Science Page: An Overview of Porcine Astrovirus

This is our Friday rubric: every week a new Science Page from the Bob Morrison’s Swine Health Monitoring Project. The previous editions of the science page are available on our website.

This week, we are sharing a disease sheet on porcine astrovirus by Drs. Arruda and Schwartz.

Key points:

  • Further research is needed in all areas of the virus in order to better understand, treat, and prevent Astrovirus.
  • Astrovirus is a public health concern in humans as it is implicated in foodborne illnesses and has zoonotic potential.
  • Porcine Astrovirus may play a role in enteric disease, and has been associated with neurological disease.

Porcine Astrovirus (PoAstV)  is a nonenveloped RNA virus with 5 different strains present in U.S herds. It has been detected in both healthy and diseased pigs, so more research is needed to determine the clinical implications of a PoAstV infection. Recently a U.S swine production system reported PoAstV-associated neurological disease. In the sow farm 100% of pigs affected with disease died, while in the growing-finishing farms case-mortality rate was 75%. Signs exhibited by affected animals included paralysis, ataxia, paresis, and knuckling, which eventually progressed into lateral recumbency.

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Scientific publications relating to Porcine Astrovirus are rare. The majority of information, however, supports fecal-oral as the main route of transmission. Some reports have shown PoAstV to retain infectivity in ground water for extended periods of time and can survive up to 3 hours in water with a p.H of 4.0. There is currently no vaccine available for this disease. The large antigenic diversity and high mutation rate are the biggest challenge for vaccine development. Diagnosis is typically made via PCR.

The major concern with Astrovirus is the zoonotic potential. Human Astrovirus is easily transmitted through contaminated food and water and causes moderate gastroenteritis in infants. Human-to-pig transmission is suspected due to the detection of human-porcine recombinant viruses. Pig-to-human zoonosis has not been reported, but Astroviruses can rapidly mutate, so it may be only a matter of time before a zoonotic strain emerges.

Further research into pathogenesis and vaccine development is crucial to prepare for a possible zoonotic outbreak. 

— Blog post written by Joseph Thurston.

Pioneering Structural Study of Porcine Coronavirus

Today, we are highlighting the research of a completely different team at the University of Minnesota. The Minnesota Supercomputing Institute provides advanced research computing infrastructure and expertise to advance and accelerate research and foster innovation and discoveries.

MSI PIs Wei Zhang (research associate professor, Diagnostic and Biological Sciences) and Fang Li (associate professor, Veterinary and Biomedical Sciences) have published a new paper that describes some of their continuing research into the structure of coronaviruses. These are a large group of viruses that includes such deadly diseases as SARS and MERS. Coronaviruses have four forms, known as α-, β-, γ-, and δ-coronavirus, which affect different hosts. For example, β-coronaviruses affect only mammals, while the δ form affects both birds and mammals.

The coronavirus structure includes a feature called a “spike protein,” which allows the virus to attach to the host’s cells. The spike proteins of α- and β-coronavirus have been well studied. The spike protein of the δ-coronavirus, however, is described for the first time in this paper. The researchers used cryo-electron microscopy, a fast-developing technology in which protein molecules are studied under ultra-cold temperatures with an electron microscope. This technology was used to determine the structure of the spike protein of porcine δ-coronavirus (PdCoV), a lethal virus infecting pigs, elucidating how PdCoV infects pigs cells and evades the host immune system. This is the first atomic-resolution cryo-electron microscopic study from the state of Minnesota, and is a milestone in the structural biology field at the University of Minnesota.

