Methods to Detect Viruses in Foods: Testing and Interpretation of Results

Abstract

Viruses that may be detected in foods should be considered pathogenic and treated with appropriate caution. In this discussion, specific procedures for extracting viruses from shellfish are presented for each of the major commercial species of bivalve molluscs. Other foods for which specific extraction methods are detailed include lettuce, frozen strawberries, ground beef and raw milk. Viruses that may be detected by the methods described are those which are capable of producing a perceptible effect while replicating in cultured primate cells. Both results that are apparently positive and those that are apparently negative require careful interpretation; one must be extremely skeptical if large numbers of food samples obtained at the market appear to yield viruses. The procedures that are now available have some important limitations, including inability to detect the viruses that cause most of the reported foodborne disease. Approaches to surmounting these limitations include use of serologic methods to detect viruses that do not cause perceptible effects in cell cultures and improvement of procedures for extracting all viruses from food samples.

Detecting the presence of infectious hepatitis A virus in molluscs positive to RT-nested-PCR

“…One of the most clearly implicated foods in the transmission of HAV has been bivalve molluscs, mainly because they are often eaten raw or only slightly cooked (Wanke and Guerrant 1987; Gerba 1988). Worldwide, approximately 7% of the reported cases of HAV infection have been associated with mollusc consumption (Gerba and Goyal 1978; Cliver et al . 1983), and in 1988, the consumption of contaminated clams was reported as the cause of more than 300 000 cases of HAV infection in Shanghai, China (Xu et al .…”

Methodology for enumeration of coliphages in foods

“…Likewise, methods for quantitative recovery of coliphages and other viruses from the environment have been extensively investigated over the past several years (2-4, 26, 33). Although numerous methods for recovering animal viruses from various foods have been developed (5,6), few attempts have been made to enumerate indigenous bacteriophages in foods, and the procedures reported were not evaluated or refined in relation to recovery efficiency or applicability to various types of food (17,18,36). Development of coliphage enumeration methods which are rapid, simple, economical, and efficient as well as broadly applicable to different foods is necessary to investigate the distribution of coliphages and their possible role as indicator organisms in foods.…”

“…Techniques used for elution or desorption of viruses and phages from solid materials, e.g., membrane filters, soil, sludge, and aquatic sediments, generally involve lowering the ionic strength of the eluent or sample suspension, adding soluble proteins or other organic compounds to the suspension, raising the pH of the suspension, adding chaotropic agents to the suspension, or various combinations of these techniques (2-4, 7-12, 27, 29, 33, 37). Similar approaches have been used for desorption and recovery of animal viruses from foods with eluents or suspension media containing various concentrations of salts, acids or bases, buffers, proteins, and various combinations of these components (5,6). Little information is available on the effects of different eluent compositions and suspension medium pHs on the elution of viruses from foods (13), and no information is available on the effects of chaotropic agents.…”

“…A number of methods, including shaking, stirring and blending, and homogenization, have been used for physical suspension or liquefaction of food samples to release animal viruses (5,6,22), but these methods have not been standardized or extensively evaluated for broad application to various foods. Several techniques for clarifying food sample suspensions prior to virological assay, e.g., centrifugation, filtration, chemical phase separation, and adsorptionelution, have been reported (5,6). Tierney et al (32) found the glass wool or woven fiber glass filtration technique to be more efficient than other techniques, including centrifugation, for clarification of ground beef suspensions and subsequent recovery of polioviruses.…”

Current Methods for Extraction and Concentration of Enteric Viruses from Fresh Fruit and Vegetables: Towards International Standards

“…Rather, various modifications of a basic protocol for groups of fruit and vegetables are thought to be needed to take account of the differences in the morphology and hydrophobic interactions of fruit and vegetable surfaces, differences in tissue compositions (that affect the amounts of PCR inhibitory substances in, the pH of, and other qualities of, samples from fruits and vegetables), and the processing conditions to which the produce were subjected before they were sampled (Dalton 1997;Cliver et al 1983;Gulati et al 2001;Kurdziel et al 2001;Allwood et al 2004).…”