These may have been contaminated previously by other young infected birds or by adult birds that have recovered from the condition. Wet areas around water fountains are a source of infection. Oocysts remain viable in litter for many months. In this way they can contaminate a farm from year to year. Oocysts are killed by freezing, extreme dryness and high temperatures.
Several factors influence the severity of infection.
Generally, an increase in the number of oocysts eaten is accompanied by an increase in the severity of the disease. Strain of coccidia. Different strains of a species may vary in pathogenicity. Environmental factors affecting the survival of the oocysts. Site of development within the host .