| dc.description.abstract | Because of increasing resistance of Eimeria spp. against anticoccidials, objections of consumers and legislative restrictions against medicated feed in de EU it is necessary to develop new strategies against coccidiosis. The severity of the disease is often (partially) dependent on the initial contamination dose, which has a great influence on infection dynamics within a flock. Obtaining insight into (influencing) the dynamics of Eimeria in a population is essential for optimizing and evaluating control strategies.
For this purpose two transmission experiments where carried out, in a group of 20 broilers. One SPF broiler was orally inoculated on day 2 with 5 sporulated oocysts of E. acervulina, placed in a gelatinous capsule. On day 3, the inoculated animal was placed in a 1000 cm2 litter pen with 19 non-inoculated contact birds. From day 6 to day 30 (Experiment 1) or day 31 (Experiment 2), each bird was placed in a cat transport cage during one hour per day, to produce a single dropping. Number of oocysts per gram of faeces (OPG) of the single droppings was determined, using the McMaster technique. Sedimentation flotation technique was carried out when samples where negative or when a negative result was expected.
The inoculated bird tested positive in both techniques on day 7, in both experiments. In Experiment 1 the inoculated bird tested positive during 2 days, in Experiment 2 during 1 day. Oocyst excretion in contact birds in Experiment 1 started on day 12 (n=1), day 13 (n=14), day 14 (n=3) or on day 16 (n=1). In Experiment 2, oocyst excretion in contact birds started at day 12 (n=4), day 13 (n=6), day 14 (n=4), day 15 (n=2), day 17 (n=2) or on day 18 (n=1).
Contact birds that shedded oocysts before day 16 (C1-animals) where infected by uptake of oocysts shedded by the inoculated bird. Animals who shedded oocysts from day 16 (C2-animals) where most likely infected by uptake of oocysts shedded by formerly infected contact birds. The Area Under the Curve (AUC) of oocyst output of these C2-animals is higher than the AUC of the C1-animals. The peaks in oocysts output of C2-animals is also higher than the peaks of C1-animals.
These results show that not all the animals of a flock get infected at the same time, but some animals get infected by the contact birds of the first generation. Also, C2-birds shedded more oocysts than the C1-birds. This build up of infectious oocysts can result in high infectious doses for the following generations of susceptible contact birds and might cause severe clinical signs. These results have increased the understanding of the infection dynamics of an Eimeria infection in a flock. This can make a contribution towards the development of better control strategies. | |
