Contents
Organism
Borrelia Burgdorferi (spirochaete)
Incubation: 7-14 days
Transmission
Vector=ticks
Animal hosts=deer/rodents
Epidemiology
Commonest vector borne illness in USA
Focally endemic in woodland of north America – infections mostly occur in summer.
Pathogenesis
- Tick bite
- B. burgdorferi is injected into the skin in tick saliva
- This contains substances that disrupt the immune response at the bite site
- Allows infection establish
- The bacteria multiply in the dermis
- Host inflammatory response causes circular EM lesion
- Spirochaetes spread via the bloodstream.
The spirochetes may avoid the immune response by a form of molecular mimicry, causing a pathogen-induced auto-immune disease by causing inflammatory substances such as cytokines.
Clinical features
- Early localized:
- Skin reaction around bite site (erythema migrans)
- Regional lymphadenopathy
- Fever
- Headache
Early disseminated
- Arthralgia
- Malaise
- Pronounced systemic reaction
- Carditis (sometimes with AV conduction defects)
- Neurological involvement
Complications
- Polyneuritis
- Arthritis
- Encephalopathy
- Acrodematitis chronic atropicans
Diagnosis
Primarily clinical diagnosis, confirmed by antibody detection.
Culture from biopsy
Treatment
Doxycycline/amoxicillin (14 days, longer if disseminated)
IV cefotaxime in neurological disease
Prevention
- Protective clothing/insect repellants
- Special care in handling and allowing outdoor pets inside homes
- Prompt remova of attatched ticks
- Reduction in the number of primary hosts for the tick(i.e. rodents, other small mammals, and deer)
