Mathematical model of the life cycle of taenia-cysticercosis: transmission dynamics and chemotherapy (Part 1)

Abstract

BackgroundTaenia solium is the aetiological agent of human taeniasis, pig cysticercosis and human neurocysticercosis, which are serious public health problems, especially in developing countries.MethodsA mathematical model of the transmission dynamics of taeniasis-cysticercosis is formulated. The model consists of a coupled system of differential equations, which are density-dependent equations for describing the flow of the parasite through the life cycle. The model is hybrid since it comprises deterministic equations with stochastic elements which describe changes in the mean parasite burden and incorporates the overall pattern of the parasites’ distribution.ResultsSensitivity and bifurcation analyses were carried out to determine the range of values of the model. The model can reproduce the observed epidemiological patterns of human taeniasis, pig and human cysticercosis. For example, for a wide range of parameter values, the mean intensity of adult worms tends to rapidly stabilize in one parasite per individual host. From this model, we also derived a Susceptible-Infected model to describe the prevalence of infection in humans and pigs. Chemotherapeutic interventions against pig cysticercosis or human taeniasis may reduce rapidly and effectively the mean intensity of human taeniasis, pig cysticercosis and human cysticercosis. This effect can be achieved even if the protective efficacy of the drug is of the order of 90% and the coverage rate is 90%. This means that health in humans infected either with adult worms or cysticerci may be achieved by the application of anthelmintic drugs against pig cysticercosis. However, treatment against human cysticercosis alone, does not influence neither human teniasis nor pig cysticercosis. This is because human cysticercosis infection does not influence the value of the basic reproductive number (Ro).ConclusionsEven coverage of 100% in the administration of anthelmintics did not eliminate the infection. Then elimination of the infection in all hosts does not seem a feasible goal to achieve by administering only chemotherapeutic interventions. Throughout the manuscript a discussion of our model in the context of other models of taeniasis-cysticercosis is presented.Electronic supplementary materialThe online version of this article (10.1186/s12976-018-0090-0) contains supplementary material, which is available to authorized users.

Modeling and analysis of taeniasis and cysticercosis transmission dynamics in humans, pigs and cattle

“…To analyze the possible number of positive real roots of polynomial (14) when R 0 < 1 and R 0 > 1, we adopt the approach in Okosun et al [25]. Using this approach, the number of possible real roots when R 0 < 1 and R 0 > 1 are summarized in Table 4.…”

“…Over the past two decades, various mathematical models have been formulated and analyzed to study the dynamics and control of parasitic foodborne diseases such as cholera, brucellosis and echinococcus [6,20,24,28,32,37,38]. In particular, some statistical and deterministic models with some stochastic elements that have been formulated and analyzed to study the transmission dynamics and control of taeniasis and cysticercosis in humans and pigs can be found in Gonzalez et al [12], Kyvsgaard et al [16], Braae et al [2], Winskill et al [34], José et al [14] and Sánchez-Torreset al [27]. The study done by Winskill et al [34] has assumed that human taeniasis occurs when susceptible humans interact with pigs that are infected with cysticercosis something that is practically wrong.…”

Modelling for Taenia solium control strategies beyond 2020

“…However, technical definitions of both intensified control and hyperendemicity need clarification for progress towards these goals over the next decade to be effectively evaluated. A key modelling activity should involve predicting, in a variety of epidemiological settings, the effect of various interventions in the currently available set • yes, if realistic control targets are proposed • modelling can inform the design and evaluation of pilot and large-scale control programmes with current and complementary intervention strategies 8,13 • cystiSim and EPICYST, computational transmission models, are applicable; 17,18 cystiSim is already in use in Zambia and Latin America, and an additional transmission model has also been developed for Latin America 23,24 What is required to achieve the target?…”

“…• true prevalence of T. solium infection in humans and pigs because of poor diagnostic methods • adult tapeworm life span • effect of pig-to-people population ratio on transmission • processes regulating parasite acquisition in humans and pigs 26 • health and economic burden 2,3 and cost-effectiveness of interventions (DALYs likely to underestimate disease burden); possible use of the zoonotic zDALY metric 21 • linking infection to disease models, particularly to human neurocysticercosis and epilepsy 27 What are the biggest risks?…”

The World Health Organization 2030 goals for Taenia solium: Insights and perspectives from transmission dynamics modelling

“…Models included a decision-tree 34 , Reed-Frost 35 , individual-based 36 , and population-based 37 frameworks. (Other models have been published since this review 38, 39 .) On-going development of cystiSim 36 and EPICYST 37 within a collaborative umbrella, has led to the establishment of ‘CystiTeam’, a partnership between the groups that developed these two models (based at the University of Copenhagen/Scientific Institute of Public Health, Brussels, and Imperial College London, respectively) and groups of epidemiologists, veterinarians, clinicians, one-health experts and program stakeholders.…”