Zhang Li spike protein porcine deltacoronavirus

Image Description: Overall structure of PdCoV S-e in the prefusion conformation. (A) Schematic drawing of PdCoV S-e (spike ectodomain). S1, receptor-binding subunit. S2, membrane fusion subunit. GCN4-His6, GCN4 trimerization tag followed by His6 tag. S1-NTD, N-terminal domain of S1. S1-CTD, C-terminal domain of S1. CH-N and CH-C, central helices N and C. FP, fusion peptide. HR-N and HR-C, heptad repeats N and C. Residues in shaded regions (N terminus, GCN4 tag, and His6 tag) were not traced in the structure. (B) Cryo-EM maps of PdCoV S-e with atomic model fitted in. The maps have a contour of 6.6 σ. (C) Cryo-EM structure of prefusion PdCoV S-e. Each of the monomeric subunits is colored differently. (D) Structure of a monomeric subunit in the prefusion conformation. The structural elements are colored in the same way as those in panel A. Image and description, J Shang et al., J Virol. 92:e01556-17 (2018). © American Society for Microbiology.

The paper was published in late 2017 on the website of the Journal of Virology: J Shang, Y Zhang, Y Yang, Q Geng,W Tai, L Du, Y Zhou, W ZhangF Li. 2018. Cryo-Electronic Microscopy Structure of Porcine Deltacoronavirus Spike Protein in the Prefusion StateJournal of Virology 92 (4): e01556-17. doi: 10.1128/JVI.01556-17.

This report comes from the MSI research highlights.

 

Science Page: Actinobacillus pleuropneumoniae: a case of suspected lateral transmission (Part 2: outbreak investigation)

This is our Friday rubric: every week a new Science Page from the Bob Morrison’s Swine Health Monitoring Project. The previous editions of the science page are available on our website.

This week, we are sharing the second part of a report regarding an Actinobacillus pleuropneumoniae outbreak in the Midwest, across 3 systems and 5 farms.

If you missed part 1, you can find it here.

Key Points:

  • Communication between veterinarians and farm managers can help unravel patterns that might seem unique in one system.
  • Even though the source of APP was not determined outbreak investigation can help to find common links between sources.

A series of Actinobacillus pleuropneumoniae (APP) outbreaks involving five farms belonging to three different production companies were reported. Serotype 8 was confirmed as the source of the clinical signs in all the cases. The outbreak started with the two southernmost located farms (Company A Farm 1 and Company B Farm), followed by Company C (Farm 1) four weeks later. The distance among these growing pig sites ranged from 0.6 to 8.3 miles and the region where they are located can be considered as a high hog density area (Picture 1).

APP farm locations
Map of the farms involved in the APP outbreak

Common links between several sites were revealed after conversations among veterinarians and production managers. The main transmission route for this bacterium is introducing APP carrier pigs. In this case, it can be easily ruled out as these are sites that flow independently.

Other possibilities include indirect transmission through fomites and aerosol. Although these production companies do not share employees or tools they do have a common link in that some did share the same rendering company which could have been servicing other sites that were APP positive. As for manure removal, companies do not use the same manure removal company. One company did have the same individual doing the manure removal procedure at one site while breaking and then proceeded to the next one. Airborne transmission has been suggested as another possibility and after preliminary wind direction analyses during the outbreak dates it was inconclusive.

Swine Influenza virus A: podcast 3/3

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Podcasts are perfect for summer! We are presenting you with a new series on swine influenza from “At The Meeting… Honoring Dr. Bob Morrison in collaboration with SwineCast.

Previous episodes can be found here:
Episode 1
Episode 2

In this final episode,  Dr. Montserrat Torremorell (University of Minnesota), Dr. Amy Vincent (USDA Agricultural Research Service), Dr. Christa Goodell (Boehringer Ingelheim), Dr. Gordon Spronk (Pipestone Veterinary Services), and Dr. Tom Wetzell (Boehringer Ingelheim) discuss the control of IAV-S, the research & development of vaccines for IAV-S, and the products that are being developed from the research.

Click to listen to the entire recording (19 min).

NHF: Developing targeted disease surveillance and control plans

Our monthly collaboration with the National Hog Farmer continues; this month Dr. Kim VanderWaal shares her research regarding swine disease surveillance.

