INTRODUCTION.
The common name blacklegged refers to their dark legs which are in contrast to the paler
body and that of deer because the preferred adult host is the white- tailed deer; in the
midwest, it is called the bear tick. This tick is of medical importance because it is an
important vector of Lyme disease. Blacklegged ticks are found primarily in the
northeastern, Midwestern, and southeastern states in the United States, but extend into
Mexico. In error, this tick was described in 1979 as the new species Ixodes dammini by
Spielman, Clifford, Piesman & Corwin; this error was corrected by Olivier, Jr., et.
al. in 1993.
RECOGNITION.
Unengorged female about 1/8" (2.7 mm) long, male smaller (about 1/16"/2 mm).
Body oval, dorsoventrally flattened (top to bottom), not hard-shelled. Color orangish
brown except legs, mouthparts and scutum (dorsal shield just behind mouthparts) dark
reddish brown but abdomen darker when engorged; male body reddish brown overall. Scutum
present, longer than wide, almost completely covering dorsum in male. Eyes lacking.
Capitutum (mouthparts and their base) visible from above; hypostome (toothed median
mouthpart) with apex sharply pointed. Coxa I (I st pair of legs) with internal spur
(projection from coxal base) overlapping coxa 11 (2nd pair of legs). Abdomen with anal
groove in front of anus; lacking abdominal festoons (rectangular areas divided by grooves
along posterior margin).
Unengorged lst instar larvae about 1/32" (0.7-0.8 mm) long, with 6 legs; 2nd
instar nymphs about 1/1 6" (1.1 -1.8 mm) long, with 8 legs.
SIMILAR GROUPS.
Pacific/western blacklegged tick (Ixodes pacificus) with scutum
(dorsal shield) almost round (subcircular);
Soft ticks (Argasidae) lack a scutum (dorsal shield), with capitulum
(mouthparts and their base) ventral, not visible from above.
BIOLOGY.
Although the life cycle (egg to egg) can be completed in 2 years in nature, it may be
extended to 4 years if hosts are scarce. Adult ticks feed during the winter primarily on
the white-tailed deer, Odocoileus virginianus (Zimmermann). Here they mate, with the male
dying shortly after mating and the female remaining on the host. In the spring, the female
drops off the host and deposits about 3,000 eggs. The 6-legged larvae hatch out in several
weeks (48-135 days) and can be found June through September. They feed for 3-9 days but
only once, usually on small mammals such as mice, chipmunks, voles, etc. but the preferred
larval host is the white-footed mouse, Peromyscus leucopus Rafinesque. Larvae feeding
before September molt promptly and overwinter as 8-legged nymphs; those which feed later,
overwinter engorged and molt into nymphs the following spring. Nymphs feed for 3-8 days
but only once during the summer, usually on mice or larger mammals such as squirrels,
raccoons, opossums, skunks, dogs, and humans, or on birds. Nymphs can be found from April
through August, with the population usually peaking in June or July. These fed nymphs then
require 25-56 days to molt into adults in the autumn. The adults attach primarily to the
white-tailed deer, engorge, and mate. The male dies after mating but the female continues
to feed until egg development is completed and remains on the deer until spring when she
drops off to lay eggs. Shortly after her eggs are laid, the female dies.
If adults do not feed during their first season (autumn through spring), they die
before summer's end. If nymphs do not feed their first season (summer), most die off but
they can survive through 2 seasons (May through August of the next year); they develop
into adults in the same year in which they feed. Unfed larvae survive less than one year,
they usually survive the winter but die during the following year.
Lyme disease is caused by the spirochete, Borrelia burgdort@eri Johnson, Schmid, Hyde,
Steigerwalt & Brenner, which is a corkscrew-shaped bacteria. Its primary wild
reservoir is the white-footed mouse which is infected by the spring-feeding, pathogen-
infected blacklegged/deer tick nymphs. These white-footed mice then serve to infest the
later-feeding blacklegged/deer tick larvae, which keeps the disease cycle going. Tick eggs
don't contain the spirochete, so it is acquired via feeding.
