BIOLOGICAL EFFECTS OF GAMMA-IRRADIATION ON LABORATORY AND FIELD ISOLATES OF EIMERIA-TENELLA (PROTOZOA, COCCIDIA)

Sporulated oocysts of a field strain (FS-111) and a laboratory strain (WIS) of Eimeria tenella were exposed to 0, 50, 100, 150, or 200 Gy of gamma-radiation from a Co-60 source. Irradiated oocysts of WIS and FS -111 were not significantly more fragile after irradiation as shown by the release of sporocysts after 5-105 s of vortex agitation with glas s beads. Excystation was normal in both strains after treatment of the sporocysts with trypsin and sodium taurodeoxycholate, even in groups exposed to 200 Gy of radiation. Sporozoite release from irradiated spo rocysts was more rapid than that from unirradiated sporocysts, primari ly because of a shorter lag phase during the first 30 min. Irradiated sporozoites were slower to parasitize cultured chick kidney cells than were control sporozoites (4 h postinoculation), but after 24 h there was no significant difference (P < 0.05) between irradiated and contro l groups except for the WIS treated with 200 Gy. After 48 h, developin g schizonts were reduced by 77-94% on exposure to 50-200 Gy. Strain FS 111 did not develop as well as WIS in vitro, but the effect of irradi ation was similar. When irradiated oocysts of WIS or FS-111 were inocu lated into chickens the prepatent period was unaffected, but fewer ooc ysts were produced, lesion scores were lower, and the weight gain was less strongly affected in proportion to the doses of radiation. These results suggest that the effects of radiation damage were largely conf ined to the mechanism of nuclear and cellular reproduction rather than other physiological processes.