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Spirochetes-Syphilis and Rickettsia

Spirochetes and Rickettsia


 Spirochetes have many structural characteristics in common, as typified by Treponema pallidum the agent of syphilis
 They are long, slender, helically coiled, spiral or corkscrew-shaped bacilli.

The Spirochetes 

 Spirochetes are a large, heterogeneous group of spiral, motile bacteria. 
 Most species stain poorly with Gram staining or Giemsa’s methods and are best observed with the use of dark-field or phase-contrast microscopy. These organisms are considered to be microaerophilic  Two important families – Spirochaetaceae and Leptospiraceae 
Treponema: Treponema pallidum subspecies pallidum – syphilis; T. p subspecies pertenue – yaws; T. p subspecies endemicum – endemic syphilis or bejel; T. carateum - pinta 
Borrelia: B. recurrentis – relapsing fever; vectors are human body louse for epidemic and ticks (ornithodoros) for endemic relapsing fever; B. burgdoferri – Lyme disease; Vector is tick (ixodes spp) 

Leptospiraceae (zoonosis) 
 Leptospira interrogans 
 Leptonema 
 Turneriella

The Spirochetes 
 Gram-negative human pathogens 
 Free living saprobes, or commensals of animals, not primary pathogens with the unusual morphologic features of axial fibrils and an outer sheath. 
 Most species stain poorly with Gram staining or Giemsa’s methods and are best observed with the use of dark-field or phase-contrast microscopy. These organisms are considered to be microaerophilic  Four important clinical genera: 
 Treponema 
 Leptospira 
 Borrelia 
 Spirochaeta

Typical Spirochetes

Genus Treponema 
 Thin, regular, coiled cells 
 Live in the oral cavity, intestinal tract, and perigenital regions of humans and animals 
 Pathogens are strict parasites with complex growth requirements 
 Require live cells for cultivation

Treponema Pallidum: The Spirochete of Syphilis 

 Although the mechanisms by which damage is done to the host are unclear, T. pallidum has a remarkable tropism (attraction) to arterioles; infection ultimately leads to endarteritis (inflammation of the lining of arteries) and subsequent progressive tissue destruction. 
 Human is the natural host 
 Extremely fastidious and sensitive; 
 cannot survive long outside of the host 
 Sexually transmitted and transplacental 
 Globally, estimated 12 million cases of syphilis annually.

Pathogenesis and Host Response in Syphilis

 Spirochete binds to epithelium (mucous membrane or abraded skin), multiplies, and penetrates capillaries 
 Moves into circulation and multiplies 
 Untreated syphilis marked by 4 clinical stages: 
 Primary, secondary, latent (early-<1yr; late->1yr) and tertiary.

 Tertiary syphilis is the tissue-destructive phase that appears 10 to 25 years after the initial infection in up to 35% of untreated patients. 
 Complications of syphilis at this stage include central nervous disease (neurosyphilis), cardiovascular abnormalities, eye disease, and granuloma-like lesions, called gummas, found in the skin, bones, or visceral organs. 
 Congenital syphilis is transmitted from mother to the unborn fetus during any stage of infection, but is most often associated with early syphilis. 
 The unborn fetus may develop an asymptomatic infection or symptomatic infection with damage to the bone and teeth, deafness, neurosyphilis, or neonatal death. 
 Spirochete appears in lesions and blood during first 2 stages – communicable

Primary syphilis (2 -6 wks)– appearance of hard chancre at site of inoculation; chancre heals spontaneously
 Secondary syphilis – fever, headache, sore throat, red or brown rash on skin, palms, and soles; rash disappears spontaneously– rash – may be recurrent – mucous patches – condylomata lata – spirochetemia 
 Latent phase (early and late) - during this latent period,diagnosis can be made using serologic methods. Relapses are common during early 
 Tertiary syphilis – about 35% of infections enter into tertiary stage; can last for 20 years or longer; numerous pathologic complications occur in susceptible tissues and organs 
 Neural, cardiovascular symptoms, gummas develop 
 Congenital syphilis – nasal discharge, skin eruptions, bone deformation, nervous system abnormalities

Oral and Genital Syphilitic Chancres

Skin Lesions of Secondary Syphilis

Tertiary Syphilis - Gumma

Congenital Syphilis Syndrome

Saber Shins in Congenital Syphilis

Laboratory Diagnosis of Syphilis

Darkfield Microscopy

 Specimen is tissue fluid or exudate from lesion.                                                                                     
 Useful only if lesion is present 
 Not useful for oral lesions 
 Positive sooner than serology test


 Tissue fluid or exudate is spread on a glass slide, air dried, and sent to the laboratory. 
 It is fixed, stained with a fluorescein-labeled antitreponeme antibody, and examined by means of immunofluorescence microscopy for typical fluorescent spirochetes.

Non-Treponemal Screening Tests 

 Are serological tests 
 Historically, the cardiolipin was extracted from beef heart or liver with added lecithin and cholesterol to enhance reaction with syphilitic “reagin” antibodies. 
 Reagin is a mixture of IgM and IgG antibodies reactive with the cardiolipin– cholesterol–lecithin complex. 
 All of the tests are based on the fact that the particles of the lipid antigen remain dispersed in normal serum but flocculate when combining with reagin.

