Figuring out feed biosecurity is a priority and data from Swine Health Information Center (SHIC)-sponsored research continues to arrive. While feed has been demonstrated as a potential vector for bacteria and viruses, there is no approved method for its evaluation. Validating feed testing methodology is a focus for SHIC. Recently completed work by Dr. Cassandra Jones from Kansas State University validates standardized dust swabbing techniques as means of detection for Seneca Virus A (SVA) at feed mills albeit with less precision than directly analyzing feed samples. Of particular interest, she also simultaneously determined the prevalence and distribution of SVA in United States swine feed mills, as an indicator of risk of domestic and foreign animal disease transmission through feed. The good news: prevalence for SVA is low in US feed mills. But, where SVA was found on feed mill worker shoes, a farm that mill fed went positive for SVA after detection.
Why is feed mill detection important for SVA in particular? Not only is SVA considered a surrogate for Foot and Mouth Disease (FMD); from October 2014 to March 2016, the Brazilian swine industry experienced idiopathic vesicular disease and epidemic transient neonatal losses, two emerging disease syndromes associated with SVA, in up to 80% of their industry. Transmission was positively associated with pelleted feed (Defra, 2016). Recent research sponsored by SHIC shows that feed-based transmission routes may be a risk for both domestic and foreign animal disease entry into the U.S. swine herd (SHIC, 2017). As an example, SVA can survive for up to 37 days in animal feed ingredients (SHIC, 2017). Once present, viruses in feed, feed ingredients, and feed mills are difficult to mitigate. Also, research shows that when Porcine Epidemic Diarrhea Virus (PEDV) enters a feed mill, infectious viral particles spread rapidly to all surfaces, making decontamination tough and heightening the risk for feed transmission (Gebhardt et al., 2017; Huss et al., 2017).
Dr. Jones’ research demonstrated that feed sample type impacted the quantity of detectable SVA. Results are reported as the quantity of detectable SVA as determined by threshold cycle (Ct) in qRT-PCR. When the Ct is higher, we are less likely to detect virus. Feed samples were approximately 8 Ct higher than the inoculum, and swab samples were approximately 4 Ct higher than feed. The research showed that an environmental swab can be used to detect SVA but with 4 Ct less precision than analyzing feed samples direct. A freeze/thaw cycle did not impact detectable SVA compared to samples that were analyzed immediately. In summary, swab samples did work for SVA, but feed samples were better.
Five of 375 samples analyzed positive for SVA, with Ct ranging from 37.4 to 39.9. One positive sample was collected in late fall. The other four positive samples were collected in winter. No positive samples were identified in summer. Where were they found? Two samples were from load-out augers, one from fat intake inlet, one from floor dust, and of note, one was from worker shoes.
SVA was not widespread throughout the swine feed mills analyzed in this experiment, but its presence in a mill may be indicative of disease risk or entry into pig populations, particularly through worker shoes. A sow farm being fed by the mill with SVA on worker shoes was subsequently diagnosed with SVA after the sample was collected.
Swine Health Information Center (SHIC) and the other swine industry organizations intentionally look for gaps in domestic swine disease surveillance and testing as part of ongoing preparedness efforts. With the occurrence of African swine fever (ASF) in China, domestic surveillance for this disease is critical yet currently lacking. The organizations’ review showed classical swine fever (CSF) surveillance tissue testing needs to be expanded to include tissues veterinarians are likely to submit during disease investigations. And the US industry doesn’t have a USDA-validated pseudorabies virus (PRV) nucleic acid detection (PCR) should this disease reappear in our domestic swine herds. If any of these diseases are suspected in the US, veterinary diagnostic labs (VDLs) need to be prepared with the tools to quickly and accurately diagnose these potentially devasting foreign animal diseases. With three widely supported US Animal Health Association (USAHA) resolutions, strong pork-industry requests were sent to USDA to help fill these gaps and, ultimately, protect the health of the US swine herd.
SHIC, National Pork Board, National Pork Producers Council, and American Association of Swine Veterinarians jointly authored and offered three important resolutions individually addressing ASF, CSF, and PRV during the USAHA annual meeting last week. The pork industry resolutions requests ASF surveillance right away, asks USDA to expand and harmonize accepted tissues to test for CSF and ASF because it is possible they could be clinically similar or be confused with current diseases, and asks for a PRV PCR test to be validated by USDA for use in in the National Animal Health Laboratory Network (NAHLN) labs. The resolutions passed review of six USAHA committees and were approved by the entire body without dissent. They were also supported by 26 state pork producer associations: Arizona, Colorado, Florida, Hawaii, Illinois, Indiana, Iowa, Kansas, Kentucky, Michigan, Minnesota, Missouri, Mississippi, Montana, Nebraska, New York, North Carolina, North Dakota, Oklahoma, Ohio, Pennsylvania, South Dakota, Texas, and Wisconsin.
