Evaluation of high hydrostatic pressure effect on human adenovirus using molecular methods and cell culture

Aspects of high hydrostatic pressure food processing: Perspectives on technology and food safety

The last two decades saw a steady increase of high hydrostatic pressure (HHP) used for treatment of foods. Although the science of biomaterials exposed to high pressure started more than a century ago, there still seem to be a number of unanswered questions regarding safety of foods processed using HHP. This review gives an overview on historical development and fundamental aspects of HHP, as well as on potential risks associated with HHP food applications based on available literature. Beside the combination of pressure and temperature, as major factors impacting inactivation of vegetative bacterial cells, bacterial endospores, viruses, and parasites, factors, such as food matrix, water content, presence of dissolved substances, and pH value, also have significant influence on their inactivation by pressure. As a result, pressure treatment of foods should be considered for specific food groups and in accordance with their specific chemical and physical properties. The pressure necessary for inactivation of viruses is in many instances slightly lower than that for vegetative bacterial cells; however, data for food relevant human virus types are missing due to the lack of methods for determining their infectivity. Parasites can be inactivated by comparatively lower pressure than vegetative bacterial cells. The degrees to which chemical reactions progress under pressure treatments are different to those of conventional thermal processes, for example, HHP leads to lower amounts of acrylamide and furan. Additionally, the formation of new unknown or unexpected substances has not yet been observed. To date, no safety-relevant chemical changes have been described for foods treated by HHP. Based on existing sensitization to non-HHP-treated food, the allergenic potential of HHP-treated food is more likely to be equivalent to untreated food. Initial findings on changes in packaging materials under HHP have not yet been adequately supported by scientific data.

Public health risks associated with hepatitis E virus (HEV) as a food-borne pathogen

Hepatitis E virus (HEV) is an important infection in humans in EU/EEA countries, and over the last 10 years more than 21,000 acute clinical cases with 28 fatalities have been notified with an overall 10-fold increase in reported HEV cases; the majority (80%) of cases were reported from France, Germany and the UK. However, as infection in humans is not notifiable in all Member States, and surveillance differs between countries, the number of reported cases is not comparable and the true number of cases would probably be higher. Food-borne transmission of HEV appears to be a major route in Europe; pigs and wild boars are the main source of HEV. Outbreaks and sporadic cases have been identified in immune-competent persons as well as in recognised risk groups such as those with pre-existing liver damage, immunosuppressive illness or receiving immunosuppressive treatments. The opinion reviews current methods for the detection, identification, characterisation and tracing of HEV in food-producing animals and foods, reviews literature on HEV reservoirs and food-borne pathways, examines information on the epidemiology of HEV and its occurrence and persistence in foods, and investigates possible control measures along the food chain. Presently, the only efficient control option for HEV infection from consumption of meat, liver and products derived from animal reservoirs is sufficient heat treatment. The development of validated quantitative and qualitative detection methods, including infectivity assays and consensus molecular typing protocols, is required for the development of quantitative microbial risk assessments and efficient control measures. More research on the epidemiology and control of HEV in pig herds is required in order to minimise the proportion of pigs that remain viraemic or carry high levels of virus in intestinal contents at the time of slaughter. Consumption of raw pig, wild boar and deer meat products should be avoided.

Effect of Nonthermal, Conventional, and Combined Disinfection Technologies on the Stability of Human Adenoviruses as Fecal Contaminants on Surfaces of Fresh Ready-to-Eat Products

Over one-half of foodborne diseases are believed to be of viral origin. The ability of viruses to persist in the environment and fresh produce, as well as their low infectious dose, allows even a small amount of contamination to cause serious foodborne problems. Moreover, the consumer's demands for fresh, convenient, and safe foods have prompted research into alternative food disinfection technologies. Our study focuses on viral inactivation by both conventional and alternative nonthermal disinfection technologies on different fresh ready-to-eat food products. The use of chlorine, as well as that of nonthermal technologies such as UV light and ultrasound (US), was tested for different treatment times. UV nonthermal technology was found to be more effective for the disinfection of human adenoviruses (hAdVs) compared with US, achieving a log reduction of 2.13, 1.25, and 0.92 for lettuce, strawberries, and cherry tomatoes, respectively, when UV treatment was implemented for 30 min. US treatment for the same period achieved a log reduction of 0.85, 0.53, and 0.36, respectively. The sequential use of US and UV was found to be more effective compared with when the treatments were used separately, for the same treatment time, thus indicating a synergistic effect. In addition, human adenoviruses were inactivated sooner, when chlorine treatment was used. Therefore, the effect of each disinfection method was dependent upon the treatment time and the type of food.

