Story Highlights• CDC: Lyme disease cases in the U.S. have doubled since 1991
• Lyme disease most common U.S. illness transmitted by bugs or animals
• Lyme disease can cause long-term effects if not treated with antibiotics
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WASHINGTON (Reuters) -- The number of cases of Lyme disease has doubled in the United States since 1991 and these numbers are probably underestimated, the U.S. Centers for Disease Control and Prevention said Thursday.
More than 21,000 cases of the tick-borne disease are now reported every year, the CDC said, making it the most common illness transmitted by bugs or animals in the United States.
The northeastern states had the most cases, with 2,335 cases reported in Massachusetts in 2005, 3,363 in New Jersey, 5,565 in New York, and 4,287 in Pennsylvania.
"This increase likely is the result of several factors, including a true increase in disease incidence and enhanced case detection resulting from implementation of laboratory-based surveillance in several states," the CDC said in its weekly report on death and disease.
Lyme disease, marked by a characteristic rash and joint pain, can cause long-term effects if not treated with antibiotics. They can include arthritis, heart disease and nervous system damage.
It is caused by bacteria called Borrelia burgdorferi and is easily treated with antibiotics.
The CDC said a Lyme disease vaccine was once available but was taken off the market in 2002, after the company that made it reported poor sales.
"Persons can lower their risk for the disease and other tick-borne illnesses by avoiding tick-infested areas when possible, using insect repellents containing DEET, and performing daily self-examination for ticks," the CDC advised.
Picking the ticks off within 24 hours also makes them less likely to transmit the bacteria.
"Tick populations around homes and in recreational areas can be reduced 50 percent to 90 percent through simple landscaping practices such as removing brush and leaf litter or creating a buffer zone of wood chips or gravel between forest and lawn or recreational areas," the CDC said.