Prepatency

Prepatency, in parasitology and infectious disease, is the interval between the initial infection by a parasite and the first time that parasite or its products become detectable by diagnostic methods. During this period the parasite is developing inside the host (or, in some contexts, inside a vector) and has not yet reached a stage that yields a positive test result, such as eggs, larvae, cysts, antigens, or nucleic acids detectable by microscopy, serology, culture, or molecular assays.

The term is used to describe the non-symptomatic development phase before a detectable infection is established. It is distinct from the incubation period, which refers to the onset of clinical symptoms, and from the patent period, when the parasite is detectable and often transmissible. In some diseases, the prepatent period is followed by a patent period during which diagnostic tests reliably identify the parasite.

Duration of prepatency varies widely among parasites and depends on factors such as species, life cycle, inoculum size, route of infection, host immunity, and the sensitivity of the diagnostic method employed. It can range from days to weeks or months and may differ between experimental settings and natural exposures. Understanding prepatency is important for timing diagnostic testing, assessing transmission risk, and designing surveillance and control strategies.