Ehrlichiosis Now Second Most Prevalent Tick-Associated Disease, Yale Study Shows

Ehrlichiosis, a recently described disease that causes flu-like symptoms similar to Lyme disease, is now the second most common tick-transmitted ailment in southeastern Connecticut, a Yale study shows.

Ehrlichiosis causes symptoms such as headache, fever and muscle aches, but unlike Lyme Disease, it does not produce a tell-tale expanding skin rash.

The study published in the April issue of the Journal of Infectious Diseases was conducted by researchers from the Rheumatology section of the Department of Internal Medicine and the the Department of Epidemiology and Public Health at the Yale School of Medicine in collaboration with the Connecticut Agricultural Experiment Station (CAES) and the Connecticut Department of Public Health.

A three-year surveillance study among residents in southeastern Connecticut, where rates of Lyme disease are high, found annual rates of illness ranging from 24 cases to 51 cases of ehrlichiosis per 100,000 inhabitants per year.

In comparison, the annual rate of Lyme disease in the same area is about 275 cases per 100,000 persons. The rate of Lyme disease has climbed steadily from about 50 cases per 100,000 people per year since the disease was identified in the mid-1970s.

“As doctors and patients become more familiar with ehrlichiosis, it is likely there will be a greater recognition factor, as has happened in the past for Lyme disease,” said Dr. Jacob IJdo, a rheumatologist and lead author of the study. “At this point it is hard to predict if ehrlichiosis will become as frequent as Lyme disease.”

“The rate of ehrlichiosis, even at 24 to 51 cases per 100,000, is still much higher than previous estimates,” he added. In addition, the same tick can carry the bacteria for both Lyme disease and ehrlichiosis, IJdo said.

The surveillance for ehrlichiosis was conducted from 1997-1999 as part of the Connecticut Emerging Infections Program’s ehrlichiosis project and was supported through grants from the Centers for Disease Control and Prevention.

The investigators contacted physicians in southeastern Connecticut and asked them to submit blood samples from patients that they suspected might have ehrlichiosis. The samples were tested at Yale University and CAES. Approximately 25 percent of all patients tested were found to have ehrlichiosis.

Last year, the same investigators reported on the development of a better laboratory test for ehrlichiosis. “The test has been validated for accuracy and is ready for use,” said Dr. Louis Magnarelli, a researcher at CAES and co-author of the new study. “The combination of a better test and increased awareness of ehrlichiosis will contribute to improved diagnosis and treatment of this disease in the future.”