Regulation of parasite populations

Abstract

The mechanisms by which parasite populations are regulated may be grouped into three types: regulation by the transmission process (type I), by the host population by such means as host mortality or sterile immunity (type II), and by the host individuals (type III), often by premunition and similar forms of incomplete acquired resistance. The last two types are density-dependent feedback processes. The concept of endemicity implies that these two types are operating. The spatial arrangement of hosts and transmission patterns particularly affects type II regulation as does the distribution of parasites among hosts. Highly endemic infections may sometimes have their focal variation in intensity of transmission obscured, and may show relatively separate yet contiguous transmission foci. The most suitable control measures will depend on the type of parasite population regulation, and epidemiological study should include an experimental measure of the stability of the infection. Types II and III of regulation here roughly correspond to the density-dependent regulation of animal ecologists, though type I may fall sometimes into this category.