lyme disease Flashcards
what causes lyme disease? describe the pathogen
borrelia burgdorferi is the major cause
a spirochete bacteria isolated from ticks – also found in skin, blood, and cerebral spinal fluid of patients
BUT, other species can also cause it: B burgdorferi sensu lato – this is spread by “hard” ticks
describe lyme disease. vector? symptoms?
prototype, a recently emerging infectious disease
—- an epidemic of polyarthritis, mostly in children
most common vector-borne illness in North America – transmitted by tick bites
symptoms:
— “bulls eye” rash/skin lesions
— migrant, grows in skin
— if untreated, can lead to arthritis, carditis, and nervous system manifestations (multisystemic disorder)
many children with lyme disease were misdiagnosed with what?
rheumatoid arthritis
describe borrelia burgoerferi. what type of bacteria is it?
gram-, spirochete
thin and long, spiral shaped
what’s the reservoir/carriers for borrelia burgoerferi?
white footed mice
transmitted to different mammalian hosts thru ticks
mammal -> tick -> mammal
note, borrelia burgdorferi is only found in vertebrate or arthropod hosts
in north america, what’s the major vector of borrelia burgdorferi?
ioxdes scapularis and ixodes pacifica
both are hard bodied ticks (black legged or deer ticks)
different ones in europe and asia
describe transmission of lyme disease at the tick’s level
ticks sit on grass/shrubs and wait for host to pass by (do not fly or jump)
— often bite in ‘hard-to-see’ areas
— dogs & cats can get Lyme disease
— no evidence of direct person to person transmission
— ticks can’t obtain pathogen from other ticks, only mammals (e.g. mice, squirrels, birds)
tick inserts feeding tube w/ barbs & secretes local anesthetic
— transmission does not occur within first 24 hours of bite
tick sucks blood slowly for several days, then fall off
— transmission increases after 24 hours
— appear grey when engorged
note: disease normally transmitted by nymphs
describe the life cycle of the ixodes ticks
larva —> nymph —> adult
ticks require blood meals between stages
most human infections come from nymphs, adults are larger and more visible
how to remove ticks if attached to you?
use fine tipped tweezers to grab tick as close to skin as possible, then pull upwards
thoroughly wash area & keep tick
do NOT… squish tick body, burn tick off, or apply petroleum jelly (will suffocate & regurgitate)
what is hematogenous dissemination in regards to borrelia burgdorferi? how do ticks promote this event?
central event for transmission/development of the pathogen following initial infection
bacteria spreads to joints, CNS, PNS, heart, and skin via blood stream
—- must be done for a tick to be able to pick it up
compounds in tick saliva are
thought to inhibit DC
function on multiple levels
—- decreased phagocytosis
—- decreased maturation
—- decreased inflammatory
mediators
—- decreased antigen
presentation
it is believed that compounds in the saliva of ticks serve what function?
thought to inhibit DC
function on multiple levels
—- decreased phagocytosis
—- decreased maturation
—- decreased inflammatory
mediators
—- decreased antigen
presentation
what is a key virulence factor of borrelia burgdorferi?
periplasmic flagella
unusual outer membrane (no lipopolysaccharides – even tho gram-)
describe borrelia burgdorferi’s periplasmic tail
it contains a periplasmic (between the outer and inner membranes) flagella called axial filaments which wrap around the cell to produce the cork-screw shape
rotation of the axial filament causes the bacteria to move in a corkscrew like manner
promotes movement thru extracellular matrix of host tissues and invasion vasculature
describe borrelia burgdorferi’s unusual outer membrane
no lipopolysaccharides, despite being gram-
contains many surface proteins that act as adhesions
escape from vasculature requires adhesions to slow down the pathogen
repetitive motility required to invade the endothelium
— transient interaction: blood travels in blood, adhesions grab the endothelium
— bacteria drags along membrane
— flagella are “turned on” and bacteria burrows into the endothelium
describe borrelia burgdorferi’s unusual genetic structure
linear chromosomes (most bacteria has circular)
multiple plasmids (some linear, some circular)
small chromosomes (limited metabolic activity that reflects pathogens with unique life cycle – must live in hosts)
so we test for test for plasmid antigens when testing for lyme disease
— issue: plasmids are required for infection, but vary from strain to strain (different complement)
what are the stages of lyme disease? describe them and symptoms
early localized stage
— 1-2 weeks after tick bite
— most common symptom: bulls eye rash – but 25% do not have the rash; rash expands if untreated
— flue-like symptoms: fever, chills, fatigue, and body aches
early disseminated stage (days to week)
— occurs in untreated patients
— dissemination indicated by multiple rashes
— symptoms: heart palpitations, chronic meningitis (via paracellular traversal - between cells), bell’s facial palsy (loss of muscle tone on one or both sides of face – effects peripheral nerves)
late disseminated stage (months to years)
— can cause serious long-term disability
— response to antibiotics takes longer
— symptoms: muscle pain, arthritis, severe pain/joint swelling, few develop neurological problems
describe the post-treatment experience of lyme disease (symtoms, etc.)
10-20% experience symptoms following treatment w/ antibiotics
cause is unknown
— may involve an autoimmune response or persistent infection
lingering symptoms :
— fatigue
— muscle & joint pain
— cognitive defects
— sleep disturbances
most patients recover after a number of months
long-term antibiotics are thought not to help
why are ticks moving north?
migratory birds and warmer climate
—- birds can now survive in winter
what are some prevention tips for ticks or borrelia burgdorferi?
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
how is borrelia burgdorferi diagnosed for?
erythema migrans and other ‘typical’ symptoms
tick bite or reason to suspect tick exposure
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
submission of tick for testing (if you have it) to the National
Microbiology Laboratory
what’s treatment for borrelia burgdorferi?
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
without treatment, can lead to joint, heart, nervous
system problems
~10-20% of patients, typically with a late diagnosis, have
post-treatment Lyme disease syndrome
describe chronic lyme disease
very controversial…
some think it is caused by chronic infection by B. burgdorferi
can be diagnosed w/o evidence of prior Lyme Disease (or even a tick bite)
— medical side = NO
— patients who “have” it = YES
persistent symptoms: fatigue, headaches, sleep disturbances, cognitive dysfunction & other
neurological problems
long-term antimicrobial therapy NOT helpful
what’s the status of the lyme disease vaccine?
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
pulled from the market in 2002 due to ‘lack of demand’ –
only now approved for dogs
what’s the lyme disease vaccine made of?
LYMErix – based on an outer membrane protein