Rickettsia (Woychik) - 5/2/16

Question 1

Rickettsia Classification:

General Characteristics:

Transmission:

Clinical Symptoms:

Lab Identification:

Treatment:

Answer 1

Rickettsia

• Spotted Fever Group: Rickettsia rickettsia
• Typhus Group: Rickettsia prowazekii

Characteristics:

• Obligate intracellular bacteria (unable to produce NAD+ and CoA so they need eukaryotic cells)
• Coccobacillary
• Gram staining - poor but slightly gram (-)

Transmission:

• Transmitted to humans by arthropod vectors (fleas, lice, mites, ticks)
• Seasonal and geographical distribution of diseases caused by these organisms dependent on habitat of vector (e.g., fleas found worldwide as are diseases caused by them; ticks - more specific)
• Organisms need host to survive

Clinical Symptoms:

• Headache and fever early in Rickettsial infection
• Vasculitis = unique symptom + bump rash
• Diagnosis based on serology and PCR since culture is extremely difficult; however, serological diagnosis problematic due to high level of cross reactivity between species
• Weil Felix Test (diagnostic tool) - agglutination test that tests for cross-reactivity between Rickettsia and Proteus vulgaris

Treatment: doxycycline or other tetracyclines (bind to 30S ribosomal subunit - block elongation step)

Question 2

Rickettsia rickettsia

General Characteristics:

Answer 2

Obligate intracellular

Poor gram staining (use giemsa stain to visualize)

CoA and NAD+ necessary for growth and provided by host

Question 3

Rickettsia rickettsia

Transmission:

Answer 3

Via derma center tick bites

Tick is both vector and reservoir (*not same tick that causes Lyme disease)

Question 4

Rickettsia rickettsia

Pathogenesis:

Answer 4

1) Rickettsia rickettsia attach to receptors on host vascular endothelial cells via outer membrane proteins OmpA or OmpB
2) Induce phagocytosis
3) Escape from phagosome into host cytosol and proliferate
4) Proliferation in cytosol –> leads to cell damage –> increased vascular permeability
5) Spread to adjacent cells through host cell actin-mediated propulsion
6) Characteristic petechial rash (manifesto of networks of contiguously infected cells)

Question 5

Rickettsia rickettsia

Clinical manifestation

Answer 5

Rocky Mountain Spotted Fever

Incubation period: 2-14 days

Disease begins with:

• Fever
• Severe headache
• Rash (starts at extremities and moves centrally)
• Myalgia (severe muscle pains)

Question 6

Rickettsia akari & rickettsialpox

Transmission:

Clinical Characteristics:

Answer 6

Transmission - to humans through mouse mite
Target cells - macrophages/monocytes, NOT endothelial cells

Clinical Characteristics of rickettsialpox:

• At site of mite bite, a primary papule forms, ulcerates, and forms dark ESCHAR (clinical hallmark - present 100% of the time)
• Fever develops + rash (but NOT ON PALMS AND SOLES as with RMSF)

Question 7

Rickettsia prowazekii & louse-borne typhus

General Characteristics:

Transmission:

Clinical Manifestations:

Answer 7

Obligate intracellular w/ poor gram staining

Require CoA and NAD+ from eukaryotes

Outbreaks historically have paralleled times of war, natural disasters (floods/earthquakes) –> clothing is not changed, hot water bathing is infrequent, crowding is common

Transmission:
Lice become infected upon taking a blood meal from persons infected with R. prowazekii
–> R. prowazekii enters louse gut epithelial cells
–> R. prowazekii replicates until cells burst
–> Large numbers of dormant, extracellular form of R. prowazekii in louse feces on skin and clothes
–> scratching introduces Rickettsia into blood

Clinical Manifestions:
Rash starts at trunk and spreads outwards toward extremities (opposite of RMSF); spares face, palms, and soles
- Severe headache, fever, myalgia

Question 8

Rickettsia typhii & murine typhus

General Characteristics:

Transmission:

Clinical Manifestations:

Answer 8

Found worldwide - but esp. prevalent in tropical and subtropical seaboard regions (e.g., South Texas and Southern California)

Transmission:
Rat = reservoir, rat flea = vector –> transmits disease from rat to rat and occasionally rat to human (infected flea feces into flea bite wound)

Cat fleas = also vectors (primary source of US cases)

Question 9

Ehrliche and Anaplasma?

Human Monocytic Ehrlichiosis (HME)?

Answer 9

Cause of recently discovered TICK borne zoonoses

Unlike most Rickettsia, infection does NOT occur through endothelial cells:

• Ehrlichia - monocytes and macrophages
• Anaplasma - neutrophils

Multiply within cytoplasmic membrane-bound vesicles that look like inclusion bodies but are referred to as MORULA

Cell walls are thin b/c they lack peptidoglycan and LPS

HME: mammalian host = white tailed deer
Symptoms: fever, headache, myalgia, LEUKOPENIA, THROMBOCYTOPENIA (uncommon in RMSF or Lyme disease)

Question 10

Coxiella burnetii

Characteristics:

Transmission:

Clinical Presentation:

Treatment:

Answer 10

Gram negative
Obligate intracellular organism

Transmission:

• Via ticks or other arthropods whose bite infects animals
• Reservoir: sheep, goats, and cattle
• Infected animals shed organisms in urine, feces, milk, and especially birth products such as placenta

Coxiella forms SPORES that can survive digestive system and be excreted in animal feces –> aerosol transmission to humans

Clinical Presentation:
- fever, NO RASH, hepatitis

Treatment is usually not needed - usually goes away in two weeks but can cause endocarditis in immunocompromised patients (rare)

Question 11

Differential Diagnosis:

1. Rash
2. Leukopenia/Neutropenia
3. Morale
4. Vasculitis

Answer 11

1. RMSF, HME, HGA
2. Leukopenia = HME, neutropenia = HGA; either is uncommon in RMSF
3. Morale - occasionally in neutrophils of patients with HGA, but not with RMSF
4. Vasculitis: hallmark of RMSF