Lyme Disease on Druid Hill

October 12, 1990

Epidemiologists don't yet know what to make of the discovery of Lyme disease spirochetes in ticks found on mice in Druid Hill Park. So far, the likelihood of a mass disease outbreak is small, even though the park borders crowded neighborhoods, according to Brian S. Schwartz, the Johns Hopkins entomologist who found the bacteria.

That's because of the way the disease is spread. Young deer ticks live on white-footed mice, the type in which Dr. Schwartz found the disease, and they live exclusively in wooded areas. Adult ticks feed on the blood of deer, but there are few deer in the park. Thus, unless the disease is more widely spread throughout the park and two other nearby parks, there is little likelihood of a big outbreak.

Still, although Lyme disease has been found all over Maryland, there is the mystery of just how it got into a city park and how long it's been there. It came to light because an elephant keeper at the Baltimore Zoo, located in the park, contracted Lyme disease last year. The man walked frequently through a grassy area outside the elephants' exercise ground, Dr. Schwartz said, and reported getting numerous ticks on him. Disease hunters called to the scene trapped many small animals, finally catching the two infected woodlands mice.

Deer are sometimes known to come down the Jones Falls into the park, and could have brought the infected ticks. If that is how they got there, the disease pocket should dry up as the ticks mature and, finding no deer on which to feed, die out. But if other animals, such as raccoons, can substitute for deer, it may mean the disease is more widely spread and more persistent in areas close to highly developed neighborhoods than anyone thought. Whether one of those other animals could bring it into the city and spread it would then become a prime subject of inquiry.

For now, it's safest to check for ticks after any visit to the park, as with any wooded area. Research indicates the Lyme disease spirochete doesn't pass to a new victim on the first day a tick begins to suck blood, Dr. Schwartz says. Thus, getting any ticks off early could prevent infection. They are small and their mouths penetrate skin without being noticed by most people, so it's best to use a mirror or have others check backs and hard-to-see places. Antibiotics can prevent the more serious consequences of an infection, but it's far better to take preventive steps before then.

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