Syphilis pathophysiology

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief:  Aysha Anwar, M.B.B.S[2]; Nate Michalak, B.A.Muhammad Saad, M.B.B.S.[3]

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## Overview

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Syphilis is caused by a spirochete, Treponema pallidum. It has an average incubation period of 3 - 12 weeks. However, it may vary according to the size of innoculum. Spirochete penetrates intact mucous membrane or microscopic dermal abrasions and rapidly enters systemic circulation with the central nervous system being invaded during the early phase of infection. The histopathological hallmark findings are endarteritis and plasma cell-rich infiltrates reflecting a delayed-type of hypersensitivity reaction to the spirochete.[1][2][3][4][5][6][7]

## Pathogenesis

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The pathogenesis of syphilis may be described in the following steps:[1][2][3][4][5][6][7][8][9][10][11]

### Transmission

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Treponema pallidum is usually transmitted via direct contact with the infected lesion (sexual contact) or blood transfusion (rare).Following table summarizes the transmission of syphilis form sexual contact.[12][13]

Sexual Exposure to Syphilis:

* * *

Direct contact with infectious lesion during
❑ vaginal
❑ anal
❑ oral sex

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Primary Syphilis:

* * *

❑Painless ulcer(chancre)
❑ Non-tender lymphadenopathy

Secondary Syphilis:

* * *

❑Systemic signs
❑ maculopapular rash
❑ Mucocutaneous lesion
❑ Generalized lymphadenopathy

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Tertiary Syphilis:

* * *

❑Gumma
❑ Aortitis
❑ General paresis
❑ Tabes dorsalis

### Incubation

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The incubation period varies with the size of innoculum (9-90 days).

### Dissemination

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* Following transmission, Treponema pallidum uses the intact or abraded mucous membrane to enter the body.
* It then disseminates to the lymphatics and blood stream to gain access to any organ of the body.

### Seeding

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* Syphilis uses fibronectin molecules to attach to the endothelial surface of the vessels in organs resulting in inflammation and obliteration of the small blood vessels causing vasculitis (endarteritis obliterans).
* Organism has slow replication rate (30-33 hrs) and evades the initial host immune response.
* It may seed to different organs of the body especially the cardiovascular system and central nervous system resulting in tertiary syphilis.

### Immune response

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Different stages of syphilis results from the interaction between the antigen and the host immune response.[1][2]

Acute response

* The initial infection in primary syphilis is limited due to Th1 response and lack of the antibody response.
* It is speculated that there is a shift from Th1 to Th2 response during secondary syphilis.

Chronic

* Cytotoxic T cells and an incomplete humoral response is mainly responsible for persistence of infection and tissue damage in tertiary syphilis.
* Ineffective type 4 delayed hypersensitivity reaction containing macrophages and sensitized T cells is mainly responsible for the gumma formation in various organs.

### Genetics

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There is no known genetic association of syphilis. However, neurosyphilis may be associated with the gene polymorphism for IL-10 production with increased levels seen in the patients with neurosyphilis.[11]

### Associated conditions

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Syphilis is associated with increased transmission of HIV. The underlying mechanism may be related to the accumulation of dendritic cells containing CCR5 co-receptors at the site of infection, the same receptor entity binding the HIV.[9]

### Microscopic pathology

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On microscopic histopathological analysis, characteristic findings of syphilis depends on the stage of the disease:

Primary syphilis

* Mononuclear leukocytic infiltration, macrophages, and lymphocytes
* Swelling and proliferation of small blood vessels

Secondary syphilis

* Swelling and dilatation of blood vessels in the dermis
* Epidermal hyperplasia and neutrophilic infiltration
* Inflammatory cell infiltrate, predominantly plasma cell

Tertiary syphilis

* Small vessel inflammation (endarteritis obliterans)
* Granulomatous lesions (gumma) containing central necrosis, inflammatory cells, such as lymphocytes, macrophages, plasma cells and fibroblasts.

