Survival of Porcine teschovirus as a surrogate virus on pork chops during storage at 2°C

Heat stability of foodborne viruses - Findings, methodological challenges and current developments

Heat treatment of food represents an important measure to prevent pathogen transmission. Thus far, evaluation of heat treatment processes is mainly based on data from bacteria. However, foodborne viruses have gained increasing attention during the last decades. Here, the published literature on heat stability and inactivation of human norovirus (NoV), hepatitis A virus (HAV) and hepatitis E virus (HEV) was reviewed. Data for surrogate viruses were not included. As stability assessment for foodborne viruses is often hampered by missing infectivity assays, an overview of applied methods is also presented. For NoV, molecular capsid integrity assays were mainly applied, but data from initial studies utilizing novel intestinal enteroid or zebrafish larvae assays are available now. However, these methods are still limited in applicability and sensitivity. For HAV, sufficient cell culture-based inactivation data are available, but almost exclusively for one single strain, thus limiting interpretation of the data for the wide range of field strains. For HEV, data are now available from studies using pig inoculation or cell culture. The results of the reviewed studies generally indicate that NoV, HAV and HEV possess a high heat stability. Heating at 70-72 °C for 2 min significantly reduces infectious titers, but often does not result in a >4 log10 decrease. However, heat stability greatly varied dependent on virus strain, matrix and heating regime. In addition, the applied method largely influenced the result, e.g. capsid integrity assays tend to result in higher measured stabilities than cell culture approaches. It can be concluded that the investigated foodborne viruses show a high heat stability, but can be inactivated by application of appropriate heating protocols. For HAV, suggestions for safe time/temperature combinations for specific foods can be derived from the published studies, with the limitation that they are mostly based on one strain only. Although significant improvement of infectivity assays for NoV and HEV have been made during the last years, further method development regarding sensitivity, robustness and broader applicability is important to generate more reliable heat inactivation data for these foodborne viruses in future.

Prevalence and phylogenetic analysis of human enteric emerging viruses in porcine stool samples in the Republic of Korea

Emerging infectious diseases (EID) in humans and animals are proving to be a serious health concern. This study investigated the prevalence of emerging or re-emerging human enteric viruses in porcine stools and swabs. Eleven enteric EID viruses were selected as target viruses for the current study and ranked based on their impact on public health and food safety: enterovirus (EV), hepatitis E virus, norovirus GI and GII, sapovirus (SaV), adenovirus (AdV), astrovirus, rotavirus, hepatitis A virus, aichivirus, and bocavirus. Using real-time RT-PCR or real-time PCR, EID viruses were detected in 129 (86.0%) of 150 samples. The most prevalent virus was EV, which was detected in 68.0% of samples, followed by AdV with a detection rate of 38.0%. In following sequencing and phylogenetic analyses, 33.0% (58/176) of the detected viruses were associated with human enteric EID viruses, including AdV-41, coxsackievirus-A2, echovirus-24, and SaV. Our results show that porcine stools frequently contain human enteric viruses, and that few porcine enteric viruses are genetically related to human enteric viruses. These findings suggest that enteric re-emerging or EID viruses could be zoonoses, and that continuous monitoring and further studies are needed to ensure an integrated “One Health” approach that aims to balance and optimize the health of humans, animals, and ecosystems.

Natural Host-Environmental Media-Human: A New Potential Pathway of COVID-19 Outbreak

Identifying the first infected case (patient zero) is key in tracing the origin of a virus; however, doing so is extremely challenging. Patient zero for coronavirus disease 2019 (COVID-19) is likely to be permanently unknown. Here, we propose a new viral transmission route by focusing on the environmental media containing viruses of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) or RaTG3-related bat-borne coronavirus (Bat-CoV), which we term the "environmental quasi-host." We reason that the environmental quasi-host is likely to be a key node in helping recognize the origin of SARS-CoV-2; thus, SARS-CoV-2 might be transmitted along the route of natural host-environmental media-human. Reflecting upon viral outbreaks in the history of humanity, we realize that many epidemic events are caused by direct contact between humans and environmental media containing infectious viruses. Indeed, contacts between humans and environmental quasi-hosts are greatly increasing as the space of human activity incrementally overlaps with animals' living spaces, due to the rapid development and population growth of human society. Moreover, viruses can survive for a long time in environmental media. Therefore, we propose a new potential mechanism to trace the origin of the COVID-19 outbreak.

