An international inter-laboratory study to compare digital PCR with ISO standardized qPCR assays for the detection of norovirus GI and GII in oyster tissue

An optimized digital RT-PCR (RT-dPCR) assay for the detection of human norovirus GI and GII RNA was compared with ISO 15216-conform quantitative real-time RT-PCR (RT-qPCR) assays in an interlaboratory study (ILS) among eight laboratories. A duplex GI/GII RT-dPCR assay, based on the ISO 15216-oligonucleotides, was used on a Bio-Rad QX200 platform by six laboratories. Adapted assays for Qiagen Qiacuity or ThermoFisher QuantStudio 3D were used by one laboratory each. The ILS comprised quantification of norovirus RNA in the absence of matrix and in oyster tissue samples. On average, results of the RT-dPCR assays were very similar to those obtained by RT-qPCR assays. The coefficient of variation (CV%) of norovirus GI results was, however, much lower for RT-dPCR than for RT-qPCR in intra-laboratory replicates (eight runs) and between the eight laboratories. The CV% of norovirus GII results was in the same range for both detection formats. Had in-house prepared dsDNA standards been used, the CV% of norovirus GII could have been in favor of the RT-dPCR assay. The ratio between RT-dPCR and RT-qPCR results varied per laboratory, despite using the distributed RT-qPCR dsDNA standards. The study indicates that the RT-dPCR assay is likely to increase uniformity of quantitative results between laboratories.

Thermal Inactivation of Hepatitis E Virus in Pork Products Estimated with a Semiquantitative Infectivity Assay

Hepatitis E virus genotype 3 (HEV-3) is a food-borne pathogen causative of hepatitis E infections in humans. In Europe, HEV-3 is mainly transmitted through the consumption of raw or undercooked pork. In order to determine the effectiveness of control measures that can be taken in the industry or by the consumer, it is pivotal to determine the infectivity of HEV present in pork products after thermal food-processing steps. First, we implemented a method for the detection of infectious HEV-3c and HEV-3e in a cell culture medium and in extracts from inoculated pork products. Next, we investigated the effect of the thermal inactivation of HEV by mimicking food-processing steps specific for dried sausage and liver homogenate matrices. After four weeks, HEV-inoculated dried sausage subjected to 21 °C or lower temperatures was still infectious. For the liver homogenate, the highest HEV-3c/e inactivation of the conditions tested was observed at 71 °C for five min or longer. Finally, our method was able to successfully detect and estimate viral loads of infectious HEV in naturally infected pig livers. Our data provide a basis for the future use of the quantitative microbial risk assessment of infectious HEV in pork products that are subjected to thermal food processing steps.

High prevalence of acute hepatitis E virus infection in pigs in Dutch slaughterhouses

Hepatitis E is caused by hepatitis E virus (HEV), one of the causes of acute viral hepatitis. Domestic pigs are considered as the main reservoir of HEV-3. The recently reported high prevalence of HEV in liver- and meat products on the Dutch market warranted a cross-sectional prevalence study on HEV infection among 5-6 months old pigs slaughtered in the Netherlands (n = 250). For this, liver, caecum content and blood samples were analyzed for the presence of genomic HEV RNA by RT-PCR. In addition, a serological test was performed to detect HEV IgG. Background information was retrieved on the corresponding farms to evaluate potential risk factors for HEV at pig slaughter age. HEV IgG was detected in sera from 167 pigs (67.6 %). HEV RNA was detected in 64 (25.6 %) caecum content samples, in 40 (16.1 %) serum samples and in 25 (11.0 %) liver samples. The average level of viral contamination in positive samples was log₁₀ 4.6 genome copies (gc)/g (range 3.0-8.2) in caecum content, log₁₀ 3.3 gc/ml (range 2.4-5.9) in serum and log₁₀ 3.2 gc/0.1 g (range 1.7-6.2) in liver samples. Sequence analyses revealed HEV-3c only. Ten times an identical strain was detected in two or three samples obtained from the same pig. Each animal in this study however appeared to be infected with a unique strain. The presence of sows and gilts and welfare rating at the farm of origin had a significant effect (p < 0.05) on the distribution over the four groups representing different stages of HEV infection based on IgG or RNA in caecum and/or serum. The observed proportion of tested pigs with viremia (16 %) was higher than in other reported studies and was interestingly often observed in combination with a high number of HEV genome copies in liver and caecum content as detected by RT-qPCR. Data provided will be useful for risk assessment for food safety of pork products, will provide baseline data for future monitoring of HEV infections in pigs and new thoughts for mitigation strategies.

