How Oral Secondary Syphilis is Contracted
Oral secondary syphilis is contracted through direct contact with infectious mucocutaneous lesions during oral sex with an infected partner who has primary or secondary syphilis, or less commonly, through kissing when oral lesions are present. 1
Transmission Mechanism
Treponema pallidum is transmitted only when syphilitic mucocutaneous lesions are present, meaning the organism enters through mucous membranes or abraded skin during direct contact with infectious lesions. 1
The primary route to oral involvement is oral-genital contact with a partner who has a primary chancre (genital ulcer) or secondary syphilis lesions on the genitals. 2, 3
Transmission can also occur through oral-oral contact (kissing) when one partner has infectious oral lesions of primary or secondary syphilis, though this is less common. 1
The organism does not transmit through casual contact such as handshakes, sharing utensils, or ordinary social interactions—only direct contact with mucocutaneous lesions is infectious. 1
Timeline and Infectiousness
After initial infection (typically through sexual contact), secondary syphilis develops 2-8 weeks after primary inoculation and represents the disseminated stage of disease. 4
During secondary syphilis, patients develop highly contagious mucocutaneous lesions including oral manifestations such as mucous patches, "snail-track" ulcers, and erosive lesions. 4, 5, 6
These contagious manifestations are rare after the first year of infection, making early syphilis (primary and secondary stages) the most infectious period. 1
Clinical Context
Oral lesions in secondary syphilis include mucous patches on the tongue (53% of cases), subacute erosive or ulcerative lesions (55%), and less commonly nodular or leukokeratotic lesions. 6
The rash and mucocutaneous lesions of secondary syphilis are contagious through direct contact, but not through casual ordinary contact. 1
Individuals at highest risk include men who have sex with men (who comprised 32.7% of primary and secondary syphilis cases in 2023), people with HIV, and those engaging in condomless sex with multiple partners. 2
Important Clinical Pitfall
Oral manifestations can occur in isolation (37% of patients with oral secondary syphilis have only oral symptoms), making diagnosis challenging and often delayed—mean time to diagnosis is 8.8 months for isolated oral symptoms versus 1.8 months when other manifestations are present. 6
Clinicians should maintain high suspicion for syphilis in patients with subacute oral lesions who have epidemiologic risk factors, as this is a contagious and curable disease. 6