Fig. 1

Sensitivity of the endemic microfilarial (Mf) infection prevalence breakpoint values and threshold vector biting rates to changes in the shape parameter of the negative binomial distribution, (k) describing the distribution of mf among human hosts (a and b), the strength of the immune response to infection, β (c and d), and per capita worm fecundity, α (e and f). The upper panel of graphs are for culicine-mediated filariasis, whereas the graphs belonging to the lower panel represent simulation results for anopheline filariasis. When the intermediate host is culicine, the results indicate that the maximum value of the mf breakpoint (values on Y-axes for all graphs) can change with k, but the vector biting thresholds (units are bites per month on X-axes for all graphs) will not change (TBR = 9) (a). For anopheline intermediate hosts (b), both the maximum mf breakpoint and the TBR increased with increasing k (curves iii to i). The parameter β can be thought of as an index governing the strength of host immunity in reducing establishment of parasites in the human hosts. The β values were varied by 10% so that the values used here were: i) 0.1, ii) 0.112, and iii) 0.123. When the intermediate host is culicine (c), the maximum value of the mf breakpoint changed with β; but the TBR does not change from its value of 9. For anopheline intermediate hosts (d), the maximum mf breakpoint increased and the TBR decreased with decreasing β. Graphs e and f depict the mf prevalence values found for values of per capita worm fecundity, α, of either i) 0.4 or ii) 0.2. Whether the intermediate host is e culicine or f anopheline, the maximum value of the mf breakpoint rises and the TBR lowered with increasing α. Results as per Gambhir & Michael [34]