Lyme
disease is bad enough. But it's just the beginning of a host of odd and ugly
diseases ticks transmit, public health officials are finding.
 |
| An electron microscope image of the mouth of an Argas monolakensis shows why ticks are generally hard to remove once they've latched on for a blood meal. Researchers are recognizing that ticks carry a host of nasty diseases, too. Photo courtesy of the National Institute of Allergies and Infectious Diseases. |
By Marianne Lavelle, The Daily Climate
Editor's
Note: "Climate at Your Doorstep" is an effort by The Daily Climate to
highlight stories about climate change impacts happening now. Find more stories
like this here.
Ticks that spread Lyme disease don't always deliver their misery
neat. They can serve up a cocktail of pathogens with one infectious bite.
"They are nature's dirty needle," said Kathryn
Fishman, who suffered for years from fatigue and mental confusion before blood
tests revealed she had Lyme and two other lesser-known pathogens. She is office
manager for her physician husband's practice in Maryland and Virginia that
focuses on tick-borne diseases.
Lyme disease has gotten the headlines. But the wide array of
potential diseases ticks carry is one reason that public health officials
remain greatly concerned about the geographic spread – linked to both global
warming and suburbanization – of the black-legged tick and other ticks in North
America.
Some scientists believe infection with other tick-borne bacteria
or viruses may be one reason that many Lyme disease patients feel chronically
ill long after treatment. Testing for Lyme may not pick up signs of those other
infections. And the drugs used in treating Lyme are not always effective in
treating co-infections picked up from ticks.
"Lyme disease is the tip of the iceberg," cautioned
Durland Fish, epidemiologist at Yale School of Public Health. "There are
worse diseases coming down the pike."
Some examples:
Red
meat allergy
If you enjoy a juicy steak, better avoid the Lone Star tick.
This parasite, with a range once limited to the southeastern United States but
now extending as far north as the Great Lakes and New England, can trigger an
immune response that renders victims allergic to red meat – perhaps
permanently. In at least 2,000 known cases, patients suffered severe reactions
– from hives to anaphylactic shock – after eating beef, pork or venison, due to
what researchers believe is an antibody response to the tick saliva.
The immune system becomes wired to fight not only the tick but
any exposure to a carbohydrate called alpha-galactose that is present in the
tissues, muscle, fat, and blood of non-primate mammals. Vanderbilt University Medical Center in Tennessee said earlier this year
that its allergy clinic was seeing one or two new patients with the condition
every week.
Scientists are still uncertain if the condition is permanent;
most victims are advised to keep epinephrine pens always at hand. The Lone Star
tick may not be the only carrier. Swedish researchers last year confirmed that
alpha-galactose was present in the European tick,Ixodes ricinus, the
castor bean tick, which also transmits Lyme disease.
The same study found that
tick-bite victims who have a B-negative blood type are most at risk for
developing a red meat allergy. The syndrome is just one reason National Science
Foundation-funded researchers said in a recent paper it was important for public health
officials to look "beyond Lyme," and consider the growing risk from
other tick species and pathogens.
Heartland
virus
An Oklahoma man's death reported by state authorities this past May was the second known
fatality attributed to a newly identified disease, the Heartland
virus, which apparently is transmitted by the bite of the
Lone Star tick.
Health authorities have confirmed about 10 cases of the disease, mostly
in Missouri, but also in patients in Tennessee and Oklahoma. Patients reported
fever, loss of appetite, muscle and joint pain, and nausea, with symptoms so
severe they required hospitalization in most cases. They were found to have
abnormally low white blood cell and platelet counts.
Health officials are still learning about the disease, but
patients who have other chronic conditions at the time of an infection seem the
most vulnerable. Because it is caused by a virus, antibiotics are ineffective.
Patients may receive fluids and medication to alleviate fever, but there is no
known medical treatment or vaccine for the illness.
Babesiosis
A malaria-like illness, babesiosis can cause multiple organ
failure or death in people with compromised immune systems. But some people who
contract the infection through a tick bite can feel fine. As a result,
babesiosis has become one of the most prevalent contaminants in the blood supply, and there is no screening
test for prospective blood donors.
The disease is not spreading as quickly as Lyme disease, even
though it is carried by the same tick species, Ixodes scapularis, the deer
tick or black-legged tick. Yale University's Fish said one reason may be that
the bacteria is carried only in rodents, and not in birds.
"It can only
spread as fast as the mice move," he said. Still, one CDC study showed a
20-fold rise in babesia incidence in New York's Lower Hudson Valley from 2001
to 2008, and another
study found that
babesia incidence in tick-endemic sites in southern New England may be
approaching that of Lyme disease.
Powassan
virus
The disease caused by the tick-borne Powassan virus can range from mild muscle pain to
encephalitis or meningitis and permanent brain damage or death. Powassan can be
passed from tick to host in as little as 15 minutes (For contrast, Lyme
requires a tick be attached 36 to 48 hours before the bacteria enters the
blood). Fish said scientists have seen "a dramatic increase" in
Powassan virus in black-legged ticks: "It wasn't there 30 years
ago."
Powassan previously was known to be transmitted by a tick that
fed primarily on skunks and weasels and rarely bit humans. "What's
happened is this scapularus seems to be able to transmit Powassan just as
efficiently as that skunk tick, and there's millions of these scapularus ticks
out there," Fish said. "I don't know why we aren't seeing more
cases."
Borrelia
miyamotoi
A newly discovered pathogen closely related to the Lyme-disease
bacteria, tick-borne Borrelia miyamotoi can cause fever, muscle aches
and relapsing fever.
Researchers at Yale University recently
reported evidence of miyamotoi infection in about 4 percent of healthy people
living in southern New England (about 10 percent have evidence of a previous
Lyme disease infection).
Researchers who developed a new antibody test to check for prevalence of infection
say the disease may be occurring in other areas where Lyme is endemic. Indeed,
a study earlier
this year in the San Francisco Bay area showed miyamotoi as prevalent as Lyme
disease bacteria, even though human infections haven't been reported. The researchers
said it was possible that cases were not being accurately diagnosed.
Tick-borne
relapsing fever
It was a medical mystery: Five people developed severe fever,
rash, muscle and joint pain after a stay in a western Montana cabin in 2002.
Health officials inspected the site on Wild Horse Island in Flathead Lake, and
found Ornithodoros hermsi ticks, a species known for feeding
quickly at night and then retreating into attics or walls.
Researchers concluded that one of the men staying in the
cabin unwittingly triggered the wave of illness by removing a rodent or small
animal nest in the attic. Some ticks likely fell through the spaces between the
ceiling boards to the two bedrooms below.
Until that point, the O.hermsi tick had never before found in
Montana, but it was known as the vector for the relapsing fever in other
Western states and British Columbia. The bacteria, Borrellia hermsii, is just
one of a number of pathogens that cause Lyme-like illnesses but are carried by
different species of ticks.
Marianne
Lavelle is a staff writer for The Daily Climate, an independent news service
covering energy, the environment and climate change. Follow her on Twitter @mlavelles.
Photos,
from top: Lone Star tick courtesy CDC
public health image library. Tick drag in Mansfield, Conn., and Borrelia miyamoti tick on a finger nail for scale, both
courtesy Yale University.
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