Rickettsia Flashcards
Rickettsia Species
1) Obligate Intracellular Pathogens
2) Cause Spotted Fevers and Typhus in Humans
3) Pathogenesis: Intracellular Cell Destruction
4) Transmission: Via Arthropod Vector to Humans; All species.
5) Some infections can be Fetal
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Clinically Relevant Species:
Spotted Fever Group: 1) Rocky Mountain Spotted Fever (RMSF) (Rickettsia rickettsii) _Most Severe _Most Frequent Rickettsial in US
2) Rickettsialpox (Rickettsia akari)
Typhus Group:
1) Louse-Borne Typhus Fever
(Rickettsia prowazekii)
2) Endemic (Murine) Typhus
(Rickettsia typhi)
3) Scrub Typhus
(Rickettsia orientia tsutsugamushi)
Rocky Mountain Spotted Fever
RMSF) (Rickettsia rickettsii
Bacteriology:
1) Gram Negative; Small
2) Grow ONLY in Eukaryotic Cells (Tick, Human)
(Obligate Intracellular)
3) Fails to survive outside of cells b/c Requires *Nucleotide Cofactor (Coenzyme A, NAD, ATP)
4) Outside Host cell, bacteria loses infectivity quickly b/c leaks proteins, nucleic acids, and essential small molecules
5) Binary Fission: Doubling Time 9-12 Hours
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Pathogenesis 1:
1) Infects Host Cells via Endocytosis
2) Escape the Phagosome
3) Multiplies intracellularly
–2 Methods to Spread Adjacent Cells:
1) Actin-Dependent Transfer to Adjacent Cells via Filopodia
Or
2) Cell Lysis, and subsequent Endocytosis
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Pathogenesis 2:
1) Enters Skin via Tick Bite
2) Tropism for Vascular Endothelium
3) Multiplies within Endothelial Cells lining Small Blood Vessels
4) Endothelial Cell Hyperplasia, Thrombosis, *Vasculitis
5) Disease:
_Vascular Lesion in Skin (RASH)
_and Adrenal Glands
6) Loss of Fluid from Vessel can Damage Fingers, Toes, Limbs
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Epidemiology:
1) Highest @ Mid-Atlantic States
2) Children Under 15
(Over 2/3 Cases)
3) April - September
4) = Parasite of Hard Ticks
_Doesn’t Kill Tick
_Adult Female Ticks require blood meal and transmit disease
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Manifestations:
1) Incubation: 2 - 14 Days
2) Sudden Onset: Fever + Headache
3) Nausea, Vomiting, Lack Appetite
4) Muscle Tenderness is Characteristic
5) Conjunctival Injection (Red Eyes)
6) Rash (2 - 5 Days After Fever) _90%. (10% never develop rash) _Some don't develop it until late in disease. _Rash Migrates From Extremities --> Trunk Within HOURS _First @ Wrists, Forearms, Ankles. (**Central Spread)
Red to Purple, Spotted Rash
_Usually not seen until 6th Day after onset of symptoms
_35 - 60% pts
*Early symptoms may be Non-specific.
Few patients will develop all symptoms.
Symptoms vary greatly among patients.
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Diagnosis:
1) **Clinical Signs
2) **Confirm afterwards with Lab tests
3) Treat within First 5 Days of Symptoms to Prevent Death
Do best to start treatment Prior to Onset of Rash!!!
Symptoms vary by pt.
Test for Antibodies:
_Negative in First 7 - 10 Days
_No diagnostic test can provide a conclusive result soon after infection.
Lab Confirmation:
1) Gold Standard: IFA with R. rickettsii Antigen
_First Samples in the First Week of Symptoms
_Second Sample 2 - 4 Weeks Later
(IFA: immunofluorescent assay)
2) Rapid: PCR or Immunohistochemical Staining of Skin Biopsy taken from Rash Site
Note: Blood specimens are not always useful.
_Low yield in blood unless very severe phase of infection.
