Rickettsial Diseases

General introduction  Gram-negative, obligate intracellular coccobacilli bacteria that infect mammaols and arthropods  Rickettsiae are transmitted in the arthropods,which serves as both vector and reservior  Both DNA and RNA  Is sensitive to antibiotic.

Category of rickettsia  Genus Rickettsia, Coxiella,Orientia,Ehrlichia Bartonella Rickettsia, Coxiella,Orientia,Ehrlichia Bartonella  Species Rickettsia prowazekii (epidemic typhus), Rickettsia typhi (endemic typhus), Rickettsia rickettsii (spotted fever), Rochalimaea quintana (trench fever), Coxiella burnetii (Q fever) Rickettsia prowazekii (epidemic typhus), Rickettsia typhi (endemic typhus), Rickettsia rickettsii (spotted fever), Rochalimaea quintana (trench fever), Coxiella burnetii (Q fever)

Bilogical features  Variable shape, coccobacilli  Gram negative  Microcapsule and slim layer  Culture : in york sacs of embryonated eggs

Replication cycle of Rickettsia and Orientia

Antigenic structure  LPS Rickettsia tsutsugamushi Rickettsia tsutsugamushi Coxiella burnetii (Q fever) Coxiella burnetii (Q fever) LPS Ⅰ smooth LPS Ⅰ smooth LPS Ⅱ rough LPS Ⅱ rough Weil-Felix reacrion Weil-Felix reacrion  Surface protein(SPA)

Transmission  Typhus, spotted fever and trench fever are transmitted via arthropod vectors;  Q fever is acquired via inhalation or ingestion of contaminated milk or food.

Pathogenesis  Virulence factors: endotoxin, phospholipase A, and slime layer  Sites: vascular system producing vasculitis 血管炎  Characteristic triad of symptoms: fever, headache and rash (no rash with Q fever).

Rickettsia prowazekii 普氏立克次体  epidemic typhus  average incubation periods (days):8  the louse  Respiratory tract and conjunctiva  Latent period: 2 weeks  Abrupt onset,fever,chills,headache, myalgia,arthralgia myalgia,arthralgia

Rickettsia typhi 地方性斑疹伤寒立克次体  endemic typhus  7-14 days  Mice  the louse&flea  Mouth,nose and conjunctiva  Gradual onset,fever,headache,myalgia, cough cough

Rickettsia tsutsugamushi 恙虫病立克次体  Tsutsugamushi disease(scrub typhus)  Mice  tsutsugamushi  Black eachar 焦痂

Coxiella burnetti 贝纳柯斯体  Q fever  Cow and sheep  tick  High resistance abrupt onset,fever,headache,chills, myalgia,granulomatous hepatitis chronic diaease with subacute onset,endocarditis,hepatic dysfunction

Replication of C. burnetii

Generalized Life Cycle of Dermacentor variabilis and Dermacentor andersoni Ticks

Bartonella henselae 汉赛巴通 体  CSD (cat scratch disease)  Cat and dog  Conjunctiva inflammation and lymph node swell

Ehrlichia 埃里希体属  Ehrlichia chaffeensis: human monocytotropic ehrlichiosis  Ehrlichia sennetsu : human granulocytotropic ehrlichiosis

Replication of Ehrlichia 埃里希 体

Proposed life cycle for the agent of Human Granulocytic Ehrlichiosis 埃里希体病

Diagnosis  The use of immunofluorescent antibodies to examine a biopsy can be diagnostic.  The organism can be inoculated into tissue culture and grown over 4-7 days but this is very hazardous to personnel.  The Weil-Felix test looks for the production of serum antibody that is reactive against Proteus OX19, OX2 or OXK antigens but it is not always reliable.

Control  Sanitary: Arthropod and rodent control  Immunological: No vaccines are currently available.  Chemotherapeutic: Tetracycline or chloramphenicol are drugs of choice.