Effect of chemicals, heat, and histopathologic processing on high-infectivity hamster-adapted scrapie virus

Abstract

High-titered (greater than 10(10) LD50 [50% lethal dose[/g) preparations of scrapie virus-infected hamster brain were subjected to inactivation by various chemicals, autoclaving, and histopathologic processing. Sodium hypochlorite, which reduced infectivity by approximately 4 log LD50/g of brain (99.99%), was somewhat superior to sodium metaperiodate and clearly superior to chlorine dioxide, Lysol (National Laboratories, Montvale, N.J.), iodine, potassium permanganate, and hydrogen peroxide. Most inactivation occurred within 15-30 min of exposure to a chemical, and little if any additional inactivation occurred after 1 hr. Brains processed for histopathologic examination (formalin fixation followed by dehydration in methanol, clearing in chloroform, and embedding in paraffin) retained greater than or equal to 6.8 log LD50/g of the infectivity present in unprocessed control tissues (9.6 log LD50/g). One hour in an autoclave at 121 C reduced the titer of scrapie virus by approximately 7.5 log LD50/g of brain but left 2.5 log LD50/g of residual infectivity. A combination of exposure to chemicals and autoclaving may be necessary to sterilize high-titered scrapie virus-infected tissue.