Environmental Effectors on the Inactivation of Human Adenoviruses in Water

Environmental factors are highly relevant to the global dissemination of viral pathogens. However, the specific contribution of major effectors such as temperature and sunlight on the inactivation of waterborne viruses is not well characterized. In this study, the effect of temperature (7, 20, and 37 °C), UVB and UVA radiation on viral inactivation was evaluated in phosphate buffered saline (PBS), mineral water, wastewater, 1,000-fold diluted wastewater and seawater. The stability of human adenoviruses infectivity, known as human pathogens and indicators of fecal contamination, was monitored during 24 h, both in the dark and exposed to UV radiation by immunofluorescence assays. In the dark, no Human adenovirus (HAdV) inactivation was observed in PBS and mineral water at any of the temperatures studied, whereas at 37 °C in reactors with higher microbial concentration (wastewater, diluted wastewater, and seawater), decays between 2.5 and 5 log were recorded. UVB radiation showed a dramatic effect on HAdV inactivation and 6-log were achieved in all reactors by the end of the experiments. The effect of UVA showed to be dependent on the water matrix analyzed. At 20 °C, HAdV showed a 2-log decay in all reactors radiation while at 37 °C, results in wastewater, diluted wastewater, and seawater reactors were equivalent to those observed in the dark. These results suggest UVB radiation as the major environmental factor challenging viral inactivation, followed by biotic activity indirectly associated to higher temperatures and finally, by UVA radiation.

Inactivation of internalized and surface contaminated enteric viruses in green onions

With increasing outbreaks of gastroenteritis associated with produce, it is important to assess interventions to reduce the risk of illness. UV, ozone and high pressure are non-thermal processing technologies that have potential to inactivate human pathogens on produce and allow the retention of fresh-like organoleptic properties. The objective of this study was to determine if UV, ozone, and high pressure are effective technologies compared to traditional chlorine spray on green onions to reduce enteric viral pathogens and to determine the effect of location of the virus (surface or internalized) on the efficacy of these processes. Mature green onion plants were inoculated with murine norovirus (MNV), hepatitis A virus (HAV) and human adenovirus type 41 (Ad41) either on the surface through spot inoculation or through inoculating contaminated hydroponic solution allowing for uptake of the virus into the internal tissues. Inoculated green onions were treated with UV (240 mJ s/cm(2)), ozone (6.25 ppm for 10 min), pressure (500 MPa, for 5 min at 20°C), or sprayed with calcium hypochlorite (150 ppm, 4°C). Viral inactivation was determined by comparing treated and untreated inoculated plants using cell culture infectivity assays. Processing treatments were observed to greatly affect viral inactivation. Viral inactivation for all three viruses was greatest after pressure treatment and the lowest inactivation was observed after chlorine and UV treatment. Both surface inoculated viruses and viruses internalized in green onions were inactivated to some extent by these post-harvest processing treatments. These results suggest that ozone and high pressure processes aimed to reduce the level of microbial contamination of produce have the ability to inactivate viruses if they become localized in the interior portions of produce.

Effect of temperature and sunlight on the stability of human adenoviruses and MS2 as fecal contaminants on fresh produce surfaces

Determining the stability, or persistence in an infectious state, of foodborne viral pathogens attached to surfaces of soft fruits and salad vegetables is essential to underpin risk assessment studies in food safety. Here, we evaluate the effect of temperature and sunlight on the stability of infectious human adenoviruses type 2 and MS2 bacteriophages on lettuce and strawberry surfaces as representative fresh products. Human adenoviruses have been selected because of their double role as viral pathogens and viral indicators of human fecal contamination. Stability assays were performed with artificially contaminated fresh samples kept in the dark or under sunlight exposure at 4 and 30°C over 24h. The results indicate that temperature is the major factor affecting HAdV stability in fresh produce surfaces, effecting decay between 3 and 4 log after 24h at 30°C. The inactivation times to achieve a reduction between 1 and 4-log are calculated for each experimental condition. This work provides useful information to be considered for improving food safety regarding the transmission of foodborne viruses through supply chains.

Evaluation and molecular characterization of human adenovirus in drinking water supplies: viral integrity and viability assays

Background

Human adenoviruses (HAdVs) are the second-leading cause of childhood gastroenteritis worldwide. This virus is commonly found in environmental waters and is very resistant to water disinfection and environmental stressors, especially UV light inactivation. Molecular techniques, such as PCR-based methods (Polymerase Chain Reaction), are commonly used to detect and identify viral contamination in water, although PCR alone does not allow the discrimination between infectious and non-infectious viral particles. A combination of cell culture and PCR has allowed detection of infectious viruses that grow slowly or fail to produce cytopathic effects (CPE) in cell culture. This study aimed to assess the integrity and viability of human adenovirus (HAdV) in environmental water and evaluate circulating strains by molecular characterization in three sites of the water supply in Florianópolis, Santa Catarina Island, Brazil: Peri Lagoon water, spring source water, and water from the public water supply system.

