Unit 2 - Vector-Borne Spirochetes and Rickettsia Flashcards
what is the bacteriology of Borrelia burgdorferi?
-shape? stains?
- motile spirochete - flat-wave shape
2. stainable with giemsa, silver stain, IF; visible by standard microscopy
epidemiology of B. burgdorferi? vectors? how long does it take to transmit?
- tick-borne (I. scapularis in east, I. pacificus in west), most common one in US, esp east (when deer herds increase)
- highest risk in summer (many nymphs are feeding on many people)
- small mammal reservoirs (rodents) preferred by nymphs; large hosts (deer) by adults
- almost always requires 24 hours attachment to transmit
how does one remove ticks with Lyme? treatment?
- tweezers + gloves
- bag + freeze (can culture B. burgdorferi from tick, seldom positive from humans)
- promptly (needs 24 hours to transmit)
- doxycycline if the patient is not pregnant or allergic to tetracyclines
explain the pathogenesis of Lyme disease?
asymptomatic clearance possible
- symptoms spread from bite site to blood (bacteremia) to hearts, joints, CNS
- doesn’t involve toxins, as is primarily immune evasion
what is the timeline for Lyme disease?
6 mo after bite, organism spreads
- erythema migrans rash (75%), anti-spirochete Ab raised
- very persistent skin infection established
months to 1 year after infection, immune and/or neurological issues arise
-arthritis predisposed by HLA-DR4/2 genotymes, and by certain strains of B. b.
post-Lyme, 80% of untreated/undertreated cases report nerological sequelae
-reinfections occur
what is the diagnostic exam for Lyme disease?
get history of outdoor activity (season and location)
- divided into 4 stages:
- -1 (days) erythema chronicum migrans
- -2 (months) cardiac and neurological involvement
- -3 (months) arthritis in large joints
- -4 (post-treatment) fatigue, joint pain, mental status changes
what is the rash when a tick is still attached? what must you be aware of?
hypersensitivity, not Lyme (yet)
-coinfection with Ehrlichia or babesioa (b/c all tick-borne) will cause high fever
what is stage 1 Lyme?
(days) : erythema migrans expanding rashes at/near bite site (bull’s-eye minority)
- may have flulike symptoms (fatigue, aches, lympadenopathy, fever)
what is stage 2 Lyme?
(months) : musculoskeletal and/or neurologic symptoms
- intermittent arthritis lasting about a week, and recur (esp. knee)
- aseptic meningitis, Bell’s palsy, particularly bilateral facial nerve palsy (MRI/CT useful)
- rarely cardiac involvement (arrhythmia or transient block, EKG; must admit)
- rarely ophthalmic symptoms
what are unique features of Lyme disease in Europe?
occur in stage 2 (months)
- bluish borrelial lymphocytoma on earlobe (peds) or nipple (adult)
- chronica atrophicans: progressive fibrosing skin process on extremities
what is stage 3 Lyme?
months: now chronic Lyme disease
- arthritis in large joints (knees)
- subacute encephalopathy
- chronic progressive encephalomyelitis
- late axonal neuropathies
- fibromyalgia
- patients may recall earlier episodes of Bell’s palsy, aseptic meningitis
what happens in post-treatment Lyme?
lingering fatigue, joint pain, mental status changes
-never back to 100%`
what happens in Lyme lab?
- serology, ELISA, and IFA can confirm exposure, but not current activity, and not until 6-8 weeks later
- patients with the vaccine will be seropositive, and seropositivity remains long term
- equivocal-positive titers can be confirmed by Western blot or PCR
- seronegativity is reliable (consider alternative diagnoses)
- elevated synovial and spinal fluid cell coints suggest current activity
- biopsy of lymphocytoma or acrodermatitis may be useful
are Ab raised against Lyme protective?
no, they are not protective
what should one lab for Lyme if one has neurological symptoms?
CSF should be examined for mononuclear cells and anti-Lyme IgM, IgG
-remember that Ag = exposure, NOT current disease
treatment for Lyme? what should you do if the erythema migrans expands?
- if stage 1 (mild): doxycycline or amoxicillin
- improves rapidly with antibiotics, but only for 2 months (contraindicated if pregnant/peds)
- if late stage (severe): ceftriaxone
- will see Jarisch-Herxheimer reaction
- rash may expand for 2-3 days, but DON’T add steroids for arthritis
prevention of Lyme?
- protective clothing, DEET, avoiding woods, tick collars on pets
- daily close inspection for family and pets
- prophylaxis with doxycycline may be recommended in some geographic areas, and if tick attached >24 hr
what is the bacteriology of relapsing fever? pathogens? vector? reservoir? endemic? transmission?
includes both Borrelia recurrentis and hermsii
-both microscopically visible on blood smears and grow on special media
B.r. vector is body louse, reservoir is human
- endemic to Africa and homeless shelters
- transmit by louse crushing/inoculation by scratching (b/c louse feces/blood gets into bloodstream)
B.h. et al fector is soft ticks, reservoir is small mammals and ticks
- endemic to W. US, S. BC, Mexico, C/S. America, Asia, Africa, Mediterranean
- transmit by bite (usually nocturnal, unnoticed)
pathogenesis of relapsing fever?
- spirochetes invade blood from bite site, access vasculature, and multiply in many tissues (spleen, BM, liver, lungs, kidneys, CNS)
- general malaise and organ dysfunction follow
- neutralizing Ab and strong IL-10 response develop and halt sepsis –> fever
- selective pressure for Ag variation; bacterial surface Ag not recognized by current Ab come to predominate
- disease resumes, and cycle repeats (as immune response improves, lower fever and longer breaks)
- pathogenesis doesn’t seem to involve toxins, primarily immune evasion
what is the average relapse and mortality of louse-borne relapsing fever?
(B.r.)
average of 1 relapse
-mortality 4% if treated, 40% if untreated
what is the average relapse and mortality of tick-borne relapsing fever? complications?
(B.h.)
average of 3 relapses
-mortality <2% if treated, 4-10% if untreated
-causes complications in pregnancy (abortion, premature birth, neonatal death up to 50%)
what does the exam look like for relapsing fever?
- history (2+ episodes of 3-5 days of high fever >39C with low BP, then well week between)
- chills, arthralgias, N/V, ab pain, mental changes, nonproductive cough, dizziness, diarrhea,, neck pain, photophobia, rash, dysuria
