Studies on the dynamics of transmission of onchocerciasis in a Sudan-savanna area of North Cameroon I

Modelling exposure heterogeneity and density dependence in onchocerciasis using a novel individual-based transmission model, EPIONCHO-IBM: Implications for elimination and data needs

“…The degree of exposure heterogeneity and density dependence in parasite establishment in humans were estimated by fitting the model simultaneously to pre-intervention microfilarial prevalence and intensity (mean number of microfilariae per mg of skin) data and their corresponding annual biting rate (ABR, the number of bites per person per year) from savannah settings in [44,45] (Northern Cameroon) and [46] (Burkina Faso and Côte d'Ivoire). Although the model explicitly considers hypothetical individuals (which then allow the calculation of microfilarial prevalence and mean microfilarial infection intensity in the population), no individual-based data on exposure were used for its parameterisation as these data are not yet available at suitable scales.…”

“…The microfilarial prevalence and intensity data used to fit the model [44,45,46] were complemented with additional data from [9] (OCP, microfilarial prevalence only) and other epidemiological settings with simuliid species without cibarial armatures and vector competence characteristics similar to those of Siumulium damnosum sensu stricto (s.s.)/S. sirbanum [7], namely Amazonian focus communities with transmission by S. guianense sensu lato (s.l.)…”

“…For microfilarial prevalence data, binomial 95% confidence intervals (95% CIs) were calculated using the Clopper-Pearson method [51]. Individual host microfilarial intensity data were only available for [44] and these were used for calculating 95% CIs around the arithmetic means using bootstrapping [52].…”

“…Fig 2 shows the relationship between pre-control microfilarial prevalence, arithmetic mean microfilarial intensity and ABR, using the parameters obtained by LHS that achieved the minimum squared residuals compared with the observed data from [44,45,46] for each value of k E . A value of k E = 0.3 and the associated density dependence parameters (δ H0 = 0.186, δ H1 = 0.003, c H = 0.005) gave the lowest squared residuals.…”

“…The EPIONCHO-IBM predictions are based on a host population size of 500 and 100 runs for 80 years to reach endemic equilibrium (human demography was simulated to equilibrium before simulating the epidemiology to equilibrium). The error bars are binomial (Clopper-Pearson) 95% confidence intervals for prevalence and bootstrapped 95% CIs for intensity (for which the raw individual microfilarial intensity data were available [44]). The main vectors in each setting are Simulium damnosum s.s./S.…”