Transcript Lecture 12
PCMS 2007 DR JEANNETTE WADULA Consultant Microbiologist CMID/NHLS 1 SPIROCHETES SPIROCHETES OBJECTIVES Describe the characteristics and classification of Spirochetes Discuss the etiology and epidemiology of spirochetal diseases Identify the pathogenic and clinical similarities of spirochetes Discuss briefly the principles of diagnosis and management 2 Characteristics of Spirochetes Spirochetes are unusual gram-negative, helically curved bacteria with a complex peptidoglycan-cytoplasmic membrane,referred to as protoplasmic cylinder surrounded by an outer membrane(lipid bilayer sheath) Free-living or host associated (colonize) bacteria widespread in nature 3 Their motility differs from other bacteria owing to the unique structure (presence of periplasmic flagella within the periplasma) 4 Periplasmic fibrils, are responsible for their cockscrew movement 5 CLASSIFICATION Class Spirochaetes Order spirochetales Leptospiraceae Leptospira (Zoonosis) Spirochaetaceae Treponema (human-human contact) Borrelia (Zoonosis) Other 6 Of the six genera, three- Treponema, Borrelia and Leptospira contain organisms pathogenic for humans 7 Human Spirochetal diseases and their etiologic agents Infecting organism Treponema T. carateum T. pallidum subspecies pertenue T. pallidum subspecies endemicum T. pallidum subspecies pallidum Disease Pinta Yaws Bejel, Endemic syphilis Syphilis 8 Human spirochetal diseases and their etiologic agents Leptospira interogans Leptospirosis Borrelia spp ( recurrentis, hermsii, turicatae) Relapsing fevers (epidemic or) sporadic Borrelia burgdoferi Lyme disease 9 Epidemiology Treponemes- except for congenital syphilis (transplacental), syphilis is transmitted through sexual contact Pinta, Yaws and endemic syphilis – nonvenereal trepomatoses are not spread by sexual contact but by close skin-skin contact between humans and there is no known animal reservoir. Leptospira and Borrelia are zoonotic i.e., animal reservoirs exist and infect humans via direct or indirect contact. Human leptospirosis is acquired by direct contact with contaminated urine from rats, pigs, dogs, cats... 10 Epidemiology Many animals are asymptomatic carriers of L. interrogans in their kidneys –no arthropod or insect vector Relapsing fever is transmitted by either infected human louse(LBRF)/tick(TBRF) (B. recurrentis- transovarial passage doesn’t occur ) by bites-epidemic form Ticks (ornithodoros) are vectors of sporadic cases of relapsing fever These infected ticks transmit infection transovarily for generations and remain infective for many years without feeding Lyme disease is transmitted to humans by a minute tick (ixodes) 11 Pathogenic features Spirochetes invade host tissue at mucus or skin membranes (portal of entry), cause infection and gain access to the lymph systems and blood Spirochetemia early in the course, wide dissemination throughout tissues, and body fluids, one/more stages of disease, often intervening latent periods (1o2o3o) Such illness suggests that pathogenic spirochetes 12 Pathogenic features share unique virulence characteristics Once pathogen has entered host, it is successful at evading defense mechanisms by not being immunogenic In most cases, spirochetes persist in host for extended periods, late presentation of disease appears to be due to the presence of viable organisms 13 Clinical similarities common tropism for the skin, bone, and central nervous system Myocardial disease is found in leptospirosis, relapsing fever, possibly syphilis and Lyme disease Chronic arthritis uniquely occurs in Lyme disease, but can occur in syphilis also 14 Principles of diagnosis and management Based on recognition of clinical features of patient illness with a history of possible exposure to the causative organism Based on either direct detection (dark-field microscopy /culture) or serology(IFA/ELISA). Treponema spp have not been cultured, do not take up aniline stains gram stain not effective. Dark field illumination allows visualisation, nontreponemal (RPR, VDRL-) and treponemal tests (fluorescently labeled antibody..) can be used 15 Principles of diagnosis and management L.interrogans can be grown on artificial culture media can be isolated from patients blood. Serologic diagnosis is made using convalescent serum Borrelia relapsing fevers – blood smears with typical spirochetes, blood cultures possible but serologic diagnosis difficult Borreliae stain well with aniline dyes and can be observed with the ordinary light microscope!!! Lyme disease – culture of B. burgdoferi from patients blood is definitive but rare except from skin biopsy samples. Determination of specific antibody titers – most helpful 16 References Manual of Clinical Microbiology seventh edition, Murray. 17 18 Frambesia- T. pertenue 19 Bone disfiguration-tertiary T. pertenue infection 20