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Same disease, different transmission.

On the U.S. West Coast, the bacterium responsible for Lyme disease is transmitted through a more complex network of infected animal hosts and tick vectors than on the East Coast, according to a new study. This finding has important implications for controlling the spread of this disease, which causes severe arthritis-like symptoms.

On the East Coast, white-footed mice serve as the reservoir of infection for the Lyme-causing bacterium, Borrelia burgdorferi. The bacteria thrive in the mice and are picked up by the deer tick Ixodes dammini when young tick nymphs feed on the blood of the mice during early summer. The infected nymphs then spread the infection to other animals, including humans (SN: 3/25/89, p.184).

On the West Coast, the process is much more involved, reports entomologist Robert S. Lane of the University of California, Berkeley. Wood rats, not mice, serve as the reservoir for B. burgdorferi in northern California, he says, so efforts to control the disease in that region must target these animals. Moreover, the ticks that transmit the bacterium to humans in northern California do not belong to the same species as the ones that spread it among the wood rats. And northern California harbors more different types of B. burgdorferi than does the East Coast--a factor that could complicate the development of a vaccine against Lyme disease in that state, Lane says.

Lane and Richard N. Brown, a biologist at the University of California, Berkeley, also present their results in the June 5 SCIENCE.

According to statistics compiled by the Centers for Disease Control in Atlanta, California has the fourth-highest incidence of Lyme disease among the 50 states, with 56 cases reported so far this year. The top three states--New York, Pennsylvania and New Jersey--reported 701, 247 and 79 cases, respectively, between Jan. 1 and May 15. However, most scientists believe that Lyme disease is vastly underreported by physicians and that many more cases exist.

Brown says he expects Lyme researchers will find that the disease spreads through different networks of hosts and vectors in various areas of the country.

"We should expect that in some communities, the hosts and vectors will interact differently," he concludes. "It won't be as simple as we once thought."
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Title Annotation:Lyme disease is transmitted in different ways according to region
Author:Ezzell, Carol
Publication:Science News
Article Type:Brief Article
Date:Jun 13, 1992
Previous Article:A biological orientation.
Next Article:Success on the vaccine front.

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