USAHA resolutions will next be given to USDA for their response. Typically, USAHA receives a USDA response on resolutions by spring of the following year. All of the USAHA resolutions for 2018 can be found here – Resolution 4 is on ASF, Resolution 5 on CSF, and Resolution 6 on PRV.
USDA has no formal ASF surveillance program active in the US and had allowed an official ASF PCR test to be done only on whole blood submitted to the NAHLN veterinary diagnostic labs. The Iowa State University (ISU) VDL reports that fewer than 200 whole blood samples have been submitted from approximately 50,000 diagnostic case investigations into clinically ill swine that involved the submission of a case history and tissues for histopathological evaluation by a diagnostic pathologist over the past five years. In response to a request from the pork industry, on October 1 USDA also approved testing tonsillar tissue for ASF. The USDA “Foreign Animal Disease (FAD) Investigation Manual” (FAD PReP Manual 4- 0) (2017) lists whole blood, tonsil, spleen, and lymph nodes as specimens for collection during ASF investigations. USAHA Resolution 4 requests USDA to immediately begin an ASF surveillance program and approve these additional tissues for official ASF PCR testing.
In the absence of an effective surveillance program that includes official CSF testing of tissues routinely submitted to the NAHLN laboratories for diagnostic case investigations, low virulence CSF strains may become widespread before detected. The ISU VDL reports that, outside of the USDA CSF surveillance testing, over the past five years only 383 diagnostic tests were performed on porcine tonsils submitted with the approximately 50,000 diagnostic case investigations into clinically ill swine that involved the submission of a case history and tissues for histopathological evaluation by a diagnostic pathologist. The USDA “Foreign Animal Disease (FAD) Investigation Manual” (FAD PReP Manual 4- 0) (2017) lists tonsil, spleen, and lymph nodes as specimens for collection during CSF investigations. USAHA Resolution 5 requests USDA approve tonsil, spleen, and lymph nodes as additional tissues for official CSF testing in the NAHLN labs, matching the tissues requested for official ASF testing.
US PRV surveillance now relies solely on antibody detection. If the virus again infects our commercial pig herds, capable, rapid response will necessitate the use of PCR for detection of the virus in tissue samples sent to the VDLs. There is currently no USDA-validated PCR for NAHLN VDLs to use to detect PRV in submitted tissue samples. Resolution 6 urges USDA to actively pursue validating a PRV PCR assay for NAHLN lab detection of PRV in swine oral fluids, and other appropriate samples. Currently SHIC, NPB and USDA are funding research to validate PCR testing of oral fluids for foot and mouth disease virus, classical swine fever virus, and African swine fever virus.
In October 2018, greater than 6,000 porcine reproductive and respiratory (PRRS) PCR cases were reported for the first time in a single month according to the Swine Health Information Center Domestic Disease Monitoring Report. This volume perhaps indicates the beginning of the PRRS season for the 2018-2019 winter. Level of detection of porcine epidemic diarrhea virus (PEDV) by PCR continues to meet the expected value, indicating the increased detection level is within the expected for the beginning of the winter season. Porcine deltacoronavirus PCR testing still has positivity above expected for the year of 2018. There was one case of E. rhusiopathiae in the 2018 fall season, and similar detection number for porcine corona virus 2, and PSV for 2018 and 2017 fall seasons. There were two cases of pestivirus (Shaker Pig Syndrome) for fall season of 2018, which is above the same season of 2016 and 2017. Association of influenza A virus and S. suis (IAV S. suis) in respiratory tissues was more frequent in fall season of 2018 than previous years. L. intracellularis (L.intra) and Salmonellas (Salm) had increased frequency of detection in fall seasons over the recent years. From the last report information, coccidia (COCC) continues to be a frequently detected agent. All COCC cases were diagnosed as enteritis.
The most significant event this month per the Swine Health Information Center Global Disease Monitoring Report was the identification of African swine fever positive farms in southern China. The report of infected farms in Yunnan Province suggests a substantial spread of the disease within China, and an increased risk for neighboring countries, particularly Vietnam, Myanmar, and Laos, which share a porous border with this province. In Colombia, outbreaks of foot-and-mouth disease were reported after being declared free with vaccination in 2017. Initially it was observed in cattle, however later on, other outbreaks were reported in the northern area of the country in cattle, swine farms, and backyard pigs. The region has good vaccination coverage for cattle, however not for pigs, making the mitigation process challenging. Also in early October, Brazil reported an outbreak of classical swine fever outside the Free-Zone, in the state of Ceará (northeastern area of the country), identified through passive surveillance. Later on, an active surveillance plan identified other outbreaks in the surrounding districts. The current epidemiological investigation is focused in eliminating infection from the region, aiming to control the spread of the disease.