Journal of Hospital Infection (1997) 36, 141-145 Effect of a commercial disinfectant (‘Virkon’) on mouse experimental infection by Cryptosporidium parvum E. Ares-Ma&s, M. J. Lorenzo, J. A. Casal, B. Fernhndez Da Ponte, J. A. Castro and F. Freire Labovatoyy of Parasitology, Department of Microbiology and Parasitology, Faculty of Pharmacy, University of Santiago de Compostela, 15706 Santiago de Compostela, La Covun”a, Spain Received 1 August 1996; revised manuscript accepted 15 January 1997 Summary: Cryptosporidium parvum oocysts obtained from naturally-in- fected calves were exposed to l-10% ‘Virkon’ for lo-360 min, then inoculated intragastrically into coccidium-free neonatal mice. Prevalence and intensity of infection were determined seven days later by examination of intestinal homogenates. Although we were unable to abolish infectivity for the mice, the intensity of infection was considerably reduced after long periods of exposure (up to >90%, depending on disinfectant concentration), indicating that this product may have some value for disinfection when extended exposure is possible (e.g., soaking laboratory glassware). Keywords: Oyptospojidium payvum; experimental infectivity; ‘Virkon’ Introduction Cryptosporidiosis is a diarrhoeal disease of humans and animals caused by Cryptosporidium parvum which occurs worldwide. Infections are contracted by the ingestion or inhalation of oocysts, so effective control must aim to reduce or prevent oocyst transmission. When excreted from infected hosts most oocysts are fully sporulated and infective, can resist a range of environmental conditions, and remain viable for long periods.‘-3 Cryptospovidium oocysts are remarkably resistant to chemical disinfection. Of 35 disinfectants tested,4 only five were effective with relatively short exposure periods: 50% ammonia, 3% hydrogen peroxide, 10% formalin, Exspor (chlorine dioxide based cold sterilant, Alcide Co.) and Oo-tide (two-phase product producing ammonia, Antec International Ltd). How- ever, 0.35% peracetic acid abolished excystation of oocysts in an excystation medium after 5 min.5 ‘Virkon’ (Antec International Ltd, U.K.) is recommended for hospital Correspondence to: Dr E. Ares-Mazis. 0195-6701/97/060141+05 012.00/O 141 0 1997 The Hospital Infecrmn Socmy