Minimum Lethal Temperature for the Cottontail Parasite Eimeria environ

Abstract

During a survey of cottontail parasites in Illinois, Ecke and Yeatter (1956) discovered that storage by refrigeration often destroyed coccidian odcysts. The high natural rate of infection in adult rabbits (over 90 per cent in the above study) results in a massive accumulation of oocysts in manure deposits-particularly in areas of heavy rabbit density. If the o6cysts remain infective, a vast reservoir is accumulated over winter as a potential danger to the young, susceptible rabbits in the spring. The effects of cold temperature on this disease reservoir thus become an important consideration to the game manager. The present study was undertaken to determine the lower temperature tolerances of the organism. The results herein reported were included as a part of a Master's thesis submitted to the University of Illinois in 1947. The coccidia used for experimentation were of the species Eimeria environ. A supply of organisms was available from a captive juvenile rabbit that was infected when taken from its nest. Oocysts were recovered by collecting freshly deposited droppings from the litter pan under the animal's cage. The pan was thoroughly cleaned prior to collecting so that all o6cysts were less than 12 hours old when collected and sporulation could not have commenced. Constant low temperatures were maintained within two degrees of accuracy by placing a thermostatically controlled, heated box inside ot a freezertype refrigerator. Temperature control could thus be maintained between + 100 and -250 Centigrade. A series of experiments was conducted to test the survival of E. environ at temperatures of 0%, -50, -10 and -15C. Four petri dishes containing freshly collected pellets from the infected rabbit were placed in the control box for exposure at each of these different temperatures. For each temperature level, a dish was removed at the end of 12, 24, 48, and 72 hours. At the time of removal, the contents of the dishes were placed in 23 per cent potassium di-