Quantitative levels of norovirus and hepatitis A virus in bivalve molluscs collected along the food chain in the Netherlands, 2013-2017

Contamination of bivalve molluscs with viruses is well recognized as a food safety risk. A microbiological criterion for norovirus (NoV) and hepatitis A virus (HAV) in shellfish, however, does not exist in the European Union currently. The aim of this study was to evaluate the contamination levels of these viruses for fluctuation over a long period (2013-2017) in oyster (n = 266) and mussel samples (n = 490) using a method based on ISO/TS 15216-1: 2013. Samples were taken at different points in the food chain, either directly post-harvest, at Dutch dispatch centers or in retail stores, from September until March of each year. Altogether, 53.1% of the mussel and 31.6% of the oyster samples tested positive for NoV RNA. Simultaneous presence of NoV GI and GII RNA was observed in 31.6% of mussel and 10.2% of oyster samples. Contamination levels in NoV positive mussel samples collected post-harvest from B-areas were significantly higher than in those collected post-harvest from A-areas, or at dispatch centers or retail stores. Levels in oysters from dispatch were significantly lower than those collected in retail stores. Ready for sale mussels and oysters contained 2.04 and 1.76 mean log₁₀ transformed NoV genome copies/gram (gc/g), respectively. GII levels were at a constant level in ready for sale mussels throughout all sampling periods in the study. This seemed to be true for oysters as well. HAV RNA was detected in only one of the tested mussel samples (n = 392) (typed HAV 1A) and in none of the tested oyster samples (n = 228). Critical evaluation of NoV and HAV levels in shellfish can be of help for risk assessment and risk management actions.

Detection and quantification of hepatitis E virus RNA in ready to eat raw pork sausages in the Netherlands

The aim of the present study was to assess raw pork sausages collected on the Dutch market for the presence of hepatitis E virus (HEV) RNA. 46 of 316 (14.6%) products sampled from Dutch retail stores in 2017-2019 were positive for HEV RNA. HEV RNA was detected in 10.8% of "cervelaat" (n = 74), 18.5% of salami (n = 92), 26.1% of "metworst" (n = 46), 16.3% of "snijworst" (n = 43) samples. This was significantly more often than in other raw pork sausages like dried sausages, fuet or chorizo (3.3%, n = 61). The percentage of HEV RNA positive products was not significantly different for products sold as either sliced or unsliced deli meat. The average viral load in positive tested products was 2.76 log₁₀ genome copies per 5 g, incidentally reaching up to 4.5 log₁₀ genome copies per 5 g. The average HEV RNA level was significantly higher in samples collected in 2017 than those in samples collected in 2018, and most of the samples in 2019. Typing by sequence analysis was successful for 33 samples, all revealing genotype 3c. The results support recent epidemiological studies that identified specific raw pork sausages as risk factor for hepatitis E virus infection in the Netherlands. Persons at risk, including Dutch transplant recipients, have been advised to avoid the consumption of raw pork sausages. The study warrants a continuation of monitoring to follow the HEV RNA levels in pork products for use in risk assessments and risk management.

