Yale and State Researchers Develop Improved Test for New Tick Disease

Yale and state scientists have developed a new, simpler and more reliable blood test to detect a recently discovered disease called ehrlichiosis, which is carried by deer ticks.

The test will make it less cumbersome for patients with the telltale flu-like symptoms to be screened for the disease. It also will allow researchers to determine whether ehrlichiosis may be as widespread as Lyme Disease in the Northeast.

The new ELISA test was developed by Dr. Jacob IJdo and Dr. Erol Fikrig in the Rheumatology section of Yale Medical School’s Department of Internal Medicine in collaboration with Dr. Louis Magnarelli at the Connecticut Agricultural Experiment Station. Details of the test were published in the November issue of the Journal of Clinical Microbiology.

The organism, Ehrlichia equi, is carried by the same tiny deer tick that carries the Lyme Disease bacteria and, like Lyme Disease, causes flu-like symptoms such as headache, fever and muscle cramps. But unlike Lyme disease, Ehrlichia equi does not produce a bull’s eye rash, which makes it more difficult to diagnose, said Dr. IJdo, a physician-scientist.

Another problem hampering diagnosis is that testing for ehrlichiosis is time-consuming, costly, and is only performed in specialized research laboratories. “With the old test a person could test two dozen blood samples a day,” Dr. IJdo said. “With the new test it is easy to scale up the testing for large numbers of blood samples.”

There are indications that ehrlichiosis infections could be more prevalent because the numbers of confirmed cases are increasing each year, Dr. IJdo said.

“The state of Connecticut started doing surveillance for ehrlichiosis in 1995, and each year the number of cases has doubled,” he said. “Last year there were more than 200 cases in Connecticut.”

Because the same tick is responsible for transmission of both organisms, ehrlichiosis can be expected in the same areas where there is Lyme disease, which are principally the Northeast and the upper Midwest. The new ELISA test uses a recombinant protein that can be produced in large quantities. The test is better because it is standardized, automated and more sensitive, said Dr. IJdo.

“Now we can conduct better surveillance of the disease,” he said. “It took several years to educate people about Lyme Disease, and it may take some time to inform people about Ehrlichia equi. With the ELISA we are set up for next summer’s tick season.”

Testing for ehrlichiosis is conducted by the Connecticut Department of Public Health and Yale’s Department of Epidemiology and Public Health with financial support by the Centers of Disease Control and Prevention (CDC). The test is free for any physician who suspects a patient of having ehrlichiosis. “This is to encourage physicians to submit blood samples so that we can get a better idea how prevalent the disease is,” Dr. IJdo said.

It is not yet known if ehrlichiosis can have the same serious long term effects as Lyme Disease if untreated, Dr. IJdo said. Untreated Lyme Disease, which is caused by the spirochete Borrelia burgdorferi, can result in chronic arthritis and nerve and heart dysfunction.

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