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3. LYME DISEASE

Since its first recognition in Lyme, Connecticut in 1975, Lyme disease has become the most frequently reported vector-borne disease in the United States. Some 23,763 cases were recorded by the Centers for Disease Control during 2002. Three regions stand out: the northeast; two north-central states - Wisconsin and Minnesota; and the coastal counties of northern California.

Between 1989 and 1999 there were 1,938 cases of Lyme disease reported in California. Many others surely went undiscovered. The highest frequency is along the north coastal ranges between Marin and Trinity Counties. Dogs, horses and some other domestic and wild animals are also susceptible.

Sonoma County records show 361 confirmed human cases between 1989 and mid 1996. Endemic localities are known in Marin, Sonoma and Mendocino Counties, and sites with significant risk of infection appear to be highly focal.

The causative agent is a corkscrew-shaped bacteria named Borrelia burgdorferi (the syphilis bacteria is in the same spirochete group). It lives in blood system and is carried by ticks of the genus Ixodes. A widespread reservoir of Borrelia occurs in wild mammal populations in northern regions of both the New and Old Worlds. Dogs and some other domestic animals can become infected and develop arthritis.

Knowledge of Ixodes biology is important, since the only practical way to avoid Lyme disease is to avoid getting bitten by infected ticks. In California the major carrier is the western black-legged tick, Ixodes pacificus, found in 55 of the state's 58 counties. It lives for about two years, with the tiny larvae and nymphs feeding mostly on mice and other small mammals, lizards and occasionally on birds. Adults tend to feed on larger mammals like deer. All stages can feed on man and domestic animals.

Ticks acquire Borrelia when they take a blood meal from infected mammals. Infection rates in both tick and mammal populations vary markedly. During a survey in the Sonoma Valley, district workers found three of 282 (1%) adult and nine of 300 (3%) nymphal Ixodes pacificus carrying the Lyme disease agent. Similar studies in the northeastern states have shown much higher infection rates in local ticks.

Ixodes are slow feeders and may require 2-3 days to complete a blood meal before disattaching. Nymphal stages measure about the size of a pinhead and are easily overlooked; while adults are larger and more likely to be seen and removed. Infected ticks usually do not transmit the Lyme organism during the first 24 hours, and the risk of infection increases the longer the tick remains attached.

Lyme disease often begins with fatigue, chills and fever, headache, muscle and joint pain, and a characteristic rash on the skin. These symptoms help establish a diagnosis, since reliable routine laboratory tests are still being developed. If left untreated the disease can produce debilitating arthritis and nerve damage. Treatment with antibiotics is usually effective, especially in the earlier stages.

Recent Newspaper Reports:

• Tick season's arrival calls for Lyme awareness. Santa Rosa Press Democrat, May 8, 2007 D1, D3;
• Lyme disease cases up in county. Santa Rosa Press Democrat, June 17, 2006 B1, B3;
• Educating Californians on Lyme disease. San Francisco Chronicle, September 2, 2005 (F1-2).

Helpful references:

Lyme disease in northwestern coastal California. by C. Ley et al.. Western Journal of Medicine. Volume 160(6):534-39 (1994).   Video: Lyme Disease - A Guide to Prevention. 2001. An outstanding summary, produced by Conneticut Public Television and the Centers for Disease Control. $19.95. Call 1 (800) 443 2156.

Internet References:

• Lyme disease in California University of California, Pest Management Guidelines, Pulb. No. 7485 (December 2000).
• CDC Lyme Disease Home Page Communicable Disease Center, Atlanta.
• Lyme Disease in California California Department of Health Services brochure, June, 2002.