The multi-site pig production structure of the U.S. swine industry requires frequent movement of swine, making swine populations vulnerable to disease spread. This scenario becomes even more relevant in highly dense regions that concentrate thousands of pigs.

Super spreader
Farm icon created by Ferran Brown for the Noun Project

By targeting sites that play an important “connectivity” role such as gilt producing sites, prevention and control strategies for disease containment can be developed together with targeted surveillance for early detection of disease.

Swine movement data in three large production systems in the United States were analyzed to measure how a specific farm could influence a potential disease spread. Several network metrics were measured including:

  • the number of other farms to which a specific farm sent or received pigs,
  • the Mean Infection Potential (MIP), which measures potential incoming and outgoing infection chains.

For example, if a nursery farm received pigs from several sow farms and then sent pigs to multiple finisher farms, that farm would likely have a high MIP and could be called a “super-spreader” :  a farm that could contribute to a high number of infections.

The study found that by directing disease interventions toward farms based on their MIP, the potential for infectious disease transmission in the production system can be substantially reduced. Interestingly, production type (sow, nursery, finishing, farrow-finish and wean-to-finish) did not seem to be a key determinant of the MIP.

When we really break it down, it’s all about incoming and outgoing contacts and the impact on risk. For more information about analysis of movement data, identifying super-spreaders farms and implications for disease control for farms in your system, contact Kim VanderWaal.

Science Page: Actinobacillus pleuropneumoniae: a case of suspected lateral transmission (Part 1: diagnostics)

This is our Friday rubric: every week a new Science Page from the Bob Morrison’s Swine Health Monitoring Project. The previous editions of the science page are available on our website.

This week, we are sharing the first part of a report regarding an Actinobacillus pleuropneumoniae outbreak in the Midwest, across 3 systems and 5 farms.

Key points:

  • Actinobacillus pleuropneumoniae can significantly contribute to increase the costs of the growing period by increasing mortality and antimicrobial treatments.
  • All-in all-out of the affected sites accompanied with standard cleaning and disinfection procedures may suffice to ensure elimination of the bacteria.

A series of outbreaks with a sudden increase in mortality in growing pig herds located in Northwest Iowa were reported beginning in late October and early November.

Five wean-to-finish farms belonging to three different production companies were affected by a sudden onset (within 12-36 hours) of lethargy, respiratory distress and septicemia across hundreds of pigs. Clinical signs quickly spread through the sites and mortality rapidly increased with pigs having foamy bloody nasal discharge. Post-mortem examination revealed acute pleuritis and severe necrotizing bronchopneumonia. In all cases, Actinobacillus pleuropneumoniae (APP) was cultured from multiple sections of fresh lung. The APP isolate from each case was submitted to the University of Montreal for serotyping and it was confirmed to be serotype 8.

Each veterinarian intervened by rapidly mass injecting the growing herd with antibiotics suggested from the antibiotic susceptibility test together with either in-feed or water medication. Mortality rates for each site are shown on the figure below.

AAP associated mortality rates

The estimated cost of APP for each of these outbreaks was $30-$35/pig, considering treatment costs and a $2/pig cost for each 1% mortality.

Each site was completely emptied of pigs, washed and disinfected following a standard procedure. Sites were reloaded with new groups of pigs that have remained free of clinical signs associated with APP.

Swine Influenza virus A: podcast 2/3

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Podcasts are perfect for summer! We are presenting you with a new series on swine influenza from “At The Meeting… Honoring Dr. Bob Morrison in collaboration with SwineCast.

If you missed it, click here to listen to the first episode from last week.

In this second episode,  Dr. Montserrat Torremorell, Dr. Adam Schelkopf (Pipestone Veterinary Services), Dr. Gordon Spronk (Pipestone Veterinary Services), and Dr. Tom Wetzell (Boehringer Ingelheim) continue the conversation on the challenges of IAV-S in day to day operation, the approaches to identifying infected pigs, and the processes that need to be put in place to reduce infection and increase survivability of pigs.

Click to listen to the entire recording (20min).