Syphilis has become less common in Europe in the last decade, but has once again become a major problem in the USA, and remains so in many developing countries. Several treponemal genes have now been cloned and expressed in Escherichia coli, allowing study of treponemal
proteins. The importance of cell mediated immunity in
syphilis has been demonstrated in animal models. A diagnosis of
syphilis is usually confirmed by dark-field microscopy or serological tests. Seroconversion may be delayed in HIV infected individuals. A positive reaginic test in cerebrospinal fluid (CSF) has a high specificity but low sensitivity in the diagnosis of
neurosyphilis. Indeed, virulent treponemes can be identified in CSF samples which have negative reaginic tests, normal cell counts and
protein levels. In the CSF, the FTA-Abs test has a high sensitivity but low specificity for
neurosyphilis.
Penicillin remains the treatment of choice for all stages of
syphilis, although it penetrates the blood brain barrier poorly. Treatment with intramuscular
benzathine penicillin 2.4 million units stat, or 600,000 units
procaine penicillin daily does not produce treponemicidal levels within the CSF. However, the incidence of
neurosyphilis is low in immunocompetent patients treated with such regimens during early
syphilis. Acceptable alternatives in
penicillin-allergic patients include
ceftriaxone and
doxycycline.
Erythromycin is not recommended as it has produced unacceptably high rates of treatment failure. Recently, a strain of
macrolide-resistant Treponema pallidum was isolated from a patient with
secondary syphilis. For the treatment of
neurosyphilis, treponemicidal levels of
penicillin can be achieved in the CSF using 2.4 million units
procaine penicillin daily with concurrent
probenecid 500 mg 4 times a day, or an
intravenous infusion of benzyl
penicillin 12-24 million units daily. Early
syphilis can be treated adequately over 10 days, but 21 to 28 days is appropriate for
late syphilis. In HIV-infected patients
syphilis may present atypically with initially negative serological tests. Treatment of early
syphilis in HIV-positive patients has been associated with the early development of
neurosyphilis. It is advisable to treat all patients co-infected with HIV with an
antibiotic regimen that achieves adequate levels within the CSF.