Evidence of the Internalization of Animal Caliciviruses via the Roots of Growing Strawberry Plants and Dissemination to the Fruit

Abstract

Human norovirus (NoV) is the leading cause of foodborne disease in the United States, and epidemiological studies have shown that fresh produce is one of the major vehicles for the transmission of human NoV. However, the mechanisms of norovirus contamination and persistence in fresh produce are poorly understood. The objective of this study is to determine whether human NoV surrogates, murine norovirus (MNV-1) and Tulane virus (TV), can attach and become internalized and disseminated in strawberries grown in soil. The soil of growing strawberry plants was inoculated with MNV-1 and TV at a level of 10 8 PFU/plant. Leaves and berries were harvested over a 14-day period, and the viral titer was determined by plaque assay. Over the course of the study, 31.6% of the strawberries contained internalized MNV-1, with an average titer of 0.81 ؎ 0.33 log 10 PFU/g. In comparison, 37.5% of strawberries were positive for infectious TV, with an average titer of 1.83 ؎ 0.22 log 10 PFU/g. A higher percentage (78.7%) of strawberries were positive for TV RNA, with an average titer of 3.15 ؎ 0.51 log 10 RNA copies/g as determined by realtime reverse transcriptase quantitative PCR (RT-qPCR). In contrast, no or little virus internalization and dissemination were detected when TV was inoculated into bell peppers grown in soil. Collectively, these data demonstrate (i) virally contaminated soils can lead to the internalization of virus via plant roots and subsequent dissemination to the leaf and fruit portions of growing strawberry plants and (ii) the magnitude of internalization is dependent on the type of virus and plant.H uman norovirus (NoV) is the major cause of nonbacterial gastroenteritis, contributing to over 95% of the cases of nonbacterial acute gastroenteritis and an estimated 58% of all foodborne illnesses reported annually in the United States (1-4). In recent years, fresh produce has been identified as a leading cause of foodborne illness in the United States (3, 5, 6). Human NoV alone accounts for over 40% of the fresh produce-related illnesses reported each year in the United States (1, 2, 4-8). Human NoV has been attributed to outbreaks in many diverse types of produce, including fresh cut fruit, lettuce, tomatoes, melons, salads, green onions, strawberries, blueberries, raspberries, and salsa, as well as many others (5-7, 9-15). Human NoV is resistant to common disinfectants, has a low infectious dose, and is highly stable in the environment, which contributes to the high prevalence of foodborne outbreaks associated with the virus and its presence and persistence in food commodities (3,16,17).Foods can become contaminated with human NoV at any point from farm to fork, including production, processing, and preparation. Infected food handler contamination and exposure to fecally contaminated water are thought to be the most frequent modes of human NoV contamination of foods (2, 5, 10, 18). The use of irrigation water that is contaminated with fecal matter is considered a significant cause of viral contamination in soft b...

Selected Viruses Detected on and in our Food

“…Metagenomic analysis of romaine and iceberg lettuce has shown the presence of wide range of plant and animal/ human viruses already on the field [63•]. It has also been shown that NoV can be internalised by some plants such as lettuce and strawberries through the root system and can therefore be present inside the plant and fruits rather than just contaminating the surface [64,65]; similar to the internalisation and retention of acid resistant viruses in water filtering molluscs [66]. Even though being internalised, NoV, such as most animal and human viruses, is not able to infect or replicate in plant cells [67].…”

PathogenicEscherichia coliand enteric viruses in biosolids and related top soil improvers in Italy

“…) and strawberry (DiCaprio et al . ) confirming that the use of faecally contaminated soil may pose a risk to the safety of some ready‐to‐eat products.…”

Attachment and localization of human norovirus and animal caliciviruses in fresh produce

“…Third, the persistence of viruses in produce could be due to the small size of the virus, which would allow them to enter small crevices and spaces on the produce surface and hence be protected from removal or inactivation (Wei et al, 2010). Finally, viruses may be internalized via roots and/or leaves, and disseminated to other portions of the plants which would render traditional sanitization strategies ineffective against internalized viruses (DiCaprio et al, 2015;Dicaprio et al, 2012;Esseili, Wang, Zhang, et al, 2012;Hirneisen and Kniel, 2013;Wei et al, 2011).…”