1. RICKETTSIA AND COXIELLA Prof. Khalifa Sifaw Ghenghesh
بسم الله الرحمن الرحيم
RICKETTSIA
AND
COXIELLA
Prof. Khalifa Sifaw Ghenghesh

2. Rickettsia species Gram-negative bacilli
Obligate intracellular parasites
All associated with an arthropod vector
Pathogenic species parasitize endothelial cells almost exclusively
2 antigenically distinct groups
Typhus group
Spotted fever group

3. Pathogenesis
The organisms enter the body through the bite or faeces of an infected arthropod vector
Disseminate through bloodstream >> endothelial cells by induced phagocytosis >> escape from phagosome >> multiply intra-cellularly >> destroy host cell

4. Rickettsial Diseases Epidemic typhus
Transmitted from human to human by R. prowazekii
Vector: body louse (Pediculus humanus)
Incubation period: 5-15 days
Macular rash: 4-7 days after illness and begin to fade after 1-2 days
In severe: rash may last longer and become haemorrhagic

5. Flea-borne fevers (Murine typhus)
R. typhi
Rats and their infected fleas
Tropical and subtropical coastal regions
Ports with large number of rats
Disease: similar to epidemic typhus but milder
Tick-borne spotted fever (group)
Example: R. rickettsii
Can be life-threatening
Maintained in enzootic cycle (ticks and their wild animal hosts)

6. Scrub typhus Orientia tsutsugamushi (previously R. tsutsugamushi )
Larval stages (chiggers) of mites (Leptotrombidium)
Hosts: Rats or other small mammals

7. Laboratory Diagnosis Serological Methods
Weil-Felix test (Agglutination test)
Somatic Ags of non-motile Proteus species
Not reliable >> low levels of sensitivity and specificity
Detection of Abs to Rickettsia species by:
Immunofluorescence
Latex agglutination
Enzyme immuno-assay
Death may occur before detectable levels of Ab are present

8. Isolation of the Organism
In cell culture
In susceptible laboratory animal
Not practicle
Detection of the organism in tissue
Specimen: Skin biopsies from petechial lesions
Examined by:
Immuno-fluorescence or
immuno-enzyme methods

9. Treatment Rickettsiostatic antibiotics Tetracyclines Chloramphenicol
Intensive nursing care and management of fluids and electrolytes

10. Child's right hand and wrist displaying the characteristic spotted rash of Rocky Mountain spotted fever caused by Rickettsia rickettsii

11. Rickettsia tsutsugamushi free within the cytoplasm of a mouse brain capillary endothelial cell. Capillary wall appears in cross section

12. Dorsal view of an American Dog Tick, Dermacentor variabilis, a known carrier of Rocky Mountain Spotted Fever caused by the bacterium Rickettsia rickettsii.

13. IFA reaction of a positive human serum on Rickettsia rickettsii grown in chicken yolk sacs, 400X

14. Red structures indicate immunohistological staining of Rickettsia rickettsii in endothelial cells of a blood vessel from a patient with fatal RMSF

15. Removing attached ticks

17. Coxeilla burnetii Gram-negative, Pleomorphic, coccobacillary bacteria
Obligatory intracellular
Q fever
Typhoid-like illness
Almost worldwide distribution
Reservoirs: wild and domestic animals
Infection results from inhalation of aerosols containing the organism

18. Coxiella burnetii

19. Coxiella burnetii

20. Laboratory Diagnosis Treatment Control Demonstration of specific Abs
Complement fixation test
Indirect immunofluorescence assay
Isolation of organism
Not recommended
Treatment
Doxycycline
Control