Background 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 variabilis

Image of American dog tick female. © SBJacobs PSU Entomology

Distribution: Dermacentor variabilis 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

Image of blacklegged tick female. © SBJacobs PSU Entomology

Distribution: 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

Lone star tick Photo by Jim Kalisch Univ. of Nebraska Entomology Department

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

Image of groundhog tick nymph © SBJacobs PSU Entomology.

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.


Lyme Disease

Lyme Disease or Lyme borreliosis is an infection caused by the spirochete Borrelia burgdorferi which is transmitted to humans by ixodid ticks. It is a multisystem illness characterized initially by erythema migrans and a series of common nonspecific complaints and symptoms including headache, fever, sore throat, nausea, etc. and to late phase symptoms which left untreated may progress to debilitating rheumatologic, cardiac, and neurologic conditions, but rarely directly to death.

A skin lesion appears as a red macule or papule and expands to form a large round lesion, over a period of days or weeks. The center of this lesion often tends to progressively clear. This condition is called erythema migrans (EM) and for the purpose of CDC surveillance definition, the lesion must reach a size of 5 cm (approximately 2 inches). Associated or secondary lesions may be present. This symptom is generally accompanied with intermittent fatigue, fever, headache, a stiff neck, arthralgias or myalgias.

Later musculoskeletal, nervous, and cardiovascular systems exhibit more profound manifestations. Weeks or months after the initial erythema migrans there is recurrent swelling of the joints which may become a chronic condition in one or more sites. Lymphocytic meningitis, cranial neuritis, bilateral facial palsy (Bell’s palsy), radiculoneuropathy and occasionally encephalomyelitis occur alone or in combinations. Atrioventricular conduction problems may arise which may lead to myocarditis. Additional symptoms of arthralgia, myalgia, fibromyalgia, headache, fatigue, stiff neck, palpitations, and bundle branch block may be associated, but are not confirmative of Lyme disease.

Rocky Mountain Spotted Fever (RMSF)

RMSF was first recognized in the United States during the 1890s, but until the 1930s it was reported only in the Rocky Mountains. By 1963, over 90 percent of all cases were reported east of the Rockies. In the west, the disease was limited mainly to men who worked and spent time in wooded areas, while in the east, cases occur when people come in contact with infected ticks from their pets or in their yards.

RMSF is caused by a rickettsia, Rickettsia rickettsii. The vector in the east is the American dog tick (Dermacentor variabilis), but the disease is also carried by the lone star tick and the Rocky Mountain wood tick (Dermacentor andersoni). Symptoms include a red-purple-black rash, usually on the wrists and ankles, which appears from two days to two weeks after infection. A fever, headaches, and malaise also are characteristic. Broad-spectrum antibiotics are used to treat RMSF. Diagnosis can be made with a blood test, but treatment should not wait for serological confirmation, as fatalities do occur.


Also known as rabbit fever, tularemia is carried by the Rocky Mountain wood tick, the rabbit tick (Haemaphysalis leporispalustris), the lone star tick, and the American dog tick. Rabbits serve as a reservoir for the bacterium, Francisella tularensis. The number of cases in the United States has dropped considerably in the last 50 years. In 1989 only 144 cases were reported, compared to nearly 2,300 cases in 1939.

Symptoms include a sudden onset of fever, chills, loss of appetite, general body aches, and swollen lymph nodes. An ulcer forms at the site of the bite. Serological tests are used in diagnosis, and treatment consists of antibiotics. If not treated, symptoms intensify. Tularemia causes a few deaths each year.


Caused by a protozoan, Babesia microti, the disease is transmitted by the blacklegged tick (Ixodes scapularis). Fatigue and loss of appetite are followed by a fever with chills, muscle aches, and headaches. In more extreme cases, blood may appear in the urine. Babesiosis is more severe in older people and those with no spleen. Fatalities can occur in older patients. The condition has been treated with drugs that are used to treat malaria, but with limited success. Generally, the disease is self-limiting and symptoms disappear on their own.


Most common in the southern United States, erlichiosis usually occurs in rural areas during May, June, and July. It is caused by a rickettsia belonging to the genus Erlichia. The clinical signs are similar to those of Rocky Mountain spotted fever: chills, headache, body aches, fever, and a rash, though the rash occurs with a lower frequency. Often the symptoms are very mild. Tetracyclines are the treatment, as with RMSF. Originally identified as an animal disease, erlichiosis was believed to be limited to dogs.

Tick Paralysis

Tick paralysis is not a disease, but a condition caused by toxins that a tick injects into its host during feeding. Most mammals seem to be affected, but smaller and younger mammals (children) are more susceptible.

Symptoms begin a day or two after initial attachment. The victim loses coordination and sensation in the extremities. The paralysis progresses in severity, the legs and arms becoming useless; the face may lose sensation; and speech becomes slurred. If the breathing center of the brain is affected, the victim may die. If the tick or ticks are found and removed, recovery begins immediately, and the effects disappear within a day.

Generally, this condition is associated with ticks attached around the head area, particularly at the base of the skull. Ticks that have been implicated in tick paralysis in the United States are the Rocky Mountain wood tick, the lone star tick, and the American dog tick. However, not all members of a species cause tick paralysis. The toxin that causes this condition is part of the salivary fluid that the tick injects. Because the problem is associated with ticks attached on the head, and because recovery is quick upon removal of the tick, it is theorized that the toxin acts locally and is broken down in the body rapidly. Tick paralysis occurs only sporadically; the important thing is to be aware that it exists and, when symptoms occur, to attempt to find the tick and remove it.

Lyme Disease and Dogs

Most dogs, even though they have been exposed to Borrelia burgdorferi, never exhibit any signs of Lyme disease. In certain highly endemic areas of New York and New Jersey dogs exhibit almost a 90% rate of exposure as evidenced by serosurvey. However, only about 4% of the dogs exhibit signs of Lyme disease including lameness, poor appetite and fever. Treatment of these animals with antibiotics typically results in rapid recovery.

A few dogs can develop lesions on the kidneys (Lyme nephropathy) and may not respond to antibiotic treatment. Interestingly, dogs susceptible to this condition may not be protected by the Lyme vaccines currently available. In fact, there are concerns that the vaccine may possibly sensitize a genetically predisposed individual to having a more intense immune-mediated reaction to Lyme antigens, or the vaccine may add to antigen-antibody complex deposition in tissues (Meryl P. Littman, VMD, DACVIM, University of Pennsylvania - personal comm. 2001).

Kennels, runs, or yards can be treated with a variety of residual insecticides labeled for tick control at these locations. Tick pesticides that are labeled for exterior tick control include bifenthrin, cyfluthrin, deltamethrin, esfenvalerate, permethrin and tralomethrin. Follow all label instructions. Do not apply materials labeled for kennels, yards and other exterior sites on your pets.

Partially reproduced from the Penn State College of Agricultural Sciences House Flies Fact Sheet
Authored by: Steve Jacobs, Sr. Extension Associate Revised August 2007
For the Complete Fact Sheet please go to this link: http://ento.psu.edu/extension/factsheets/ticks

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