lyme disease

Question 1

what causes lyme disease? describe the pathogen

Answer 1

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

Question 2

describe lyme disease. vector? symptoms?

Answer 2

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)

Question 3

many children with lyme disease were misdiagnosed with what?

Answer 3

rheumatoid arthritis

Question 4

describe borrelia burgoerferi. what type of bacteria is it?

Answer 4

gram-, spirochete

thin and long, spiral shaped

Question 5

what’s the reservoir/carriers for borrelia burgoerferi?

Answer 5

white footed mice

transmitted to different mammalian hosts thru ticks

mammal -> tick -> mammal

note, borrelia burgdorferi is only found in vertebrate or arthropod hosts

Question 6

in north america, what’s the major vector of borrelia burgdorferi?

Answer 6

ioxdes scapularis and ixodes pacifica

both are hard bodied ticks (black legged or deer ticks)

different ones in europe and asia

Question 7

describe transmission of lyme disease at the tick’s level

Answer 7

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

Question 8

describe the life cycle of the ixodes ticks

Answer 8

larva —> nymph —> adult

ticks require blood meals between stages

most human infections come from nymphs, adults are larger and more visible

Question 9

how to remove ticks if attached to you?

Answer 9

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)

Question 10

what is hematogenous dissemination in regards to borrelia burgdorferi? how do ticks promote this event?

Answer 10

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

Question 11

it is believed that compounds in the saliva of ticks serve what function?

Answer 11

thought to inhibit DC
function on multiple levels

—- decreased phagocytosis
—- decreased maturation
—- decreased inflammatory
mediators
—- decreased antigen
presentation

Question 12

what is a key virulence factor of borrelia burgdorferi?

Answer 12

periplasmic flagella

unusual outer membrane (no lipopolysaccharides – even tho gram-)

Question 13

describe borrelia burgdorferi’s periplasmic tail

Answer 13

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

Question 14

describe borrelia burgdorferi’s unusual outer membrane

Answer 14

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

Question 15

describe borrelia burgdorferi’s unusual genetic structure

Answer 15

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)

Question 16

what are the stages of lyme disease? describe them and symptoms

Answer 16

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

Question 17

describe the post-treatment experience of lyme disease (symtoms, etc.)

Answer 17

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

Question 18

why are ticks moving north?

Answer 18

migratory birds and warmer climate

—- birds can now survive in winter

Question 19

what are some prevention tips for ticks or borrelia burgdorferi?

Answer 19

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

Question 20

how is borrelia burgdorferi diagnosed for?

Answer 20

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

Question 21

what’s treatment for borrelia burgdorferi?

Answer 21

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

Question 22

describe chronic lyme disease

Answer 22

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

Question 23

what’s the status of the lyme disease vaccine?

Answer 23

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

Question 24

what’s the lyme disease vaccine made of?

Answer 24

LYMErix – based on an outer membrane protein