Lyme Disease Flashcards
Lyme Disease (Lyme Borreliosis)
- prototype emerging infectious disease
- a multisystemic disorder
- commonly presents as skin lesions (erythema migrans)
- most common vector-borne disease in North America
What can result if lyme disease is left untreated?
if untreated, can lead to arthritis, carditis and nervous system manifestations
How was Lyme Disease first recognized?
- first recognized in 1975 in rural communities surrounding Lyme, Connecticut
- noticed that children had a distinct rash that was associated with a tick bite
- eventually isolated the bacteria rom the ticks, skin, blood and CSF of patients
Borrelia burgdorferi
- gram negative spirochete
- thin (0.5 um) and long (10um), spiral shaped
- found throughout temperate zones in the Northern Hemisphere
- major cause
- spread by the bite of “hard ticks” = vector born disease
What is the reservoir for B. burgdoferi?
- transmitted to different mammalian hosts through ticks
- only found in vertebrate or arthropod hosts
- white footed mice are the major reservoir
Ixodes tick (black legged or deer tick)
- hard bodied ticks
- In North America, B. burgdorferi is transmitted primarily by Ixodes scapularis and Ixodes pacifica
- other species transmit in Europe and Asia
Ixodes Life Cycle
3 stages:
larva -> nymph -> adult
- ticks require blood meals between stages
- no adult to egg transmission (ticks must acquire B. burgdorferi)
- larva are not born infected!
- mice, squirrels and birds can carry B. burgdorferi
- majority of human infections come from nymphs
Why do majority of human infections from from nymphs?
- because they are very small and difficult to see
Lyme Disease Transmission
- ticks do not fly or jump
- ticks sit on grasses/shrubs and wait for a host to pass by
- bites often occur in ‘hard-to-see’ areas
- dogs and cats can get Lyme disease
- no evidence of direct person to person transmission
How do Ticks transmit the disease?
- tick inserts a feeding tube with barbs
- secretes a local anesthetic
- suck blood slowly for several days
- ticks appear grey when engorged
Following a bite, when does transmission occur?
After 24 hrs
Tick Removal
- use fine tipped tweezers
- grasp the tick as close to the skin as possible
- steadily pull upwards
- thoroughly was the area
- keep the tick
Things you should not do during tick removal
- do not squish the tick body
- do not burn the tick off
- do not apply petroleum jelly
What must occur after initial infection for B. burgdorferi to propagate through its life cycle?
Hematogenous dissemination and persistent infection
What functions of DC do the bacteria, B. burgdorferi inhibit?
- decreased phagocytosis
- decreased maturation
- decreased inflammatory mediators
- decreased antigen presentation
Axial Filaments of B. Burgdorferi
- periplasmic flagella
- filaments wrap about the cells to produce a cork-screw shape
- rotation causes the bacteria to move in a cork-skrew manner
- promotes movement through extracellular matrix of host tissues and invasion of vasculature (like a drill)
Outermembrane of B. burgdorferi
- no LPS
- many surface expressed lipoproteins that can act as adhesins
- escape from the vasculature requires adhesion to slow down B. burgdorferi
- repetitive motility required to invade endothelium
Genetic Structure of B. burgdorferi
- linear chromosome
- multiple plasmids (both linear and circular)
- plasmids are required for infection but are variable from strain to strain
- limited metabolic capability (gets things like amino acids, through the host)
Early Localized Stage of Lyme Disease
- most common symptom is erythema migrans – ‘Bulls-eye rash’ (~25% of patients do not have a rash)
- occurs ~1-2 weeks after tick bite
- groin, axilla, waist, back, legs, (head and neck in children)
- rash will expand and if untreated can reach >12 inches diameter
- flu-like symptoms including fever, chills, fatigue, body aches
Early Disseminated Stage (days to weeks)
- occurs in untreated patients
- multiple rashs would indicate dissemination of B. burgdorferi
- pain and swelling of large joints
- heart palpitations – interference with heart electrical signals
- meningitis - severe headaches and neck stiffness
- Bell’s (facial) palsy – loss of muscle tone on one or both sides of the face
Late Disseminated Stage (months to years)
- can cause serious long-term disability
- response to antibiotics takes longer
- muscle pain
- arthritis
- severe pain and swelling in large joints
- ~5% of patients develop neurological problems (shooting pains, numbness, tingling in hands and feet, and memory)
Post - treatment Lyme Disease Disorder
- 10-20% experience symptoms following treatment with antibiotics
- cause is unknown
- lingering symptoms including fatigue, muscle and joint pain, cognitive defects, sleep disturbances
- may involve an autoimmune response or possibly persistent infection
- most patients recover after a number of months
long-term antibiotics are not thought to help
Prevention of Lyme Disease
- avoid wooded areas endemic with Lyme disease
- stay on paths, avoid low lying brush and long grass
- wear long pants (tucked into socks) and long-sleeved shirts
- light coloured clothing
repellants (containing DEET) - check for ticks and remove them
Diagnosis of Lyme Disease
- erythema migrans and other ‘typical’ symptoms
- tick bite or reason to suspect tick exposure
- submission of tick for testing (if you have it) to the National Microbiology Laboratory
Diagnosis of Lyme Disease
- erythema migrans and other ‘typical’ symptoms
- tick bite or reason to suspect tick exposure
- anti-B. burgorferi antibody tests
- submission of tick for testing (if you have it) to the National Microbiology Laboratory
anti-B. burgdorferi antibody tests
- no ‘Gold-standard’
- detect antibodies to a laboratory strain of B. burgdorferi
- false negatives often due to early testing (no antibody response yet) and genetic diversity of B. burgdorferi
- sensitivity is somewhat controversial
Treatment of Lyme Disease
- if bitten by a black legged tick, watch for a rash (30 days) and be aware of symptoms
- patients when diagnosed early will recover following antibiotic treatment
- 2 - 4 week course of an antibiotic
- lack of treatment can lead to joint, heart, nervous system problems
- ~10-20% of patients, typically with a late diagnosis, have post-treatment Lyme disease syndrome
Chronic Lyme Disease
- very controversial
- some think this is due to chronic infection by B. burgdorferi
- can be diagnosed without evidence of prior Lyme Disease
- persistant symptoms including fatigue, headaches, sleep disturbances, cognitive dysfunction and other neurological problems
- long-term antimicrobial therapy is not helpful – demonstrated by 4 clinical trials
- medical community says that this does not exist
Lyme Disease Vaccine
- LYMErix – based on an outer membrane protein
human trial (11,000 adults) showed it to be 75% effective - ‘should be considered’ for those in high risk areas (not ’recommended’)
- claims (and lawsuits) that the vaccine caused arthritis – no evidence (but in control population, just as many people developed arthritis)
- pulled from the market in 2002 due to ‘lack of demand’ – only now approved for dogs
Transversing the BBB (B. burgdorferi)
most likely paracellular transversal
