Treponema pallidum Flashcards
What are the characteristics of T.Pallidum
Long and slender corkscrew shape (spirochetes)
Unicellular
Obligate parasite
Does not stain with gram method (gram-negative)
Has endoflagella, 3 axial fibrils that are attached to each end of the organism between cytoplasmic and the outer membrane
What surrounds the cytoplasm of T.Pallidum?
It is surrounded by:
- Trilaminar cytoplasmic membrane
- peptidoglycan layer
- inner mucopeptide layer
- outer lipoprotein membrane
- phospholipid rich outer membrane
Where does T.Pallidum grow?
Rabbits testis
What are the virulence factors of T.Pallidum and their functions?
Sialic acid on its surface inhibits activation of complement by alternate pathway
Hyaluronidase breaks down hyaluronic acid in the ground substance of tissue and enhances its invasiveness
Explain the pathogenesis of T.Pallidum
Human infection transmitted by sexual contact and the infectious lesions is on the skin or mucous membranes of genitalia
It can penetrate intact mucous membranes or enter through a break in the epidermis
they multiply locally at the site of entry and spread to nearby lymph nodes and reach the blood stream
within 2-10 weeks, a papule develops at the site of infection, and breaks down to form an ulcer with a clean hard base
Inflammation characterized by predominance of lymphocytes and plasma cells
primary lesion heals spontaneously, but 2-10 weeks later, secondary lesion appears consisting of red maculopapular rash on the body but also subside spontaneously
The patient may also have syphilitic meningitis,
chorioretinitis, hepatitis, nephritis or periostitis.
In about 30% of cases, early syphilitic infection
progresses spontaneously to complete cure
without treatment.
30% of untreated cases remain latent,
the rest develop to tertiary stage characterised by development of granulomatous lesions in the skin, bones, and liver as well as degenerative changes in the CNS and/or CVS
What specimens are required for laboratory diagnosis of T.Pallidum
Tissue biopsy
Blood for serology tests
Exudates from chancre, condylomata, mucus patch, skin lesion and lymph nodes
What can cause biological false positives in test for T.Pallidum?
Malaria vaccination Tuberculosis Leprosy Pregnancy Autoimmune disorders Chronic liver disease
Discuss Fluorescent treponemal antibody absorption along with its advantages and disadvantages.
It uses specific T.Pallidum antiges to detect the presence of antibodies against treponemal antigens
Its advantages are:
-specific and sensitive
- positive early in the disease (2 weeks)
Disadvantages: - expensive difficult to standardize -interpretation is subjective - difficult to use as quantitative test - once positive remains positive for a long time
Discuss VDRL test and its advantages and disadvantages.
It is a test that screens for IgG and IgM antibodies to a cardiolipin-cholesterol-lecithin antigen and becomes positive early in the disease (2-3 weeks)
Advantages:
- rapid and inexpensive
- determines the activity of the disease
- used for monitoring therapeutic response
- Only RPR and VDRL can monitor disease activity and assess response to antibiotic therapy
Disadvantages:
- Gives biological false positive in other diseases
- Gives negative results in secondary syphilis due to prozone phenomena
- Gives positive results in other treponemal disease
- problems interpreting the test in chronic persisters after therapy
What are some Nontreponemal reaginic tests that can be used to detect T.pallidum?
VDRL
RPR
CFT
What are some specific Treponemal antibody tests?
-Fluorescent treponemal antibody absorption (FTA-Abs)
- Treponema pallidum hemagglutination
assay (TPHA)
- Treponema pallidum immobilisation test
(TPI)
Explain the primary stage of acquired syphilis
Happens 1-3 weeks after T.Pallidum lands on skin or mucous membrane
Spirochetes destroy the soft tissue wherever they enter the body forming ulcers called syphilitic chancres
chancres have fluid rich in spirochetes that can spread to other parts of the body as well as other individuals.
If it was acquired through sexual contact, primary chancre can form on external genitalia
If acquired through physical touch, can appear on other parts
Chancres usually heal on their own in a few months, or they can go to nearby lymph nodes causing lymphadenopathy and then enter lymph and blood stream
Explain secondary syphilis
Occurs 6-12 weeks after infection.
T.Pallidum enters blood stream causing spochetemia and generalized lymphadenopathy through out the body
Spirochetes attach to endothelial cells in small capillaries near skin causing non itch maculopapular rash which starts on the trunk and and spread to arms and legs, genitalia and other mucous membranes.
Sometimes rashes can be pustular(filled with pus) and papulosquamous
(scaly and hard)
Condyloma lata may be present, smooth white painless wart-like lesions mainly around genitals, anal region and armpits.
This makes the secondary stage the most infectious stage.
Usually resolves within a few weeks to months
Explain latent syphilis
Dormant and asymptomatic
spirochetes can be found in tiny capillaries in various organs and tissue.
Can be divided into early and late syphilis;
early syphilis occurs within a year of infection and during that time spirochetes can re-enter the blood
Can cause severe immune response that damages the cells and cause tertiary syphillis
What are the 3 main antigens of T.Pallidum?
Group specific antigen
Species specific antigen
Cardiolipin
