Ticks are here in Michigan Too!
Lyme disease is an illness caused by a spirochete
bacterium (Borrelia burgdorferi). This disease is transmitted to
people and animals primarily by the bite of the black-legged tick,
Ixodesscapularis.
In 1975, Lyme disease was first recognized in the United
States in children from Lyme, Connecticut. However, the bacterium that causes
Lyme disease was not identified until 1982. Since then, Lyme disease has been
reported with increasing frequency. The majority of cases occur along the east
coast from Delaware to Massachusetts and the upper Midwest in Wisconsin and
Minnesota. Lyme disease has now been reported from 43 states, including
Michigan.
In Michigan, the first official reported human case of
Lyme disease was in 1985. Cases have now been reported in both the upper and
lower peninsula and in most of Michigan's 83 counties. It is anticipated that
the number of cases reported will continue to increase.
Transmission and Development
The black-legged tick, Ixodes scapularis, is the
most common carrier of Lyme disease in the mid-western and eastern states.
I. pacificus is known to be the vector in the west. Other species of
ticks such as the dog tick or wood tick, the lone-star tick and the rabbit
tick, and biting insects such as mosquitoes, deer flies and horse flies have
been shown to carry the Lyme disease bacterium. However, their ability to
transmit the disease is not known at this time. Studies are continuing in
Michigan to determine the extent of the black-legged tick
population.
The black-legged tick has a rather complex life cycle
involving development from an egg to a larva, larva to a nymph, and finally
from a nymph to an adult. This process usually takes two years. Larvae and
nymphs require blood to proceed to the next development stage, and adult
females need blood to lay their eggs. At each of these stages, the tick seeks
an animal host for a single blood meal and then drops off the host.
In their two years of life, black-legged ticks spend very
little time (only about two and a half weeks) on hosts. The rest of the time is
spent off the host, developing into the next stage and waiting for another host
to come along.
In the spring, the eggs hatch into larvae. During the
summer, the larvae feed on mice, squirrel, raccoon, rabbit and other animals.
In the fall, the larvae mature into nymphs, which then hibernate over winter.
In the spring and summer these nymphs become active again, preferring to feed
on mice. It is during the time the tick is in the nymphal stage that it is most
likely to infect humans. At the end of its life cycle the female tick lays eggs
and dies.
Clinical Signs and Pathology
Lyme disease in humans is usually not a life-threatening
illness and one should regard the health risks it does pose with concern rather
than alarm. It is most often a mild illness mimicking a summer flu, but serious
problems involving the heart, joints and nervous system may develop in some
individuals.
Lyme disease in humans may progress through three stages,
depending upon the individual. In stage 1, people may have any combination of
the following signs and symptoms: headache, nausea, fever, spreading rash,
aching joints and muscles and fatigue. These signs and symptoms may disappear
altogether, or they may reoccur intermittently for several months. A
characteristic red rash, called erythema migrans (EM) may appear within 3 to 32
days after a person is bitten by an infected tick. The rash is circular in
shape and can attain a diameter of 2 to 20 inches. EM is not restricted to the
bite site and more than one lesion may occur on the body. Up to 30% of the
people who have Lyme disease do not develop EM lesions, making diagnosis more
difficult.
In stage 2 (weeks to months after initial exposure to the
bacterium or after the first symptoms appear), some people may develop
complications involving the heart and/or nervous system. Specific disorders may
include various degrees of heart block, nervous system abnormalities such as
meningitis, encephalitis and facial paralysis (Bell's palsy), and other
conditions involving peripheral nerves. Painful joints, tendons, or muscles may
also be noted during this stage of the disease.
Arthritis is the most commonly recognized long-term sign
of Lyme disease (stage 3). From one month to several years after their first
symptoms appear, people may experience repeated attacks of
arthritis.
Dogs, cats, cattle, horses and other domestic animals may
also exhibit a variety of signs, including fever and lameness. Wild animals
such as deer, raccoon and mice show no signs and apparently suffer no ill
effects from the disease.
Diagnosis
Lyme disease is difficult to diagnose because the disease
mimics many other diseases and there is no definitive test for it at this time.
A diagnosis should be based on a history of tick bite, the presence of a
circular rash, an examination by a physician for other symptoms, and laboratory
tests. The most reliable indication of Lyme disease is a large circular rash
(erythema migrans). If you develop any of the symptoms or recall being bitten
by a tick, discuss your suspicions of Lyme disease with your
physician.
