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 Varieties of the blacklegged tick that may carry bacteria
responsible for Lyme disease are present in 45 percent of counties
nationwide, compared with just 30 percent in 1998, researchers
found.
“It’s important for people to be aware that there may be ticks in
areas where they haven’t seen them previously so that they can take
steps to help protect themselves and their families,” lead study
author Rebecca Eisen, a research biologist at the CDC, said by
email.
Since the late 1990s, the number of reported Lyme disease cases in
the U.S. has more than tripled, Eisen and colleagues report in the
Journal of Medical Entomology.
Lyme disease is a bacterial infection spread by the blacklegged
tick, Ixodes scapularis, also known as deer ticks, and the western
blacklegged tick, Ixodes pacificus. These ticks are typically found
in wooded and grassy areas.
Bacteria called Borrelia burgdorferi cause Lyme disease. Common
symptoms can include fever, headache, and fatigue, all of which can
be easily confused with the flu. Some patients, but not all, develop
a characteristic “bull’s eye” rash soon after the tick bite.
If caught early, Lyme disease can be treated with antibiotics. But
untreated Lyme disease can lead to lasting cognitive problems, joint
and muscle pain and mood disorders.
To assess changes in the tick population, researchers analyzed data
reported by counties using the same surveillance methods from 1998.
They found deer ticks in 1,420 out of 3,110 counties in the
continental U.S., or about 46 percent of counties, and found western
blacklegged ticks in 111 counties, or about 4 percent. Combined,
this is a 45 percent increase from 1998 when ticks were reported in
1,058 counties.
Deer ticks are now established in 842 counties across 35 states,
compared with 396 counties in 32 states in 1998. These ticks used to
be concentrated in northeastern states but have move west and south.
Western blacklegged ticks are now established in 95 counties across
six states, up from 90 counties in 1998. These ticks remain
concentrated in Pacific coast states.
Outside of the U.S., ticks carry the disease in forested areas of
Asia, northwestern, central and eastern Europe, according to the
World Health Organization.
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Even though the tick population is spreading, the risk of catching
Lyme disease isn’t the same everywhere the ticks live, because the
number of ticks infected with Lyme bacteria varies, as do the odds
that infected ticks may bite people, Eisen noted.
To minimize the risk of catching Lyme disease from ticks, people can
spray skin and clothing with insect repellants such as DEET or lemon
permethrin, said Dr. Keith Berndtson of the Center for Research on
Biotoxin Associated Illness in Pocomoke, Maryland. Long sleeves and
pants legs tucked into socks can also keep ticks away, and
light-colored fabrics can make the ticks easier to spot.
After a day outdoors, tossing all clothes in the dryer for about 20
minutes can kill most ticks. People should also have a friend or
family member check their body for ticks, and check any pets. Saving
ticks for testing can also help assess whether the bugs carried
bacteria that can lead to Lyme disease, Berndtson, who wasn’t
involve in the study, added by email.
Environmental and climate changes may be helping ticks to expand
their territory in the U.S., noted Dr. Bobbi Pritt, director of
clinical parasitology at the Mayo Clinic in Rochester, Minnesota.
“Warmer temperatures, increases in rainfall, and milder winters can
favor tick survival,” Pritt, who wasn’t involved in the study, said
by email. “These factors can also favor survival and expansion of
the mammals and birds that the ticks feed on.”
SOURCE: http://bit.ly/1OslYEC Journal of Medical Entomology,
published online January 18, 2016.
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