Figure 1.
Diagram of the model structure.
Boxes show types of agents. Solid arrows show where agents can change from one type into another. Dashed lines show the production of one type of agent by another. Dotted lines indicate infection. Red outlines and arrows indicate the presence of schistosomes. Agents of all types can die and be removed from the model.
Figure 2.
Comparison of parameters used in models of B. pfeifferi, B. glabrata and B. alexandrina.
a) Juvenile development. Heat units gained per hour. Snails become adults and start producing eggs once they have gained 100 heat units. b) Egg production. Eggs per snail per hour. c) Egg development. Heat units gained per hour. Egg hatch once they have gained 100 heat units. d) Egg mortality rate per hour. e) Uninfected and prepatent snail mortality rate per hour. f) Parasite development within the snail. Heat units gained per hour. Snails become infectious once they have gained 100 heat units. Blue lines show parameters for B. pfeifferi, red for B. glabrata, green for B. alexandrina, and turquoise for both B. pfeifferi and B. alexandrina.
Figure 3.
Number of snails and relative infection risk, with high and low mortality rates.
a) Mean total number of snails in the model. b) Mean total number of adult snails in the model. c) Infection risk, relative to the maximum risk for the same snail species with the same mortality rates. d) Absolute infection risk (arbitrary units). Blue lines show B. pfeifferi, red lines show B. glabrata and green lines show B. alexandrina. Solid lines show results with a low mortality rate and dashed lines with a high mortality rate.
Figure 4.
Proportions of eggs and snail surviving each stage, and cercariae production by infected snails.
a) Proportion of eggs laid that hatch. b) Proportion of juvenile snails that survive to adulthood (assuming no additional density dependent mortality, and that no juvenile snails develop patent infections before they become adults). c) Proportion of infected snails that survive to patency (assuming no additional density dependent mortality). d) Median lifetime cercariae production by an infectious snail (assuming no additional density dependent mortality). Results are shown for the lower mortality scenarios. Blue lines show B. pfeifferi, red lines show B. glabrata and green lines show B. alexandrina.