Taeniasis

Designing a minimal intervention strategy to control Taenia solium in animals with a public health impact

girls with pig
©WHO

15 May 2017| Geneva −− Marshall Lightowlers and Meritxell Donadeu

Several mathematical models have been published which attempt to simulate transmission of Taenia solium and the impact of various intervention measures. These incorporate parameters which cannot be estimated with any degree of accuracy because little or no direct information is available.

This paper takes a different approach. A logical model is presented of the risk for T. solium to be transmitted by pigs which are subjected to anti-T. solium vaccination and chemotherapy, or chemotherapy alone. The quantity of risk is not evaluated, simply whether the animals present any risk for transmission or not. The potential for disease transmission is modeled on a monthly basis throughout the animals’ life for those pigs that participate fully in the interventions.

The model demonstrates that transmission ofT. solium can be prevented entirely in pigs that are slaughtered after 7 months of age, through the combined application of vaccination and oxfendazole chemotherapy applied on a 3-monthly basis. A similar intervention applied at an interval of 4 months, or use of chemotherapy alone, are unable to prevent transmission. An important advantage of the combined use of a vaccination plus chemotherapy approach is that it allows oxfendazole to be used only in young animals (≤7 months of age). This avoids the use of chemotherapy in animals that are approaching slaughter age in situations where it is unlikely or impossible to prevent treated pigs being slaughtered during the oxfendazole withholding period (3 weeks).

There are limitations in implementing this strategy, as in any intervention. The program is only effective in pigs that participate fully in the 3-monthly program, so coverage of the pig population would be vital. Immigration of people and pigs into the area, would prevent the complete elimination of transmission in the timeframes that are modelled. However, the logical model not only identifies the potential of an approach involving vaccination + chemotherapy in pigs has for control of T. solium, but it also provides a framework for modelling the impact of other intervention scenarios in pigs on the potential of the animals involved to be able to transmit the parasite.