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