Later, as part of the SSWMP program, we were asked to investigate the possibility that septic tank effluent could safely be mixed with animal manure slurry on farms, for eventual disposal to land. After a review of the literature (Snowdon et al. 1989b ), we reported some preliminary studies that indicated the manure slurry had some antiviral effect (Snowdon et al. 1989a ). More detailed study showed that bacteria from swine manure, as well as in a waste mixture of septic tank effluent and swine manure slurry, were capable of inactivating poliovirus (Deng and Cliver 1992) . Further studies showed that bacteria in either dairy or swine manure could inactivate HAV (Deng and Cliver 1995b) . Specific bacteria, isolated in pure culture, were shown to attack HAV (Deng and Cliver 1995a) ; some of the active substances were characterized as specific proteases, but others were of quite low molecular weight and unfortunately were not studied further.