As African swine fever virus(ASFV)continues to spread across Southeast Asia,classical swine fever virus(CSFV)expands within Japan,and foot and mouth disease virus(FMDV)reports continue from China,there is increased concern that foreign animal disease(FOREIGN ANIMAL DISEASE)may enter previously naïve areas.Their continued entry would be devastating to the global swine industry,but also to those that produce feed and ingredients fed to pigs.In their May 2019 Food Outlook Report,the Food and Agriculture Organization of the United Nations reported that pig feed sales were down 10 to 50%in the Guangdong Province of China,and pig feed production in the Shandong Province was only 67%of the volume of 2018(FAO,2019).
Risks for Foreign Animal Disease Entry through Ingredients<<
There are many potential routes for FOREIGN ANIMAL DISEASE entry into naïve areas,with ingredients being just one.Many entities are taking steps to limit entry through more direct methods,such as regulating the importation of live animals or smuggling of pork products,but it is the responsibility of the feed industry to minimize the potential for FOREIGN ANIMAL DISEASE entry through a feed vehicle.For FOREIGN ANIMAL DISEASE entry via an ingredient to occur,there would need to be an initial contamination event,virus survival during transport,and consumption of virus at a dose that is capable of causing infectivity.
Contamination of an Ingredient<<
通过饲料供应链引入外来动物疾病的例子有几个。FMDV进入日本和韩国都与饲料有关(Sugiura et al.,2001;Park et al.,2014)。用从野猪感染典型猪瘟的地区收获的青贮饲料喂猪也已导致此前从未感染过的猪患病(Ribbens et al.,2004)。就在五年前，猪流行性腹泻病毒(PEDV)首次在美国养猪业迅速传播，造成27个州仔猪高死亡率。PEDV进入美国的根本原因调查得出的结论是，最有可能的原因是来自中国的饲料或者饲料原料吨袋(聚乙烯材料)(USDA 2015)。用受污染的饲料喂猪已被归类为传播ASFV的危险因素(EFSA,2014;Belyanin,2013)。该报告记录了俄罗斯报告的284起疫情中的35%与饲料有关。据报告，在俄罗斯发生的284起ASFV疫情中，有35%与受污染的商品饲料有关。最近，有报告指出，中国现代化饲料厂检测的饲料原料中有1-2%为ASFV阳性，包括玉米、豆粕、大米、小麦和含可溶性的玉米干酒糟(Dee and Niederwerder,2019)。塞内卡病毒A(SVA)是一种猪病原体，能引起与FMDV类似的临床症状，在美国的猪生产中流行，最近在巴西也被发现通过被塞内卡病毒A污染的饲料原料和饲料传播(Leme et al.,2019)。病毒进入饲料的来源通常是被外来动物疾病污染的粪便，这些粪便可能在谷物干燥或原料运输过程中通过交叉污染进入原料。另外，在我们团队与越南的一个养猪体系的合作中，收集到的40份饲料或原料样本中没有一份含有可检测到的ASFV DNA。值得注意的是，这个生产体系中的所有饲料厂都使用了甲醛基添加剂。这些对比的案例表明，ASFV在饲料原料中的流行和分布有明显的差异，在评估饲料原料污染时必须考虑许多因素。
Several examples of introduction of FOREIGN ANIMAL DISEASE via the feed supply chain exist.Introduction of FMDV into Japan and South Korea have both been linked to feedstuffs(Sugiura et al.,2001;Park et al.,2014).The feeding of silage that was harvested from areas with wild boars infected with CSFV has led to illness in naïve pigs(Ribbens et al.,2004).Just five years ago,porcine epidemic diarrhea virus(PEDV)was rapidly spreading throughout the U.S.swine industry for the first time,causing high mortality in young piglets in 27 states.The root cause investigation for PEDV entry in the USA concluded the most likely cause was 1-ton polyethylene tote bags containing feed or ingredients from China(USDA 2015).Feeding contaminated feed has been categorized as a risk factor for ASFV transmission(EFSA,2014;Belyanin,2013).This report documented feed being associated with 35%of 284 reported outbreaks in Russia.Contaminated feed has been reported that 35%of the 284 ASFV outbreaks in Russia were linked to contaminated commercial feed.More recently,reports indicate that 1 to 2%of tested ingredients from modern Chinese feed mills were ASFV-positive,including corn,soybean meal,rice,wheat,and corn dried distillers grains with solubles(Dee and Niederwerder,2019).Senecavirus A(SVA),a swine pathogen that causes similar clinical signs as FMDV,is endemic in swine production systems in the U.S.and was recently found to be spread via SVA-contaminated ingredients and feed in Brazil(Leme et al.,2019).The source of virus entry into the feedstuff is oftentimes FOREIGN ANIMAL DISEASE-containing feces,which may be introduced into the ingredient through cross-contamination during grain drying or ingredient transportation.Alternatively,in our team’s work with a swine production system in Vietnam,none of the 40 feed or ingredient samples collected contained detectable ASFV DNA.Notably,the feed mills in this production system were all using a formaldehyde-based additive.These contrasting cases illustrate that there are clearly differences in the prevalence and distribution of ASFV in ingredients,and many factors must be considered when evaluating ingredient contamination.
