Rickettsial Infection Notes PDF

# Rickettsial Infection (6 Topic) ## General properties 1. Non motile 2. Gram negative 3. Coccobacilli 4. Obligate intracellular 5. Compulsory inside cell 6. Not cultivable in artificial media 7. Transmitted by arthropod vectors (tick, mite, flea) 8. Infect vascular endothelial cells ## Classific...

# Rickettsial Infection (6 Topic) ## General properties 1. Non motile 2. Gram negative 3. Coccobacilli 4. Obligate intracellular 5. Compulsory inside cell 6. Not cultivable in artificial media 7. Transmitted by arthropod vectors (tick, mite, flea) 8. Infect vascular endothelial cells ## Classification - Order - Rickettsiales - Families - Rickettsiaceae - Anaplasmataceae - Genera - Rickettsia - Orientia - Ehrlichia - Wolbachia - Anaplasma - Neorickettsia *Coxiella and Bartonella removed from family * Not obligate intracellular * Not arthropod transmission ## Rickettsia VS Virus - Have gram-ve cell wall - Contain both DNA & RNA - Multiply by binary fission - Killed by antimicrobial agent - Seen under light microscope - They cannot pass bacterial filters - Not viruses ## Rickettsia Infection - **Typhus group** - Spotted fever - R. akari - R. rickettsii - R. conorii - R. africae - Typhus - R. prowazekii - R. typhi - **Antigenic structures of Rickettsia** - OMP antigens - Species specific - Highly immunogenic - LPS antigens - Group specific - Used in Weil-Felix reaction ## Pathogenesis - Transmitted by arthropods - **Reservoirs** - Tick & mite - Louse & flea - **Transmit organism** - Bite - Rubbing/stretching on abraded surface - **How they spread in body** - Through lymphatics - Multiply in lymph node - Enter bloodstream - **Final target - to reach endothelial cells** - After reaching - Adhesion by OmpA & OmpB - Phagocytosed by endothelium - Obligate intracellular - Survive inside cells - Multiply by binary fission (slow) - cell to cell transmission - Cell lysis (Except spotted fever) ## We will discuss 5 diseases 1. Endemic typhus 2. Epidemic typhus 3. Rocky Mountain spotted fever 4. Indian tick typhus 5. Rickettsial pox ## Epidemic typhus - by prowazekii - **Vector** - human body louse - Pediculus humanus capitis - **Mode of transmission** - Rubbing/stretching of abraded skin/mucosa - Ingestion of feces contaminated with rickettsia - **Rarely by inhalation** - **Clinical manifestation** - Acute febrile disease - Muscle/Joint pain - Headache - Myalgia - Eye discharge - Rashes - Begin at upper trunk - Generalized on entire body - Incubation period - 2 weeks - Myalgia - severe (crouching position) - **Complications** - Intestinal pneumonitis - CNS - mental confusion & coma - Fatality in 7-40% cases - **Risk factors** - Louse population ↑ - Unhygienic - **Brill-Zinsser disease** - Reactivation of epidemic typhus (due to & immunity) ## Endemic typhus (Flea-borne) - **Vector** - rat flea - R. typhi - Rare - cat flea - **Mode of transmission** - same as epidemic typhus - **Reservoir** - Rodents (natural reservoir) - **Clinical manifestation** - Incubation period - 1-2 weeks - Symptoms same as epidemic typhus - Less fatal & severe ## Rocky Mountain spotted fever - By Rickettsia rickettsii - **Transmission by - tick** - **Clinical manifestation** - Incubation period - 4-14 days - Fever, headache, rash, myalgia, anorexia - **Rashes** - on extremities & trunk - First maculopapular - hemorrhagic - **Complications - late** - Vascular damage - Permeability - Edema - Hemorrhage - DIC - Interstitial pneumonitis - CNS involvement ## Indian tick typhus - Rickettsia conorii - **Vector** - tick - Rhipicephalus sanguineus - **Clinical manifestation** - RMS like - Eschar is present on tick bite ## Laboratory Diagnosis - **Serology** - Antibody detection - Non-specific (Weil-Felix test) - Less sensitive & specificity - Cheap - Test only after 5-7 days of fever - Specific (IFA/ELISA) - Principle - LPS antigen of rickettsia also present in Proteus - s. OX19, OX2, OXK - We will introduce Proteus antigen in serum - React antibody of rickettsia antigen - Procedure - Tube agglutination test - Results - Titer of 1:80 - significant - Epidemic typhus - Only Ox19 elevated - Ox2 - may/may not elevate - Tick-borne spotted fever - Both OX19 & OX2 elevated - Scrub typhus - OXK elevated - **What elevated?** - titer is elevated - False positive titer - In Proteus injection - False negative titer - When patient have excessive antibodies in sera due to any reason other than injection - **Histological** - **Isolation** - **PCR** ## Specific test - **IFA (Indirect Immunofluorescence assay)** - Gold standard - Only after 7-10 days of infection - Titer of 1:64 - significant