Food Virology – NoroCORE Food Virology

Food Virology

close up photo of cut strawberry and whole strawberries with raspberries on a white backgroundclose up photo of triangular cut sandwiches containing deli meat lettuce and tomatoclose up photo of mixed leafy greens on white background

What is Food Virology?

Food Virology is an emerging subdiscipline of Food Microbiology. Food Microbiology is the study of microorganisms in food systems. We often think of three general classifications of food borne microorganisms….the Good (fermentation microorganisms, used to produce value-added food products like cheese and yogurt); the Bad (microorganisms that spoil food, think moldy bread or sour milk); and the Ugly (microorganisms that cause food-related illnesses). The latter category encompasses all the major bacterial pathogens we hear about in the news, for instance E. coli O157:H7, Listeria monocytogenes, Salmonella, and many others.

Those of us who study the “ugly” guys are called Food Safety microbiologists. Over the last decade, it has become clear that viruses, not bacteria, are the leading cause of food borne disease. This has given rise to the field referred to as Food Virology, or the study of viruses that cause disease in humans and which can be transmitted by consumption of contaminated foods. Food Virology forms a discipline somewhat distinct from Food Microbiology because (i) most food microbiologists know little about viruses; (ii) the behavior of viruses in the environment and foods is quite different than that of disease-causing bacteria; (iii) viruses are much more difficult to work with from a research perspective; and (iv) it is very difficult to control their transmission. The USDA-NIFA Food Virology Collaborative is trying to change all this.

Why is Food Virology important?

In addition to the “big picture” of the field itself, it’s important to understand more about the specific pathogens that food virologists focus on and their impact on human health. Human noroviruses are the leading cause of food borne disease outbreaks in the U.S., responsible for more than 5 million foodborne illnesses each year (out of about 20 million total annual cases). Food borne cases result in thousands of hospitalizations and more than 100 deaths per year. Noroviruses are very easily transmitted via the fecal-oral route from person to person, through contaminated food or water, and by touching contaminated surfaces. Complex foods (i.e. foods with more than one ingredient, such as a sandwich or salsa); fresh produce; nuts and berries; molluscan shellfish (such as oysters, clams and mussels); and foods that are extensively handled just prior to consumption are at greatest risk for contamination.

drawn rendering of norovirus particle

Classic symptoms of norovirus disease are nausea, vomiting, diarrhea, and abdominal pain with occasional headache and low-grade fever. Vomiting is considered the “hallmark” symptom. The symptoms usually last no more than 2 or 3 days. Rehydration therapy is the best treatment to date, but severe illness or hospitalization is relatively uncommon except in the elderly. However, due to the sheer magnitude of cases, norovirus ranks second in causes of foodborne disease hospitalization. Death is rare. There is not currently a vaccine available. Illness may be more severe for the elderly, children, and those who are immunocompromised. cartoon drawing of a man feeling sick to his stomach

There are many high profile norovirus outbreaks from the last decade. Perhaps first widely publicized as the “cruise ship virus,” norovirus is now known to cause outbreaks in many places where people are kept in tight quarters: long term care facilities, schools and dormitories, military establishments, even hotels. Relative to foodborne disease, there are many notable outbreaks. For instance, in 2012, thousands of school children in Germany were sickened with norovirus-contaminated imported strawberries. Food handler hygiene is of particular importance. In early 2014, over one thousand Japanese school children were infected by bread that appears to have been contaminated by food handlers who were shedding virus in their feces but were perhaps asymptomatic. Besides feces, norovirus is released during vomiting, and there have been outbreaks resulting from foods that were contaminated because individuals vomited in preparation kitchens.

The other major food borne virus of interest is Hepatitis A virus (HAV). Fortunately, there is an effective vaccine available to help combat the effects of this pathogen and HAV is estimated to account for only a couple thousand foodborne cases each year (compared to the millions caused by noroviruses). Mostly, people with HAV infection recover without needing treatment and it is rarely fatal, but the symptoms are unpleasant and can last for weeks or months. Like norovirus, HAV is spread through the fecal-oral route, by coming into contact with infected individuals, or contaminated foods, surfaces, or liquids. Symptoms may include fever, jaundice (yellowing of skin and eyes), nausea, and vomiting. Like norovirus, it may be spread even if infected individuals are not showing symptoms. The long incubation period can make it difficult to track. A high profile example of an HAV outbreak is the one caused by frozen berry mixes containing virus-contaminated pomegranate seeds that occurred in June 2013 in the U.S. This outbreak sickened over 100 individuals across 10 states. For the most part, HAV outbreaks tend to be sporadic and smaller in scale.