transmission include contact,
ingestion, inhalation, arthropod vectors (like tick bites) and
Weinberg described how he once drank water from a clear-running
brook "which had already been used by non-toilet-trained beavers." Giardia (a
nasty bug that hits the GI tract) left him reeling.
He explained how, in 1978, Florida raccoons imported to a West
Virginia hunting camp caused a major rabies epidemic in raccoons
up the east coast, extending to Ohio.
Drawing on his clinical and teaching experience at Massachusetts
General Hospital, Weinberg presented several cases in the art of
diagnosis. In one, a 55-year-old man discovered a dead rabbit in
the road. Its body was still warm, and he brought it home for stew. "The
wife served as a control in this case," said Weinberg. "She said
to her husband, 'Are you crazy?' and didn't touch it. He got sick
and she didn't." The man developed typhoidal tularemia.
Another case involved an epidemic in war-torn Kosovo; patients
presented with fever, pharyngitis, cervical adenitis and suppurating
nodes. "This is as an example of how the pathogen was probably
on the wild-animal level," he explained, "and rodent-contaminated
food and water allowed it to enter the domestic plane; then human
disease followed." Once rodents were controlled, the epidemic disappeared.
Each case resonated with his theme: "Conservation medicine is
an idea whose time has come, and none too soon," he said. "Earth
is the only planet — that we know of — that supports
life. We should do everything in our power to preserve it. We want
to keep people healthy, and also protect the diversity of all life."