For the first time, doctors have shown that a quick dose of antibiotics can ward off Lyme disease after a tick bite, but they caution against overusing the treatment.
Some physicians already give antibiotics to people who are bitten by deer ticks, the bugs that spread Lyme disease. However, many experts oppose this, because there has been no clear evidence the treatment actually prevents the disease, even though antibiotics can clear up Lyme disease once it occurs.
Now there is proof the approach works. A study conducted in New York's Westchester County, where Lyme disease is common, found that just two pills of doxycycline are highly effective if given within three days of a bite.
"Ours is the first study to show that Lyme disease can be prevented after a tick bite," said the study's chief author, Dr. Robert B. Nadelman of New York Medical College in Valhalla, N.Y.
The study, to be published in the July 12 issue of the New England Journal of Medicine, was released on the journal's Web site early today because of its importance.
About 15,000 cases of Lyme disease are reported annually in the United States, mostly in the Northeast from Maine to Maryland; the Midwest in Wisconsin and Minnesota, and the West in northern California and Oregon.
Tick Bites Rarely Lead to Infection
While confirming the effectiveness of so-called prophylactic antibiotics, the study also shows that even in a Lyme-infested area, deer tick bites rarely result in infection. In fact, only nymphal stage bugs filled with blood posed a risk.
The latest study involved 482 people who had removed an Ixodes scapularis tick — the deer tick — from their bodies within the previous 72 hours and took it with them to the doctor for identification. They were randomly given either a 200-milligram dose of doxycycline or dummy pills.
The antibiotic was 87 percent effective at preventing Lyme disease, even though the overall risk was low, just 3 percent among those getting the dummy pills. This means it would be necessary to treat about 40 people to prevent one case of Lyme disease.
Still, Nadelman said it may make sense to treat people if they are bitten by a blood-filled nymphal stage deer tick in an area where Lyme disease is common.
Deer ticks go through three stages. Larval stage ticks have six legs, while nymphal and adult ticks have eight. An unfed nymphal tick is the size of a poppy seed and an adult the size of a sesame seed. Nymphal ticks exist in most places only from May through July.
Lyme disease causes fatigue, fever and joint pain that can persist for weeks, and some patients develop severe arthritis. Lyme also can badly damage the heart and nervous system if it goes untreated by antibiotics.
Signs include rash and flulike symptoms. Daily tick checks, vaccinations and insect repellent are recommended as preventive measures.
The idea of giving antibiotics to tick bite victims even before they show signs of Lyme disease has long been controversial. Last year, the Infectious Diseases Society of America released guidelines saying this should not be done routinely.
"Guidelines are made to be revised and revisited," said Nadelman, who helped draw up last year's recommendations. However, he said doctors should use antibiotics judiciously, because the medicine can cause nausea, especially if taken on an empty stomach.
"The danger is whether it will be used in situations where there is a very low chance of someone having Lyme disease," said Dr. Alan Barbour of the University of California at Irvine.
"People hear about this and ask their doctor, and the doctor is more likely than not to go along with their requests."
Barbour said doctors should be taught in medical school how to identify deer ticks. Some confuse them with other creatures, such as tiny spiders, lice and other more common kinds of ticks.
Most people who get Lyme disease can be cured with antibiotics, although occasionally people have lingering symptoms. Other research in the journal from Dr. Mark S. Klempner of Boston University School of Medicine found that prolonged antibiotic treatment is ineffective against this condition.