(BSE) illustrate this point. In 1980, in England, the combination of increasing fuel prices and tighter restrictions on the use of organic solvents for lipid extraction led to changes in the processing of offal, the viscera and trimmings of butchered animals that are a major component of animal feed. The new methods do not appear to inactivate sufficiently the BSE agent, and increased incidence of BSE in domestic animals has been linked to offal. There is considerable controversy, at least in England, about whether the BSE agent may also infect humans (Dealer and Lacey, 1990, 1991; K. C. Taylor, 1991). To date, however, no human infections have been detected.

In addition to modifications of traditional farming methods, the introduction of new types of agriculture can have an impact on the emergence of microbial threats. Aquaculture and mariculture, for example, are rapidly becoming important methods of producing fish and seafood. Yet there has been relatively little effort to understand the potential microbial impact of this new technology. As aquaculture and mariculture farmers attempt to increase their yields of freshwater and marine animals, the stresses of overcrowding and overfeeding create ideal conditions for Aeromonas hydrophila, a common fish pathogen found in fresh and estuarine waters (Plumb, 1975; Hazen et al., 1978). Increasingly, A. hydrophila, A. veronii (biovariant sobria), A. caviae, A. jandaei, A. trota, A. schubertii, and A. veronii (biovariant veronii ) are being implicated as causes of nosocomial, wound, waterborne, and food-borne infections in humans (Daily et al., 1981; Buchanan and Palumbo, 1985; Hickman-Brenner et al., 1987, 1988; Janda and Duffey, 1988; Carnahan et al., 1989; Carnahan and Joseph, 1991; Joseph et al., 1991; Samuel Joseph, Professor, Department of Microbiology, University of Maryland, personal communication, 1992). These bacterial infections are being found in immunocompromised individuals and those in otherwise poor health (W. A. Davis et al., 1978). Although there are a number of potential sources of infection with Aeromonas species, aquaculture and mariculture are probably the most common sources, since the incidence of these organisms in the products of these agricultural methods approaches 100 percent.

The use of human and animal fecal material to enrich pond cultures in parts of China and India raises additional concerns about the safety of some imported aquaculture products (Ward, 1989). Such practices may enhance the spread of pathogens transmitted by an oral-fecal route. In the Calcutta region of India, where this method of enrichment is used to raise prawns, a high incidence of non-O1 Vibrio cholerae contamination has been reported (Nair et al., 1991).

FOOD PROCESSING AND PRESERVATION TECHNOLOGIES

The application of new food processing and preservation technologies can have unexpected effects on the microbial safety of foods. Something



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