Spirochetes and Rickettsia
Outline
Spirochetes:
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
Spirochaetaceae
Treponema: Treponema pallidum subspecies pallidum – syphilis; T. p subspecies
pertenue – yaws; T. p subspecies endemicum – endemic syphilis or bejel; T.
carateum - pinta
Leptospiraceae (zoonosis)
Leptospira interrogans
Turneriella
Relapsing Fever:
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
Immunofluorescence
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
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
Leptospira
• 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
Leptospirosis
Epidemiology
• 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
Rickettsiae
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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