Use of coccidiostats in broiler feed will become increasingly restricted due to anticoccidial resistance, consumer objections and legislation. Cost-effectiveness of alternative interventions cannot be assessed by looking at individual birds, but is determined by effects on the course of infection in a flock. In broilers, timing of exposure to different doses of (vaccine of wild-type) oocysts and uniformity of oocyst uptake determine clinical outcome and economic losses. Therefore we focus on Eimeria infection dynamics by combining transmission experiments and mathematical models.
In one study effects of oocyst dose on rate of Eimeria acervulina transmission were studied. Analysis with a susceptible-infectious (SI) transmission model showed that oocyst dose did not affect E. acervulina transmission between broilers. Fitting different models for transmission rate showed that a build-up period of infectivity in the environment had to be included in the model to fit experimental data. Control measures should therefore also focus on exposure to infectious fecal material rather than only on reducing fecal oocyst load. Another study showed that a live E. acervulina vaccine was efficiently transmitted. Challenge with a homologous wild-type strain showed that, although transmission of the wild-type strain was unhampered, directly and by transmission ‘contact-vaccinated’ broilers were equally protected against high oocyst excretions. Factors influencing vaccine transmission are therefore important targets to improve vaccine efficacy.
The powerful combination of transmission experiment and mathematical model identifies targets to improve control. By adding experimental and field data to the model, e.g. on oocyst quantities and production performance, infection dynamics and associated clinical and economic effects in flocks can be predicted. Such models can be used to evaluate cost-effectiveness of interventions and gives direction to new research and development activities.