## References

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1. ↑ 1.0 1.1 1.2 Carlson JA, Dabiri G, Cribier B, Sell S (2011). "The immunopathobiology of syphilis: the manifestations and course of syphilis are determined by the level of delayed-type hypersensitivity". Am J Dermatopathol. 33 (5): 433–60. doi:10.1097/DAD.0b013e3181e8b587. PMC 3690623. PMID 21694502.CS1 maint: Multiple names: authors list (link)
2. ↑ 2.0 2.1 2.2 Fitzgerald TJ (1992). "The Th1/Th2-like switch in syphilitic infection: is it detrimental?". Infect Immun. 60 (9): 3475–9. PMC 257347. PMID 1386838.
3. ↑ 3.0 3.1 Singh AE, Romanowski B (1999). "Syphilis: review with emphasis on clinical, epidemiologic, and some biologic features". Clin Microbiol Rev. 12 (2): 187–209. PMC 88914. PMID 10194456.
4. ↑ 4.0 4.1 Engelkens HJ, ten Kate FJ, Vuzevski VD, van der Sluis JJ, Stolz E (1991). "Primary and secondary syphilis: a histopathological study". Int J STD AIDS. 2 (4): 280–4. PMID 1911961.CS1 maint: Multiple names: authors list (link)
5. ↑ 5.0 5.1 Thomas DD, Navab M, Haake DA, Fogelman AM, Miller JN, Lovett MA (1988). "Treponema pallidum invades intercellular junctions of endothelial cell monolayers". Proc Natl Acad Sci U S A. 85 (10): 3608–12. PMC 280263. PMID 3285346.CS1 maint: Multiple names: authors list (link)
6. ↑ 6.0 6.1 Quatresooz P, Piérard GE (2009). "Skin homing of Treponema pallidum in early syphilis: an immunohistochemical study". Appl Immunohistochem Mol Morphol. 17 (1): 47–50. doi:10.1097/PAI.0b013e3181788186. PMID 18800002.
7. ↑ 7.0 7.1 Tanabe JL, Huntley AC (1986). "Granulomatous tertiary syphilis". J Am Acad Dermatol. 15 (2 Pt 2): 341–4. PMID 3734178.
8. ↑ Baker-Zander S, Sell S (1980). "A histopathologic and immunologic study of the course of syphilis in the experimentally infected rabbit. Demonstration of long-lasting cellular immunity". Am J Pathol. 101 (2): 387–414. PMC 1903600. PMID 7001910.
9. ↑ 9.0 9.1 Sheffield JS, Wendel GD, McIntire DD, Norgard MV (2007). "Effect of genital ulcer disease on HIV-1 coreceptor expression in the female genital tract". J Infect Dis. 196 (10): 1509–16. doi:10.1086/522518. PMID 18008231.CS1 maint: Multiple names: authors list (link)
10. ↑ Abell E, Marks R, Jones EW (1975). "Secondary syphilis: a clinico-pathological review". Br J Dermatol. 93 (1): 53–61. PMID 1191529.CS1 maint: Multiple names: authors list (link)
11. ↑ 11.0 11.1 Pastuszczak M, Jakiela B, Jaworek AK, Wypasek E, Zeman J, Wojas-Pelc A (2015). "Association of Interleukin-10 promoter polymorphisms with neurosyphilis". Hum Immunol. 76 (7): 469–72. doi:10.1016/j.humimm.2015.06.010. PMID 26100683.CS1 maint: Multiple names: authors list (link)
12. ↑ "Syphilis - StatPearls - NCBI Bookshelf".
13. ↑ Denman J, Hodson J, Manavi K (June 2022). "Infection risk in sexual contacts of syphilis: A systematic review and meta-analysis". J Infect. 84 (6): 760–769. doi:10.1016/j.jinf.2022.04.024. PMID 35447230 Check `|pmid=` value (help).

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