Geographic distribution of ticks that bite humans
Of the many different tick species found throughout the world, only a select few bite and transmit disease to humans. These maps provide general insight into the expected distribution these human-biting ticks in the contiguous United States. Populations of ticks may be found outside noted areas. Although there are more than 800 species of ticks found throughout the world, fewer than 60 are known to bite and transmit disease to humans. Here are some of the more common ticks and the geographic locations where you'll most likely encounter them.
* Note that adult ticks are the easiest to identify and male and female ticks of the same species may look different. Nymphal and larval ticks are very small and may be difficult to identify. Cases are reported from the infected person’s county of residence, not necessarily the place where they were infected.
Where found: Widely distributed in the northeastern and upper midwestern United States.
Transmits: Lyme Disease, babesiosis,
anaplasmosis, and Powassan disease.
Comments: The greatest risk of being bitten exists in the spring, summer, and fall. However, adults may be out searching for a host any time winter temperatures are above freezing. Stages most likely to bite humans are nymphs and adult females
ROCKY MOUNTAIN WOOD TICK
Where found: Rocky Mountain states and southwestern Canada from elevations of 4,000 to 10,500 feet.
Transmits: Rocky Mountain spotted fever, Colorado tick fever, and tularemia.
Comments: Adult ticks feed primarily on large mammals. Larvae and nymphs feed on small rodents. Adult ticks are primarily associated with pathogen transmission to humans.
GULF COAST TICK
Where found: Coastal areas of the U.S. along the Atlantic coast and the Gulf of Mexico.
Transmits: Rickettsia parkeri rickettsiosis, a form of spotted fever.
Comments: Larvae and nymphs feed on birds and small rodents, while adult ticks feed on deer and other wildlife. Adult ticks have been associated with transmission of R. parkeri to humans.
BROWN DOG TICK
Where found: Worldwide.
Transmits: Rocky Mountain spotted fever
Comments: Dogs are the primary host for the brown dog tick in each of its life stages, but the tick may also bite humans or other mammals.
WESTERN BLACKLEGGED TICK
Where found: Along the Pacific coast of the U.S., particularly northern California.
Transmits: Anaplasmosis and Lyme disease.
Comments: Nymphs often feed on lizards, as well as other small animals. As a result, rates of infection are usually low (~1%) in adults. Stages most likely to bite humans are nymphs and adult females.
AMERICAN DOG TICK
Where found: Widely distributed east of the Rocky Mountains. Also occurs in limited areas
on the Pacific Coast.
Transmits: Tularemia and Rocky Mountain spotted fever.
Comments: The highest risk of being bitten occurs during spring and summer. Dog ticks are sometimes called wood ticks. Adult females are most likely to bite humans.
Where found: Throughout the western half of the U.S. and southwestern Canada.
Transmits: Tick-borne relapsing fever (Borrelia hermsii, B. parkerii, or B. turicatae)
Comments: Humans typically come into contact with soft ticks when they sleep in rodent infested cabins. The ticks emerge at night and feed briefly while the person is sleeping. The bites are painless, and most people are unaware that they have been bitten.
Where found: Throughout the eastern half of the U.S. and Canada.
Transmits: Powassan disease.
Comments: Also called woodchuck ticks. All life stages feed on a variety of warmblooded animals, including groundhogs, skunks, squirrels, raccoons, foxes, weasels, and occasionally people and domestic animals.
LONE STAR TICK
Where found: Widely distributed in the southeastern and eastern United States.
Comments: A very aggressive tick that bites humans. The adult female is distinguished by a white dot or “lone star” on her back. Lone star tick saliva can be irritating; redness and discomfort at a bite site does not necessarily indicate an infection. The nymph and adult females most frequently bite humans and transmit disease.
Tick Life Cycle
The life cycle of the hard tick Ixodes dammini, a carrier of the bacterium that causes Lyme disease in humans, requires two years for completion. Eggs are deposited in the spring, and larvae emerge several weeks later and feed once during the summer, usually on the blood of small mammals.
Most ticks of public health importance follow this pattern, including members of the general
Ixodes (Lyme borreliosis, babesiosis, human granulocytic ehrlichiosis),
Amblyomma (tularemia, ehrlichiosis and Rocky Mountain spotted fever)
Dermacentor (Rocky Mountain spotted fever, Colorado tick fever, tularemia, tick paralysis),
Rhipicephalus (Rocky Mountain spotted fever, boutonneuse fever).
TICK LIFE CYCLE
©Baxter Healthcare Tick Animation
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