Magazine article Science News

New Carrier: Common Tick Implicated in Spread of Fever

Magazine article Science News

New Carrier: Common Tick Implicated in Spread of Fever

Article excerpt

A wide-ranging tick previously considered to be little more than a nuisance to people is responsible for at least 11 eases of Rocky Mountain spotted fever in eastern Arizona, researchers report. The lethal bacterial disease had been virtually unknown in that area.

The cases represent the first documented U.S. outbreak of the disease directly attributable to the brown dog tick, Rhipicephalus sanguineus. Health officials had presumed that the fever spreads exclusively through American dog ticks and Rocky Mountain wood ticks--species that typically feed on wild rodents and other small mammals, including dogs. These ticks also prefer moist climates. In contrast, brown dog ticks feed almost exclusively on dogs and are more common in dry climates than the other ticks are.

In Arizona, feral dogs that lived in and around two towns carried the disease, says epidemiologist Linda J. Demma of the Centers for Disease Control and Prevention in Atlanta. Although residents didn't allow the dogs into their homes, they fed the animals and children played with them.

Demma went to Arizona in 2002 to investigate an unusual report of Rocky Mountain spotted fever. She wasn't surprised to learn that people who showed symptoms of the disease had been exposed to tick-covered dogs. "We found more than 100 ticks on some of the dogs," she says.

But Demma was stunned when she found only brown dog ticks on the dogs and near the patients' houses. However, laboratory analysis soon confirmed that some of the ticks carried Rickettsia rickettsii, the bacterium that causes Rocky Mountain spotted fever. …

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