Porcine Epidemic Diarrhoea virus appears to be transmitted through feed and air. In Canada, fingers were pointed to the feed ingredient spray-dried porcine plasma (SDPP). This overview aims to show SDPP is safe to use.
By Javier Polo, Carine van Vuure and Isabelle Kalmar, technical committee, European Animal Protein Association (EAPA)
Porcine Epidemic Diarrhoea virus (PEDv) causes high mortality in young pigs and causes great economic losses to the pork industry. Especially in cold and wet environments, its spread is difficult to control. The virus is transmitted by the faecal-oral route and spreads quickly and easily on pig farms. Direct contact with infected pigs or indirect contact through contaminated food or surfaces are thought to be the primary sources of infection. Yet, the possibility of airborne spread should not be ruled out. Under experimental conditions, airborne spread of infectious PEDv particles has already been demonstrated.
In field conditions, however, only non-infectious PEDv genetic material has been detected in air samples so far. Still, PCR analysis showed the presence of PEDv genetic material up to 16 km (10 m) away from natural infected farms. Recently, there has been much speculation on the potential role of feed and its ingredients in the rapid geographic dissemination of PEDv. This has generated an extensive and controversial debate on the role of feeding animal protein sources as feed ingredients in the spread of the disease.
Use of plasma products
Following inquiries into the first case of PEDv in Canada, in Ontario in January 2014, it was thought that feed containing spray-dried porcine plasma (SDPP) was the source of the virus. After analyses on samples collected at a feed mill, the Canadian Food Inspection Agency (CFIA) reported the presence of infectious virus in samples of the SDPP used in the feed, but infectious virus could not be detected in the particular feed. The US Food and Drug Administration (FDA) could not confirm the presence of infectious virus in the particular lot of SDPP when sampled at the processing plant. Despite conflicting data, several industry professionals concluded that SDPP was a plausible vector of the virus.
This led to recommendations to no longer use plasma products in pig feed. Past studies on viruses that are more resistant than PEDv, however, have proven inactivation of infectivity by processing. Moreover, years of experience and many scientific studies clearly demonstrate beneficial effects of dietary SDPP on gut health of weaner piglets. Therefore, this article intends to review the results obtained in different controlled experiments conducted in order to test whether spray-dried porcine plasma is safe relative to PEDv.
In a very recent study performed by the Research Centre for Animal Health (CReSA), of which the publication is still in progress, liquid bovine plasma was inoculated with the PED virus. Three inoculated liquid plasma aliquots were spray-dried using laboratory equipment at an inlet temperature of 200°C (392°F). The normal outlet temperature in production plants is 80°C (176°F). Still, samples were also obtained and tested at a lower outlet temperature (70°C/158°F) in order to determine whether the virus can remain infective at that temperature. Both liquid and spray-dried samples were analysed for PEDv infectivity. The results confirmed that spray-drying is effective in inactivating the virus, even with shorter treatment times and lower temperatures than in industrial production standards (Table 1).
In another experiment conducted by CReSA, spray-dried bovine plasma was inoculated with PEDv and was maintained at room temperature (20-22°C/68-71.6°F) for one week. After seven days of storage, no infective PEDv was detected in the inoculated SDPP. Studies conducted at the University of Minnesota (2013) with infected dry feed reported similar results and demonstrated that the inactivation of PEDv by storage occurs much faster in dry products than in products with high moisture content and water activity.
In addition, a recent study conducted by Paul Thomas and others in 2014 demonstrated that faeces of PEDv infected pigs stored at 20°C for only seven days lost infectivity when fed back by intragastric tube to naïve pigs. Spray-dried products have a moisture content below 8% and a biological water activity lower than 0.6. All these studies show that even when the product would be stored at 4°C (39.2°F), the virus loses infectivity within 21 days.
Analysis by bioassay
As the – in Canada contested – plasma was produced in the US, the CFIA requested the FDA to conduct an investigation. Therefore, the FDA inspected the American production plant, reviewed all production records and collected samples from the specific suspected lot of spray-dried plasma. After reviewing all the records, it was found that the investigated lot had been manufactured under normal production conditions. Samples from the lot investigated by the CFIA, as well as samples from two randomly selected production lots were used in bioassays with piglets.
Such assays included the feeding of potentially contaminated material to susceptible young piglets in order to test whether said samples are infectious or not. Three samples collected by the FDA and four samples collected by the North American Spray Dried Blood and Plasma Producers Association (NASDBPP) were sent for independent bioassays. In contrast to the results of the CFIA bioassay, neither the FDA (Table 2) nor the NASDBPP bioassay (Table 3) revealed infectivity of any of the test samples. It is noteworthy that samples collected and investigated by the CFIA were taken after the product was collected by the customer, delivered to the feed producing company and stored there until feed manufacture.
Trials with SDPP
In 2014, researcher J.M. Campbell and others conducted a trial on a commercial farm with 48 PEDv naïve 21-day-old piglets that were randomly distributed into two dietary treatment groups with six pens per treatment and four pigs per pen.
What is spray-dried plasma?
Spray-dried animal plasma is a diverse and complex mixture of proteins that provide a nutritional foundation, which supports a range of beneficial biological effects, improving the young piglets’ ability to cope with post-weaning stress. Benefits associated with spray-dried porcine plasma are key factors for including it in post-weaning diets.
The two experimental diets were:
Control meal diet without SDPP: Formulated according to the commercial standard for weaners.
