Treponema pallidum is a pathogenic spiral-shaped, delicate, and motile bacteria made of distinct subspecies responsible for causing syphilis; thus, it is sometimes referred to as the syphilis spirochete. When coiled, Treponema pallidum is usual between 6 to 15 micro millimeters in length and roughly 0.15 micro millimeters in width with a turbinate structure of the letter T or corkscrew shape in other cases (Haynes et al., 2021). This microorganism comprises an outer membrane made of lipoproteins encircles the periplasmic flagella that intertwine to form the cell envelop, protoplasmic cylinder, and peptidoglycan cytoplasm. It also has a cone-like structure that is found in the periplasm. This delicate outer membrane can be removed tenderly, with the cytoplasm intact (Lu et al., 2021). Through isolation, amplification, and reverse engineering, scientists have been to identify the DNA and RNA of T. pallidum, which have distinct percentages during different stages of syphilis (Lian et al., 2022). Being gram-negative and minute in nature, researchers have recommended using Ryu’s stain and silver impregnation stain to view Treponema pallidum cells under a compound microscope. T. pallidum has limited metabolic activities due to its small structure. It is important to note that this bacterium can only be transmitted to human beings.
Virulence Factors
T. pallidum being a bacterium, brings about different diseases such as syphilis and chronic illnesses like fever once it invades the human body. Following the genome sequence of Treponema pallidum, it is difficult to pinpoint which one of its virulence factors causes syphilis in human beings (Lu et al., 2021). The absence of lipopolysaccharides on the outer membrane of this bacterium causes inflammation and fever upon invasion of the host’s body. Additionally, the gram-negative feature of Treponema pallidum uses the type three secretion system to produce proteins that are virulence-related into the human body’s cytoplasm, thus causing infections; however, these bacteria lack the necessary homologs which are essential in recognition of the type three secretion system components (Lu et al., 2021). Scientists have illustrated that cytotoxins and other cytolytic enzymes produced by T. pallidum do not play an active role in the pathogenesis of syphilis in the human body. However, many of these bacteria can result in cytophasis on cell membranes (Haynes et al., 2021). Protein components in T. pallidum play different roles in the pathogenesis of syphilis.
Immunity
Invasion of the human body by Treponema pallidum causes syphilis; however, the continuous attack causes the human body to develop an immunity against this disease. Despite hypersensitivity to oxygen, decreased viability to high temperatures, and low metabolism, T. pallidum finds a way of surviving in the host’s body dependent on an individual’s immunity, time, and site of invasion (Lian et al., 2022). Time translates to the stages of infection in this scenario, i.e., primary, secondary, and tertiary stages, which are clinically represented by different symptoms. One’s ability to defend themselves against the disease is dependent on the stages of infection, with the first stage being the easiest and the final stage being the hardest (Lian et al., 2022). It is easier to develop an immunity against syphilis in the first stage as the bacteria have not multiplied significantly. At the same time, it’s hard in the last stage as one’s nerves have been damaged, making it hard to respond to stimuli.
Essentially, the survival of T. pallidum in the human body is dependent on one’s body temperature. The temperatures have to be optimal for the bacteria to thrive and multiply to different places, which will be sites of infection (Lu et al., 2021). The average body temperatures of a human body are too high for the survival of T. pallidum; thus, during an invasion, the body temperatures may rise beyond normal to prevent the bacteria from thriving hence immunity against the disease. During secondary and tertiary stages, CD8+ cytotoxic T-cells in the host’s body cannot defend one against the disease or prevent spreading as delayed hypersensitivity (DTH) is ineffective (Haynes et al., 2021). The host’s body can develop immunity against these pathogens by making its conditions inadequate for survival; however, it is essential to note that in extreme cases, the human body cannot defend itself, thus using prescribed drugs to boost one’s immunity.
Pathology
Treponema pallidum is a highly pathogenic bacteria that cause infectious diseases such as syphilis and other conditions like inflammation and fever. Each subspecies of Treponema causes a different kind of syphilis, i.e., subspecies endimicum causes endemic syphilis, Treponema carateum causes pinta syphilis, while Treponema pertenue leads yaws (De Lay et al., 2021). Syphilis, an infectious disease caused by different subspecies of Treponema, tends to affect various body organs, especially the internal ones, which include but are not limited to blood vessels, heart, liver, bones, the brain, and joints. In most cases, an ulcer or chancre develops at the point of invasion in the host’s body. These ulcers that may form on genitals or mouth tend to be painless and firm (Lian et al., 2022). Treponema pallidum is a stealth pathogen since it only manifests once it has invaded the human body and is inactive outside the human body. Infections like syphilis, fever, and inflammation caused by T. pallidum are chronic and may affect the nervous system. If not treated for long, syphilis may lead to brain damage, dementia, and blindness.
Epidemiology
Syphilis, a chronic infection caused by T. pallidum, is sexually transmitted from mother to child. It has infected over twelve million people since 1999. A significant percentage of this population is found in developing countries, i.e., sub-Saharan Africa.
Prevention
Syphilis can be transmitted from mother to child and through sexual contact. Treating an expectant mother with syphilis can prevent it from spreading to the child. Syphilis in expectant mothers tends to lead to stillbirth, miscarriages, and abortions in extreme cases (De Lay et al., 2021). Attempts to develop a vaccine for prevention have been futile; however, strategies are still underway. The only effective way of preventing the spread of syphilis from mother to child during pregnancy is by treating these women and their partners.
Treatment
Once diagnosed, it is essential to treat syphilis infections to prevent their spread. Antibodies like penicillin can be used to treat by killing T. pallidum, bacteria that causes syphilis. The most common drug used is Benzathine penicillin G, which injections administer (Haynes et al., 2021). If one is allergic to penicillin, their doctor may recommend other antibodies which kill T. pallidum. It is crucial to treat syphilis in its early stages to prevent progression, which may cause blindness and dementia in extreme cases.
Clinical Relevance
Continuous exposure to antibiotics has made some strains of Treponema pallidum resistant drugs (De Lay et al., 2021). This is especially common in developing countries. An example of these MDR strains is methicillin-resistant Staphylococcus aureus which is resistant to penicillin. Scientists have developed a second-line penicillin alternative for treating these MDRs. A combination of ceftriaxone and azithromycin can be used to treat MDRs.
References
De Lay, B. D., Cameron, T. A., De Lay, N. R., Norris, S. J., & Edmondson, D. G. (2021). Comparison of transcriptional profiles of Treponema pallidum during experimental infection of rabbits and in vitro culture: Highly similar, yet different. PLoS pathogens, 17(9).
Haynes, A. M., Giacani, L., Mayans, M. V., Ubals, M., Nieto, C., Pérez-Mañá, C., … & Mitjà, O. (2021). Efficacy of linezolid on Treponema pallidum, the syphilis agent: A preclinical study. Biomedicine, 65.
Lian, T., Zhang, B., Giacani, L., Kou, C., Yang, X., Zhang, R., & Wang, Q. (2022). Full-length Turk of Treponema pallidum subsp. Pallidum in lipid nanodiscs is a monomeric prion: enzyme and Microbial Technology, 153.
Lu, S., Zheng, K., Wang, J., Xu, M., Xie, Y., Yuan, S., … & Wu, Y. (2021). Characterization of Treponema pallidum Dissemination in C57BL/6 Mice. Frontiers in Immunology, 11.
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