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Ticks May Be Culprits for More Diseases

Friday April 20, 2001

By AliciaMarie Belchak

NEW YORK (Reuters Health) - Ticks may spread more diseases than previously thought, California researchers have found.

Ticks carry bacteria that cause disease, including Lyme disease and Rocky Mountain spotted fever. New evidence published in this month's Journal of Clinical Microbiology implicates ticks in other maladies, including cat scratch fever. This infection, as well as another illness known as ``trench fever,"" are caused by members of a family of bacteria known as Bartonella.

``We cannot say for certain that ticks are the vectors of these diseases, but at the least we can say they carry Bartonella DNA and could be potential (transmitters),"" Dr. Bruno Chomel of the University of California at Davis and one of the study's authors, said in a prepared statement.

Chomel and his colleagues are beginning to suspect ticks in many diseases where the pathways of transmittal seem fuzzy. One bacterium, Bartonella quintana, caused the ``trench fever"" World War I troops caught on the battlefield. In the trenches, lice spread the disease. But in a recent outbreak in Seattle, Washington, lice were not a factor, the researchers note.

Another infection, cat scratch disease, raises more questions about transmission. While generally mild and self-limiting among people with healthy immunity, the disease can lead to potentially fatal complications in people with weak immune systems.

Scientists had thought that cat scratch fever, which is caused by Bartonella henselae, was passed to humans from cat bites or scratches, as the name would suggest. But past research has found that as many as 30% of human patients infected may not have been bitten or scratched by a cat, and another study linked the infection to tick bites.

For the current study, Chomel and colleagues set out to determine if ticks might really be a possible channel of Bartonella-related disease. If Bartonella organisms could be found in ticks before they fed on larger animals, it would suggest that ticks played an important role in spreading these illnesses. To help answer this question, Chomel and colleagues collected hard ticks at three sites in Santa Clara County and extracted DNA from their bodies, hoping to match specific genes to those of Bartonella bacteria. Of the 151 ticks they examined, the researchers found nearly 20% carried a Bartonella species, including those known to cause disease in humans.

``That's even higher than for known tick-borne diseases like Borrellia burgdorferi (the cause of Lyme disease),"" Chomel said in a press release.

The study doesn't provided positive proof that ticks are responsible for the spread of these diseases in humans, he noted, but it does suggest that the arthropods are worthy of more investigation.

SOURCE: Journal of Clinical Microbiology 2001;39:1221-1226.

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