Heterogeneity in transmission parameters of hookworm infection within the baseline data from the TUMIKIA study in Kenya

Abstract

Background As many countries with endemic soil-transmitted helminth (STH) burdens achieve high coverage levels of mass drug administration (MDA) to treat school-aged and pre-school-aged children, understanding the detailed effects of MDA on the epidemiology of STH infections is desirable in formulating future policies for morbidity and/or transmission control. Prevalence and mean intensity of infection are characterized by heterogeneity across a region, leading to uncertainty in the impact of MDA strategies. In this paper, we analyze this heterogeneity in terms of factors that govern the transmission dynamics of the parasite in the host population. Results Using data from the TUMIKIA study in Kenya (cluster STH prevalence range at baseline: 0–63%), we estimated these parameters and their variability across 120 population clusters in the study region, using a simple parasite transmission model and Gibbs-sampling Monte Carlo Markov chain techniques. We observed great heterogeneity in R0 values, with estimates ranging from 1.23 to 3.27, while k-values (which vary inversely with the degree of parasite aggregation within the human host population) range from 0.007 to 0.29 in a positive association with increasing prevalence. The main finding of this study is the increasing trend for greater parasite aggregation as prevalence declines to low levels, reflected in the low values of the negative binomial parameter k in clusters with low hookworm prevalence. Localized climatic and socioeconomic factors are investigated as potential drivers of these observed epidemiological patterns. Conclusions Our results show that lower prevalence is associated with higher degrees of aggregation and hence prevalence alone is not a good indicator of transmission intensity. As a consequence, approaches to MDA and monitoring and evaluation of community infection status may need to be adapted as transmission elimination is aimed for by targeted treatment approaches.

Individual adherence to mass drug administration in neglected tropical disease control: a probability model conditional on past behaviour

“…In this section we illustrate the impact of adherence, as described by our mathematical model, on the predictions made by simulations for the outcome of MDA on the chances Table 3. The positive predictive value (PPV) for elimination evaluated by fully age-structured stochastic individual-based simulations of hookworm (with adult worm and eggs/larvae mortality rates set to µ 1 = 0.5 and µ 2 = 26.0 per year, respectively and the density dependent fecundity factor is set to γ = 0.01, as considered in Ref [16]) with two different clustered community types specified by the TUMIKIA transmission parameters inferred from the baseline epidemiological data in Ref [16]. The parameters quoted are the endemic prevalence P , parasite aggregation parameter k, basic reproduction number R 0 and cluster population number N , where the age profiles are all assumed to be exactly flat for simplicity.…”

Deworming Women of Reproductive Age During Adolescence and Pregnancy: What is the Impact on Morbidity From Soil-transmitted Helminths Infection?

“…There are two important differences between the ICL and the EMC model. Firstly, the ICL model assumes that the relative exposure to hookworm infections and contribution to the environmental reservoir of infection are the same for all age groups and just depend on the burden of adult worms in an age group [14]. In other words, the FoI is xed an independent of age.…”

Stochastic challenges to interrupting helminth transmission

“…Using Eqs. (25) and (32), we have plotted a calculation of both the probability of the number of net growers for communities with configurations C1 and C2 (see Table 1) in Fig. 4 and the expected number of net growers as a function of the prevalence in Fig.…”

“…is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint Table 1: The particular configurations with hookworm parameters [32] used for demonstration in this work.…”