Some Effects of Temperature Upon Development of the Oocysts of Coccidia.

Abstract

Pérard 1 has shown that while the oocysts of the rabbit coccidia are extremely resistant to chemicals, they are, on the other hand, quite susceptible to heat. For example, Eimeria perforans was rendered incapable of sporulating if kept in an aqueous medium at a temperature of 40°C. for one day. Eighty per cent. of the oocysts were killed within 20 minutes in water at 55°C., within 10 seconds in water at 80°C., and within 5 seconds by boiling water.

In our experiments with E. perforans and E. magna the temperatures were maintained by an electric thermo-regulator water bath which did not fluctuate much beyond 0.1°C. The oocysts were kept in a 2% aqueous solution of potassium dichromate aerated by a constant succession of bubbles of air which was humidified and equated to the temperature of the bath prior to coming into contact with the culture solution.

At 25°C. about 50% of the oocysts of E. magna completed the sporulation process within 84 hours, while E. perforans required but 48 hours to attain the same percentage of development. At 33°C. 80% of E. magna sporulated within 72 hours, while all of E. perforans sporulated within 48 hours. A comparison of both the rapidity of development and the percentage of degeneration at higher and lower temperatures indicates that 33°C. is the optimal temperature for the sporulation of oocysts of both species. At 35° and 36°C. the number of degenerated oocysts after 72 hours varied considerably in the different trials, but in nearly all cases it was at least 50%. Although the developmental process sometimes progressed to the sporoblast stage, we were unable to find any sporozoites in E. magna which had been kept at 36°C. for any length of time.