Virus Survival during Transport at Concentrations Capable of Causing Infection<<
Theoretical survival of FMDV(via a Senecavirus A surrogate)and ASFV has been demonstrated by Dee et al.(2018),while CSFV does appear to be as likely to survive transportation.Niederwerder et al.(2019)reported that pigs consuming ASFV-contaminated feed can become infected when consuming a single 100 g meal of feed containing a single dose of ASFV(104 TCID50/g)ASFV.By modelling this data,it is expected exposure of pigs to 30 meals containing a low dose of ASFV(100 TCID50/g)will lead to a significant probability of infection.Feed industry equipment and processes are designed to efficiently mix low inclusion products uniformly throughout a batch of feed,and then deliver feed in a method that provides multiple meals with the same consistency to many pigs housed in the same location.If ASFV or another FOREIGN ANIMAL DISEASE enters the feed supply chain and is mixed into a batch of feed,the results could be catastrophic contamination across multiple herds.For example,Schumacher et al.(2016)reported that if 1 g of feces from an acutely infected pig with porcine epidemic diarrhea virus(PEDV)entered a receiving pit,it could potentially contaminate 500 metric tons of feed,with each gram having a dose capable of causing infectivity.That is the equivalent of twenty 24-ton feed trucks,all carrying infectious material to different facilities.Simultaneously,the entry causes contamination of the feed manufacturing equipment.In 2017,Schumacher et al.reported that entry of PEDV into a feed mill leads to nearly 100%of surfaces being contaminated,including non-contact surfaces such as walls and floors.Finally,Huss et al.(2017)reported that the cleaning and disinfection necessary to sanitize a virus-contaminated feed mill includes complete organic material removal,followed by wet-cleaning with a glutaraldehyde and later bleach sanitizer.The feed industry is not designed for this type of cleaning and disinfection,so the primary focus must be on keeping pathogenic viruses out of feed mills.This includes a focus on both the source of the ingredients,but also their transportation.The incubation period for ASFV is 5 to 21 days and it may be up to 3 weeks after an animal is exposed before signs of the disease occur.During this time,the feed supply chain may be unknowingly transmitting virus.Therefore,strenuous actions are necessary to prevent feed mills from being a source of cross-contamination.
Recommendations for Swine Feed Manufacturers to Minimize the Potential for ASFV and other FOREIGN ANIMAL DISEASE Entry and Transmission via the Feed Supply Chain:
Know your supplier.It is key that facilities can identify the supplier of the ingredients coming into their facility.This process helps maintain transparency across the feed supply chain.In some facilities,procurement is independent from quality control and feed safety.These need to be fully integrated,with a system for checks and balances to ensure that the most economical ingredients are used,but only if they are not a potential risk for disease entry.Knowledge of the ingredients supply chain should extend from the point of ingredient manufacture through transportation to the feed mill,including any intermediaries or blending locations.
Do not use grains or oilseeds(or their resultant meals)from regions with foreign animal disease.Feed mills manufacturing feed for multiple species should follow this for the entire mill,not just exclude it from swine feed.For example,it has been reported that mills manufacturing feed for sow multiplication facilities are also manufacturing organic dairy feed,with imported organic soybean meal from China being used only in dairy feed.Because of the potential for batch-to-batch and environmental contamination,these high-risk ingredients should be excluded from the mill altogether.