Successful Use of Advertisement Pictures to Assist Recall in a Food-Borne Hepatitis A Outbreak in The Netherlands, 2017

This study describes an outbreak investigation of 14 hepatitis A cases in the Netherlands. The hepatitis A virus (HAV) genotype IB sequences in cases were highly similar (459/460 nt). The origin of strains could be narrowed to Bulgaria based on information from EPIS-FWD. As an association with consumption of soft fruit was suspected, a case-control study was initiated using a questionnaire and a list of pictures of soft fruit available at the supermarket chain involved. Twelve out of 13 cases consumed a specific frozen raspberry/blueberry product shown on the list (OR 46.0, 95% CI 5.0-27). In multivariable regression analysis this product was the only risk factor (aOR 26.6, 95% CI 2.0-263). Laboratory analyses could not demonstrate HAV-RNA in batches that had been on the market in the incubation period of patients. Trace back of frozen fruit showed that raspberries had been traded by a producer in Bulgaria. After withdrawal of the product from the supermarket no new cases were reported. Use of advertisement pictures of consumed food was helpful in this investigation. Suspicion of the source was strengthened by data from molecular typing and food trace back activities, underlining the importance of good (inter)national cooperation between public health and food safety organisations.

Surveillance study of hepatitis A virus RNA on fig and date samples

A total of 91 fig and 185 date samples were analyzed by reverse transcription (RT) real-time PCR for the presence of hepatitis A virus (HAV) RNA. Two batches of dates tested positive, and the HAV RNA detected was genotyped as IA. These findings warrant further development of methods applicable to food which is consumed untreated and is exported from countries in which HAV is endemic.

Environmental swabs as a tool in norovirus outbreak investigation, including outbreaks on cruise ships

In this study, we investigated whether environmental swabs can be used to demonstrate the presence of norovirus in outbreak settings. First, a procedure was set up based on viral RNA extraction using guanidium isothiocyanate buffer and binding of nucleic acids to silica. Subsequently, environmental swabs were taken at 23 Dutch restaurants and four cruise ships involved in outbreaks of gastroenteritis. Outbreaks were selected based on clinical symptoms consistent with viral gastroenteritis and time between consumption of suspected food and onset of clinical symptoms (>12 h). Norovirus RNA was demonstrated by real-time reverse transcriptase PCR in 51 of 86 (59%) clinical specimens from 12 of 14 outbreaks (86%), in 13 of 90 (14%) food specimens from 4 of 18 outbreaks (22%), and in 48 of 119 (40%) swab specimens taken from 14 of 27 outbreaks (52%). Positive swab samples agreed with positive clinical samples in seven outbreaks, showing identical sequences. Furthermore, norovirus was detected on swabs taken from kitchen and bathroom surfaces in five outbreaks in which no clinical samples were collected and two outbreaks with negative fecal samples. The detection rate was highest for outbreaks associated with catered meals and lowest for restaurant-associated outbreaks. The use of environmental swabs may be a useful tool in addition to testing of food and clinical specimens, particularlywhen viral RNA is detected on surfaces used for food preparation.

An efficient and rapid method for recovery of norovirus from food associated with outbreaks of gastroenteritis

Noroviruses have emerged as the most common cause of foodborne outbreaks of acute nonbacterial gastroenteritis. In this study, two methods for the extraction of viruses from deli ham were compared. Using both methods, as little as 1 to 10 reverse transcription (RT)-PCR units of inoculated norovirus and enterovirus could be detected by nested RT-PCR assays. The fastest and most efficient extraction method based on TRIzol LS Reagent was chosen to identify viruses in food items associated with three different outbreaks. Norovirus was detected using nested (real time) RT-PCR assays that target the genome region routinely used for diagnosis of human cases, thereby facilitating the comparison of sequences detected in food and clinical specimens. For one outbreak, a norovirus sequence (163/163 nucleotides) identical to those detected in clinical samples was found on salami sliced by a food handler with a recent history of gastroenteritis. For the other two outbreaks, norovirus was detected on leftovers of spareribs and ham, but fecal samples from affected persons were not available. The methods used in this study may be useful in future outbreak investigations because the extraction method is easy to perform and suitable for this particular type of food and the detection method facilitates direct comparison of patient and food data.

