Rickettsiae, Orientia and Coxiella Flashcards
General Features of the Rickettsia Genus
Gram – (stains poorly with Gram staining)
Pleomorphic shape- resembles coccobacillus (very small)
Biochemical Properties of the Rickettsia Genus
Unable to produce sufficient ATP, CoA and NAD+ required for growth and replication Rely on eukaryotic host to receive these
Obligate intracellular- in capillaries’ endothelial cells
Pathogenesis of the Rickettsia Genus
Spread by insect (arthropod) vectors (e.g. ticks or louse)
Clinical Features of the Rickettsia Genus
Headache and high fever are early symptoms of infections (flu-like symptoms)
Vasculitis (proceed to rash)
Rash may be associated with vasculitis
May also cause circulation problems, kidney failure and encephalitis
Diagnosis of the Rickettsia Genus
Too small to be stained with Gram staining
Weil-Felix agglutination test for rickettsial infections (not much used these days). Slide or tube agglutination with patient’s sera containing rickettsial antibodies which cross-react with antigens of Proteus spp. strains (OX-19, OX-2 or OXK)
Giemsa or Giemenez staining Direct Immunofluorescence (IF) or microimmunofluorescence (MIF)
Treatment of the Rickettsia Genus
Doxycycline (Tetracycline) Fluoroquinolones, Rifampin
Prevention of the Rickettsia Genus
Non-specific- against insects vectors
Generał Features and Habitat of Rickettsia prowazekii
Gram – (stains poorly with Gram staining)
Pleomorphic shape- resembles coccobacillus (very small)
Reservoir- human (unlike R. rickettsii)
Biochemical Properties of Rickettsia prowazekii
Unable to produce sufficient ATP, CoA and NAD+ required for growth and replication Rely on eukaryotic host to receive these
Obligate intracellular- in capillaries’ endothelial cells
Pathogenesis of Rickettsia prowazekii
Reservoir- human (unlike R. rickettsii)
Transmitted by louse’s feces- inhalation or scratching can cause the ricketssia to enter the blood from the feces on the skin
Affects crowded, unsanitary groups- for example military camp recruits or prisoners
Obligate human pathogen
Incubation of 1-3 weeks before symptoms occur
Clinical Features (Epidemic Typhus) of Rickettsia prowazekii
Headache and high fever are early symptoms of infections (flu-like symptoms)
Myalgia (muscle pain) and arthralgia (joint pain)
Pneumonia
Encephalitis with dizziness and confusion, can lead to coma (lethal if untreated) Can also persist asymptomatic and relapse after decades as Brill-Zinsser disease Similar symptoms only milder, but still infectious
Rash (maculopapular exanthemas) may be associated with vasculitis
Starts from the center of body and spreads outward toward extremities
Usually the head, hands and feet are spared
Diagnosis of Rickettsia prowazekii
Too small to be stained with Gram staining
Giemsa or Giemenez staining
Direct Immunofluorescence (IF) or micro-immunofluorescence (MIF)
Treatment of Rickettsia prowazekii
Doxycycline (Tetracycline)
Prevention of Rickettsia prowazekii
Inactivated vaccine (only for the epidemic typhus
General Features of Rickettsia rickettsii and habitat
Gram – (stains poorly with Gram staining)
Pleomorphic shape- resembles coccobacillus (very small) Obligate intracellular- in capillaries’ endothelial cells
Reservoir- ticks, rodents and dogs (wild and domestic animals)
Biochemical Properties
Unable to produce sufficient ATP, CoA and NAD+ required for growth and replication Rely on eukaryotic host to receive these
Obligate intracellular- in capillaries’ endothelial cells
Pathogenesis
Transmitted by tick biting (Dermacenter ticks)
Incubation of 2-14 days before symptoms occur
High-risk groups- elderly, alcoholic and G6PD deficient
Clinical Features (Rocky Mountain Spotted Fever)
Symptoms start from extremities, eventually spreading to the whole body (i.e. systemic appearance)- unlike R. prowazekii which starts from the center
Rash (maculopapular exanthemas) may be associated with vasculitis
Rash turn into petechia after 2-6 days (begins on wrists and ankles- extremities)
After then- spreads to whole body
Headache and high fever, malaise and myalgia (flu-like symptoms) DIC and shock if left untreated (20-25% mortality if untreated)
Diagnosis
Too small to be stained with Gram staining
Giemsa or Giemenez staining
Direct Immunofluorescence (IF) or microimmunofluorescence (MIF)
Treatment
Doxycycline (Tetracycline)
Prevention
Non-specific- against insects vectors
Oritentia general features
Orientia tsutsugamushi
Gram negative, small coccobacilli that lacks peptidoglycan layer, LPS and flagella
Obligate intracellular (found in the cytoplasm of infected cells)
Reservoir- mites
Pathogenesis of Orientia tsutsugamushi
Transmitted by mites (chiggers, red mites)
Degrade the phagosome membrane by producing a phospholipase and must be released into the cytoplasm, or the organism will not survive
Multiplication in the host cell by binary fission is slow (generation time, 9 to 12 hours)
Disease: Scrub Typhus
Abrupt fever, headache, myalgia, in less than 50% also maculopapular rash
1-15% mortality rate
Diagnosis of Orientia tsutsugamushi
Giemsa or Gimenez staining
Treatment of Orientia tsutsugamushi
doxycycline
General features and habitat of Coxiella burnetii
Gram – (stains poorly with
Gram staining)
Pleomorphic shape- resembles coccobacillus (very small)
Reservoir- animal (farm animals mostly) and feces or placenta of animal
Biochemical Properties
Can survive harsh environment (“spore-like”)- survive in feces of animal
Obligate intracellular- replicate in phagosome of macrophages and monocytes
Pathogenesis
Reservoir- animal (farm animals mostly) and feces or placenta of animal
Transmitted by inhalation (aerosol) or ingestion of unpasteurized milk (rarely)
Coxiella survive inside the phagosome of macrophages and monocytes
It is slowly replicating inside, interfering with the signaling pathway of cell death (apoptosis) to prevent its own death.
The fusion of phagosome with lysosome may also kill the bacteria, but it is prevented with IL-10 (in chronic inflammation) that inhibit this fusion
Clinical Features Q Fever
Does not cause a rash (to distinguish from rickettsia)
Headache
Fever
Pneumonia
Hepatitis (important symptom of Q fever used for differential diagnosis)
Complication- can develop endocarditis, especially in immunocompromised patients or patients with previous heart valve problems
Diagnosis
Too small to be stained with Gram staining
Giemsa or Giemenez staining
Serology (most commonly used to diagnose)- IF (test of choice) and ELISA
Treatment
Self-limiting
Doxycycline (Tetracycline)
Prevention
Acellular vaccine given to veterinaries (high-risk population), pasteurize the milk
