Table 2.

Model of force of infection with a and b as composite parameters

Code	Model
(From 1.1)	a = {rate of a host contacting contaminated water per unit time} × { density of cercariae} × {probability that a cercarial encounter leads to the establishment of an adult parasite}
(From 1.1)	b = {rate of egg–laying} × {probability of an egg developing into a miracidium} × {probability that a miracidium penetrates a snail} × {probability that a miracidial penetration into an uninfected snail develops into patent infection}