Detection of noroviruses in shellfish in the Netherlands

Shellfish from oyster farms in the Netherlands and imported from other European countries were examined for viral contamination. A method that allows sequence matching between noroviruses from human cases and shellfish was used. The samples of shellfish (n = 42) were analyzed using a semi-nested RT-PCR that had been optimized for detection of norovirus in shellfish (SR primer sets). In addition, a different genome region was targeted using a second primer set which is routinely used for diagnosis of norovirus infection in humans (JV12Y/JV13I). To improve the detection limit for this RT-PCR a semi-nested test format was developed (NV primer sets). One of 21 oyster samples (4.8%) from Dutch farms was norovirus positive, whereas norovirus was detected in 1 out of 8 oyster samples (12.5%) and 5 out of 13 mussel samples (38.5%) collected directly after importation in the Netherlands. RNA from samples associated with an outbreak of gastro-enteritis in the Netherlands in 2001 was re-analyzed using the NV primer sets. At least one identical sequence (142/142 nt) was found in three fecal and in two oyster samples related to this outbreak. Further surveillance of norovirus by detection and typing of viruses from patients with gastroenteritis and shellfish is warranted to clarify the causes of future outbreaks.

Induction of HSP27 nuclear immunoreactivity during stress is modulated by vitamin C

For the investigation of the skin irritancy potential of chemicals in an in vitro model it is necessary to have sensitive endpoints that predict the effects of those compounds on native human skin. Recently, we have identified that 27-kDa heat shock protein (HSP27) can serve as a sensitive marker of skin irritation, as exposure of human skin to sodium lauryl sulfate (SLS) both in vitro and in vivo induced relocalization of HSP27 from the cytoplasm to the cell nucleus. The aim of the present study was to determine whether nuclear localization of HSP27 could be used as a parameter for evaluation of potential skin irritants in screening assays in vitro. For this purpose, human skin equivalent consisting of epidermis reconstructed on de-epidermized dermis was exposed to SLS or UV light. Stress-induced nuclear relocalization of HSP27 was observed in excised skin exposed to SLS or UV light and in reconstructed epidermis only when the latter was generated in the absence of vitamin C. The omission of vitamin C results in an impaired barrier function. In the presence of vitamin C, however, the barrier function was comparable with excised skin, suggesting that vitamin C may control the response to stress in the reconstructed epidermis. Besides the presence of vitamin C, the response of skin equivalents may strongly depend on other conditions under which they are generated, because the stress-induced HSP27 relocalization was not detected in the commercially available epidermal kit EpiDerm. The results of the present study show that HSP27 nuclear staining can serve as a sensitive marker for skin irritation or cellular stress in excised skin as well as in certain well-characterized human skin equivalents in vitro.

Proteomic analysis of skin irritation reveals the induction of HSP27 by sodium lauryl sulphate in human skin

BACKGROUND

There is an increasing need for screening of mild irritants in vitro to reduce animal testing.

OBJECTIVES

Proteomics were used to search for new markers of which the expression changes after mild irritation.

METHODS

Sodium lauryl sulphate (SLS) was applied topically on excised human skin. Epidermal proteins were isolated from SLS-treated skin specimens that showed hardly any morphological changes. The proteins were analysed by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) and proteins that significantly increased or decreased after SLS treatment in a dose-dependent way were characterized by mass spectrometry. Subsequently, immunohistochemistry was performed on skin samples treated with SLS in vivo and nonanoic acid (NAA) or benzalkonium chloride (BC) in vitro to evaluate one of the identified proteins for its predictive value.

RESULTS

We identified seven proteins as potentially new epidermal markers for skin irritation. Among these seven proteins, the 27 kDa heat shock protein (HSP27) was identified as the most prominently upregulated protein. A strong nuclear HSP27 staining was seen in the SLS-treated skin, whereas in the vehicle controls only cytoplasmic staining was observed. Moreover, nuclear staining was also observed after topical application of SLS in vivo and after exposure to NAA and BC in vitro.

CONCLUSIONS

Our findings suggest that HSP27 may serve as a sensitive marker of skin irritation and eventually as a novel tool in clinics for testing the sensitivity of the patient for a panel of irritants.