Table 1 System variables for the SWB model

  k Δw ≤ w < (k + 1)Δw

{h _k (t) : k = 0, 1, …}

 with worm burden increment Δw

∑ _k h _k  = 1

Demographically structured SWB:

 Child

h ^C _k (t)

 SAC

h ^S _k (t)

 Adult

h ^A _k (t)

Population densities per unit habitat:

 human

H(t)

 SEI (susceptible, infected, patent) snail

N(t) = x(t) + y(t) + z(t)