Spirochaetes PDF

Chapter (19): SPIROCHAETES Characteristic features: • Slender, flexible, spiral rods • They have Gram-nega�ve cell wall structure • Three genera of Spirochetes cause human infec�ons: 1- Treponema 2- Borrelia 3- Leptospira • Have characteris�c corkscrew mo�lity due to presence of axial filaments (...

Chapter (19): SPIROCHAETES Characteristic features: • Slender, flexible, spiral rods • They have Gram-nega�ve cell wall structure • Three genera of Spirochetes cause human infec�ons: 1- Treponema 2- Borrelia 3- Leptospira • Have characteris�c corkscrew mo�lity due to presence of axial filaments (endoflagella) Treponema Introduction Culture • The most important species is T. pallidum, which causes syphilis (sexually transmi�ed disease) • T. pallidum is human parasite → it has no animal or environmental reservoirs (because of its rapid death outside the host) Morphology • T. pallidum has regular coils with pointed ends • The organism is very thin (1/5 diameter of E. coli) • It can only be seen by: 1- Dark-field microscopy: in wet unstained prepara�ons 2- Direct immunofluorescence • In vitro: T. padillum cannot be grown on ar�ficial culture media • In vivo: it can be maintained in laboratory by inocula�on of posi�ve specimens into rabbit tes�cles Mode of transmission 1- Sexually: → leading to venereal syphilis 2-Transplacentally: → leading to congenital syphilis 3- Fresh blood transfusion: → T. pallidum is not transmi�ed by stored blood → because it dies when stored at 4°C within 3-5 days Latent (may last for years) Ter�ary (years later) 30% of untreated cases • Serologic tests • Direct detection of organism . r D • Gumma formation (in skin and bones) • Cardiovascular syphilis • Neurosyphilis m a h s e H Serologic tests only Serologic tests only 1 Direct detection • Of organism from chancre, mucous patches or chondyloma lata by: 1- Dark-field microscopy of wet unstained prepara�on → which detects characteris�c mo�lity 2- Direct immunofluorescene a�er staining with fluorescein-labelled an�-treponemal an�bodies → this method is highly sensi�ve & specific Laboratory diagnosis: Diagnosis of congenital syphilis: Comparison between non-treponemal and treponemal tests Non-treponemal Non-specific Reagin Ab Cardiolipin VDRL, RPR Inexpensive, Rapid, Simple u Screening v Follow up of treatment 6-18 months after treatment • Done by detec�on of treponemal IgM an�bodies in newborn’s serum by EIA Treponemal Specific Anti-treponemal Ab Treponemal antigens FTA, TPHA, EIA Expensive, Time consuming, Difficult to perform Confirmation t a m s E Serologic tests of syphilis: Bacteria (36) • They include: 1- Non-treponemal tests → which are non-specific tests used for screening Congenital syphilis (1-3 months later) • Four cardinal features: 1- Generalized maculopapular skin rash 2- Mucous patches in mouth 3- Chondyloma lata around the genitals or anus 4- Generalized lymphadenopathy • Highly infectious • Spontaneous healing (within 3 months) None • In utero infec�ons can lead to: 1- Abor�on or s�llbirth 2- Congenital abnormali�es → which may be obvious at birth 3- Silent infec�on → in which manifesta�ons may not be apparent un�l about 2 years of age (facial & tooth deformi�es) Secondary • Direct detection of organism • Serologic tests → reactive only late Acquired (venereal) syphilis Clinical forms (2-6 weeks a�er exposure) • Hard painless genital or oral ulcer (chancre) • Contagious (infectious) • Heals spontaneously (within 3-6 months) 2 • Classically, untreated syphilis occurs in the stages: Primary 3- Light microscopy a�er impregna�on (thickening) by silver staining (e.g. Fontana stain 2- Treponemal tests → which are specific tests used for confirma�on • These tests detect non-treponemal antibodies known as reagin (heterophil antibodies) • These antibodies are produced in response to lipoidal material released from damaged host cells The antigen used is called cardiolipin → which is extract from beef heart muscle with added lipids Non-treponemal tests include the following flocculation tests: u Venereal disease research laboratory (VDRL) test in which flocculation is seen by microscopic examination v Rapid plasma reagin (RPR) test in which flocculation is seen with naked eye j Screening As these tests are inexpensive, rapid & simple, → they are used for screening However, being non-specific → they may give positive results in other conditions like autoimmune diseases, pregnancy, leprosy, viral infections and immunization → therefore, positive results should be confirmed by one of specific treponemal tests k Follow up Since reactivity declines within 6-18 months after successful treatment → these tests are used for follow up These tests detect specific treponemal antibodies The antigen used is T. pallidum antigen Treponemal tests include the following tests: u Fluorescent treponemal antibody (FTA) test v T. padillum haemagglutination assay (TPHA) w Enzyme immune-assay (EIA) & Western blot Confirmation Being specific → they are used in confirming or ruling out reactive non-treponemal test results N.B. • Treponemal tests are not used for screening → as they are more expensive and more difficult to perform then non-specific tests • They cannot be used to determine response to treatment → as they remain reactive for life even after effective treatment For life Treatment • Penicillin is drug of choice for treatment of syphilis → no resistance to penicillin has been recorded • Tetracycline, erythromycin & chloramphenicol → can be used as alterna�ve an�bio�cs for pa�ents allergic to penicillin. • Only penicillin or chloramphenicol → can be used for pa�ents with neurosyphilis • Syphilis pregnant mothers → should be adequately treated to prevent congenital syphilis