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Pathogen Transmission White Paper

Modeling the transboundary survival of foreign animal disease pathogens in contaminated feed ingredients.

 

Introduction: The North American swine industry is under constant threat of foreign animal disease (FAD) entry. Should a pathogen such as Foot and Mouth Disease Virus (FMDV) ever infect our swine populations via accidental or intentional means, it would cripple our export markets and produce significant animal suffering and economic loss.  In recent years, the emergence of 2 strains of PEDV, Porcine Delta-Coronavirus and Seneca Virus A to the US has exposed significant gaps in our ability to biosecure our livestock populations. While the root cause of pathogen entry has not been determined, current and published data suggest that contaminated feed ingredients may have played a role (1,2). To better understand this risk, models simulating the transboundary movement of contaminated ingredients were developed to identify “high risk combinations” of viruses and feed ingredients (2). Once identified, evaluation of the efficacy of several chemical mitigants will ensue.

 

Materials & Methods: Based on the Swine Health Information Center pathogen matrix, FAD “target” viral pathogens were identified as significant risks to the US swine industry. Due to the inability to work with certain target pathogens, we used “surrogate viruses”, which allowed us to study closely related and structurally similar viruses. The designated FAD target pathogen and its (surrogate) were as follows: Foot and Mouth Disease Virus (Seneca Virus A), Classical Swine Fever Virus (Bovine Virus Diarrhea Virus), Pseudorabies Virus (Bovine HerpesVirus-1), Nipah virus (Canine Distemper Virus), Swine Vesicular Disease Virus (Porcine Sapelovirus) and Vesicular Exanthema Virus (Feline Calicivirus). Other selected pathogens (Porcine Reproductive and Respiratory Syndrome Virus 174, Porcine Circovirus, African Swine Fever Virus, Influenza A Virus of Swine H1N1 and Vesicular Stomatitis Virus) were also included in our study. Using a model previously validated to study the risk of contaminated feed ingredients for the transboundary spread of PEDV (1), we selected feed ingredients known to be imported from China (Beijing) to the USA (Des Moines) based on the US Govt Harmonized Tariff Schedule. These included organic & conventional soybean meal, soy oil cake, DDGS, lysine, choline, vitamin D, pork sausage casings, and several pet foods (dry & moist). Samples were incubated in an environmental chamber for 37 days programmed using actual T and % RH data recorded during a journey from China to the US. For the purpose of ASFV evaluation, an Eastern European model (Warsaw, Poland to Des Moines) was developed. At designated intervals post-inoculation, samples were tested by PCR for the presence of viral nucleic acid and viability by virus isolation and swine bioassay (as needed).

 

Results: Preliminary data indicate the survival of the Seneca Virus A, Bovine Herpesvirus-1, Feline Calicivirus and PRRSV 174 during the 37 day study period. Notably, ingredients that frequently supported virus survival include soy products, lysine, choline and Vitamin D. In contrast, the Classical Swine Fever Virus surrogate (Bovine Viral Diarrhea Virus), Vesicular Stomatitis Virus, and the Nipah virus surrogate (Canine Distemper Virus) did not survive the 37-day journey. In addition, a subset of viruses have also been recovered from casings and pet foods. It is important to note that none of the viruses survived the 37-day incubation period in the absence of a feed matrix. Of particular interest are the PRRSV results, as the virus survived in conventional soybean meal and DDGS. Viruses currently under evaluation include African Swine Fever Virus, Porcine Circovirus, Swine Vesicular Disease (Porcine Sapelovirus) and IAV-S H1N1.

 

Discussion: These preliminary results suggest that a subset of contaminated feed ingredients could serve as vehicles for FAD introduction to the US. The PRRSV data provide new insights on the role of area spread. Follow-up studies will evaluate the role of various feed additives to serve as mitigants for the purpose of risk reduction. This project will apply candidate mitigants pre-contamination and post-contamination to select ingredients and evaluate their ability to neutralize virus using the transboundary model.

 

References:

  1. Dee S, et al. Modeling the transboundary risk of feed ingredients contaminated with porcine epidemic diarrhea virus BMC Vet Res, 2016, 12:51.
  2. Dee S, et al. An evaluation of contaminated complete feed as a vehicle for porcine epidemic diarrhea virus infection of naïve pigs following consumption via natural feeding behavior: Proof of concept. BMC Vet Res 2014,10:176.