Treatment and Prevention
Prompt diagnosis and treatment with antibiotics can cure
the infection and prevent later complications in both humans and domestic
animals. Treatment during later stages of the disease often requires more
intensive antibiotic therapy.
While there is no sure way to completely eliminate the
chance of contracting Lyme disease, there are several specific preventative
measures one can take:
Significance
Be aware of Lyme disease, but do not be so concerned that
you cannot enjoy the outdoors. The risk of developing the illness is minimal in
Michigan and even if infection occurs the disease can be diagnosed and treated
with antibiotics.
The relationship between deer and the disease is complex.
Deer show no symptoms of the disease. Deer may carry small numbers of the
spirochete that causes Lyme disease but they are dead-end hosts for the
bacterium. Deer cannot infect another animal directly and no deer hunter has
acquired the disease from dressing out a deer. Infected ticks that drop from
deer present little risk to humans or other animals since the ticks are now at
the end of their life cycle and will not feed again. There is no evidence that
humans can become infected by eating venison from an infected deer. In
addition, the Lyme organism is killed by the high temperatures that would be
reached when venison is cooked or smoked. Deer supply the tick that transmits
the bacterium with a place to mate and provides a blood meal for the female
tick prior to production of eggs. Research has shown that white-tailed deer are
important to the reproductive success of the black-legged tick. In the absence
of deer, this tick will opportunistically feed on other medium sized mammals
and humans. As a management tool for Lyme Disease, there is still debate in the
scientific community as to whether reducing the number of deer present in an
area will effectively or dramatically reduce Lyme Disease "risk".
There is very little risk of hunters contracting Lyme
disease when pursuing game. This is because hunters are in the woods from
October through March when the nymphal stage of the tick is inactive. Even
though the adult stage of the tick is active in the fall (when temperatures are
above 40º F), the heavier clothing that hunters wear makes it difficult for
ticks to find and attach to bare skin. In addition, the risk of picking up
ticks from game animals is insignificant compared with that from the
environment (meadows, brushland or woods).
bacterium (Borrelia burgdorferi). This disease is transmitted to
people and animals primarily by the bite of the black-legged tick,
Ixodesscapularis.
In 1975, Lyme disease was first recognized in the United
States in children from Lyme, Connecticut. However, the bacterium that causes
Lyme disease was not identified until 1982. Since then, Lyme disease has been
reported with increasing frequency. The majority of cases occur along the east
coast from Delaware to Massachusetts and the upper Midwest in Wisconsin and
Minnesota. Lyme disease has now been reported from 43 states, including
Michigan.
In Michigan, the first official reported human case of
Lyme disease was in 1985. Cases have now been reported in both the upper and
lower peninsula and in most of Michigan's 83 counties. It is anticipated that
the number of cases reported will continue to increase.
Transmission and Development
The black-legged tick, Ixodes scapularis, is the
most common carrier of Lyme disease in the mid-western and eastern states.
I. pacificus is known to be the vector in the west. Other species of
ticks such as the dog tick or wood tick, the lone-star tick and the rabbit
tick, and biting insects such as mosquitoes, deer flies and horse flies have
been shown to carry the Lyme disease bacterium. However, their ability to
transmit the disease is not known at this time. Studies are continuing in
Michigan to determine the extent of the black-legged tick
population.
The black-legged tick has a rather complex life cycle
involving development from an egg to a larva, larva to a nymph, and finally
from a nymph to an adult. This process usually takes two years. Larvae and
nymphs require blood to proceed to the next development stage, and adult
females need blood to lay their eggs. At each of these stages, the tick seeks
an animal host for a single blood meal and then drops off the host.
In their two years of life, black-legged ticks spend very
little time (only about two and a half weeks) on hosts. The rest of the time is
spent off the host, developing into the next stage and waiting for another host
to come along.
In the spring, the eggs hatch into larvae. During the
summer, the larvae feed on mice, squirrel, raccoon, rabbit and other animals.
In the fall, the larvae mature into nymphs, which then hibernate over winter.
In the spring and summer these nymphs become active again, preferring to feed
on mice. It is during the time the tick is in the nymphal stage that it is most
likely to infect humans. At the end of its life cycle the female tick lays eggs
and dies.
