2: tickborne diseases Flashcards
3 major diseases, organisms, and ticks
- Lyme disease - Borrelia burgdorferi (ixodes tick/deer tick)
- RMSF - Rickettsia rickettsii (american dog tick)
- human monocytotropic ehrlichiosis - Ehrlichia chaffeensis (lone star tick)
what type of organism is Borrelia burgdorferi
spirochete
vector of Lyme disease
- ixodes tick (hard-bodied tick)
- blacklegged tick/deer tick = sole vector in hyperendemic regions of eastern US
sx/signs of stage 1 Lyme disease
- localized (incubation 3-32d)
- rash (erythema migrans)
sx/signs of stage 2 Lyme disease
- disseminated
- multiple annular skin lesions
- meningitis (headache, fever, stiff neck)
- cranial neuritis (CN7 - facial hemiparesis)
- carditis (AV block)
- arthralgia
sx/signs of stage 3 Lyme disease
- persistent
- oligoarticular arthritis (knee joints)
- encephalopathy (mood, memory, sleep disturbance)
- axonal polyneuropathy (tingling feet, weakness)
- acrodermatitis (skin changes on hands and feet)
describe erythema migrans
target “bull’s eye” rash with central clearing and potentially a necrotic center/vesicular lesions
-blanching rash!
differential diagnosis of CN7 palsy
- idiopathic (Bell’s palsy)
- lyme disease
- HSV (usually no rash)
- Herpes zoster/ Ramsay Hunt syndrome (vesicles in external auditory canal)
describe post-lyme disease “chronic lyme disease”
- pain syndrome (arthralgias)
- chronic fatigue
- neurocognitive symptoms
-sx occur for years after eradication of infection
what can sx of chronic lyme disease be confused with?
chronic fatigue syndrome - fibromyalgia
serologic testing for lyme disease
IgM and IgG - often retrospective diagnosis using paired sera (acute and convalescent, draw at presentation and 2-4 weeks later)
*better results from 2-4 weeks later
ELISA with Western blot verification - similar to older HIV testing methods
other ways to diagnose lyme disease besides serologic testing
- PCR of joint fluid from arthrocentesis done in patient with arthritis
- PCR of CSF (but has low sensitivity)
if a patient is high risk/ highly worried about lyme disease, what should you do?
draw sera at time of presentation
empirically start them on doxy
then draw sera at 2-4 weeks again
short answer for treatment of lyme disease
doxycycline!
vaccine for lyme disease?
not for humans (there is a canine vaccine)
name some tick prevention methods
- examine self after potential exposure, remove ticks
- use insecticides with DEET
- tuck pants into socks
- pre-treat clothes with permethrin insecticides
- insect shield clothing
causative organism of RMSF
rickettsia rickettsii
- small, obligate intracellular
- G(-) bacilli
trophism of rickettsia rickettsii
for vascular endothelial cells
RMSF vector
american dog tick in eastern US
incubation for RMSF
about 1 week
basic pathophysiology of RMSF
(vasculitis)
- increased vascular permeability
- edema, hypovolemia
- hyponatremia d/t compensatory ADH release
- thrombocytopenia
-DIC is rare
clinical presentation of RMSF
classic triad: fever, rash, history of tick exposure***
symptoms:
- fever
- headache
- myalgia
- malaise
describe progression of rash of RMSF
- starts as faint macules
- progresses to vasculitic rash w/ non-blanching petechiae
- may involve palms and soles
if you have someone who has faint rash, but not sure if RMSF or not, where is another place you can look for petechiae?
axillary folds
sx of progressing RMSF
- hypovolemia
- hypotension
- fluid third spacing
- respiratory failure
- cardiac dysrhythmia
- CNS symptoms - confusion, lethargy, encephalopathy
- ATN (acute tubular necrosis)
- shock
- elevated transaminases- acute hepatitis/liver failure
diagnosis of RMSF
- clinical presentation
- risk for or history of tick exposure
- lab testing
lab testing for RMSF
- thrombocytopenia (low platelets)
- hyponatremia (low sodium)
- azotemia (increased BUN, potentially increased Cr if ATN develops)
R. rickettsii testing
- no completely reliable test in early stages of disease
- skin biopsy w/ direct immunofluorescence staining (obtain before or w/i 12h of antibiotic therapy)
- serologic testing of IgM and IgG (first set after 5d of illness, second set 14-21d after symptom onset)
differential diagnosis of patient w/ fever, petechial rash on palms and soles, potential tick exposure
- meningococcal disease
- tick-borne disease RMSF
- enterovirus
- secondary syphilis
- rubella
- drug eruption
- Kawasaki disease
- Coxsackie virus (hand foot and mouth disease)
what would you do when a patient w/ fever, petechial rash on palms and soles, and potential tick exposure comes in?
- obtain blood and consider CSF
- consider skin biopsy
- empiric therapy for both meningococcal disease and RMSF
- **ceftriaxone and doxycycline
why is it important to treat early with RMSF?
delay in treatment (more than 5d past onset of sx) associated with increased risk of mortality
what are 3 factors that are independent predictors of failure of clinician to initiate anti-rickettsial therapy?
- absence of skin rash
- presentation w/i the first 3 days of illness
- presentation b/w Aug 1 and Apr 30 (not tick season)
treatment of RMSF
**doxycycline! (except preggers - chloramphenicol)
potential side effect of doxycycline in kids
can cause dental staining in kids
chloramphenicol
-RMSF treatment of choice for pregnant women
BUT problems:
-difficult to obtain
-less effective
-in some cases benefits of doxycycline outweigh risks in pregnancy
causative organism of ehrlichiosis
ehrlichia chaffeensis (obligate intracellular organism)
vector of ehrlichiosis
lone star tick
incubation period of ehrlichiosis
~8d
sx of ehrlichiosis
- fever
- headache
- myalgias
disease ranges from mild to severe
lab findings of ehrlichiosis
- leukopenia
- thrombocytopenia (low platelets)
- elevated transaminases
treatment for ehrlichiosis
doxycycline!
distribution of ehrlichiosis
more southeast US
how can you differentiate RMSF from ehrlichiosis?
- RMSF infects endothelial cells -> vasculitis (rash)
- ehrlichiosis infects phagocytes -> rash much less common
how do you identify a tick when it is engorged?
check the scutum (shield) - the typical pattern will still be visible despite the size of the engorged body
recommended way to remove a tick
- use a pair of tweezers and find where tick’s mouthparts have entered skin
- place ends of tweezers around base of mouthparts and while applying gentle pressure, pull the tick up slowly and steadily until it releases its hold
- dispose of the tick in a sealable plastic bag in the trash outside your home
what are things to not do when removing a tick?
- do not twist, poke, squash, or burn the tick
- do not smother the tick with any substance
