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
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