(B) Lecture 17: Lyme Disease Flashcards
Lyme Disease
- first recognized in Conneticut
- epidemic of ‘polyarthritis’ mainly in kids
- most were misdiagnose w/ rheumatoid arthritis
- BULLS EYE RASH
- spirochete isolated from ticks
Borrelia burgdorferi characteristics
- gram NEGATIVE
- long spirochete
- mostly found in temperate zones
- main cause in North America
- VECTOR borne disease = spread by bite of ‘hard’ ticks
B. burgdorferi sensu lato
Whole group of species
Reservoir for B. burgdorferi
Tick is required for transmission
- WHITE FOOTED MICE are the major reservoir
- uninfected/unfed larva eat to get bloodmeal and become fed
Ixodes Tick
black legged or deer tick
- hard bodied ticks
- B. burgdorferi is mainly transmitted by Ixodes scapularis (East coast) and Ixodes Pacifica (West coast)
Lyme Disease transmission
- ticks do not fly or jump
- ticks wait in grasses/shrubs and wait for host to pass by
- bites in ‘hard-to-see’ areas - groin, armpits, hairline, neck
- no evidence of person-to-person transmission`
Ixodes life cycle
3 stages: large –> nymph –> adult
- no adult to egg transmision
- mice, squirrels and birds can carry B. burgorferi
- MAJORITY of human infections are from NYMPHS (so small = hard to see)
How does a tick infect?
- tick inserts feeding tube w/ BARBS = secretes anaesthetic
- transmission doesn’t occur in first 24h after a bite
- ticks appear grey when engorge
Tick removal
- use sharp, fine-tipped tweezers
- grasp as close to skin as possible
- keep tick + send in for Lyme testing
B. burgdorferi infection
After initial infection, B. burgdorferi causes disseminated and persistent infection to spread through its life cycle
Hematogenous dissemination is important for development of Lyme disease
B. burgdorferi virulence factors
- compound in tick saliva
- periplasmic flagella
- unusual outer membrane
- genetic structure
Tick saliva
B. burgdorferi
Compounds in saliva inhibit DC function (immune function)
- decreased phagocytosis
- decreased maturation
- decreased inflammatory mediators
- decreased antigen presentation
Periplasmic flagella
B. burgdorferi
Periplasmic flagella: btwn cytoplasmic membrane + outer membrane
- contain axial filaments that wrap around cells
- rotation of axial filament causes the bacteria to move in corkscrew-like manner
important for invading + escaping vessels
Outer membrane of B. burgdorferi
Unusual outer membrane
- no LPS
- many surface expressed lipoproteins that can act as ADHESINS
- escape from vasculature needs adhesion to slow down B. burgdorferi
Genetic structure of B. burgdorferi
Unusual genetic structure
- LINEAR chromosome = weird
- multiple plasmids
- plasmids are needed for infection and are variable from strain to strain
- limited metabolic capacity
Early Localized Stage of Lyme Disease
- ERYTHEMA MIGRANS = BULLS-EYE RASH is most common symptom
- 1-2 weeks after tick bite
- groin, axilla, waist, back, legs
- flu-like symptoms: fever, chills, fatigue, body aches
Early Disseminated Stage of Lyme Disease
- days to weeks
- in untreated patients
- pain + swelling of LARGE JOINTS
- heart palpitations
- meningitis - severe headaches + neck stiffness
- BELL’S FACIAL PALSY - loss of muscle tone on one or both sides of face
How does B. burgdorferi traverse the BBB?
Paracellular traversal using flagella
- squeezing btwn tight junctions
How does meningitis pathogen traverse the BBB?
Transcellular traversal
- invades inside endothelial cell
Late Disseminated Stage of Lyme Disease
- months to years
- can cause long-term disability
- muscle pain, arthritis, severe pain and swelling in large joints
- 5% of patients get neurological problems
Post-treatment Lyme disease syndrome
- 10-20% experience symptoms after antibiotics
- cause is unknown
- may involve AUTOIMMUNE disease
- long-term antibiotics are not thought to help
Lyme Disease in Canada
Ticks continue to expand due to
- migratory birds
- warmer climate
Prevention of Lyme Disease
- avoid wooded areas endemic w/ Lyme disease
- stay on paths, avoid low lying brush and long grass
- wear long pants tucked into socks
- repellants w/ DEET
- light coloured clothing (more likely to see)
Diagnosis of Lyme Disease
- erythema migrans and other symptoms
- tick bite or reason to suspect tick exposure
anti-B. burgdorferi antibody tests (no ‘Gold-standard’
- detect antibodies to a lab strain of B. burgdorferi
- false negatives often due to early testing and genetic diversity
Treatment of Lyme Disease
- if bitten by black legged tick, watch for a rash
- early diagnosis = recovery after antibiotic treatment
- 2-4 weeks of antibiotic (usually protein synthesis inhibitor)
- w/o treatment –> joint , heart + nervous system problems
Chronic Lyme Disease
- very controversial
- can get diagnosis w/o proof of ever having Lyme disease
- persistent symptoms like fatigue, headaches, sleep disturbances, cognitive dysfunction, neurological problems
Manhattan Project to combat Chronic Lyme Disease
- most common in children and women
- case definition may have been too narrow - many symptoms in chronic Lyme disease are not properly recognized
- commercial tests probably not sensitive enough for B. burgdorferi
- treatment may be too restrictive + short
Lyme Disease Vaccine
- LYMErix is not recommended but can be considered for those in high risk
- claims that it caused arthritis
- pulled from market and won’t come back