Non Treponemal Tests 
Veneral Disease Research Laboratory (VDRL) and Unheated Serum Reagin (USR) needs microscope to observe the flocculation. 
Toluidine Red Unheated Serum Test (TRUST) and Rapid Plasma Reagin (RPR) have colored particles embedded into the test that makes microscopic magnification unnecessary. 
• Screening test – inexpensive, easy and quick 
• Cardiolipin, lecithin, cholesterol antigens 
• Can be titered – rising titer indicates active disease – falling titer indicates adequate therapy 
• Reflect overall activity of disease 
• Limitations - Less sensitive in early syphilis – may become reactive in late primary disease (2-3 wks after infection) – some patients who have been treated late in course of disease may become “serofast” for life – false positives in some autoimmune, viral or acute febrile states

RPR Non-treponemal Test

Treponemal Antibody Tests 

 Are also serological tests 
 The treponemal tests measure antibodies against T pallidum antigens. The tests are used to determine if a positive result from a nontreponemal test is truly positive or falsely positive. 
 A positive result of a treponemal test on a serum specimen that is also positive on a nontreponemal test is a strong indication of T pallidum infection. 
 The traditional treponemal tests are less useful as screening tests because once positive after initial syphilitic infection the tests remain positive for life independent of therapy for syphilis. 
 The T pallidum–particle agglutination (TP-PA) test is the most widely used treponemal test. 
 Others are T Pallidum Haemaglutination (TP-HA), and Micro-Haemagglutination-Tpallidum (MHA-TP)

Treponemal Test

 Treponema pallidum Particle Agglutination (TPPA)
–Gelatin particles sensitized with TP antigen
–No absorption needed
 In TPHA and MHA-TP, sheep red cells are sensitized with TP antigen

Florescent  Treponemal Antibody Absorbed Test - FTA-ABS

Enzyme Immunoassay & Chemiluminescence 

 Multiple relatively similar treponemal antibody tests using enzyme immunoassay (EIA) or chemiluminescence (CIA) formats for T pallidum are available. 
 These tests use antigens obtained by sonication of T pallidum or recombinant 
 antigens. An aliquot of serum at a standard dilution is added 
 to a sensitized well of a microdilution plate. 
 After washing, addition of an enzyme-labeled conjugate, and further washing, a precursor substrate is added. A color change or CIA indicates a reactive serum.

CDC Algorithms for Confirming Positive Syphilis tests 

 There are some concerns about variability in assay performance among these tests that result in more false positives when testing low-prevalence populations. 
 Because of this, the CDC has recommended an algorithm for confirming a positive EIA or CIA test result with a quantitative RPR or other nontreponemal test. 
 If the RPR result is positive, a current or past infection with syphilis is likely. 
 If the RPR result is negative, then additional testing with a traditional treponemal test such as the TP-PA is recommended. 
 If the TP-PA result is positive, syphilis is likely; if it is negative, syphilis is unlikely

Control of Syphilis
 Control measures depend on: 
 (1) prompt and adequate treatment of all discovered cases, 
 (2) follow-up on sources of infection and contacts so they can be treated, and 
 (3) safe sex with condoms. Several sexually transmitted diseases can be transmitted simultaneously.  Therefore, it is important to consider the possibility of syphilis when any one sexually transmitted disease has been found.


Borrelia Characteristics 
• Large spirochetes 20-30 μm in length 
• Motile • Stainable with aniline dyes (Giemsa) 
• May be observed with conventional microscopy 
• Cultivable in artificial media

Relapsing Fever: 
B. recurrentis & others 

– Endemic in Western U.S. 
– Transmission 
» Ornithodoros - ticks on rats 
» Pediculus 
– human body lice » Infected rats by contact with blood 
– Clinical 
» Febrile bacteremia with chills and headache 
» 3-10 recurrences common 
– Diagnosis 
» Culture – rarely successful 
» Antibody detection 
» Antigenic shifts confound diagnosis and serology

Lyme Disease - Borrelia burgdoferi

• Agent identified in 1984 
• Most in Western countries -USA 
• Transmitted mainly by Ixodes ticks 
• Reservoir in mice • Clinical 
• bloodstream invasion seeds tissues – nerves, heart, joints 
• three distinct stages 1. erythema chronicum migrans rash at site of tick bite 2. neural and heart problems – months 3. joints – arthritis – years 
• Diagnosis – antibody production –problematic

Ixodes Tick Vector for Lyme Disease


• Spirals – thin, tightly coiled 10-20 μm 
• Obligate anaerobes 
• Grow in artificial media supplemented by rabbit serum (Fletcher’s) 
• May require 4 weeks 
• Leptospira interrogans


• parasitize animals, i.e., dogs, cats, pigs, other livestock, who carry them in kidney. 
• Occasionally infect humans who come in contact with soil or water contaminated with urine. 
• Pathogenesis – entry through mucous membranes or breaks in skin, gain access to bloodstream, kidney, liver, CNS 
• Clinical – FUO, aseptic meningitis, jaundice, nephritis – Weil’s disease (L. interrogans serovar icterohaemorrhagiae) 
• Diagnosis – culture: blood, CSF, urine – serology – darkfield examination


Rickettsia in the cytoplasm of host cell

• Obligate intracellular organisms 
• Most (except Coxiella) transmitted to humans by arthropods 
• Contain both RNA and DNA 
• Cell walls similar to Gram negative bacteria 
• Stain with Giemsa 
• Reproduce by binary fission 
• Not routinely grown in diagnostic microbiology labs 
• Quickly destroyed by heat, drying and bactericidal chemicals 
• Use serology for diagnosis

Rickettsia: Pathology 
• Organisms multiply in endothelium of small vessels → vasculitis 
• Cells swell, become necrotic → thrombose vessel 
• Disseminated Intravascular Coagulation 
• Organism may replicate within phagocytic cells

Rickettsial, Ehrlichial and Q fever Diseaeses

Rickettsial, Ehrlichial and Q fever Diseaeses cont’d

Selected Rickettsial Diseases of USA

Macular Rash of RMSF

Ehrlichia chafeensis in a monocyte



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