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Ticks

Where Ticks Come From

Medical Authors: Barbara K. Hecht, PhD, Frederick Hecht, MD
Medical Editor: William C. Shiel Jr., MD, FACP, FACR

Learn how to reduce your risk of exposure to ticks. Ticks carry the bacteria that cause Lyme disease. People contract Lyme disease by being bitten by these ticks.

In order to investigate whether specific human behavior increases the risk of tick exposure, researchers from the University of California at Berkeley took to the woods. They found that sitting on a log carried with it the greatest risk of picking up a tick. If you sit on a log (at least in Northern California) for only five minutes, you have a 30% chance of getting a tick on you! Gathering wood was also cited as a risky activity as well as leaning up against a tree.

Comment: Aside from issuing a press release (below) about this study, it was also published in the current issue of the Journal of Medical Entomology. In case you aren't familiar with this journal, it is chock-full of everything you might want to know (or not know) about the dangers that mosquitoes, cat fleas, ticks, flies, scorpions, mange mites and other insects pose to you. We don't recommend it for bedtime reading.

Read the press release and learn how to avoid ticks »

Top Searched Ticks Terms

removal, Rocky Mountain spotted fever, Lyme disease, babesiosis, ehrlichiosis, tularemia

Ticks Overview

Ticks are the leading carriers (vectors) of diseases to humans in the United States, second only to mosquitoes worldwide. It is not the tick bite but the toxins, secretions, or organisms in the tick's saliva transmitted through the bite that causes disease.

Ticks are arthropods, like spiders. There are more than 800 species of ticks throughout the world.

Two families of ticks, Ixodidae (hard ticks) and Argasidae (soft ticks), are important to humans because of the diseases or illnesses they can transmit or cause. Hard ticks have a tough back plate or scutum that defines their appearance. The hard ticks tend to attach and feed for hours to days. Disease transmission usually occurs near the end of a meal, as the tick becomes full of blood. Soft ticks have more rounded bodies and do not have the hard scutum found in hard ticks. These ticks usually feed for less than one hour. Disease transmission from these ticks can occur in less than a minute. The bite of some of these ticks produces intensely painful reactions. Ticks can transmit disease to many hosts; some cause economic harm such as Texas fever (bovine babeiosis) in cattle that can kill up to 90% of yearling cows.

The following is a list of tick-borne diseases, the usual tick vector(s), and the pathogen(s) the tick transmits:

Lyme disease -- Ixodes species including deer ticks (hard ticks) -- vectors for Borrelia species of bacteria

Babesiosis -- Ixodes species (hard ticks) -- vectors for Babesia, a protozoan

Ehrlichiosis -- Amblyomma americanum or lone star ticks (hard ticks) -- vectors for Ehrlichia chaffeensis and Ehrlichia ewingii bacterial species

Rocky Mountain spotted fever -- Dermacentor variabilis (American dog tick) and Rocky Mountain wood tick (Dermacentor andersoni) (hard tick) are the primary vectors and occasionally the brown dog tick (Rhipicephalus sanguineus); Amblyomma cajennense (hard tick) is the vector in countries south of the United States -- vectors for Rickettsia bacteria

Southern tick-associated rash illness (STARI) -- Amblyomma americanum or lone star tick (hard tick) -- infectious agent not yet identified according to U.S. Centers for Disease Control and Prevention (CDC)

Tick-borne relapsing fever -- Ornithodoros moubata or African tick (soft tick) -- vectors for Borrelia species of bacteria

Tularemia -- Dermacentor variabilis (American dog tick) (hard tick) and Amblyomma americanum or lone star tick (hard tick) - vectors for Francisella tularensis bacteria

Anaplasmosis (human granulocytic anaplasmosis or HGA) -- Ixodes species (hard tick) -- vectors for Anaplasma phagocytophilum bacteria

Colorado tick fever -- Dermacentor andersoni (hard tick) -- vectors for Coltivirus, a RNA virus

Powassan encephalitis -- Ixodes species and Dermacentor andersoni (both hard ticks) -- vectors for Powassan encephalitis virus, an RNA arbovirus

Q fever -- Rhipicephalus sanguineus, Dermacentor andersoni, and Amblyomma americanum (all three are hard ticks) -- vectors for Coxiella burnetii, a bacterium

Outbreaks of tick-related illnesses follow seasonal patterns (about April to September in the U.S.) as ticks evolve from larvae to adults. Ticks go through life cycles that involve mating and larval formation and usually have several hosts; the last Web citation shows the complicated life cycles of ticks. Ticks hide in low brush; this location allows them to physically contact a host. A recent study suggested that leaning against a tree or sitting on an old log was the quickest way to acquire ticks (about 30 seconds) in tick-infested areas. Ticks require a "blood meal" to grow and survive, and they are not very particular upon whom or what they feed. If ticks don't find a host, they may die.

Once a tick finds a host (such as a human, a pet dog or cat, a deer, or a rabbit) and finds a suitable site for attachment, the tick begins to burrow with its mouthparts into exposed skin. Tick mouthparts are barbed, which helps to secure them to the host.

Often the tick secretes "cementum" to more firmly attach its mouthparts and head to the host. Ticks may secrete or regurgitate small amounts of saliva that contain neurotoxins. These nerve poisons cleverly prevent the host from feeling the pain and irritation of the bite. Consequently, individuals may never notice the tick bite or its feeding. The saliva may contain a blood thinner to make it easier for the tick to get its blood meal. Some people are allergic to these secretions and may have a quick and severe allergic reaction to a tick bite.