Treponema pallidum

Treponema pallidum is a species of bacterium, of the genus Treponema, made up of between eight and twenty coiled whorls, which gives it a rotational movement similar to a corkscrew. It is 5 to 20 microns long and 0.5 in diameter, and is a spirochete [does not stain with gram stain]. Highly contagious, it is the cause of several human diseases, mainly syphilis. Its basic structure consists of an axial filament embedded in a helical cylinder of cytoplasm. The filament is morphologically similar to the bacterial flagellum, and gives it mobility.

There are at least three known subspecies: T. pallidum pallidum, which causes syphilis; T. pallidum pertenue, which causes yaws (also called buba or yaws), and T. pallidum endemicum, which causes bejel (endemic syphilis or dichuchwa). Sometimes the Treponema carateum (or Treponema pallidum carateum) is also included as a subspecies, causing the pinta (mal de pinto or mal del pinto.). The classification of these subspecies is based both on the different symptoms caused by their infection and on genetic changes. In the case of genetic changes, these are minimal, for example the degree of similarity between T. pallidum pallidum and T. pallidum pertenue is somewhat higher than 99.6%.

It's a pretty fragile bacterium. Outside the body, it does not support dry climates or temperatures above 42°C. It is not resistant to penicillin, one of the best antibiotics that can be used against this bacterium.

Cultivation

Some researchers have proposed the culture of T. pallidum in complex media (Smith-Noguchi medium) under anaerobic conditions, but this is certainly not a method of practical use. The organism can be transmitted by inoculation into the testes of rabbits and can be maintained by a series of steps (one similar organism, T. cuniculi, is a natural pathogen of rabbits). In practice, the microorganism does not survive for long outside the body. At 4 °C (blood bank temperature) it survives for four days; at room temperature, for a few hours, and only one hour, at 41.5 °C. Being a virtually uncultivable bacterium, its study is complicated, and there are many things that are still unknown regarding its mechanisms of action, pathogenesis, and evolution.

Pathogenesis

As a virulence factor, it has the ability to attach itself to the host cells of the skin and/or mucous membranes, and reach subepithelial tissues through inapparent lesions or perhaps through cells, giving rise to to a primary lesion. It spreads through the blood, and binds to the vascular epithelium, secreting a substance similar to the mucopolysaccharide of the host tissues, thus camouflaging the antigen and thus passing into the perivascular space, where it causes destruction of the vessels, endarteritis obliterans, and inhibition of blood supply. blood, necrosis and ulceration, and gives rise to chancre and spread, through blood vessels, throughout the body.

The Treponema pallidum takes advantage of ulcerations on the skin or mucous membranes and is its main route of entry. When it enters, it binds through Tp155 and Tp483 to fibronectin, present in the epithelial membrane, and through Tp751 to laminin, also present in the epithelial outer membrane. Once attached, it begins to colonize and begins to penetrate tissues via a metalloproteinase MMP-1, which degrades collagen and endothelial junctions. It should be noted that T. pallidum does not have LPS, despite being Gram -, and syphilitic sores are caused by the same host, in response to Tpn47, the main protein of this spirochete, since it triggers a generalized immune response that is very little effective in carrying out the elimination of treponema because it is very low antigenic; has a protein, called Neelaredoxin, which converts O₂- released by macrophages into H₂O₂, and membrane hydroxyperoxidase converts to H₂O, evading the reactive O₂ species of the immune system. It is highly invasive, thanks to its endoflagella (3-6) and an MCP protein, which detects histidine and glucose in tissues and serves as a chemotactic factor for treponema. In addition, it causes antigenic variation of the TprK membrane proteins, making their elimination difficult. And B-lactamase activity has been found in Tpn47.

Stages of the disease

Primary stage of syphilis

After an incubation period of 10 days to 6 weeks (average 3 weeks), a painless papule develops at the site of inoculation—the mouth, penis, vagina, or anus—that quickly ulcerates, turning into a circular or oval sore with a reddish edge, similar to an open wound, this is called a chancre.

Its cartilaginous consistency is characteristic, with a hard base and edges.

In men, chancres are usually located on the penis or inside the testicles, but also in the rectum, inside the mouth or on the external genitalia, while in women, the most frequent areas are: cervix and the greater or lesser genital lips.

During this stage it is easy to become infected with the secretion generated by the sores. A person infected during this stage can infect their partner by having unprotected sex.

The chancre disappears after a month or a month and a half, but not because the patient is healing, but because the second stage is about to begin.

Secondary stage of syphilis

It can present half a year after the chancre disappears and lasts three to six months, causing painless pinkish bumps called "pox nails" on the palms of the hands and soles of the feet (which can sometimes appear in other places as well). such as chest, face or back), fever, sore throat and joints, weight loss, hair loss, thinning eyebrows, headaches and lack of appetite.

Sometimes, flat rashes called condyloma latum break out around the genitals and anus. Syphilitic nails can be very contagious if there are wounds, and can even infect someone by shaking hands. When the second phase ends, syphilis remains in the body for a long time, until it reawakens in the third phase.

Tertiary stage of syphilis

In the third phase (also called the final phase), between one and twenty years after the onset of infection, syphilis reawakens to directly attack the nervous system or an organ.

In this phase the most serious problems occur and can even cause death. Some of the problems are:

• eye disorders,
• heart disease,
• brain injuries,
• spinal cord injuries,
• loss of coordination of limbs
• syphilitic or luetic aneurysm
• syphilitic rubber or syphilim, etc.Lession (in the nose) in the third stage of syphilis.

Although treatment with penicillin can kill the bacteria, the damage it has done to the body may be irreversible.

Laboratory identification

Micrograph showing T. pallidum (black and thin) – Dieterle stain

T. pallidum was first identified microscopically in syphilitic shins by Fritz Schaudinn and Erich Hoffmann at the Charité in Berlin in 1905. This bacterium can be detected with special stains, such as Dieterle's stain. T. pallidum by serology, including nontreponemal VDRL, rapid plasma reagination, treponemal antibody tests (FTA-ABS), T. pallidum and TPHA test for syphilis.

Treatment

Treatment with penicillin can kill the bacteria, but it does not reverse the damage done. During the primary and secondary phase, treatment with penicillin is easy, however.

In the tertiary stage, penicillin is effective, but in g-sodium forms, which allow it to diffuse through the cerebrospinal fluid, since the bacteria are located in this area in the final stage.

Treating syphilis on time leaves no sequelae. But this disease increases the chances of contracting other sexually transmitted infections.

Evasion of the immune system

Even though it can be easily treated, having syphilis doesn't mean you can't get it again. The human body is not capable of developing effective immunity against T. pallidum. This is due to several factors:

• Shortness of external membrane proteins. The immune system recognizes the proteins present in the outermost layer of the bacteria and develops antibodies against them. Treponema pallidum has very few proteins in your outer membrane (100 times less than other bacteria such as E. coli), which makes it difficult to recognize them.
• Tpr proteins (T. pallidum repeat proteins). Family of 12 paralogue proteins. Its predicted function is to join and train pores. They play an important role in the evasion of the immune system because they have hypervariable regions. The TprK protein is believed to play the most important role in evasion.
• Subpopulations. The high variability of proteins such as TprK causes two distinct populations to be generated within the same patient, one that antibodies are able to recognize and another that they are not. While the subpopulation able to unite antibodies causes an inflammatory response to occur, the other subpopulation continues to repel and spread through the organism.

Prevention

Prevention is based on: - Use of prophylactics. - Use of condom during sexual intercourse. - Avoid polygamous couples.

Gallery

Treponema pallidum