21: Vector-Borne Infections

Question 1

For Rocky Mountain Spotted Fever:

1. Bug
2. Vector
3. Reservoir
4. Location/Season
5. Incubation
6. Pathogenesis
7. Clinical
8. Diagnosis
9. Treatment

Answer 1

1. Rickettsia rickettsii; GNC, obligate intracellular
2. Hard ticks, dermacentor species: american dog tick, brown dog tick, RM wood tick
3. Hard tick
4. SE/S. Central states; spring (June/July)
5. 1 week
6. Rickettsii travels via lymphatics, invades endothelial cells, escapes phagosome, replicates in cytosol, cell to cell spread, increases vascular permeability by disrupting junctions
7. Flu-like sx, macular eruption on wrists/ankles, blanching and papular, centripetal (moves proximally); palms and soles involved; late: edema, ischeia, hypovolemia, MOSF
8. Labs: hyponatremia, thrombocytopenia, elevated liver enzymes; immunohistochem on skin biopsy, serological tests (IFA), PCR
9. Doxycycline (even kids); do not wait

Question 2

For Epidemic Typhus:

1. Bug
2. Vector
3. Reservoir
4. Location/Season
5. Incubation
6. Pathogenesis
7. Clinical
8. Diagnosis
9. Treatment

Answer 2

1. Rickettsia prowazekii; GNC
2. Human body louse
3. Humans
4. Crowded, unsanitary conditions, anytime
5. 1 week
6. Scratch feces ino bite; targets brain and lung; bacteria lyse cells
7. Fver, myagia, cough, severe HA, delerium, +/- cetrifugal petechial rash (spread out) but spares face, palm and soles; MOSF, Brill-Zinsser disease (reactivated form)
8. Clinical
9. Doxycycline

Question 3

For rickettsialpox:

1. Bug
2. Vector
3. Reservoir
4. Location/Season
5. Incubation
6. Pathogenesis
7. Clinical
8. Diagnosis
9. Treatment

Answer 3

1. Rickettsia akari; GNC
2. Mite
3. Mouse
4. NYC (big cities), anytime
5. 9-14 days
6. -
7. Regional lymphadenopathy, flu-like sx, papulovesicular eschar at bite site
8. Clincal; IHC
9. Doxycycline, although self-limited

Question 4

For Ehrlichioses:

1. Bug
2. Vector
3. Reservoir
4. Location/Season
5. Incubation
6. Pathogenesis
7. Clinical
8. Diagnosis
9. Treatment

Answer 4

1. Ehrlichia chaffeensis (Human Monocytic Ehrlichiosis [HME]), Anaplasma phagocytophilium (Human Granulocytic Anaplasmosis [HGA]); obligate intracellular GNC w/ berry clusters of organisms (morulae)
2. Hard tick (lone star tick) (HME), hard tick (blacklegged or deer tick) (HGA)
3. White-tailed deer (HME), small mammals, esp. white-footed mice (HGA)
4. SE, S.central, mid-Atl (HME), NE, mid-Atl, upper MW, Pacific NW (HGA), May-Aug
5. -
6. Binds membrane of target WBC, internalized and forms clusters, prevents fusion of phagosome w/ lysosome
7. Mild flu-like sx, if immunocompd, severe, fatal infx; similar sx to ricksettial disease but less likely to have rash (esp. HGA)
8. Clinical, PCR, seologic (4x titer rise), peripheral blood for morulae
9. Doxycycline

Question 5

For Lyme Disease:

1. Bug
2. Vector
3. Reservoir
4. Location/Season
5. Incubation
6. Pathogenesis
7. Clinical
8. Diagnosis
9. Treatment

Answer 5

1. Borrelia burgdorferi, GNS
2. Hard tick (I. scapularis), usually the nymph (must feed 24+ hrs to infx)
3. Small mammals, esp. white-footed mice (HGA)
4. NE, upper MW, June-Aug
5. Must feed 24 hours
6. OspC facilitates transmission, OspA facilitates hematogenous spread, DbpA/B mediate binding to surface of collagen; other surface proteins bind endo/epithelial cells
7. Stage 1 (early localized LD): flu-like sx, erythema migrans rash (bull’s eye); Stage 2 (early disseminated LD): cranial nerve palsy, meningitis, radiculopathy, arthritis, heart block,, pericarditis; Stage 3 (late disseminated LD): recurrent arthritis, CNS/PNS sx
8. Clinical, CSF exam i(ymphocytosis, elevated protein, normal glucose), IFA, serology
9. Doxycyline (amoxicillin if 8 or younger) for rash; IV ceftriaxone (3GC) for cardiac/CNS disease

NB: Co-infx w/ HGA and babesia (infx of RBCs) may occur.