The Effect of Physical and Chemical Agents on the Oocyst of Eimeria zurnii (Protozoa, Coccidia)*

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Abstract
SYNOPSIS.: A study was made of the effects of solar radiation, temperature, relative humidity, centrifugation, oxygen, pH, and certain chemical agents on the sporulation of oocysts of Eimeria zurnii of cattle. Of various chemical agents and bactericides tested, only HgCl2 exhibited a high level of activity against unsporulated oocysts. Extreme pH values of 1 and 13 did not alter sporulation. Oocysts required at least 10% of the normal amount of oxygen to sporulate at a normal rate. Physical factors found to be lethal for E. zurnii were: sunlight for as short a time as 4 hours, drying at 25% or less relative humidity, and freezing below about ‐7° C. Survival was directly proportional to relative humidity, but within the limits of the observations reported here, there was no correlation with time or temperature. Normal sporulation occurred from about 8° up to 32.5° C. Below 12° the time required for sporulation was exceedingly long, and at 35° sporulation was morphologically abnormal. The optimal temperature for sporulation was about 30° at which temperature some organisms completed the process in 23 hours. Fifty % of the oocysts required 65 hours to begin sporulating at 20° and 36 hours at 25° C.