CANNOT Culture/Gram Stain because
1) Requires Intracellular Growth!!
2) Long Doubling Time!!
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Treatment:
1) **Doxycycline (1st-Line)
Within First 5 Days!!
Rickettsiapox
Rickettsia akari
Benign disease
Transmitted by Rodent Mites
Key Signs:
1) **Eschar @ Bite Site
2) Vesicular Rash
Biphasic Illness
1) Local Lesion @ Bite
2) Fever Follows as bug disseminates
3) Diffuse Rash randomly distributed on body
Self-Limiting: ~ 1 week
No deaths
Treatment: Doxycycline Shortens illness to 1-2 Days
Epidemic
Louse-Borne Typhus Fever
(Typhoid Group)
Rickettsia prowazekii
Transmission: Body Louse
_in louse feces while feeding on human
Epidemiologoy:
1) Homeless ppl!!
Symptoms: 1-2 Weeks After Bite 1) Fever 2) Headache 3) Rash: **Spreads From Trunk to Extremities (Peripheral Spread)
Diagnosis: Clinical
Treatment: Doxycycline
Fatality rate increases with Age: 10% - 60%
Endemic (Murine) Fever
Typhoid Group
Rickettsia typhi
Transmission: Rat Flea
_flea feces into bite wound
Symptoms: 1-2 Weeks After Bite 1) Fever 2) Headache 3) Rash: Spreads From Trunk to Extremities (Peripheral Spread)
Treatment: Doxycycline
Scrub Typhus
Typhoid Group
Orientia tsutsugamuchi
Geography: Far East, China, India
Reservoir and Vector: Rodent Mites _Mite Larvae (Chiggers) Deposit rickettsiae during feeding
Symptoms:
1) Black Eschar @ Bite Site
2) Followed by Fever, Headache, Rash, Lymphadenopathy
Diagnosis:
_IFA or PCR @ Blood or Biopsy
Treatment: Doxycycline
Coxiella
Coxiella burnetii:
1) Gram Negative
2) Multiplies in Phagolysosome
3) Resistant to Drying
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Among Cattle, Sheep, Goats
Grows well in Placental Tissue
Transmission: Inhalation
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Q Fever:
1) Most Asymptomatic
2) No Rash
3) Abrupt Onset:
Fever, Chills, Headache
20 Days After Inhalation
4) Pneumonia and Endocarditis may occur
5) Fetal cases are rare
Ehrlichia
Associated with White Blood Cell
Diagnosis: Intracytoplasmic Inclusions
Treatment: Doxycycline
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Ehrlichia chaffeensis:
1) Causes Human Monocytic Ehrlichiosis (HME)
2) Transmission: Deer Ticks
(White-Tailed Deer is Animal Reservoir)
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Anaplasma phagocytophilum:
1) Causes Human Granulocytic Anaplasmosis (HGA)
2) Transmission: Ticks; Small Mammals are Animal Reservoir (Mice, Rats, Voles)
Bartonella
**Can be Cultured on Artificial Media
(Unlike Rickettsia!)
B. quintana:
1) *Trench Fever (WWI)
2) Reservoir: Human
3) Vector: Body Louse
Manifestations: Mild or Subclinical
When Symptomatic:
1) Sudden Onset Chills, Headache, Relapsing Fever, Rash @ Trunk and Abdomen
2) Can last 4-5 Days
3) *Can Recur in Repeated 4-5 Day Bouts
6) Or Can Persist for Weeks
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B. bacilliformis:
=> Acute Oroya Fever
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B. henselae:
=> Catscratch Disease
Febrile Lymphadenitis
Sometimes Persists for Weeks - Months
Transmission:
1) Cat Scratches
2) Bites from Cat Fleas
Manifestations:
1) Skin Rashes
2) Conjunctivitis
3) Encephalitis
4) Prolonged Fever
AIDS and other Immunocompromised States are associated with More Severe, Prolonged Disease.
