Micro: Vector Borne Inf I

Question 1

What is the microbiology of ricketssiae?

Answer 1

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

Question 2

What is the epidemiology of ricketssiae?

Answer 2

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

Question 3

What is the pathogenesis of rickettsiae?

Answer 3

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

Question 4

What is the epidemiology of RMSF?

Answer 4

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

Question 5

What are the clinical features of RMSF?

Answer 5

sudden onset - fever, chills, headaches, myalgias

rash 3-5 days after fever - moves from extremities in, goes from blanching macules to non-blanching petechia

Question 6

What is rickettsial pox?

Answer 6

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

Question 7

What are the different species of tick typhus?

Answer 7

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

Question 8

What are the manifestations of african tick bite fever?

Answer 8

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

Question 9

What are the features of african tick typhus?

Answer 9

usually after being around game, usually men

fever, inoculation eschar, lymphadenopathy, cutaneous rash, apthous stomatitis

Question 10

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

Answer 10

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

Question 11

How is epidemic typhus transmitted?

Answer 11

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

Question 12

What are the clinical features of epidemic typhus?

Answer 12

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

Question 13

What are the clinical features of endemic typhus?

Answer 13

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

Question 14

What are the features of scrub typhus?

Answer 14

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

Question 15

How are RMSF and typhus diagnosed?

Answer 15

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

Question 16

What is the treatment of RMSF and typhus?

Answer 16

doxy, MUST treat on suspicion

no vaccine available

Question 17

What is Brill-Zinsser dz?

Answer 17

reactivation of epidemic typhus several decades later

mild and generally resolves w minimal sequelae

Question 18

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

Answer 18

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

Question 19

What is the epidemiology of erlichia and anaplasma?

Answer 19

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

Question 20

What are ixodid ticks?

Answer 20

vectors for: anaplasma, babesia, borrelia

coinfection w 2 reported, possible to have all 3

Question 21

What are the clinical features of erlichiosis and anaplasmosis?

Answer 21

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

Question 22

How are erlichia and anaplasma diagnosed?

Answer 22

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

Question 23

What is the treatment and prevention of erlichia and anaplasma?

Answer 23

doxy, no vaccine

Question 24

What is the microbiology of coxiella burnetii?

Answer 24

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

Question 25

What is the epidemiology of coxiella burnetii?

Answer 25

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

Question 26

What is the pathophysiology of coxiella burnetii?

Answer 26

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

Question 27

What are the clinical features of Q fever?

Answer 27

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

Question 28

How is Q fever diagnosed?

Answer 28

serology: IFA, ELISA vs LPS antigens

sometimes PCR and culture

Question 29

What is the treatment and prevention of Q fever?

Answer 29

doxy
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