What is Lyme disease?
Lyme disease is an infection caused by the bacteria Borrelia burgdorferi and Borrelia mayonii, which are carried primarily by the deer tick, also known as the black-legged tick. People bitten by an infected tick may develop an inflammatory condition, which first affects the skin and then may spread to the joints, nervous system, and other body systems.
The ticks that cause Lyme disease are tiny, about the size of the head of a pin or a speck of dirt. They can be found anywhere on the body but tend to attach themselves to areas such as the scalp and groin. People who have exposure to ticks but have not been bitten will not be infected by Borrelia, and many who are bitten will not develop Lyme disease. This is because not every tick is infected and because it can take the tick from 24 to 72 hours after attachment to transmit the bacteria.
Lyme disease is found throughout the northern hemisphere, but the strains of bacteria that cause it and the insects that carry it vary from region to region. In the U.S., Lyme disease is the most commonly reported illness spread by insects (vectorborne). It was the fifth most common Nationally Notifiable disease in 2013, but this does not apply across all states. Lyme disease occurs most frequently in northeastern and midwestern states. The vast majority of the cases occur in the spring and summer when people spend more time outside and the ticks are active.
According to statistics available from the Centers for Disease Control and Prevention (CDC), about 30,000 cases of Lyme disease are reported in the U.S. each year. Roughly 95% of Lyme disease cases are reported from 14 states (see map on this CDC web page).
However, the CDC estimates that the actual number of people in the U.S. who are diagnosed with Lyme disease each year is roughly 10 times the number reported. The higher estimate of 300,000 cases annually is based on data from ongoing studies. This higher estimate does not mean that many Lyme disease cases go untreated, says the CDC, only that they may go unreported to state and federal public health laboratories. Low disease estimates from under-reporting can create an inaccurate picture of the scope of a public health problem such as this, especially when the incidence may be so much higher than previously thought. Better estimates obtained from the ongoing studies can help increase awareness of the issue, providing additional incentive for the general public, government, and medical community to focus on this disease and its prevention.
Post-Treatment Lyme Disease Syndrome
For some people with Lyme disease, after treatment with antibiotics, there are lingering symptoms of fatigue, pain, or joint and muscle aches. For a small percentage of cases, these symptoms can last over 6 months. This is known as Post-Treatment Lyme Disease Syndrome (PTLDS). The exact cause of PTLDS is unknown. PTLDS is sometimes mistakenly referred to as chronic Lyme disease. Research is ongoing to better understand the cause of this syndrome. For more information, see the CDC's web page on PTLDS.