م ي ح ر ل ا ن م ح ر ل ه ا ل ل م ا س بRICKETTSIA AND COXIELLA Prof. Khalifa Sifaw Ghenghesh
May 11, 2015
بسم الله الرحمن الرحيم
RICKETTSIA AND
COXIELLAProf. Khalifa Sifaw Ghenghesh
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
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
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
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)
Scrub typhus• Orientia tsutsugamushi (previously
R. tsutsugamushi )• Larval stages (chiggers) of mites
(Leptotrombidium)• Hosts: Rats or other small mammals
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
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
Treatment
Rickettsiostatic antibiotics•Tetracyclines•Chloramphenicol
Intensive nursing care and management of fluids and electrolytes
Child's right hand and wrist displaying the characteristic spotted rash of Rocky Mountain spotted fever caused by Rickettsia rickettsii
Rickettsia tsutsugamushi free within the cytoplasm of a mouse brain capillary
endothelial cell. Capillary wall appears in cross section
Dorsal view of an American Dog Tick, Dermacentor variabilis, a known carrier of
Rocky Mountain Spotted Fever caused by the bacterium Rickettsia rickettsii.
IFA reaction of a positive human serum on Rickettsia rickettsii grown in chicken
yolk sacs, 400X
Red structures indicate immunohistological staining of Rickettsia rickettsii in endothelial
cells of a blood vessel from a patient with fatal RMSF
Removing attached ticksRemoving attached ticks
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
Coxiella burnetii
Coxiella burnetii
Laboratory Diagnosis•Demonstration of specific Abs
Complement fixation test Indirect immunofluorescence assay
• Isolation of organism Not recommended
Treatment•Doxycycline
Control