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In this article we will discuss about Treponema Pallidum:- 1. Evolution of Treponema Pallidum (Tr. Pallidum) 2. Staining of Treponema Pallidum (Tr. Pallidum) 3. Cultivation 4. Viability of Treponema Pallidum 5. Viability 6. Pathogenesis 7. Laboratory Diagnosis 8. Serology 9. Tests for Lipoidophil Antibody.
Contents:
- Evolution of Treponema Pallidum (Tr. Pallidum)
- Staining of Treponema Pallidum (Tr. Pallidum)
- Cultivation of Treponema Pallidum (Tr. Pallidum)
- Viability of Treponema Pallidum (Tr. Pallidum)
- Pathogenesis of Treponema Pallidum (Tr. Pallidum)
- Laboratory Diagnosis of Treponema Pallidum (Tr. Pallidum)
- Serology of Treponema Pallidum (Tr. Pallidum)
- Tests for Lipoidophil Antibody of Treponema Pallidum (Tr. Pallidum)
1. Evolution of Treponema Pallidum (Tr. Pallidum):
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The causal agent of Syphilis Treponema pallidum was first discovered in 1905 by a German scientist Schaudinn in the primary sores (Chancres, pronounced shankers) of a syphilitic patient. In electron micrograph, T. pallidum is seen to be covered by an outer periplast which covers the whole organism when the periplast is removed by digestion with trypsin or pepsin, the fine filaments are seen twisted around the organism.
It seems likely that they are contractile and maintains the characteristic shape of motility of the organism. Tr. pallidum shows rotary corkscrew like highly characteristic motility (Angulation) which can be easily seen under dark field microscope.
2. Staining of Treponema Pallidum (Tr. Pallidum):
Tr. pallidum can be stained by Giemsa stain in 1: 10 dilution over a long period, it appears pink in colour in contrast to the purplish colour of non-pathogenic spirochaete. The organism can be demonstrated by India ink or by Fontana’s silver impregnation method using the exudate from the chancre.
In tissues, spirochaetes can be stained by Levaditi’s silver impregnation method in which silver salts are allowed to penetrate the inside of the cells. Metallic silver is then precipitated inside the spirochaetes by means of a reducing solution. The organism appears black against a yellowish black background.
3. Cultivation of Treponema Pallidum (Tr. Pallidum):
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Tr. pallidum cannot be cultivated artificially, but the pathogenic strain (Nichol’s strain) can be grown in the testicles of experimentally inoculated rabbit. Certain other non-pathogenic strains (e.g. Reiter strain) can be cultivated under strict anaerobic condition in Smith Noguchi medium.
4. Viability of Treponema Pallidum (Tr. Pallidum):
Outside the body, Tr. pallidum cannot live. It is a strict parasite; it dies rapidly in water and is very sensitive to drying. Soap and other detergents quickly destroy it. It is readily killed by heat at 41.5°C in an hour. Secretions containing Tr. pallidum are possible source of infection to nurses, doctors and technicians who handle the syphilitic patient. The infections are virtually acquired by direct contact with an infected patient.
5. Pathogenesis of Treponema Pallidum (Tr. Pallidum):
There are four stages in the untreated cases of syphilis:
(a) Primary Syphilis:
Tr. pallidum gains entrance into the body through the skin and mucous membrane. During sexual intercourse, it generally infects genitalia, occasionally the lip during kissing; and it is not homosexually acquired. After an incubation period of 4-6 weeks, the initial sore of primary syphilis appears on the genitalia.
This lesion is at first small red purple (chancre), it gradually enlarges, becomes indurated and necrosis in the centre of an ulcer; then a generalized lymphadenopathy of the inguinal gland develops. Spirochaetes are present in large numbers in the exudate of the primary chancre.
As the sore heals, the organism becomes less numerous and may not be demonstrated in the exudate, but, at this stage, it may be possible to find them in fluid aspiration by lymph gland puncture.
(b) Secondary Syphilis:
After 6 to 12 weeks of the appearance of primary chancre, the secondary syphilis develops with the invasion of blood stream and widely distributed throughout the body. The clinical manifestadons in this stage are fever, a generalized roseolar skin rash, mucous patches in the mouth and condylomata of the anus and vulva. The severity of the lesion is extremely variable.
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Sometimes the lesions heal up and disappear completely.
