Harvard Health Letter

It's time to really get the ticks off

The warmer months are the prime time for getting tick-borne Lyme disease.

Lyme disease is by far the most common tick-borne disease in the United States. Between 20,000 and 30,000 cases have been reported in most of the past several years, and health officials suspect many more go unreported. The incidence is highest in New England, the Mid-Atlantic states, and Wisconsin. We've posted the latest state-by-state counts on our Web site, www.health.harvard.edu/healthextra. Deer ticks are responsible for the vast majority of Lyme disease cases, although a related tick, Ixodes pacificus, found in the western United States, also can transmit the Borrelia burgdorferi bacteria that cause Lyme disease.

Ticks are a source of human illness because they're able to harbor a disease-causing organism acquired at an earlier stage, which they transmit in their saliva as they enjoy a blood meal during their next one. Deer ticks, for example, pick up the B. burgdorferi when they feed on mice as larvae or nymphs. Neither the ticks nor the mice are the least bit fazed by the bacterial infection. But if an infected tick then feeds on a person, and enough B. burgdorferi gets into that person's skin, he or she may come down with Lyme disease.

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