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Flashcards in Micro: Vector Borne Inf I Deck (29)
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What is the microbiology of ricketssiae?

gram- coccobacilli
cell wall: PM, peptidoglycan, nontoxic LPS
obligate parasite - requires living cells
capsule and cell wall components are antigenic


What is the epidemiology of ricketssiae?

animal reservoir, mostly rodents
arthropod borne
rocky mountain spotted fever group (RMSF, risketssial pox, others), typhus group (louse-borne epidemic, murine endemic), scrub typhus


What is the pathogenesis of rickettsiae?

arthropod bite - local replication in skin - phagocytosis - exits phagosome into nucleus or cytoplasm - replicates in vascular endothelium --> vasculitis (capillary leakage, cell death, exposure of matrix for coagulation cascade)
spotted fever group grows in cytoplasm, orientia in nucleus, typhus in cytoplasm and lyses host cell
use host cell ATP
when it happens, death is from vascular collapse


What is the epidemiology of RMSF?

caused by rickettsia rickettsii
transmitted by hard ticks
spring and summer peaks (apr-sept)
mostly east of mississippi, rare in rocky mountains
rodents usual hosts, humans accidental, organisms maintained by vertical transmission in ticks


What are the clinical features of RMSF?

sudden onset - fever, chills, headaches, myalgias
rash 3-5 days after fever - moves from extremities in, goes from blanching macules to non-blanching petechia


What is rickettsial pox?

caused by rickettsia akari
mouse mites
transovarial passage = vertical transmission in tick


What are the different species of tick typhus?

R. australis (queensland)
R. conorii (boutonneuse fever, Mediterranean spotted fever)
R. africae (african tick typhus or african tick bite fever)


What are the manifestations of african tick bite fever?

fever, multiple tache noir, regional adenopathy, occasional morbilliform or vesicular eruption
clusters in travelers
treatment = doxy


What are the features of african tick typhus?

usually after being around game, usually men
fever, inoculation eschar, lymphadenopathy, cutaneous rash, apthous stomatitis


What is the epidemiology of the two different types of typhus?

epidemic = louse-borne, squirrels are reservoir, R. prowazekii
endemic = murine or flea-borne, rat flea, R. typhi


How is epidemic typhus transmitted?

louse feeds, bite, itches, person grounds feces into skin when scratching
facilitated by crowding/malnutrition


What are the clinical features of epidemic typhus?

sudden onset fever, chills, headache, myalgias
rash 4-7 days after fever, truncal and spreads outward, spares palms and soles (all contrast to RMSF)
no eschar/tache noir


What are the clinical features of endemic typhus?

rash less prominent, chest only
no eschar
transmission by feces while biting
becoming a problem in Texas


What are the features of scrub typhus?

transmitted by mite bite, eschar in 60%, tache noir
rash not as common, begins on trunk and spreads out
south and southeast asia


How are RMSF and typhus diagnosed?

serologies, immunofluorescent staining of skin punch biopsies, PCR
NOT usually cultures


What is the treatment of RMSF and typhus?

doxy, MUST treat on suspicion
no vaccine available


What is Brill-Zinsser dz?

reactivation of epidemic typhus several decades later
mild and generally resolves w minimal sequelae


What are the similarities and differences b/w erlichia and anaplasma?

e - monocytes, a - granulocytes
both: dual membrane but no peptidoglycan or LPS, obligate parasites, grow in intracellular membrane bound clusters = morulae
replicate w/i phagocytic vacuole (different from rickettsia)
gluatmine is major energy source, can synthesize ATP
no gram stain, giemsa or wright


What is the epidemiology of erlichia and anaplasma?

e - southern and s. central US, tick vectors, rodent reservoir
a - northeast and midwest, lyme dz tick vector, rodent reservoir
most cases occur in summer (apr-sept), increase w age


What are ixodid ticks?

vectors for: anaplasma, babesia, borrelia
coinfection w 2 reported, possible to have all 3


What are the clinical features of erlichiosis and anaplasmosis?

acute febrile syndrome, varying leukopenia, thrombocytopenia, and anemia
rash subtle and only in minority
complications can be renal failure, DIC, seizures, coma


How are erlichia and anaplasma diagnosed?

immunofluorescence assay is gold standard
exam of peripheral blood smear may show morulae
PCR on blood (unlike RMSF), no vasculitis (unlike RMSF)


What is the treatment and prevention of erlichia and anaplasma?

doxy, no vaccine


What is the microbiology of coxiella burnetii?

obligate intracellular parasite
doesn't gram stain well - gram- and has LPS, phase variation of LPS b/w phases I and II useful for diagnosis
spore-like form resistant to drying


What is the epidemiology of coxiella burnetii?

animal reservoirs = cattle, sheep, goats
causes abortions in animals
shed in feces, placenta, milk, urine
humans inf primarily by aerosol route (not vector!!)


What is the pathophysiology of coxiella burnetii?

inhaled, low inf dose, phagocytosed by macrophages and grow w/i phagolysosome (acidic pH promotes phase transition), mulitply w/i cytoplasmic vacuoles
possible bioterrorism agent


What are the clinical features of Q fever?

acute: febrile illness, atypicaly pneumonia, severe headache, granulomatous hepatitis, spontaneous resolution w/i 1 mo, diagnosed by serology
chronic: endocarditis, diagnosed serologically
presentations can be subclinical


How is Q fever diagnosed?

serology: IFA, ELISA vs LPS antigens
sometimes PCR and culture


What is the treatment and prevention of Q fever?

vaccine available for lab personnel and occupational exposures - needs to contain phase I LPS (infective form) - NOT given if previous vaccination or inf due to AEs