Simulating transmission and control of Taenia solium infections using a Reed-Frost stochastic model.

The transmission dynamics of the human-pig zoonotic cestode Taenia solium are explored with both deterministic and stochastic versions of a modified Reed-Frost model. This model, originally developed for microparasitic infections (i.e. bacteria, viruses and protozoa), assumes that random contacts occur between hosts and that hosts can be either susceptible, infected or 'recovered and presumed immune'. Transmission between humans and pigs is modelled as susceptible roaming pigs scavenging on human faeces infected with T. solium eggs. Transmission from pigs to humans is modelled as susceptible humans eating under-cooked pork meat harbouring T. solium metacestodes. Deterministic models of each scenario were first run, followed by stochastic versions of the models to assess the likelihood of infection elimination in the small population modelled. The effects of three groups of interventions were investigated using the model: (i) interventions affecting the transmission parameters such as use of latrines, meat inspection, and cooking habits; (ii) routine interventions including rapid detection and treatment of human carriers or pig vaccination; and (iii) treatment interventions of either humans or pigs. It is concluded that mass-treatment can result in a short term dramatic reduction in prevalence, whereas interventions targeting interruption of the life cycle lead to long-term reduction in prevalence.

Improving pig husbandry in tropical resource-poor communities and its potential to reduce risk of porcine cysticercosis.

To minimise the risk of cysticercosis in pigs it is necessary to raise pigs in confinement. The prevailing production system using free-range pigs is apparently very resilient although economic studies have shown that these traditional production systems are wasteful and unprofitable due to poor feed conversion, high mortality rates, low reproductive rates and poor final products. However, experiences from Africa show that intensive pig farming is stagnant and the sustainability of the traditional sector is better than that of the intensive sector. Examples from various African countries are given on the failure of intensive pig farming. This apparent paradox has various explanations. The lower fixed cost of traditional pig production compared with intensive production is one. Another explanation is that many households have some kind of kitchen waste, which can be exploited by a pig, but there is only enough for the partial feeding of a single pig. A third explanation of the paradox is that the pig has functions that are not reflected in a simple economic balance. The pig is a source of capital income, which can be realised at times of major expenses, and it can also be used as a way to put aside small amounts of money, which alternatively might evaporate. The pig's scavenging behaviour has clear nutritional benefits. Thus, a diet consisting of e.g. maize or sorghum, which are some of the feeds available on the small farms, will only provide approximately 30% of the pigs requirements of lysine and methionine, which are the most limiting amino-acids in pig feeds. Simulations with data available for green feeds and material of animal origin show that a 20% "supplement" from the fields may increase the amino-acid provision to about 80% of the optimum. If pigs are kept enclosed this supplement has to be fed to the pig which involves purchase and labour costs. The paper discusses the various options in terms of feeding, housing and use of genetic resources for the improvement of pig husbandry in tropical resource-poor countries.