The definitive method for diagnosing both primary and congenital syphilis is the identification of Treponema pallidum via dark field microscopy or through the application of molecular tests (PCR) on an exudative lesion or tissue. However, these techniques are not universally distributed and are only available in specific centers, so the diagnosis of syphilis at any stage continues to be based on treponemal and non-treponemal serological tests.2

Treponemal tests (T. pallidum passive particle agglutination [TP-PA] assay or FTA-ABS, etc.) are the most specific and the first to test positive; however, once they have tested positive, they do not go back to negative (in most cases), so their fluctuations are not useful for follow-up or new diagnoses.3 Since they are more sensitive to non-treponemal tests (Venereal Disease Research Laboratory [VDRL] or Rapid Plasma Reagin [RPR] test) false positives may occur more frequently, and they may take a few more days to test positive than treponemal tests. However, with appropriate treatment, they can go back to negative, so their fluctuations and new positivities are useful for the follow-up and diagnosis of new infections.4

To achieve a correct diagnosis, it is necessary to perform both tests.

To say that an infection is properly treated, a decrease of at least 2 dilutions (e.g., 1:16 down to 1:4, 1:32 down to 1:8) is required 6 months into therapy. The same test should be used for both diagnosis and follow-up, and if possible, in the same laboratory3 (2, C).

If both tests are positive, treatment is prescribed based on the patient's clinical stage. If the treponemal test is positive and the non-treponemal one is negative, it is advisable to perform another treponemal test using a different method; if it remains positive and there is a previous history of syphilis, no further study is recommended. If there is no prior history and/or the clinical or epidemiological suspicion is high, it is recommended to retest in 2–4 weeks, emphasizing the importance of sexual abstinence until the case is resolved.2

The treatment of syphilis is based on staging (Table 1). In all cases, the antibiotic of choice is parenteral penicillin, whose efficacy is supported by extensive clinical experience and clinical trials. There are some situations in which the administration of another antibiotic is permitted, with stricter follow-up requirements.

Clinically, it is characterized by painful, recurrent, and self-resolving vesicles and ulcers. Confirmatory diagnosis with PCR is advised whenever possible, bearing in mind that most patients seek consultation when the outbreak has already resolved6 (IIIb). Recurrences and subclinical forms in the genital area are more frequently described with HSV2 vs HSV1.7

The recommended diagnostic test is PCR due to its high sensitivity5 (Ib, A); given the low sensitivity of culture, it is only advised as a diagnostic technique when PCR is not available or for studying antiviral resistance in refractory cases. Samples should be drawn from the active lesion8 (Ib, A); sampling from random areas is ill-advised due to its low sensitivity, and because a negative result does not rule out the possibility of latent infection (Ib, A).

Regarding HSV serologies, their use is recommended only in the following scenarios5:

• 1.

  Patients with recurrent lesions or atypical presentation and where PCR or culture tests repeatedly negative or could not be performed (III, B).

• 2.

  To differentiate between a first episode or a recurrence for the purpose of counseling and management (III, B).

• 3.

  Partners of patients diagnosed with HSV who do not know if they have previously had lesions, for counseling purposes (Ib, A).

• 4.

  Asymptomatic pregnant individuals with a partner with a past medical history of herpes (IIb, B).

The goal of treatment in primary infection is to alleviate symptoms and prevent or reduce the frequency of outbreaks; and in recurrences, to reduce the likelihood of transmission. Treatment cannot eradicate the virus, and it has not been shown to affect the frequency or severity of subsequent outbreaks.2

HSV management in immunosuppressed patients and people living with HIV (PWH) (Table 6). Other special situations are considered in Table 7.

The most important risk factor for HSV reactivation is the degree of immunosuppression. Systemic antiviral treatment regimens have been shown to be just as effective in immunosuppressed patients; however, antiviral resistance is much more common in PWH, which can lead to more frequent therapeutic failures.5

Approximately 25% of LGV infections in MSM are asymptomatic.15 In symptomatic individuals, the incubation period may vary between 1 and 4 weeks, with 3 classic stages described:

• •

  First stage: A small, painless papule or pustule that may ulcerate and resolves on its own within a week. Mucopurulent discharge may occur, especially with rectal involvement.

• •

  Second stage (“inguinal stage”): Painful inguinofemoral lymphadenopathy appears 2–6 weeks after the primary lesion, typically unilateral (2 out of 3 cases). Complications may include inflammation, suppuration, and abscesses; some of these may drain spontaneously. The “groove sign” (pathognomonic) occurs due to the inflammation of inguinal and femoral lymph nodes separated by the inguinal ligament.

