Rickettsiae and Related Bacteria Flashcards
Describe pathogenesis/clinical presentations of infections
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Microbiology of Ricketsial/Orientia sp
- small, gram negative obligate intracellular bacteria in pairs of rod-shaped cells with tapered ends or single coccobacilli
- need tissue culture cell lines or embyonated eggs to culture, grow in cytoplasm, and can be readily visualized with Giemsa stain (not bacteriologic stains)
- have efficient transport systems for ATP, amino acids, metabolites from cell but capable of independent metabolism
- Free rickettsiae cease metabolic activity/lose infectivity within short pd. Readily inactivated >56C and by standard disinfectants
General clinical features of Rickettsial dz
- most infections cause clinical dz. Transmitted to humans from animal reservoirs via bites of arthropod vectors. Invade vascular endothelial cells and become disseminated. Pathology due to destruction of infected host cells
- Major clinical features: fever, headache, rash (due to focal infection causing increased vascular permeability/edema)
- Late: Thrombosis/blockage of small blood vessels with extravasation
- Petichial lesions= hallmark
clinical consequence to brain, kidneys, lung, heart > than those of cutaneous lesions
Main categories of Rickettsia diseases
1) Typhus group- rash first on trunk and progresses to extremities
2) Scrub typhus group-rash often absent
3) Spotted fever group: rash first on extremities, moves centripetally, and involves palms and soles
- diagnose with antibody levels in serum
Epidemic Typhus etiology, epidemiology, prevention
-organism: Due to Rickettsia prowazekii
Epidemiology:
- worldwide
- human/flying squirrels = common reservoir. Transmit via feces from human body louse and squirrel ecto-parasites
- favor crowding, poor hygiene; prevalent during wars/natural disaster
PREVENT
- live attenuated vaccine in armed services and ppl at risk
- insecticides to kill lice
Epidemic typhus clinical manifestations, prevention, treatment
- Erythematous macular rash starting 1-2 weeks post inoculation on trunk and progresses to extremities
- Bacteremia, high fever, prostration, renal failure, stupor
- 20-70% mortality if untreated
- life-long immunity in most cases
- possibility of latency/lifelong persistence in some
Brill’s disease
- from Rickettsia prowazekii
- similar to epidemic typhus except milder, usually no rash
- many years after primary infection as consequence of recrudescence,, usually in immigrants from Easter Europe who had typhus in WWII
- if pts infested with lice, possibility of transmission
- can be source of new outbreaks of epidemic typhus
Endemic Typhus
- Rickettsia typhi
- common reservoir: rats
- Transmission: feces from rat fleas
- prevalent throughout the world, particularly in ports, countries with warm climates and other locations where rat populations high
- clinically very similar to epidemic typhus but milder (
Rickettsial typhus diseases
Epidemic typhus
Endemic typhus
Brill’s Disease
Scrub typhus group of diseases
Scrub Typhus
Scrub typhus
-Org: Orientia tsutsugamushi
Epidemiology
- Common reservoirs: Chiggers (larval mites). bacterium can be transmitted in mites from generation to generation by transovarian transmission
- Transmission: Chigger bite
- high incidence in WWII and vietnam war
- Endemic in Asia, South Pacific, Australia
Clinical:
- similar to epidemic typhus but rash often absent/echar develops at site of chigger bite
- short-lived immunity due to antigenic variation
- 7% mortality (untreated)
Treat: doxycycline or chloramphenicol
Spotted fever group
Rocky Mountain Spotted Fever
Rocky Mountain Spotted Fever
- diseases caused by Rickettsia rickettsii and antigenically related bacteria
- various spotted fevers endemic to different areas in the world, often reflected by names
- most important rickettsial dz in US–seen throughout with highest incidence in Mid-Atlantic, Virginia, and Carolinas
- bacteria present in salivary secretions of ticks and mites and injected when then feed on humans
- 95% cases between April 1 and Sept 30 when ticks active/ppl outdoors
- > 70% pts have tick bite history
Rocky Mountain spotted fever etiology/epidemiology/clinical
- Etiology: Rickettsia rickettsii
Epidemiology:
- Reservoir: widespread in wild mammals, birds, ticks (transovarial)
- Transmission: tick bite. American dog tick in East, Wood tick in West, Lonestar tick in South/SE
- takes 4 hrs of feeding before ticks willl inoculate host w/virulent bacteria
- Geographic distribution: North, central, South America
CLINICAL
- 2-6 days post bite, similar to typhus except rash starts at extremities (wrists/ankles) and moves to trunk
- macular petichial rash
- 7% mortality if untreated
TREAT: doxycycline (except if prego/allergic)
Prevent: no vaccine; prompt tick removal
Ehrlichia and Anaplasma general characteristics
- similar to Rickettsiae; major differences are that the host target cells are phagocytic cells instead of endothelial and they multiply in phagosomes instead of cytosol.
Clinically similar to rocky mountain spotted fever (fever, headache, often multisystem involvement) but without rash. Haematologic abnormalities include leucopenia/thrombocytopenia
