Rickettsiae, Orientia and Coxiella

Question 1

General Features of the Rickettsia Genus

Answer 1

Gram – (stains poorly with Gram staining)

Pleomorphic shape- resembles coccobacillus (very small)

Question 2

Biochemical Properties of the Rickettsia Genus

Answer 2

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

Question 3

Pathogenesis of the Rickettsia Genus

Answer 3

Spread by insect (arthropod) vectors (e.g. ticks or louse)

Question 4

Clinical Features of the Rickettsia Genus

Answer 4

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

Question 5

Diagnosis of the Rickettsia Genus

Answer 5

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)

Question 6

Treatment of the Rickettsia Genus

Answer 6

Doxycycline (Tetracycline) Fluoroquinolones, Rifampin

Question 7

Prevention of the Rickettsia Genus

Answer 7

Non-specific- against insects vectors

Question 8

Generał Features and Habitat of Rickettsia prowazekii

Answer 8

Gram – (stains poorly with Gram staining)

Pleomorphic shape- resembles coccobacillus (very small)

Reservoir- human (unlike R. rickettsii)

Question 9

Biochemical Properties of Rickettsia prowazekii

Answer 9

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

Question 10

Pathogenesis of Rickettsia prowazekii

Answer 10

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

Question 11

Clinical Features (Epidemic Typhus) of Rickettsia prowazekii

Answer 11

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

Question 12

Diagnosis of Rickettsia prowazekii

Answer 12

Too small to be stained with Gram staining
Giemsa or Giemenez staining
Direct Immunofluorescence (IF) or micro-immunofluorescence (MIF)

Question 13

Treatment of Rickettsia prowazekii

Answer 13

Doxycycline (Tetracycline)

Question 14

Prevention of Rickettsia prowazekii

Answer 14

Inactivated vaccine (only for the epidemic typhus

Question 15

General Features of Rickettsia rickettsii and habitat

Answer 15

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)

Question 16

Biochemical Properties

Answer 16

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

Question 17

Pathogenesis

Answer 17

Transmitted by tick biting (Dermacenter ticks)

Incubation of 2-14 days before symptoms occur

High-risk groups- elderly, alcoholic and G6PD deficient

Question 18

Clinical Features (Rocky Mountain Spotted Fever)

Answer 18

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)

Question 19

Diagnosis

Answer 19

Too small to be stained with Gram staining

Giemsa or Giemenez staining

Direct Immunofluorescence (IF) or microimmunofluorescence (MIF)

Question 20

Treatment

Answer 20

Doxycycline (Tetracycline)

Question 21

Prevention

Answer 21

Non-specific- against insects vectors

Question 22

Oritentia general features

Answer 22

Orientia tsutsugamushi

Gram negative, small coccobacilli that lacks peptidoglycan layer, LPS and flagella

Obligate intracellular (found in the cytoplasm of infected cells)

Reservoir- mites

Question 23

Pathogenesis of Orientia tsutsugamushi

Answer 23

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)

Question 24

Disease: Scrub Typhus

Answer 24

Abrupt fever, headache, myalgia, in less than 50% also maculopapular rash

1-15% mortality rate

Question 25

Diagnosis of Orientia tsutsugamushi

Answer 25

Giemsa or Gimenez staining

Question 26

Treatment of Orientia tsutsugamushi

Answer 26

doxycycline

Question 27

General features and habitat of Coxiella burnetii

Answer 27

Gram – (stains poorly with

Gram staining)
Pleomorphic shape- resembles coccobacillus (very small)

Reservoir- animal (farm animals mostly) and feces or placenta of animal

Question 28

Biochemical Properties

Answer 28

Can survive harsh environment (“spore-like”)- survive in feces of animal

Obligate intracellular- replicate in phagosome of macrophages and monocytes

Question 29

Pathogenesis

Answer 29

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

Question 30

Clinical Features Q Fever

Answer 30

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

Question 31

Diagnosis

Answer 31

Too small to be stained with Gram staining

Giemsa or Giemenez staining

Serology (most commonly used to diagnose)- IF (test of choice) and ELISA

Question 32

Treatment

Answer 32

Self-limiting

Doxycycline (Tetracycline)

Question 33

Prevention

Answer 33

Acellular vaccine given to veterinaries (high-risk population), pasteurize the milk