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LYME DISEASE

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Lyme Disease caused by spirochaetes is the most common disease spread by ticks in the Northern Hemisphere, although Tabanidae flies may also serve as vectors. An estimate is that over 300,000 people are affected in the United States every years and 65,000 in Europe yearly. Infections are most common in springtime or early summer. Lyme disease was diagnosed as a separate condition for the firs time in 1975. Earlier it was mistaken for juvenile rheumatoid arthritis. Willy Burgdorfer first described the bacterium involved in 1981. Chronic symptoms are well described and are known as post-treatment Lyme Disease syndrome. Some healthcare providers associate this with an ongoing infection, but this has not been proven. As of 2017 there is no effective vaccine available.

The disease is an infection that is caused by bacteria of the genus Borrelia. Symptoms are an expanding area of redness that begins at the site of a tick bite about 5-7 days after the attack. A rash develops that is neither prickly nor painful. About 25-50 percent of infected people do not develop the rash. Other early symptoms include fever and headache. If untreated symptoms may extend to joint pain, severe headache, neck stiffness, heart palpitations, etc. Much later (months to years) repeated episodes of joint pain and swelling may occur. Some patients also develop shooting pains or tingling in their arms and legs. Even with treatment about 10-20 percent of people develop joint pains, memory problems and weariness for at least 6 months.

The disease is transmitted to humans by the bite of bacteria-infected ticks of the genus Ixodes: Ixodes ricinus in Europe, I. persulcatus in Eurasia, I. scapularis in eastern United States and I. pacificus in western states. Typically the tick must be attached for 36-48 hours before the bacteria can spread. In North America, Borrelia burgdorferi and Borellia mayonii are the cause. In Europe and Asia the bacteria Borrelia afzelii and Borrelia garinii are also causes of the disease. The disease does not seem to be transmitted among people, by other animals or through food. Diagnosis is based on a combination of symptoms, history of tick exposure and by testing for specific antibodies in the blood. However, blood tests are frequently negative in the early stages of the disease. Testing of the ticks themselves is not only impractical but also not reliable.

Prevention includes avoiding tick bites by wearing protective clothing or using repellants such as DEET. Certain pesticides may also be effective. Ticks can be removed using tweezers. If the removed tick was full of blood a single dose of doxycycline may prevent infection. If an infection develops there are a number of antibiotics available, including doxycycline, amoxicillin and cefuroxime. Treatments regularly require 2-3 weeks. Some patients develop a fever and muscle and joint pains from treatment that may last a few days. For persistent symptoms long-term antibiotic therapy has little effect.

Lyme Disease - Life Cycle

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Key References: <medvet.ref.htm> <Hexapoda>

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England

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Sonenshine, D. E. & T. N. Mather (eds.) 1994. Ecological Dynamics of Tick-Borne Zoonoses. Oxford Univ. Press, New York.

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Sonenshine. Washington, DC: ASM Press.