In this paper we develop a model for describing the spread of the parasitic disease bilharziasis. The detailed model first developed (Model A) is made more tractable by replacing infecting population sizes by their expected values in the transition probabilities, giving Model B. Using this approximating model it is possible to examine the nature of the spread of the disease and the effects of control measures. The effects of a particular control measure are examined in order to compare Models A and B.
