Following a request from the European Commission, the EFSA Panel on Animal Health and Welfare (AHAW Panel) was asked to deliver a scientific opinion on porcine epidemic diarrhoea virus (PEDV) and porcine deltacoronavirus (PDCoV).
The approach used for this scientific opinion consisted of extensive literature searches (finalised by the end of September 2014), followed by extraction of the relevant information and a description of the current knowledge in accordance with the terms of reference. Data gaps and a lack of scientific evidence are identified and specified. Regarding the risk assessment of potential entry routes of PEDV and PDCoV into the European Union (EU), it was agreed with the European Commission that this scientific opinion would describe the currently available scientific evidence and identify data gaps, but a full risk assessment would not be performed. The following paragraphs summarize the knowledge first concerning PEDV and then concerning PDCoV, in relation to the terms of reference of the mandate.
In the last decade, many porcine epidemic diarrhoea (PED) outbreaks have been reported by several countries in Asia. Only a few Member States of the EU have been reported PED clinical cases and/or PEDV-seropositive animals, the overall impact being very limited. This alphacoronavirus was first reported in the USA in May 2013, followed by a rapid spread throughout the country and outbreaks in several countries in the Americas. Vaccination has been used for many years in several Asian countries and might have influenced the epidemiological situation. New vaccines have been granted conditional licences in 2014 in the USA and no vaccines have been used in Europe.
Using a collection of 33 full-length PEDV genome sequences, it has been shown that all PEDV sequences (including the prototypic European isolate CV777) are closely related (the identity between the US and non-US strains varies between 96.3 and 99.5%) and that it was possible to group these into different clusters and sub-groups. Sequences from viruses circulating in Asia were present within each of the clusters and subgroups, indicating that a range of different viruses are circulating in Asia. All the US PEDV sequences were clustered into one group, but a sub-division of an original strain and a new variant strain can be made. Analysis of the European PEDV sequences is very limited, since there are only a few sequences available from viruses circulating in the 1970-80’s, and the only others are from viruses circulating recently in Germany and Italy. There is high sequence identity between these very recently circulating German and Italian viruses and the US PEDV strains, but more studies are required in order to compare the virulence of these different viruses. Additional sequence data are required to understand PEDV evolution in Europe and the possible link with PEDV strains circulating in other parts of the world.
Although differences in the virulence of PEDVs have been suggested in the scientific literature, there are not enough data available at the moment to compare their phenotypic characteristics. Comparing the virulence/pathogenicity of different PEDV isolates would require comparative animal experiments. No experimental animal studies have been reported describing the cross-protection between different PEDV strains. Serological cross-reaction between the virus isolated in Europe (PEDV-EU) and that isolated in the Americas (PEDV-Am) has been described including neutralizing antibodies raised against the early PEDV-EU towards PEDV-Am.
The impact of recently reported PED outbreaks in Asia (after 2010) and the USA seems to be more severe than that described in Europe. However, it is difficult to compare the impact between one country and another, since impact is dependent not only on the pathogenicity of the virus but also on parameters such as the production system, biosecurity, the time of detection of an outbreak, farm management, herd size, the immune status of the population and herd sanitary status (e.g. presence of other infectious agents). The severity of disease associated with PEDV within a herd is variable and is highly dependent on the age of the infected pigs and on the level of immunity in the population. Based on the scientific evidence available at the moment, the clinical disease of a PEDV infection in naive animals seems to be the same in different countries, with mortalities up to 100% in PEDV-naive newborn piglets. An apparent low impact of recent PED outbreaks caused by viruses with high sequence identity to US PEDV, has been reported in Italy and Germany. Factors which might influence the impact of a possible introduction of a US PEDV and spread of the virus into Member States include the level of cross-protection between different PEDVs and the seroprevalence (population immunity), both of which are currently unknown but are expected to vary between Member States. More knowledge on these factors is required before an accurate impact assessment can be performed.
Infected live animals and faeces have been reported to transmit PEDV. Infectious virus can survive in slurry, but at present there are no data available on the role of this matrix in PEDV transmission. High levels of infectious PEDV are shed in faeces and can contribute to contamination of various objects (e.g. vehicles, humans) and feed. Transmission of PEDV via feed has been shown, but more data are required to assess the source of PEDV contamination in feed. PEDV RNA has been detected at low levels in the serum fraction of whole blood but there are no data reporting infectious virus in this matrix to date. It is reported that spray-drying of porcine plasma (SDPP) can inactivate PEDV. However, the influence of variations in spray-drying processes has not been validated sufficiently for PEDV. Infectious PEDV has been detected in SDPP in one study but the origin of the infectious PEDV in SDPP is not clear (faecal cross contamination or inadequate spray-drying). Faecal cross-contamination of blood during collection at slaughterhouses cannot be excluded. Infectious virus has been detected in air collected under experimental conditions and so PEDV might be transmitted via the air for short distances. Low levels of PEDV RNA have been detected in semen but there are no data available on the presence of infectious virus in this matrix. Currently, there are no available data on the presence of PEDV in embryos, pork meat or other porcine derived feed components such as red blood cells, hydrolysed proteins, fat, gelatine and collagen. It can be assumed that porcine swill, particularly untreated pig intestines, can contain infectious PEDV, but there are no data available at the moment on the role of this matrix in PEDV transmission.
Detection of PDCoV has been reported in Hong Kong, the USA, Canada and China but only limited testing has been done. Serological tests specific to PDCoV and aimed at determining the immune status of the pig population have recently been developed and are currently in the process of validation.
Based on the currently available field observations from the USA, the current view is that PDCoV infections would have a lower impact than PEDV. However, the interpretation of field data is difficult since co-infections with PEDV or other intestinal pathogens are common. It is expected that further analysis of very recently performed experiments will provide a better understanding of the pathogenesis and clinical symptoms associated with PDCoV infection.
The available reports from the USA and Canada do not suggest a significant impact on animal health within these countries and no zoonotic potential of the virus has been reported. Therefore, the current knowledge of PDCoV leaves open questions on whether it can be classified as an emerging disease.
PDCoV RNA has been detected in porcine intestinal samples, faeces and feed, but no information on the presence of PDCoV in slurry, semen, embryos, porcine whole blood, SDPP, other porcine-derived feed components or air is currently available. It could be anticipated that the presence and survival of PDCoV in different matrices is comparable to that of other intestinal porcine coronaviruses such as PEDV and transmissible gastroenteritis virus.