Lyme disease is spread by the bite of ticks that are infected with Borreli burgdorferi. On the Pacific Coast, the bacteria are transmitted to humans by the western black-legged tick. For Lyme disease to exist in an area, at least three closely interrelated elements must be present in nature: the Lyme disease bacteria, ticks that can transmit them, and mammals (such as mice and deer) to provide food for the ticks in their various life stages.
Knowing the complex life cycle of the ticks that transmit Lyme disease is important in understanding the risk of acquiring the disease and in finding ways to prevent it. The life cycle of these ticks requires 2 years to complete. Adult ticks feed and mate on large animals, especially deer, in the fall and early spring. Female ticks then drop off these animals to lay eggs on the ground. By summer, eggs hatch into larvae. Larvae feed on mice and other small mammals and birds in the summer and early fall and then are inactive until the next spring when they molt in nymphs. Nymphs feed on small rodents and other small mammals and birds in the late spring and summer and molt into adults in the fall, completing the 2-year cycle.
Larvae and nymphs typically become infected with Lyme disease bacteria when they feed on infected small animals, particularly the white-footed mouse. Research has indicated that ticks transmit Lyme disease to humans during the nymph stage, Adult ticks can carry and transmit the disease, because they are larger, they are more likely to be noticed and removed from a person's body within a few hours. Also, adult ticks are most active during the cooler months of the year, when outdoor activity is limited. Nymphs are rarely noticed (They are less than 2mm.) and have ample time to feed and transmit the infection. Ticks are most likely to transmit infection after approximately 2 or more days of feeding.
The risk of exposure to ticks is greatest in the woods and garden fringe areas of properties, but ticks may also be carried by animals into lawns and gardens. Ticks search for host animals from the tips of grasses and shrubs (not from trees) and transfer to animals or persons that brush against vegetation. Ticks cannot crawl; they do not fly or jump.
Early symptoms include: fatigue, chills and fever, headache, muscle and joint pain, swollen lymph nodes and a characteristic skin rash (erythema migrans). Erthema migrans is a red circular patch that appears usually 3 days to I month after the bite of an infected tick at the site of the bite. The patch then expands, often to a large size. The center of the rash may clear as it enlarges, resulting in a bulls-eye appearance. The rash can be warm, but it usually is not painful.
Lyme disease can be difficult to diagnose because its symptoms and signs mimic those of other diseases such as simple viral infections (flu). If not detected early, later symptoms may include: brief bouts of arthritis, nervous system abnormalities and less frequently, heart rhythm irregularities.
Patients treated in the early stages with antibiotics usually recover rapidly and completely. Most patients who are treated in later stages of the disease also respond well to antibiotics. In a few patients, symptoms persist or recur, making additional treatments necessary. Varying degrees of permanent damage to joints or the nervous system can develop in patients with late chronic Lyme disease and rare deaths have been reported.