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| Orientation and Training Food and Drug Administration |
| DOCUMENT NO.: IV-02 | VERSION NO.:1.2 | Section 2 - Microbiology | EFFECTIVE DATE: 10/01/2003 | REVISED: 06/27/2008 |
2.6 Viruses
Viruses are infectious microorganisms, much smaller than most bacteria, which cannot grow or reproduce apart from a living cell. They consist of genetic material, either DNA or RNA, encased in a protein coat known as the capsid. Several viruses have been associated with foodborne illness including Rotoviruses, Noroviruses and Hepatits A. Viruses are difficult to propagate in culture but are readily detected using molecular methods such as PCR and qPCR. A. Objective - To become familiar with viral pathogens capable of causing foodborne illness.
Norovirus is a common cause of foodborne illness, causing acute gastrointestinal illness of relatively short duration. Noroviruses are transmitted primarily through the fecal-oral route, either by consumption of fecally contaminated food or water or by direct person-to-person spread. There are at least five norovirus genogroups identified in this RNA virus (GI, GII, GIII, GIV and GV) which can serve as targets for PCR methods of detection.
Hepatitis A (HAV) has also been implicated in food related outbreaks such as green onions, iced drinks and cold cuts. HAV is excreted in feces of infected people and produces illness characterized by sudden onset of fever, malaise, nausea, anorexia, and abdominal discomfort when susceptible individuals consume contaminated water or foods. - To become familiar with methods to detect viral food pathogens.
Unlike bacteria which can be readily enriched in culture for detection by biochemical means, viral pathogens rare more readily detected using molecular methods such as PCR or qPCR. The detection of RNA viruses requires the use of reverse transcriptase to first produce a complimentary DNA (cDNA) copy of the RNA genome that can be used as targets in PCR reactions. Conventional PCR is end point analysis with amplification of a target DNA sequence visualized on an agarose gel. Real-time PCR (qPCR) primers and probes have also been developed to detect both Norovirus and Hepatitis A. B. Assignment/exercise Consult the following websites for more information:
http://www.cfsan.fda.gov/~mow/chap31.html
http://www.cfsan.fda.gov/~ebam/bam-26.html C. Questions - List two ways that viruses differ from bacteria.
- What is the genetic material found in viruses?
- What step is required to be performed before performing PCR on RNA viruses?
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