Summary
Noroviruses are the leading cause of diarrheal disease in the world and many of the infections begin with the consumption of contaminated food and water. Currently, it is widely known this virus is present in the natural environment, but it is unknown what environmental factors are able to decrease norovirus survival in irrigation waters or on produce and therefore prevent disease. In order to address this multi-faceted problem, this project brings together experts in the fields of food safety, foodborne disease and noroviruses. The proposed studies will test several conditions associated with irrigation water quality on their ability to impact norovirus survival in the water, on produce and transmission to a host. The identification of factors that reduce virus survival and/or disease will allow for the development of food and water intervention and treatment processes to reduce virus contamination and thus reduce the incidence of norovirus disease.
Technical Abstract
Noroviruses (NoVs) are the leading cause of foodborne gastroenteritis worldwide and are estimated to account for 40% of produce-related outbreaks. Pre-harvest contamination of produce is commonly due to the application of pathogen containing irrigation waters. Noroviruses in particular are extremely stable in water and on produce, but there is little knowledge regarding the physicochemical and biological factors that influence this environmental persistence. This study aims to elucidate attributes of water that enhance or reduce NoV persistence in water and on produce as well as their transmission to a host. Objective 1 will examine the physicochemical properties that influence NoV survival in water and on tomatoes. Objective 2 will examine biological properties that impact NoV survival. By modifying these properties, we ultimately hope to develop rational approaches to eliminating enteric viruses from irrigation waters. Objective 3 aims to identify factors of water and/or tomatoes that impact NoV transmission to a host, thereby providing a factual basis for the development of NoV transmission risk assessment models. Identification of conditions which impact NoV survival will also provide the basis for development of intervention and/or mitigation strategies targeting a common entry point into the food supply for many viral pathogens. The gathered data will be broadly applicable to a variety of foodborne viruses and so the information gained will help prevent the spread of other pathogens and reduce both the foodborne and overall burden of disease.
Research Objectives
1. Determine the effects of specific physical, chemical and biological factors on the survival and persistence of NoVs in water.
2. Determine the effects of specific chemical and biological factors on the survival and persistence of NoVs on tomatoes under common transport and storage conditions.
3. Determine the impact of specific environmental conditions and produce contact time on tomatoassociated NoV transmission to a host.
Findings & Recommendations
This project confirmed that noroviruses are extremely stable and that factors that contribute to norovirus stability can be multi-faceted. Only UV light and very high temperatures (67°C) were able to quickly eliminate infectious virus particles. All other treatments resulted in slower declines in virus stability. However, the decline in infectious virus can be accelerated by the addition of high concentrations of ammonium chloride or potassium phosphate. Thus, the addition of these compounds to irrigation water systems may prove useful in controlling and lowering norovirus in water when contamination events occur. Sodium phosphate also demonstrated a slight protective effect for murine norovirus under certain conditions, but bacteria provided the biggest stabilizing force of all the conditions tested. Furthermore, it seems the presence of the bacteria themselves is not necessarily required for enhancing viral stability. Enhanced viral stability can be achieved through products secreted by the bacterium. These observations may help explain the stability of norovirus in water sources and particularly in wastewater treatment systems. During this project period we also learned a great deal regarding the difficulty in working with poly-microbial systems and the challenges that arise when trying to analyze experiments and data. These complications extended to evaluating transmission of this virus, which also proved to be difficult. However, through these challenges much was learned and techniques were modified or developed to aid follow-up studies.