Case Study 2
Boy with Fever and Rash
Question 3 of 6
How is Lyme disease usually transmitted?
A. Bite of infected tick
Lyme diease is spread by the bite of ticks of the genus Ixodes infected with Borrelia burgdorferi. Ticks become infected with Lyme disease bacteria when they feed on infected animals (humans, mice). A recent survey showed that in the northeaster US (Massachusetts to Maryland) more than 20% of the ticks are infected with B. burgdorferi. Ticks drop on their host animals from vegetation. They cannot jump or fly but only crawl. People who frequent wooded, brushy, and grassy areas are most likely to get in contact with ticks. Ticks feed on blood by inserting their mouth parts into the skin of the host. This allows the bacterium to enter the skin of the human host and cause disease.
B. Contact with lesion of infected person
Spread of the disease by any route other than introduction of B. burgdorferi into the blood stream by an infected tick is highly unlikely. Borrelia burgdorferi is a very "fragile" organism. It requires specific conditions for it's growth and survival which are present in the tick or it's mammalian host (lower oxygen levels, many nutrients.)
C. Ingestion of contaminated food
Ingested bacteria would not survive the passage through the highly acidic stomach and the environment in the intestine is not suitable for growth.
D. Introduction of contaminated soil in skin lesion
Survival outside its hosts in soil or food is very short and spread of the disease by this route very unlikely
The Biology Project
University of Arizona
Tuesday, August 4, 1998
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