RICKETTSIA AND COXIELLA Prof. Khalifa Sifaw Ghenghesh بسم الله الرحمن الرحيم RICKETTSIA AND COXIELLA Prof. 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 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 Treatment Control Demonstration of specific Abs Complement fixation test Indirect immunofluorescence assay Isolation of organism Not recommended Treatment Doxycycline Control