THE NATURAL-HISTORY OF SYPHILIS - IMPLICATIONS FOR THE TRANSMISSION DYNAMICS AND CONTROL OF INFECTION

Background: Syphilis remains a significant cause of morbidity in many developing countries and in some areas within North America and Europe . Mathematical models of the transmission dynamics of sexually transmi tted infections have provided insights of relevance both to the interp retation of observed epidemiological patterns and to the design of con trol programs. Their use for the study of syphilis has been limited to date. Goals and Study Design: The authors investigated the transmissi on dynamics of syphilis against a template based on the natural histor y of infection in individual patients with the aim of (1) identifying gaps in our understanding of the biology of infection, and (2) providi ng insights of relevance to the design of control policies. Results: A nalyses reveal that Treponema pallidum has a moderate to high probabil ity of transmission during contact between susceptible and infectious sexual partners. This, combined with questions over the existence of a ny immunity to reinfection, helps to ensure the long-term persistence of syphilis within ''core'' activity groups, Patterns of treatment in North America are shown to have significantly altered the relative fre quency of individuals in the different stages of disease. Conclusions: The analyses emphasize the benefits to be gained from treating infect ed people early in the primary stage of infection to reduce the effect ive period during which infected people can transmit to others, This f orm of treatment is beneficial for both the individual and the communi ty, Treatment has greatly altered the incidence of different disease s tages, but the full implications of treatment depend on whether immuni ty is present.