Meal diet containing 5% commercial SDPP that was PCR positive for PEDv: Soy concentrate was replaced by SDPP on an equal lysine basis.
The presence of clinical symptoms associated with PED, including the occurrence and severity of diarrhoea, was evaluated daily. Rectal swabs from each animal were taken on days 0, 3, 7, 14 and 21 for PCR analysis of PEDv. All animals were humanely euthanised on day 21 and underwent necropsy for gross evaluation of major organs and tissues. In addition, intestinal content, intestinal tissue and blood samples were collected for PCR, immunohistochemistry and anti-PEDv antibody analysis, respectively. None of the results indicated transmission of PED following feeding of a diet containing 5% SDPP that was highly positive for PEDv genetic material on PCR analysis.
In 2014 as well, a research team around Dr Tanja Opriessnig reported a challenge trial with 21-day-old PED naïve piglets that were randomly allotted to four treatment groups of eight pigs each.
Negative control without SDPP: Pigs were sham-inoculated with phosphate-buffered saline (PBS) at day 0, and were fed a control meal diet for 28 days without SDPP and;
Negative control with SDPP: Pigs were sham-inoculated with PBS at day 0 and were fed a meal diet with 5% SDPP for 28 days. The SDPP used was PCR positive for PEDv and contained antibodies against PEDv.
Positive control without SDPP: Pigs were inoculated with PEDv at day 0 (0 dpi, days post-inoculation) and fed the control diet from four days prior until 28 days after inoculation.
Positive control with SDPP: Pigs were inoculated with PEDv at day 0 and fed the diet containing 5% SDPP from four days prior to 28 days post-inoculation.
Regardless of the diet fed, none of the piglets from treatments 1 and 2 became infected with PEDv. Feeding sham-inoculated pigs a diet with PEDv PCR-positive SDPP thus did not result in transmission of PEDv over the 28-day test period. In pigs inoculated with infective virus (treatments 3 and 4), all animals developed serum antibodies against PEDv by 21 dpi. However, the infected pigs in the plasma group (treatment 4) appeared more active during the acute PEDv disease stage, with less pronounced diarrhoea. During acute PEDv infection at three days post-infection, adherent E. coli was not observed in any of three euthanised pigs in the plasma group, but was present in two of three PEDv infected pigs fed the control diet.
The data from these two studies demonstrate that pigs fed a diet containing SDPP that was PCR positive for PEDv, did not become infected with the virus. Only piglets that were directly inoculated with infective PEDv showed PCR positive faecal samples and seroconverted. These data also indicate a protective effect of dietary SDPP on the clinical presentation of PEDv. Finally, a study conducted by Dr Scott Dee and others (2014) demonstrated that in three separate cases, feed was the likely source of introduction of PEDv into a US pig farm. The feed of concern did not contain any source of animal by-products. This study demonstrated that feed can be a vehicle of transmission of the disease, irrespective if it contains animal proteins or not. So the implementation of biosafety measures should be in place at all levels of the pig production chain, including feed.
Up to date, regions such as Brazil and Western Canada have remained free of PEDv despite having been fed diets containing SDPP that was PCR positive for PEDv, imported from the United States. Tests were performed in a production plant in the south of Brazil that is exclusively dedicated to the processing of porcine blood. Between late December 2013 and early January 2014, several lots of SDPP from this Brazilian plant were collected for PCR tests for the presence of PEDv genetic material (Table 4). All samples were negative, confirming that the virus was not present, as also stated by the Brazilian veterinary authorities. Still, during 2013, Brazil imported sufficient amounts of SDPP from the US to feed 2.5-3.5 million pigs. Despite the use of large amounts of imported US plasma as an ingredient in pig feed in Brazil, the country remained free of PEDv. Also, between April and December 2013, Western Canada imported from the US enough SDPP to feed 3.5-4.0 million pigs. The plasma lots were from US plants and were PCR positive for PEDv. Nevertheless, during that period, no cases of PED were detected in Western Canada in relation to the feed. In late April 2014, three environmental samples that were positive for the virus were found in two high traffic density areas in Manitoba.
According to the Canadian Veterinary Office, the cases of environmental contamination in Manitoba have not been correlated with farms in the area. Therefore, the results obtained in controlled experiments, as well as the 2.5-3.5 million pigs in Brazil and 3.5-4.0 million pigs in Western Canada which were fed diets containing SDPP that was PCR positive for PEDv, support the conclusion that the SDPP did not contain infectious PEDv, and did not transmit the disease.
Regardless of these data, likewise for all other ingredients, there is a possibility that SDPP or any feed containing it, may become contaminated with infectious virus after processing.
All data supports the hypothesis that the spray-dried porcine plasma analysed by the CFIA became contaminated at some point in the chain of product distribution, after marketing and likely close to the time it was fed to the animals. PCR methods only indicate the presence of the virus genome, they do not distinguish between infectious and non-infectious virus. Therefore, it is absolutely necessary to perform controlled experiments, such as those contained herein, to truly test whether an ingredient such as SDPP is safe with regards to PEDv.
Confirming the safety of porcine blood products, on October 9th, the World Organization for Animal Health has affirmed that contrary to earlier reports, pig blood products such as dried plasma are not a likely source of infectious PEDv, provided that good manufacturing practices and biosecurity standards are followed.
Link not confirmed
American authorities and research institutes have concluded after bioassays on retained and other samples, that the initial Canadian suspicion with regards to SDPP could not be confirmed.
[Source: Pig Progress no. 9 – 2014]
References available upon request.