Coccidiosis generally occurs where lambs become infected orally from faecal contamination, with areas such as dirty bedding, contaminated feed and water troughs and pastures the main entry routes due to higher numbers of oocysts (coccidial eggs) present.

The greatest risk is in lambs aged between three and eight weeks, with clinical symptoms most evident in lambs aged six to eight weeks. Lambs develop resistance to coccidia with age (10 weeks of age and older), but at this stage, great harm can be done with lambs finding it difficult to recover.