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FOUR COMMON TICKS
OF PENNSYLVANIA
Tick-borne Diseases and Prevention, Tick
Distributions, Life Histories and Control
Back ground Information
Ticks, of which there are more than 500 species world-wide, are
parasitic arthropods closely related to mites. Most ticks feed on
the blood of warm-blooded mammals but some species also feed
on birds, reptiles and even amphibians. Fish are apparently the
only vertebrates not plagued by these little blood-suckers.
Many species of ticks can transmit diseases (zoonoses) from an
infected host to other uninfected hosts. Some of the more frequently
transmitted organisms include parasitic worms, viruses,
bacteria, spirochetes and rickettsias. The most important of these
to Pennsylvanians are spirochetes which cause Lyme disease, and
rickettsias which cause Rocky Mountain spotted fever.
Currently, more than 25 species of ticks have been identified in
Pennsylvania. Of these, four species account for nearly 90 percent
of all submissions to Penn State for identification. The four ticks
are: 1) the American dog tick, Dermacentor variablis; 2) the blacklegged
tick, Ixodes scapularis; 3) the lone star tick, Amblyomma
americanum; and 4) a ground hog tick, Ixodes cookei.
American dog tick:
Dermacentor variables
Distribution:
Dermacentor Variables
is found in the eastern
two-thirds of the United
States from Nova Scotia to
the Gulf Coast. It is the most
commonly encountered tick
in Pennsylvania and occurs in
most counties.
Hosts:
The immature stages are frequently found on small rodents
such as meadow mice. The adults are frequently found on dogs
(hence the name) and can be recognized by the distinctive white
markings on their back. The American dog tick may become
greatly engorged, achieving the size of a grape. In addition to
man, the other hosts are cat, cattle, donkey, hog, horse, mule,
sheep, coyote, deer, fox, wolf, wildcat, badger, opossum, rabbit
raccoon, rat, skunk, squirrel, weasel and ground hog.
Diseases: American dog ticks are the major carrier of Rocky
Mountain spotted fever, which is less common than Lyme disease,
but a potentially more serious illness. This tick has also been
known to transmit tularemia, and to cause tick paralysis. It cannot
transmit the spirochetes responsible for Lyme disease.
Blacklegged tick
Ixodes scapularis
Ixodes scapularis is
found throughout the eastern United
States and in parts of the northern
mid-west in wooded, brushy locations.
It has been expanding its
range in recent years and can now
be found in most of the counties in
Pennsylvania. Three areas of the state are heavily infested: (1)
the southeastern portion of Pennsylvania (in those counties
southeast of a line through Wayne to Adams Counties) (2) the
north central counties of Elk, Clearfield and Cameron; and (3)
Presque Isle in Erie County.
Hosts: The larvae feed on birds and small animals such as squirrels
mice and grouse; the nymphs also feed on small mammals and
birds, while the adults prefer deer. Any stage of the blacklegged
tick can feed on humans.
Diseases: This tick is well known as the vector of Lyme disease
and has also been known to carry human babesiosis - a fairly
rare, generally mild febrile disease. The blacklegged tick typically
requires in excess of 24 hrs. of attachment before it can
transmit the causative agent for Lyme disease.
Note: This tick was previously known as the “deer tick, Ixodes
dammini.” Recently, studies have proven that this tick is not a
new species, and therefore the original designation is used. I.
dammini is no longer a valid species designation.
Lone star tick
Amblyomma americanum
Distribution:
Amblyomma americanum is widely distributed
in the United States. It is
commonly found from Texas
north to Missouri and eastward to
the Atlantic coast. It is found most
often in the southern counties of
Pennsylvania near urbanized areas. The lone star tick may be
active from early spring to late fall.
Hosts: The larvae feed on a variety of small animals, while the
nymphs feed on many small and larger animals. Adults are usually
found on larger animals, and all stages are found on deer
and will feed on humans.
Diseases: The lone star tick is known to vector tularemia, Rocky
Mountain spotted fever, and causes tick paralysis in man and
in dogs. Although regarded as a poor vector for Lyme disease,
there are anecdotal accounts of erythema migrans developing
at the site of attachment. In Pennsylvania, this tick is known to
transmit only Rocky Mountain spotted fever.
Groundhog tick
Ixodes cookei
![](http://farm3.static.flickr.com/2257/2315466802_ca6b6cbdd1.jpg?v=0")
Distribution:
Ixodes cookei is found east
of the Rockies from Texas to South Dakota
and northeastwards through Maine.
This tick is less common, or at least less
commonly encountered, than the three
previously mentioned ticks. It is, however,
a relatively common tick in portions of
western and northern Pennsylvania.
Hosts: This tick is very host-specific for groundhogs, but occasionally
is found on birds, small animals or humans.
Diseases: It is not considered to be an important vector of Lyme
disease because it tends to feed only on groundhogs. In laboratory
studies, the larval I. cookei would not feed on Peromyscus
sp. and as such is probably not a good candidate as a vector for
Lyme borreliosis. Additionally, it is not a known vector for any
other zoonoses.
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