Taenia solium control in Zambia: The potholed road to success

Abstract

The taeniosis/cysticercosis neglected zoonotic disease complex is caused by Taenia solium, and is associated with significant economic and public health impacts. This paper reviews the current knowledge on T. solium in Zambia and the control strategies already studied, covering almost 20 years of research, and explores the way forward. Studies on occurrence of porcine cysticercosis indicated very high prevalences, ranging from 15 to 34% based on detection of circulating antigens, and of 46% to 68% based on full carcass dissection in slaughter age pigs. Taeniosis prevalences have been reported to range from 6.3% to 12% based on copro-Ag-ELISA. Human cysticercosis prevalence results ranged from 5.8% to 13% based on serum Ag-ELISA, and from 34% to 39% based on sero-antibody detection. Later on, a study in people with epilepsy suggested neurocysticercosis to be the single most important cause of epilepsy in this T. solium endemic area, with 57% of the people with active epilepsy diagnosed with probable or definite neurocysticercosis. While the need to reduce the disease burden of T. solium in Zambia is obvious, the exact short and long term goals, and the strategies to achieve these goals, are not clear. We have selected the most promising control/elimination strategies from reviews and assessed these for feasibility via discussions with local stakeholders from both medical and veterinary sectors. The proposed measures were evaluated using the newly developed agent-based disease transmission model, cystiSim and optimised using Zambian demographic and disease data. As a control option, yearly porcine treatments were selected as best option, while the preferred strategy for elimination was determined to be the combination of human and porcine mass drug administration combined with porcine vaccination of all eligible people and pigs, in a schedule of six iterations of four monthly interventions. These interventions are currently being field tested, combined with education. Several other hurdles to control, such as cost and socio-political factors and the need for an improved advocacy and awareness creation are discussed.

Keywords: Control; CystiSim; Elimination; Taenia solium; Zambia.

Fig. 1

Map of Zambia showing districts were human/porcine cysticercosis occurrence has been determined (adapted from Sikasunge et al., 2008a, Sikasunge et al., 2008b, with additional information based on Mwape et al., 2012, Mwape et al., 2013, Mwape et al., 2015a, Mwape et al., 2015b; Phiri et al., 2002; Chembensofu et al., 2017). NCC: neurocysticercosis, PWAE: people with active epilepsy, EITB: enzyme-linked immunoelectrotransfer blot, Ag-ELISA: antigen detecting enzyme-linked immunosorbent assay.

Fig. 2

CystiSim output for different intervention scenarios aiming for control of Taenia solium in Zambia. Pr_(elim): probability of elimination of PCC (porcine cysticercosis) and HT (human taeniosis), MDA: human mass drug administration (praziquantel), OXF: porcine mass drug administration (oxfendazole), XqY: a total of X iterations of the intervention given at intervals of Y months. Interventions are introduced after 200 months.

Fig. 3

CystiSim output for different intervention scenarios aiming for elimination of Taenia solium in Zambia. Pr_(elim): probability of elimination of PCC (porcine cysticercosis) and HT (human taeniosis), MDA: human mass drug administration (praziquantel), OXF: porcine mass drug administration (oxfendazole), VAC: porcine vaccination (TSOL 18), XqY: a total of X iterations of the intervention given at intervals of Y months. Interventions are introduced after 200 months.