Group of bacteria that are fastidious, obligate intracellular pathogens They are pleomorphic & coccobacillary The organisms will not show up on Gram stain, but can be seen when either Gimenez or Giemsa stains are used
Spotted Fever Group Typhus Group Transitional group The Others The outer membrane protein A (ompA) gene is present in spotted fever but not typhus group organisms
Rickettsia are usually introduced into human skin by the bite of an insect (flea or louse) or an arachnid (tick or mite) These arthropods serve as both host and vector to the rickettsia and reside on the reservoir animals (dogs, mice, rats, and flying squirrels)
Two of the rickettsial diseases are unique in that humans may acquire them by direct inhalation Q fever (Coxiella burnetii) Epidemic typhus (Rickettsia prowazekii)
very similar for all infections regardless of species Vasculitis caused by the invasion and multiplication of the organism in the endothelial and smooth muscle cells of the blood vessels
Thrombosis, occlusion, and necrosis of blood vessel walls Thrombocytopenia with hemorrhage Massive capillary leakage into the interstitial spaces results in edema, hypovolemia, hypotension, and adult respiratory distress syndrome (ARDS) Encephalitis, myocarditis, & nephritis are the common clinical consequences Hyponatremia is due to ADH response
Rocky Mountain spotted Fever: -Rash typically appears on 4th day as blanching maculopapular lesions on the extremities Louse borne or Epidemic typhus: -Rash first appears in axillary folds then involving the trunk and extremities. - Brill-Zinsser disease
Murine (fleaborne or endemic) typhus: - Relatively mild illness with less complications -Rash is non-purpuric,non-confluent,less extensive -History of a flea bite and the presence ofrats in the house support the diagnosis butthis is only reported 30% of the time.
Scrub typhus: -Occurs mostly in Asian countries -characterised by painless eschar and “satellite lymphadenopathy” Rickettsial pox: -best known because of its association with a varicelliform rash.
Usually does not affect children No vector is involved Presents as both acute or chronic forms Endocarditis in chronic variety Bioterrorist threat?
Low or normal WBC count; in the late stages there is leucocytosis Anemia, thrombocytopenia and elevated serum transaminases Hyponatremia CSF analysis is usually normal; rarely mononuclear plecytosis (<300 cells/micro L)
Serological evidence of infection usually not occur earlier than second week of illness.
Gold standard test IgM titre >1:64 IgG titres >1:64 but <1:125 suggests previous infection A single titer is neither sensitive (patients can die before seroconversion) nor specific (an elevated titer can represent prior infection) ELISA – available in India and is the preferred diagnosis at present
Slide agglutination test Tests the presence of antigenic cross- reactivity between Rickettsia spp. and certain serotypes of non-motile Proteus spp., suffers from poor sensitivity and specificity, with a recent study showing an overall sensitivity as low as 33% and specificity of 46%.
Rickettsia Agent AntigenSpotted Fever Group OX 2 (Pr.vulgaris)Typhus Group, RMSF OX 19 (Pr.vulgaris)Scrub typhus OX K (Pr.mirabilis)
Drug of choice for all ages – Doxycycline(4 mg/kg/day divided every 12 hr PO or IV, maximum 200 mg/day) Chloramphenicol – Allergy to Doxycycline, Pregnant women (50-100 mg/kg/day divided 6th hourly, max 3 g/day) Continued for minimum of 5-7 days and for atleast 3 days until patient is afebrile.
Azithromycin, Clarithromycin Fluoroquinolones Rifampicin -Found to be more effective in typhus groups.
Patient coming from endemic area. H/O contact-pets/ h/o tick bite. Classical triad Rash without coryza. hepatosplenomegaly,edema,gangrene,anemia,thrombocyto penia Fever,rash,altered sensorium, convulsions PUO and not responding to routine antibiotics
When applied to the patients presenting with fever of unknown source, a clinical score of 14 or more on the proposed scoring system has very high sensitivity and specificity for the diagnosis of spotted fever group of rickettsial diseases.