Methods

Water samples were collected, concentrated and HAdV quantified by real-time PCR. Viral integrity was evaluated by enzymatic assay (DNase I) and infectivity by plaque assay (PA) and integrated cell culture using transcribed mRNA (ICC-RT-qPCR). Samples containing particles of infectious HAdV were selected for sequencing and molecular characterization.

Results

The analyzed sites contained 83, 66 and 58% undamaged HAdV particles (defined as those in which the genetic material is protected by the viral capsid) at Peri Lagoon, spring source water and public supply system water, respectively. Of these, 66% of the particles (by PA) and 75% (by ICC-RT-qPCR) HAdV were shown to be infectious, due to being undamaged in Peri Lagoon, 33% (by PA) and 58% (by ICC-RT-qPCR) in spring source water and 8% (by PA) and 25% (by ICC-RT-qPCR) in the public water supply system. ICC-RT-qPCR, a very sensitive and rapid technique, was able to detect as low as 1 × 10² HAdV genome copies per milliliter of infectious viral particles in the environmental water samples. The molecular characterization studies indicated that HAdV-2 was the prevalent serotype.

Conclusions

These results indicate a lack of proper public health measures. We suggest that HAdV can be efficiently used as a marker of environmental and drinking water contamination and ICC-RT-qPCR demonstrated greater sensitivity and speed of detection of infectious viral particles compared to PA.

Potential of Pulsed Light to Inactivate Bacteriophage MS2 in Simple Liquid Medium and on Complex Foodstuffs

The virucidal efficacy of a pulsed light treatment applied to viral suspensions, glass beads and herb powders was studied for the F-RNA bacteriophage MS2. The experimental results obtained demonstrated the high potential of this technology to efficiently decontaminate simple matrices but underlined the complexity of application to complex food matrices.

High pressure processing and its application to the challenge of virus-contaminated foods

High pressure processing (HPP) is an increasingly popular non-thermal food processing technology. Study of HPP's potential to inactivate foodborne viruses has defined general pressure levels required to inactivate hepatitis A virus, norovirus surrogates, and human norovirus itself within foods such as shellfish and produce. The sensitivity of a number of different picornaviruses to HPP is variable. Experiments suggest that HPP inactivates viruses via denaturation of capsid proteins which render the virus incapable of binding to its receptor on the surface of its host cell. Beyond the primary consideration of treatment pressure level, the effects of extending treatment times, temperature of initial pressure application, and matrix composition have been identified as critical parameters for designing HPP inactivation strategies. Research described here can serve as a preliminary guide to whether a current commercial process could be effective against HuNoV or HAV.

Pressure inactivation of Tulane virus, a candidate surrogate for human norovirus and its potential application in food industry

Human norovirus (HuNoV) is the leading causative agent for foodborne disease. Currently, studies of HuNoV usually rely on surrogates such as murine norovirus (MNV) due to the lack of a suitable cell culture system and a small animal model for HuNoV. Tulane virus (TV), a monkey calicivirus, is a cultivable enteric calicivirus that not only recognizes the same receptors as HuNoV, but is also genetically closely related to HuNoV. In this study, we determined the pH stability of TV and MNV-1, as well as the effect of high hydrostatic pressure (HHP) on inactivating both viruses in aqueous media, blueberries and oysters. We demonstrated that both TV and MNV-1 were very stable under an acidic environment. They were more resistant to pressure at an acidic environment than at neutral pH. Pressure treatment of 600 MPa for 2 min at different temperatures (4, 21 and 35 °C) barely caused any reduction of TV, as well as MNV-1, on un-wetted (dry) blueberries. However, both TV and MNV-1 on blueberries were successfully inactivated by a pressure of ≤400 MPa when blueberries were immersed in phosphate-buffered saline during HHP. Pressure inactivation of both TV and MNV-1 in blueberries and oysters increased as sample temperature decreased in the order of 4>21>35 °C. TV was more sensitive to pressure than MNV-1 for the three matrices tested, culture media, blueberries and oysters. This study provides important information on the use of TV as a surrogate for HuNoV study. Results obtained from this study lay a foundation for designing effective HHP treatments for inactivation of HuNoV in high-risk foods such as berries and oysters.

Natural plant essential oils do not inactivate non-enveloped enteric viruses

The application of plant essential oils (EOs) (hyssop and marjoram) was evaluated for inactivation of non-enveloped viruses using murine norovirus and human adenovirus as models. No significant reduction of virus titres (TCID(50)) was observed when EOs were used at different temperatures and times.