By Fred Bove, M.D., Ph.D.
If you dive in freshwater lakes or the coastal areas of the northeastern United States, around Minnesota and Wisconsin, or along the Pacific Coast of Northern California, you should be aware of tick bites and Lyme disease. Ticks are found in forests and fields and can be contacted when you walk through brush or woods to reach a dive site. Lyme disease is spread by the bite of ticks, which are infected with the bacteria Borrelia burgdorferi, classified as a spirochete because of its corkscrew shape. It lives in the deer tick on the East Coast and the black legged tick on the West Coast.
There are several kinds of ticks you can encounter when in woods or fields. The most common is the dog tick, which is usually 3 to 4mm in diameter. It does not transmit Lyme disease. The deer tick is smaller, often only 1mm in diameter. The young deer tick is the size of a pinhead. Although the dog tick does not carry Lyme disease, it can carry an illness called Rocky Mountain Spotted Fever, caused by a bacteria called Rickettsia. The deer tick is very common in areas where deer are plentiful and the risk of Lyme disease is high if you are bitten by a tick in these areas. The ticks usually reside on grass and low bushes, they attach to clothing that brushes the grass or bush, then travel to bare skin where they bite. They remain attached for several days, drawing blood into their body. When the tick is full, it drops off the skin and begins a reproductive cycle that extends more than two years to the next crop of new ticks.
In the eastern United States, the disease is usually transmitted by the young ticks, which are barely visible, and often not noticed during their early feeding period. Usually, they must be attached for two days or more to transmit the bacteria to the person being bitten. The adult tick is usually noticed and removed before it bites. A tick walking on the skin does not cause an infection, so the presence of the tick is not enough to be concerned about Lyme disease; the tick must bite and remain in the skin for a few days. The disease is not contagious and cannot be transmitted from animals that have been bitten. You can pick up ticks from the fur of pets that have been in grass or shrubs. If there are deer near your home, you may encounter the deer tick in your yard or garden.
When a tick infected with the Lyme disease bacteria bites the skin and remains with its head under the skin for several days, the bacteria will invade the skin and blood stream of the person bitten. The first reaction is a red rash around the bite, which can spread to a large round red area with the tick bite in the center. This can be seen 3 to 30 days after the bite. Common locations for the rash (and the bite) are the legs, armpits, groin and trunk. The rash is not usually painful and should subside after a few weeks but this is not the end of Lyme disease. The bacteria, if untreated, will enter other areas of the body. Infections of the joints, the brain and nerves and the heart can occur many months later. When the bacteria enters the body, besides the rash, it may cause chills and fever, fatigue, headache, muscle and joint pain and swollen lymph nodes. Months later the bacteria can cause arthritis with swollen joints. The knee joints are commonly involved. More severe illnesses, such as meningitis, nerve injuries with numbness, pain and paralysis may occur. Lyme disease can involve the heart, causing abnormal heart rhythms and changes in the electrical signals within the heart. There is some concern that a pregnant women who contracts Lyme disease could transmit the disease to the fetus. When the nervous system is involved, Lyme disease can mimic multiple sclerosis and, when lymph glands are swollen, the disease can mimic mononucleosis.
Lyme disease can be diagnosed by a specific blood test but the test may not become positive until late in the disease and is not positive in every case. Treatment is best done when the initial rash occurs. The rash indicates the bacteria have invaded the body. Use of the antibiotic doxycycline at that time will usually eradicate the illness. If the initial phase is not treated, the bacteria will invade other tissues and organs. When arthritis, involvement of the nervous system or heart are present, antibiotics must be given intravenously for several weeks. Treatment at that time is more difficult and the prolonged illness may cause permanent damage to the joints or nervous system.
You can take measures to avoid getting bitten by a Lyme infected tick. The ticks are most abundant in May, June and July. Avoiding wooded or grassy areas during this time is effective but may not be practical. Wear light colored clothing so you can see ticks if they are on you. Tuck pant legs into boots or socks when walking in infested areas. Wear a hat and long sleeved shirt for additional protection. Insect repellents containing DEET (a common insecticide) are effective against ticks. You can also spray clothing with permethrin (another insecticide) to repel ticks.
It is always worthwhile to carefully examine your skin for ticks after walking in the woods. If you are bitten, you can pull the tick out of the skin with tweezers. Grasp the tick with the tweezers and pull along the line of the tick's body.
You can find more information on Lyme disease, including photos of the deer tick, from the Web site of the U.S. Communicable Diseases Center at http://www.cdc.gov.