Lyme Disease
What Causes It?
The causative agent, bacterium Borrelia burgdorferi, is transmitted by
a deer tick (genus Ixodes) bite. B.
burgdorferi is a flexible, helical spirochete. Spirochetes disseminate from bite site via cutaneous, lymphatic,
and blood routes.
http://www.cdc.gov/ncidod/dvbid/lyme/bburgdorferi_sm.htm
Borellia
burgdorferi
Its genome consists of a 950 kilobase
linear chromosome, 12 circular plasmids, and 9 linear plasmids. The linear plasmids encode the proteins on
the outer membrane of the bacterium.
These proteins determine the antigenic identity of the strain, and presumably
help the bacteria adapt and survive in ticks and different mammalian hosts.
Ticks
Ticks go through three different life
stages in two years: larval, nymph, and adult.
In the larva stage, a tick can become infected with B. burgdorferi by feeding on an infected rodent or non-human
vertebrate. The bacterium remains in
the tick throughout its life cycle. In
the nymph and adult stages, the infected ticks can then, in turn, pass on the
bacterium to other vertebrates, including humans.
http://www.cdc.gov/ncidod/dvbid/lyme/4ticks_cm.htm
Stages of tick growth: adult, nymph,
larva, larva, respectively. On 1cm
scale.
Ticks thrive in the leaf litter of
temperate forests with relative high humidity.
Leaf litter provides an effective shelter from the elements.
Symptoms
Humans:
Characteristic “bulls-eye” rash
Erythema migrans
Fever
Malaise
Headaches
Muscle Aches (myalgia)
Joint Aches (arthralgia)
Early neurological complications
include lymphocytic meningitis, cranial neuropathy (especially facial nerve
palsy), and radioneuritis.
Musculoskeletal complications include
migratory muscle
Although some infected patients are
asymptomatic
Domestic animals:
Lyme
disease has been described in dogs, cats, horses, cattle, and goats. Symptoms
can be intermittent and vary in intensity from mild to quite severe. They can also mimic many other conditions.
If you suspect Lyme disease in your animals, consult your veterinarian as soon
as possible.
Symptoms include:
Fever
Lameness
Soreness
Listlessness
Loss of appetite
Swollen glands
Swollen joints
Heart, kidney, liver, eye and nervous
system problems
In horses and
cattle:
Laminitis
Poor fertility
Abortions
Chronic weight loss
Incubation period:
7-14 days
Treatment
Lyme
disease can be treated with
antibiotics, and, if treated early on, chances of recovery increase and
severity of the symptoms decrease in both humans and animals. Generally a 3-4 week course of doxycyline or
amoxicillin is effective for early onset symptoms. Cefuromime axetil or erythromycin can be used for patients
allegric to penicillin or tetracyclines.
In the later stages of the disease, particularly if neurological
conditions set in, intravenous ceftriaxone or penicillin may be administered
for 4 weeks or more, depending on the severity of the disease. In the later stages of disease, treatment
may fail, or may need to be repeated.
If untreated in humans, the condition
progresses to late disseminated disease, causing swelling and pain of the
joints, especially the knees; chronic axonal polyneuropathy; and
encephalopathy.
Lyme disease morbidty can be severe, chronic, and disabling. Lyme disease is rarely, if ever, fatal.
In animals, untreated Lyme disease can
lead to progressive chronic arthritis.
Prevention
Avoid tick habitats, especially in the
spring and summer when the nymph stage is active. Ticks live in moist, shady environments in low-lying vegetation,
leaf litter, and overgrown grassy areas.
Deer and rodents must also be present for the bacterium to persist in
its enzootic cycle.
If you are in a tick-infested area:
- Wear light colored clothing, so that ticks
may be seen more easily.
- Wear long pants, tucked into your socks and
long-sleeved shirts to prevent ticks from reaching your skin.
- Insect repellants containing DEET are
effective against tick attachment.
- Permethrin, which kills ticks on contact,
can also be applied to exposed skin.
- Perform a tick check and remove any ticks
found. Transmission of the bacterium is
unlikely within the first 36 hours of attachment.
To remove a tick:
Use fine nose tweezers to grasp the
tick as close to the skin a possible, and slowly pull the tick out of the
body. DO NOT use petroleum jelly, a hot
match, nail polish, or other products to remove the tick. Mouth parts of the tick may remain in the
skin, but shouldn’t cause alarm because the bacterium lives in the midgut or
salivary glands of the tick and will have already been removed.
Risk:
Those most at risk for developing Lyme
disease are those who live in or visit areas endemic with tick
populations. These areas are grassy or
wooded locations populated by white-tailed deer, specifically in the
northeastern and upper Midwestern states and along the northern Pacific coast
of California.
http://www.cdc.gov/ncidod/dvbid/lyme/riskmap.htm
The risk for contracting Lyme disease
is highest in the spring and summer months in the US when the nymphal ticks are
most active and human and animal populations are frequently outdoors and
exposed to ticks.
References:
http://www-2.cs.cmu.edu/afs/cs.cmu.edu/user/jake/mosaic/lyme.html
http://www.cdc.gov/ncidod/dvbid/lyme/index.htm