Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/14/2004
Publication Date: 6/1/2004
Citation: Jenkins, M.C., Higgins, J.A., Kniel, K., Trout, J.M., Fayer, R. (2004) Protection of calves against cryptosporidiosis by oral inoculation with gamma-irradiated Cryptosporidium parvum oocysts. Journal of Parasitology. 90: 830-833.
Interpretive Summary: Cryptosporidiosis is an intestinal disease of humans and animals caused by the protozoan parasite Cryptosporidium parvum. The disease costs the dairy industry millions of dollars annually due to poor weight gain and even death in young calves. At present there are no approved drugs or immune therapy to prevent or treat cryptosporidiosis. Studies have shown that calves and humans once infected with C. parvum are resistant to further infection. The purpose of the present study was to determine if calves inoculated with gamma-irradiated C. parvum oocysts were resistant to challenge infection. The study showed that calves inoculated with oocysts attenuated with an 'optimum' dose of gamma irradiation were resistant to a parasite challenge 3 weeks later. Quite interesting was that the calves did not shed oocysts or show signs of cryptosporidiosis after the primary infection with irradiated oocysts. These results indicate that it is possible to protect calves against cryptosporidiosis ('calf scours') by inoculation with irradiated C. parvum oocysts.
Technical Abstract: The purpose of this study was to determine if gamma-irradiated Cryptosporidium parvum oocysts could elicit protective immunity against cryptosporidiosis in dairy calves. Cryptosporidium parvum Iowa strain oocysts (1 x 10^6 per inoculation) were exposed to various levels of gamma irradiation (350 ' 500 Gy) and inoculated into 1-day-old dairy calves. The calves were examined daily for clinical signs of cryptosporidiosis and fecal samples were processed for the presence of C. parvum oocysts. At 21 days of age, the calves were challenged by oral inoculation with 1 x 10^5 C. parvum oocysts, and examined daily for oocyst shedding and clinical cryptosporidiosis. Calves that were inoculated with C. parvum oocysts exposed to 350 ' 375 Gy shed C. parvum oocysts in feces. Higher irradiation doses (450 or 500 Gy) prevented oocyst development, but the calves remained susceptible to C. parvum challenge infection. Cryptosporidium parvum oocysts exposed to 400 Gy were incapable of any measureable development, but retained the capacity to elicit a protective response against C. parvum challenge. These findings indicate that it may be possible to protect calves against cryptosporidiosis by inoculation with C. parvum oocysts exposed to 400 Gy gamma irradiation.