Assessing HEV infectivity tops foodborne virus research priorities
The UK Food Standards Agency (FSA) and European Food Safety Authority (EFSA) workshop addressed epidemiology, detection methodology and control options across the three main viral causes of foodborne illness: norovirus (NoV), hepatitis A virus (HAV) and hepatitis E virus (HEV).
High priority areas were assessing HEV infectivity, the relationship between detection of NoV in food and public health risk, methods for evaluating NoV and HAV infectivity, standardisation of methods for HEV detection in meat products and determination of the burden of HEV in Europe.
Experts said there was a need to move beyond presence/absence methods to quantification and infectivity assays to better understand potential risks to the consumer and the burden of disease so appropriate controls can be applied.
There are thought to be >100,000 HEV infections in England each year, but in 2015 only 800 cases were laboratory confirmed.
HEV is a relatively stable virus and may remain infectious at 71C, chlorine treatment and UV light.
Assessing HEV infectivity and norovirus detection significance
Participants said HEV is a growing concern in a number of member states and the UK.
However there has been little communication between clinicians, epidemiologists, processors and primary producers to discover how it travels from farm to fork and to address ways to reduce the burden of human disease.
Quote from the UK FSA
Dr Paul Cook, FSA head of microbiological risk assessment, said: “Addressing these research areas identified by the experts at the workshop would make an important contribution to assessing as well as managing risk posed by these viruses in foodstuffs.
“This is a particular challenge for norovirus, which cannot be cultured in the laboratory despite many efforts to do so; hepatitis E virus has also proved difficult to culture.”
There has been some progress on development of culture methods for hepatitis E, but more needs to be done to ensure infectivity can be determined in a reliable and reproducible manner.
This will aid quantification in various products and allow an accurate assessment of risk to consumers.
NoV has been detected at low levels in many products, but there is a lack of clarity regarding how this relates to risk of illness in consumers. At the EU level, it is not known how much disease caused can be attributed to foodborne spread.
Studies suggest it could be significant. However, the relative contributions of shellfish, fresh produce, food handlers (including asymptomatic shedders) and the handling environment have not been determined.
Current EU surveillance for foodborne NoV illness does not capture dispersed outbreaks efficiently, and there is evidence of significant underreporting of foodborne NoV outbreaks.
This priority is related to development of methods to detect viable virus and establishing how many viable particles are sufficient to cause illness from foodstuffs.
Evaluating NoV and HAV infectivity
Methods to detect NoV and HAV in food samples are not able to discriminate between infectious and non-infectious virus.
More studies are needed on the relation between detection of virus genomic copies by PCR in food and probability of causing disease.
Guidance for outbreak investigation could be drawn up to generate the data needed for quantitative microbial risk assessment (QMRA), said attendees.
Depending on efficacy of the tests and baseline levels found in foods, this could be translated into control measures.
The European Union Reference Laboratory (EURL) for monitoring bacteriological and viral contamination of bivalve molluscs is the Cefas Weymouth Laboratory.
Detecting HEV in meat products and establishing burden
HEV can be detected using similar methods to those for HAV and NoV, but the methods are not as far along in development and require validation and standardization in products at greatest risk of transmitting HEV: meat and meat products, particularly pork.
There is no standard or ISO method for HEV detection in meat. Developing this will allow for greater confidence in the accuracy and consistency of testing and allow results to be compared across laboratories and countries.
Attendees said this is a necessary step to establishing what the baseline is with regard to contamination of meat products and beginning to address how to control risk of infection.
It is not known how many people have been exposed to hepatitis E and the number of subclinical cases every year.
Population-level estimates of incidence, source attribution and clinical impact of HEV in humans in general, and in specific risk groups such as the elderly and the immunocompromised, are needed to determine the burden of disease, including foodborne illness.
