Lyme Disease Health Article

Definition

Lyme disease is an inflammatory disease transmitted through the bite of a deer tick carrying the spiral-shaped bacterium Borrelia burgdorferi. Symptoms can include skin rash, joint inflammation, fever, headache, fatigue, and muscle pain. Lyme disease is also called Lyme borreliosis.

Description

Lyme disease is an inflammatory, systemic disease, meaning that it affects multiple body systems. Although clinical signs of Lyme disease have been reported for more than 100 years, the disease was not recognized as a distinct illness until 1975, when a cluster of unusual arthritis cases in Lyme, Connecticut, led physicians to discover that town residents living near heavily wooded areas were most affected by arthritis and other symptoms. Tick bites were then linked to the cause of the arthritis cases. Borrelia burgdorferi, the spiral-shaped bacterium called a spirochete, that causes Lyme disease, was not discovered until 1981 by Willy Burgdorfer.

Although Lyme disease is easily treated, it is not easily diagnosed, since symptoms are often attributed to other conditions. If not treated early and properly with antibiotics, Lyme disease can have long-term and disabling effects. In its early stages, Lyme disease affects the skin and produces flu-like symptoms; the disease spreads to the joints and nervous system in its later stages.

Transmission

Lyme disease is a vector-borne disease, meaning that it is transmitted from one host to another by a carrier—called a vector—that transmits but does not become infected with the disease. In the United States, the deer tick in the genus Ixodes is the vector for Borrelia burgdorferi and Lyme disease transmission. Lyme disease is transmitted when a tick carrying the Borrelia burgdorferi bacterium bites a human to feed on blood. The bacterium is transferred from the intestines of the tick through the mouthparts and into the bloodstream while the tick is feeding. Ticks are most likely to transmit Borrelia burgdorferi after remaining attached and feeding for two or more days. In most areas, ticks are most active from April to October, but in milder climates, ticks may bite year-round.

During their two-year life cycle and three life stages (larva, nymph, and adult), deer ticks feed on a number of mammals that may carry the Borrelia burgdorferi bacterium in their blood, but the white-footed mouse is the most common source of infection. In the summer, the larval ticks hatch from eggs laid in the ground and feed by attaching themselves to small animals and birds. At this stage, they are not a problem for humans. It is the next stage—the nymph—that causes most cases of Lyme disease. Nymphs are very active from spring through early summer, at the height of outdoor activity for most people. Because they are still quite small (less than 2 mm), they are difficult to spot, giving them ample opportunity to transmit Borrelia burgdorferi while feeding. Although far more adult ticks than nymphs carry Borrelia burgdorferi, the adult ticks are much larger, more easily noticed, and more likely to be removed before they have fed long enough to transmit Borrelia burgdorferi. Neither Borrelia burgdorferi nor Lyme disease can be transmitted directly from one person to another or from pets to humans.

Demographics

Lyme disease is the most common vector-borne disease in the United States. In 2002 alone, 23,763 cases were reported to the Centers for Disease Control and Prevention (CDC), a 40-percent increase over the number reported in 2001. According to the CDC, the actual number of Lyme cases may exceed 200,000 due to underreporting and limitations in disease surveillance methods. CDC statistics indicate that the largest proportion of Lyme disease cases occurs in children aged five to 14 years, and more than 50 percent of Lyme disease cases involve children under age 12. Although cases of Lyme disease have been reported in 49 of the 50 states, more than 95 percent of reported cases occur in just twelve states: Connecticut, Rhode Island, New York, Pennsylvania, Delaware, New Jersey, Maryland, Maine, New Hampshire, Minnesota, Massachusetts, and Wisconsin. In the United States, the Great Lakes region and the Pacific Northwest also have a higher incidence of Lyme disease. The disease is also found in Scandinavia, continental Europe, the countries of the former Soviet Union, Japan, China, and Australia.