• •

  Third stage (“ano-genito-rectal stage”): Initially presents as proctocolitis, characterized by severe symptoms of anorectal pain, hemopurulent discharge, and rectal bleeding, along with tenesmus and constipation. This is followed by perirectal abscesses, fistulas, or rectal stenosis. It can mimic chronic inflammatory bowel diseases, such as Crohn's disease, both clinically and histopathologically, which should be considered in differential diagnosis. Without treatment, it can lead to complications such as megacolon, chronic progressive lymphangitis with elephantiasis, esthiomene (chronic ulcerative vulvar disease), or frozen pelvis syndrome. Currently, the most common presentation of LGV is symptomatic proctitis in MSM, with genital ulcers or inflammatory inguinal adenopathies being less common.

Less frequently, it may be accompanied by systemic symptoms, such as mild fever, chills, malaise, arthralgia–myalgia, reactive arthritis, pneumonitis, and perihepatitis.

The initial diagnosis is based on clinical suspicion but should be confirmed by the detection of specific DNA of the LGV variant (L1, L2, and L3), through a 2-step procedure (1, B).16–18

• •

  Nucleic acid amplification tests (NAAT) are used on suspected clinical samples.

• •

  If C. trachomatis DNA/RNA is detected, LGV-specific genotype DNA should be identified.

Early treatment initiation is recommended to reduce potential complications, such as megacolon and chronic progressive lymphangitis (2,C) (Table 8).

After an incubation period of 3–7 days, small, painful erythematous papules appear, which quickly progress to pustules and ulcers. These are characterized by being superficial with irregular, undermined edges, a granulomatous base, and purulent exudate, which can persist for months if untreated. Up to 50% of cases are accompanied by painful unilateral inguinal lymphadenopathy that can coalesce into buboes.

Diagnosis is usually clinical (Table 9), as bacterial culture isolation is difficult (sensitivity<80%) (III,B).26 Nucleic acid amplification techniques, such as PCR, are the most commonly used and can differentiate between different microbiological agents, such as T. pallidum and HSV27,28 (III,B). Treatment details are provided in Table 10.

Patients should be reevaluated 3–7 days after treatment. The healing time depends on the size of the ulcer and lymphadenopathy, and progression is slower in PWH and uncircumcised individuals.29

Contact tracing, including sexual partners from the 10 days preceding symptom onset is advised.

The incubation period goes from 5 up to 21 days.43 The most common symptom is fever.35,36,38–42 Clinical signs are related to the transmission route44:

• -

  Respiratory/Classical (mainly endemic form): initially fever, headache, lymphadenopathy, myalgia; later, multiple papules and pseudopustules.

• -

  Subcutaneous inoculation: well-circumscribed, deep pseudopustules, often umbilicated, painful, taking weeks to resolve, which may be accompanied by local edema and regional lymphadenopathy. Lesions may also exhibit perioral/lingual involvement or present as paronychia.

Complications have been reported in up to 8.3% of cases,38–42 with the most common being bacterial superinfection, oral ulcers, and proctitis/proctocolitis/proctalgia.45–51

Diagnosis is clinical–epidemiological and confirmed by PCR and/or sequencing.52

Histopathological analysis may reveal acidophilic cytoplasmic inclusion bodies (“Guarnieri bodies”), which correspond to aggregates of viral particles.

Differential diagnosis should include varicella, herpes zoster, measles, Zika, dengue, chikungunya, herpes simplex, impetigo, MRSA, disseminated or localized gonorrhea, primary or secondary syphilis, chancroid, LGV, and molluscum contagiosum.

As of today, no specific FDA/EMA-approved treatments exist for patients with MPOX, so symptomatic management remains the cornerstone of therapy (Table 11).

The most common clinical forms are ulcerative-granulomatous, followed by hypertrophic/verrucous, necrotic, and sclerotic. Extragenital infection (6%) can occur in the pelvic area, intra-abdominal organs, bones, or the oral cavity.61

Diagnosis can be established by visualizing the bacterium using dark-field microscopy or direct microscopy with Giemsa/Leishman/Wright staining (large mononuclear cells with intracellular cysts filled with Donovan bodies), by biopsizing lesion samples, or detecting the DNA through PCR. It is a bacterium that is difficult to culture.61

Contact tracing should cover from 60 days60 to 6 months18,61 prior to symptom onset.

The main differential diagnosis is penile squamous cell carcinoma, which can mimic or complicate the infection. Therefore, biopsy of persistent lesions is recommended.64

The goal is to halt the progression of lesions; healing typically begins at the ulcer margins, requiring prolonged therapy to allow granulation and re-epithelialization. The minimum treatment duration is 3 weeks, and it should continue until lesions resolve61 (Table 12).