Lyme Disease

Epidemiology of Infectious Diseases: Lyme Disease

Causal agent
A tick-borne, spirochaetal, zoonotic disease caused by the bacterium Borelia burgdorferi.

Three genomic groups of B. burgdorferi have been identified in Europe; B burgdorferi sensu stricto, B. garinni and B. afzelii1. 

First recognized in 1975

Common clinical features

  • The first sign of infection is typically characterized by the development of a circular rash, erythema migrans (EM), which occur in approximately 70-80% of infected persons. The rash begins at the site of tick bite after 3-30 days (typically 7-10 days) following exposure.
  • A distinctive feature of the rash it that it gradually expands over a period of several days, reaching up to 30cm across (often with central clearing).
  • Multiple secondary lesions may also develop.
  • With or without EM, symptoms may include malaise, fatigue, fever, headache, stiff neck, myalgia, migratory arthralgia and/or lymphadenopathy, which may last up to several weeks1.
  • Untreated, infection may spread to other parts of the body causing symptoms including, facial palsy, severe headaches, aseptic meningitis, chorea, cerebellar ataxia, myelitis and encephalitis and cardiac abnormalites1.
  • Approximately 60% of patients with untreated infection will have intermittent bouts of arthritis, with sever joint pain and swelling (usually knee, elbow or ankle). In addition, up to 5% of untreated patients may develop chronic neurological complaints months to years following infection.

Epidemiology

  • Lyme disease occurs in the temperate regions of North America (the Northeast, mid-Atlantic and north Central regions), Europe and Asia.
  • Infection occurs primarily in the summer, with a peak in June and July.
  • In the UK an average of 300 laboratory confirmed cases are reported annually to the Health Protection Agency, of which most are acquired in the UK. Areas where infection is acquired include Exmoor, the New Forest, the South Downs, parts of Wiltshire and Berkshire, Thetford Forest, the Lake district, the Yorkshire Moors and the Scottish Highlands.
  • About, 20% of confirmed cases in the UK are acquired abroad2.
  • However, estimates suggest that between 1000 and 2000 cases of lyme disease occur each year in the UK.

Reservoir
Mice, other rodents and small mammals are the bacterial reservoirs. Birds may also be a reservoir. Deer are an important host for adult ticks2.  

Mode of transmission
Transmitted through the bite of Ixodes ticks that are infected with B. burgdorferi.

Ticks become infected when they feed on birds or mammals that carry the bacterium in their blood.

Incubation period
For EM, 3-32 days (mean 7-10 days).

Period of Communicability
No evidence of person to spread.

Prevention and control
Currently no vaccine against lyme disease is available.

Avoid tick bites.

Early treatment with antibiotics helps to prevent the development of complications.

References

  1. Heymann D L, editor, Control of Communicable Disease Manual. 18th ed. American Public Health Association, 2004.
     
  2. Health Protection Agency. Lyme Disease Fact Sheet. Available online; http://www.hpa.org.uk/infections/topics_az/zoonoses/lyme_borreliosis/faq.htm

© CM Kirwan 2006