Effects of broad-spectrum fertilizers on human picornaviruses
Date
2010
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Publisher
University of Delaware
Abstract
The presence of disease-causing microorganisms (viruses, bacteria, fungi, and protozoa) on farmlands poses a serious threat to public health. Pathogens can cause surface water contamination by many processes, such as runoff, groundwater contamination through leaching, and food contamination through direct contact or irrigation with contaminated water. This is a critical national issue because of the widespread agricultural use of manures/biosolids, the growing problem of emerging viral diseases, and the limited research base on interactions between viruses in water with soils and food crops. It has been estimated that nearly 80 million dry tons of solid manure are generated annually by the beef, dairy, swine, and poultry industries in the U.S. Land application remains by far the most common and economic method to beneficially re-use these by-products of animal production. Properly treated manure is an effective and safe fertilizer, but untreated or improperly treated manure may contain pathogens that can reach fresh produce in the field, nearby surface waters and leach to ground waters; it is these affected waters that will be used for irrigation and for pesticide applications. Although viruses are not the only pathogens of concern, they are much smaller in size than other enteric pathogens, and can move better through the subsurface. Viruses also tend to survive longer than bacteria and protozoa in the environment and therefore pose greater threats for groundwater and produce contamination. Furthermore, viruses have been shown to be responsible for approximately 80% of waterborne disease outbreaks for which infectious agents were identifiable and 75% of the estimated cases of foodborne illness. Due to the recent attention given to foodborne disease outbreaks, especially with lettuce, there is a renewed desire to understand the origin of plant contamination by viruses. Transmission of human pathogens to plants through contaminated irrigation water and contaminated hands has been documented under both laboratory and field conditions. Viruses have previously been shown to survive on the surface of vegetables for more than 2 months under suitable conditions with the potential for survival for over 2 years based on laboratory calculations of the field environment, outlasting the normal shelf-life of some products. Considerable research has been devoted to the fate and transport of viruses in soils; there is evidence that viruses can move considerable distances in specific soil layers. Such findings have raised concerns about surface and ground water contamination. Generally, viruses have been found to survive longer under moist as compared to dry conditions. In addition, when viruses are associated to a solid surface, they are generally protected from being inactivated; however, association with certain metal and metal oxides has been found to reduce virus survival. The route of viral contamination often goes unidentified for a majority of foodborne outbreaks involving fresh produce. Nearly 75% of these outbreaks are related to domestically grown produce with less than 10% from imported produce and the rest unknown. As produce consumption has increased with increasing focus on a healthy diet, foodborne illness associated with these foods has as well. Viral contamination of produce has been associated with various types of fruits, leafy vegetables, and herbs. Viruses affect large numbers of people and different food products; the CDC estimates the incidence of foodborne illness attributed to fruit and vegetable consumption at 3 million cases in the U.S. annually.