It is the pathogen-infected blacklegged/deer tick nymphs, which are most active in
mid-summer (May-July) and use a wide variety of hosts, that are primarily responsible for
Lyme disease in humans in the northeast and midwest. Larvae and nymphs have been collected
on 29 species of mammals in 7 orders, and from 49 species of birds (23 species being
migratory birds) in 17 different families.
In the west, the primary Lyme disease vector is the Pacific/western blacklegged tick,
lxodes pacificus Cooley and Kohis, while in the south the vector(s) is suspected to be the
lone star tick, Amblyomma americanum (Linnaeus).
HABITS.
Blacklegged/deer ticks climb grass and shrubs to wait for a passing host, and move very
little laterally. They concentrate on such vegetation located in transitional areas/zones
such as where forest meets field, mowed lawn meets unmowed fence line, a foot/animal trail
through high grass or forest, etc. Because these transitional areas or edge habitats are
where most animals travel sometime each 24-hour period, this is where the ticks are mostly
likely to acquire a host.
The other habitat most likely to harbor ticks is the den, nest, or
nesting area of its host such as that of skunks, raccoons, opossums, but especially the
white-footed mouse. The white-footed mouse prefers woody or brushy areas. It nests in any
place that gives shelter such as below ground, in stumps, logs, old bird or squirrel
nests, woodpiles, buildings, etc.
A favorite feeding area for these ticks on humans is at the back of the
neck, at the base of the skull; long hair makes detection more difficult. However, the
ticks will usually wonder about for up to 4 hours or so before they attach. Then, a tick
has to be attached for a period of 6-8 hours before a successful transmission can take
place.
LYME DISEASE.
The symptoms are usually divided into 3 stages, and they mimic several different commonly
occurring diseases.
Symptoms: Spreading rash, fever, flu-like symptoms, aches.
Stage 1: Expanding rash (Erythema migrans or EM rashes). 3-30 days
after bite.
- Ringlike/builseyelike appearance to rash.
- One or more rash sites.
- May or may not have flu symptoms.
- May come and go or persist.
Stage 2: Complications or disorders of the heart or nervous system.
- Heart. Varying degrees of blockage of the heart muscle.
- Nervous system. Meningitis, encephalitis, facial paralysis.
- "Bell's palsy," other conditions involving peripheral nerves.
- Migratory pain in joints, tendons, muscles, and bones, often without joint swelling
orredness.
Stage 3: Months to years after disease onset.
- Arthritis that appears and disappears intermittently for several years.
- Enlarged knee joints.
- Erosion of cartilage and bone.
Treatment notes:
- Once bitten by a blacklegged/deer tick possessing the spirochete, it may not produce
antibodies in the victim for up to 6 weeks. Therefore, it takes time to verify that one
has Lyme disease.
- Oral medications for Lyme disease can destroy the spirochetes in the blood and give an
antibody reading that the person is "cured." However, the spirochete may persist
in the brain and reappear in the person 5-10 years later. Therefore, intravenous treatment
is advised over oral medications by some physicians considered experts in this area,
especially for persons showing Stage 2 and Stage 3 symptoms.
Tick Removal:
- The best way to remove a tick found attached to a person or pet is to firmly grasp it
with a pair of tweezers as close to the skin as possible.
- Pulifirmlybutgentlybackwardsuntilthetickpulisfree.
- Do not touch the tick, but save it in rubbing alcohol for later identification.
Epidemiological Notes:
- Epidemiologists have isolated an unidentified type of spirochete from ticks collected in
southeastern Missouri which appears to be different from Borrelia burgdorferi.
- Initial studies show that infection by this "new/different" spirochete can
result in the expanding rash (EM) but that it is less often followed by multiple skin
lesions than with Lyme disease.
Therefore, more than one species of tick may be the vector. It is
best to characterize the Missouri victims as suffering from a "Lyme-like"
illness rather than Lyme disease.
