Development and application of a standardized assay for chemical disinfection of coccidia oocysts

The development and application of a standardized model for testing of anticoccidial disinfectants are described. Due to its economic impact, tenacity of oocysts, and reproducibility of the course of infection Eimeria tenella has been chosen as test organism. Oocysts of the Houghton strain were more susceptible to disinfection with 4% TP4 (Preventol) than oocysts of a field isolate (FI 292/1) as determined by sporulation inhibition and lysis. Scoring of intestinal lesions and of oocyst numbers in mucosal scrapings in chicken infected with various doses of oocysts were found unsuitable for assessment of disinfectants. Because strain differences were observed only Houghton strain oocysts were applied for further testing. Guidelines for standardized in vivo testing of disinfectants have been stipulated by the German Veterinary Society (DVG) on the basis of these studies. When applied for testing of Neopredisan (NP) in two separate laboratories similar results were obtained. Inhibitory activity (IA; proportion of inactivated oocysts) of 92.9 and 90.6% were calculated for 3% NP and of 95.2 and 96.8% for 4% NP after treatment with the disinfectant over 120 min. According to the guidelines IA of at least 95% is required for certification of sufficient disinfecting efficacy by the DVG.