Impact of seasonal temperature transition, alkalinity and other abiotic factors on the persistence of viruses in swine and dairy manures

Animal manures are a valued source of nutrients for crop production. They frequently do, however, contain zoonotic pathogens including a wide range of viruses. Ideally, manures would be treated prior to land application, reducing the burden of zoonotic viruses, and thus the potential for transmission to adjacent water resources or crops intended for human or animal consumption. In the present study, manure was obtained from four dairy and three swine farms. The manure was incubated anaerobically in the laboratory for 28 weeks at temperatures ranging from 4 to 25 °C, and multiple physical and chemical parameters were monitored. The abundance of various DNA and RNA viruses was measured throughout the incubation by amplifying virus-specific gene targets. A combination of statistical analyses were applied to identify whether the viruses are significantly impacted by temperature transition or affected by other abiotic factors. Temperature had no effect on the persistence of any of the viruses studied. An increase in pH of the manures during the incubation was significantly (P < 0.05) associated with decreased persistence, suggesting that pH manipulation during storage could reduce the abundance of viruses.

Potential Approaches to Assess the Infectivity of Hepatitis E Virus in Pork Products: A Review

The zoonotic transmission of hepatitis E, caused by the hepatitis E virus (HEV), is an emerging issue. HEV appears common in pigs (although infected pigs do not show clinical signs), and evidence suggests that a number of hepatitis E cases have been associated with the consumption of undercooked pork meat and products. Little information is available on whether cooking can eliminate HEV, since there is currently no robust method for measuring its infectivity. HEV infectivity can be clearly demonstrated by monitoring for signs of infection (e.g., shedding of virus) in an animal model. However, this approach has several disadvantages, such as lack of reproducibility and unsuitability for performing large numbers of tests, high costs, and not least ethical considerations. Growth in cell culture can unambiguously show that a virus is infectious and has the potential for replication, without the disadvantages of using animals. Large numbers of tests can also be performed, which can make the results more amenable to statistical interpretation. However, no HEV cell culture system has been shown to be applicable to all HEV strains, none has been standardized, and few studies have demonstrated their use for measurement of HEV infectivity in food samples. Nonetheless, cell culture remains the most promising approach, and the main recommendation of this review is that there should be an extensive research effort to develop and validate a cell culture-based method for assessing HEV infectivity in pork products. Systems comprising promising cell lines and HEV strains which can grow well in cell culture should be tested to select an assay for effective and reliable measurement of HEV infectivity over a wide range of virus concentrations. The assay should then be harnessed to a procedure which can extract HEV from pork products, to produce a method suitable for further use. The method can then be used to determine the effect of heat or other elimination processes on HEV in pork meat and products, or to assess whether HEV detected in any surveyed foodstuffs is infectious and therefore poses a risk to public health.

F-coliphages, porcine adenovirus and porcine teschovirus as potential indicator viruses of fecal contamination for pork carcass processing

There are concerns about the zoonotic transmission of viruses through undercooked pork products. There is a lack of information on suitable indicator viruses for fecal contamination with pathogenic enteric viruses in the meat processing chain. The study compared the incidence and levels of contamination of hog carcasses with F-coliphages, porcine teschovirus (PTV), and porcine adenovirus (PAdV) at different stages of the dressing process to assess their potential as indicator viruses of fecal contamination. One hundred swab samples (200cm²) were collected from random sites on hog carcasses at 4 different stages of the dressing process and from retail pork over the span of a year from 2 pork processing plants (500/plant). Viable F-coliphages, PAdV DNA and PTV RNA were each detected on ≥99% of the incoming carcasses at both plants and were traceable through the pork processing chain. Significant correlations were observed between viable F-coliphages and PAdV DNA and between F-coliphages and PTV RNA but not between PAdV DNA and PTV RNA at the various stages of pork processing. Detection of viable F-coliphages was more sensitive than genomic copies of PAdV and PTV at low levels of contamination, making F-coliphages a preferred indicator in the pork slaughter process as it also provides an indication of infectivity. For plant A, F-RNA coliphages were detected in 25%, 63%, and 21% of carcass swabs after pasteurization, evisceration, and retail pork products, respectively. For plant B, F-coliphages were detected in 33%, 25%, and 13% of carcass swabs after skinning, evisceration, and retail pork samples, respectively. Viable F-RNA coliphages were genotyped. Viable F-RNA GII and GIII were generally not detected at the earlier stages of the slaughter process but they were detected on 13% of carcasses after evisceration and 2% of retail pork samples at plant A, which raises concerns of potential food handler contamination during pork processing. Consumers could be at risk when consuming undercooked meat contaminated with pathogenic enteric viruses.