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Preventing tick bites could save your life

Ticks are second only to mosquitoes as transmitters of human disease, said Richard Houseman, MU associate professor and extension entomologist.

There are more than 800 species worldwide, including the common hard ticks, soft ticks and a third family consisting of a single African species.

2006 Dr. Amanda Loftis, Dr. William Nicholson, Dr. Will Reeves, Dr. Chris Paddock This photograph depicted a dorsal view of a female "lone star tick", Amblyomma americanum. An Ixodes or "hard" tick, A. americanum is found through the southeast and south-central states, and has been shown to transmit the spirochete, Borrelia lonestari, the pathogen responsible for causing a Lyme disease-like rash known as "Southern tick-associated rash illness" (STARI). Representatives from all three of its life stages aggressively bite people in the southern U.S.  Research indicates that live spirochetes are observed in only 1-3% of specimens. Note the characteristic “lone star” marking located centrally on its dorsal surface, at the distal tip of its scutum. A. americanum ticks are found through the southeast and south-central states. Their life cycle and ecologic requirements are similar to Ixodes ticks with minor exceptions not described here. All three life stages of A. americanum aggressively bite people in the southern U.S. Research indicates that live spirochetes are observed in only 1-3% of A. americanum.Even though spirochetes have been seen in A. americanum  ticks by microscopy, attempts to culture it in the laboratory have consistently failed. Modified BSK (Barbour-Stoenner-Kelly) is the best medium for cultivating the Lyme disease spirochete, B. burgdorferi, but is apparently not suitable for cultivating the spirochete found in A. americanum. However, a spirochete has been detected in A. americanum by DNA analysis, and was given the name Borrelia lonestari.

The lone star tick is common and uses mammals and birds as hosts. Whitetail deer are its preferred host. Credit: Photo by James Gathany, Centers for Disease Control and Prevention

Ticks eat only blood, and they can transmit pathogens acquired from one host when feeding on the next host. Adult female hard ticks can swell with blood to weigh 50 to 100 times their original weight.

Most hard ticks have a three-host life cycle, requiring a different host for each stage of development. The three hosts may be of the same or different species.

Development time from egg to adult may take 24 years for hard ticks and 10 years or more for soft ticks, Houseman said. Both sexes feed on the blood of a vertebrate host in all stages.

Soft tickets have varying life cycles. They usually feed repeatedly on the same animal or same family group in a nest.

Ticks spend 95 percent of their lives off of their hosts, Houseman said. They can withstand long periods of starvation, with some studies showing that they can survive more than a year without a host.

Ticks require moisture, which is why they are generally found in humid, cool environments. They find their hosts by “questing,” or climbing onto vegetation and clinging, head down, to grass or branches. They wait for a host to pass and then they latch onto the host.

Houseman said only six of the 800-plus known tick species are commonly associated with human disease in Missouri, and most of these are hard ticks.

To prevent being a tick host, Houseman recommends tucking pant legs into socks or taping them closed before going into tick-infested areas, and spraying tick repellent onto clothing and skin.

Check for infestation immediately after leaving a wooded area rather than waiting to feel a tick bite. Transmission of many diseases takes up to 24 hours of attachment and feeding, so prompt inspection is critical. Wash clothing immediately. While ticks can sometimes survive hot water, they can survive in a hot dryer for only an hour.

 

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