(c) Tertiary Syphilis:
In the tertiary syphilis, the spirochaetes become localised producing low grade inflammatory lesions in the cardiovascular and central nervous systems and in chronic granulomata (gummata) in the skin, bone and internal organs. This is also called chronic stage. Thus tabes dorsalis and meningo, en-cardiovascular syphilis may be detected 5-15 years after the appearance of primary chancre.
The late symptoms of syphilis depend on the organ that is attacked by the spirochaetes. The most frequent, serious and disabling results of syphilitic infection are disease of heart, arteries, causing sac-like dilatadon called aneurysm.
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These may burst and the patient may die of the haemorrhage. Syphilis is one of the principle causes of diseases of the aortic valves, but not responsible for arteriosclerosis; and cerebral haemorrhage may occur in young person.
In untreated cases, Tr. pallidum lodges in the central nervous system (brain and spinal cord) where they cause a chronic inflammation and destroy the nerve tissue. Various forms of insanity result. These lesions result in paresis (general paralysis) and locomotors ataxia or tabes. In paresis, spirochaetes are present in the tissue of the brain; ill tabes, in the spinal cord.
(d) Congenital Syphilis:
Tr. pallidum can cross the placental barrier and a syphilitic mother especially in secondary syphilitics—may transmit the infection to her foetus. The lesions of congenital syphilis are similar to those already described when the infection is massive, the child may be stillborn or survive for a short time.
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The most important defects of late congenital syphilis are mental deficiency, chronic meningitis, blindness and deafness.
6. Laboratory Diagnosis of Treponema Pallidum (Tr. Pallidum):
Syphilitis exudate:
In primary and secondary lesions, it is possible to find and identify Tr. pallidum by dark field microscope.
7. Serology of Treponema Pallidum (Tr. Pallidum):
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A specimen of 5-10 ml clotted blood is needed. It should be collected in a sterile dry container without any preservative. If Tr. pallidum immobilisation test is required, information must be provided about recent antibiotic treatment, because traces of penicillin or other antibiotics in the blood interfere with this test.
Specimens from the newborn babies should be taken by heel stab, cord blood from the newborn is not satisfactory.
8. Tests for Lipoidophil Antibody of Treponema Pallidum (Tr. Pallidum):
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a. Standard Test for Syphilis (STS):
These tests, made with cardiolipin antigen, are usually the first investigations arc carried out to confirm the diagnosis of syphilis. A rapid slide flocculation test, such as VDRL test, is often used for screening, although some prefer the Kahn test. A second test, i.e. Wassermann test, is carried out quantitatively, so that besides confirming previous tests, it also provides a baseline in assessing the effect of treatment.
In primary syphilis, Wassermann antibody is usually detectable about one week after the appearance of the primary chancre. In the secondary stage, virtually all cases give positive findings with high titre. There are many microbial infections and pathological lesions that may liberate lipid antigen in the tissues with the consequent formation of lipoidophil antibody and the occurrence of biological false positive reaction.
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Persons who were vaccinated against small pox or were suffering from various infections (e.g. leprosy, typhus) give weakly positive reaction.
b. Tests for Treponemal Antibodies:
When complement fixadon test (CFT) is employed to diagnose syphilis, it is called Wassermann test. CFT may be Reiter Protein complement fixation test (RPCFT) when the antigen of Reiter strain of treponemes is used. Absorbed fluorescent Treponemal antibody test (FTAABS) or Treponema pallidum immobilization (TPI) is more specific and can be used to verify STS positive reaction.
An indirect haemagglutinadon test for the serodiagnosis of syphilis has been developed by using the andgen of the Nichol’s strain of Tr. pallidum. The specific test is claimed to be similar to that of TPI test and its sensitivity is comparable to that of FTA test.
c. Tr. pallidum Antibody:
Of all serological tests, the more reliable, highly specific andtitreponemal test is Treponema pallidum immobilization (TPI) test in which the patient’s serum is incubated with living virulent Tr. pallidum (Nichol’s strain) in the presence of complement.
TPI is not useful in the diagnosis of early syphilis. It is able to distinguish between true and false positive STS. TPI is technically difficult and costly—so it is not frequently used.
If the brain or spinal cord is affected by syphilis, a positive serological test is usually given by CSF. The reactions are practically always positive and frequent in locomotors ataxia. Of the classes of Immunoglobulin’s that take part in the TPI and FTA ABS, the most important is IgG though IgM is detectable in early syphilis.
d. Chemotherapy:
Penicillin is lethal to Treponema pallidum in a concentration of 0.003 unit/ml and is the drug of choice.