Clinical Signs and Pathology
Lyme disease in humans is usually not a life-threatening
illness and one should regard the health risks it does pose with concern rather
than alarm. It is most often a mild illness mimicking a summer flu, but serious
problems involving the heart, joints and nervous system may develop in some
individuals.
Lyme disease in humans may progress through three stages,
depending upon the individual. In stage 1, people may have any combination of
the following signs and symptoms: headache, nausea, fever, spreading rash,
aching joints and muscles and fatigue. These signs and symptoms may disappear
altogether, or they may reoccur intermittently for several months. A
characteristic red rash, called erythema migrans (EM) may appear within 3 to 32
days after a person is bitten by an infected tick. The rash is circular in
shape and can attain a diameter of 2 to 20 inches. EM is not restricted to the
bite site and more than one lesion may occur on the body. Up to 30% of the
people who have Lyme disease do not develop EM lesions, making diagnosis more
difficult.
In stage 2 (weeks to months after initial exposure to the
bacterium or after the first symptoms appear), some people may develop
complications involving the heart and/or nervous system. Specific disorders may
include various degrees of heart block, nervous system abnormalities such as
meningitis, encephalitis and facial paralysis (Bell's palsy), and other
conditions involving peripheral nerves. Painful joints, tendons, or muscles may
also be noted during this stage of the disease.
Arthritis is the most commonly recognized long-term sign
of Lyme disease (stage 3). From one month to several years after their first
symptoms appear, people may experience repeated attacks of
arthritis.
Dogs, cats, cattle, horses and other domestic animals may
also exhibit a variety of signs, including fever and lameness. Wild animals
such as deer, raccoon and mice show no signs and apparently suffer no ill
effects from the disease.
Diagnosis
Lyme disease is difficult to diagnose because the disease
mimics many other diseases and there is no definitive test for it at this time.
A diagnosis should be based on a history of tick bite, the presence of a
circular rash, an examination by a physician for other symptoms, and laboratory
tests. The most reliable indication of Lyme disease is a large circular rash
(erythema migrans). If you develop any of the symptoms or recall being bitten
by a tick, discuss your suspicions of Lyme disease with your
physician.
Treatment and Prevention
Prompt diagnosis and treatment with antibiotics can cure
the infection and prevent later complications in both humans and domestic
animals. Treatment during later stages of the disease often requires more
intensive antibiotic therapy.
While there is no sure way to completely eliminate the
chance of contracting Lyme disease, there are several specific preventative
measures one can take:
- Wear long pants tucked into boots or socks and wear
long-sleeved shirts buttoned at the cuff.
- Use tick repellents containing 0.5% permethrin or mosquito
repellents containing 30% DEET.
- Examine clothing, skin and pets for ticks and remove them
promptly.
Significance
Be aware of Lyme disease, but do not be so concerned that
you cannot enjoy the outdoors. The risk of developing the illness is minimal in
Michigan and even if infection occurs the disease can be diagnosed and treated
with antibiotics.
The relationship between deer and the disease is complex.
Deer show no symptoms of the disease. Deer may carry small numbers of the
spirochete that causes Lyme disease but they are dead-end hosts for the
bacterium. Deer cannot infect another animal directly and no deer hunter has
acquired the disease from dressing out a deer. Infected ticks that drop from
deer present little risk to humans or other animals since the ticks are now at
the end of their life cycle and will not feed again. There is no evidence that
humans can become infected by eating venison from an infected deer. In
addition, the Lyme organism is killed by the high temperatures that would be
reached when venison is cooked or smoked. Deer supply the tick that transmits
the bacterium with a place to mate and provides a blood meal for the female
tick prior to production of eggs. Research has shown that white-tailed deer are
important to the reproductive success of the black-legged tick. In the absence
of deer, this tick will opportunistically feed on other medium sized mammals
and humans. As a management tool for Lyme Disease, there is still debate in the
scientific community as to whether reducing the number of deer present in an
area will effectively or dramatically reduce Lyme Disease "risk".
There is very little risk of hunters contracting Lyme
disease when pursuing game. This is because hunters are in the woods from
October through March when the nymphal stage of the tick is inactive. Even
though the adult stage of the tick is active in the fall (when temperatures are
above 40º F), the heavier clothing that hunters wear makes it difficult for
ticks to find and attach to bare skin. In addition, the risk of picking up
ticks from game animals is insignificant compared with that from the
environment (meadows, brushland or woods).