Science Page: Why are we not making more progress to decrease PRRS incidence?

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 report by Dr. Clayton Johnson from Carthage Veterinary Services on PRRSV incidence and why it has not been decreasing as expected at the past few years.

Key points

  • Enhancing biosecurity increases the chances to prevent PRRS.
  • We have learnt to deal better with the disease and that is reflected by the reduction of the economic impact of PRRS
  • Choose the level of biosecurity that economically better fits to your risk.

In his report, Dr. Johnson identifies 3 main causes that PRRSV incidence is not decreasing.

  1. We can’t Prevent PRRS Infections
  2. PRRS Cost is Decreasing: Tools and Technologies for PRRS Infection Management are Improving
  3. PRRS Prevention Strategies aren’t Cost Effective

To learn more you can read the full report or take a look at Dr. Johnson’s presentation on this very same topic during the 2017 Leman conference:

Identification of antigenically important sites in Rotavirus B

Happy New Year to all of you readers of this blog! We appreciate your presence here. In 2018, we will bring you even more quality content related to swine health and production.

Our first publication of the year features the work of Frances Shepherd, a PhD student (who recently received an award at the CRWAD meeting) with Drs. Michael Murtaugh and Douglas Marthaler. The paper is in open access in the journal Pathogens and you can read it here.

Shepherd antigenically important sites in rotaviruses B

In this experiment, 174 clinical samples from US and Canadian swine herds and positive for rotavirus B by PCR were used to sequence the gene for the protein VP7.
VP7 is a protein of interest in rotaviruses B because it is structural and can be found on the outer layer of the virus capsid. Along with VP4, they stimulate the creation of neutralizing antibodies in pigs.

Based on those sequences, 169 of the viruses were allocated to 8 defined genotypes: G8, G11, G12, G14, G16, G17, G18, and G20. However, five strains had less than 80% similarity with those genotypes and were assigned to the new genotypes G22, G23 (2 strains), G24, and G25. The G16 genotype was the most prevalent genotype each year. The predominant genotypes clustered geographically, with G12 being predominant on the east coast, G16 in the Midwest, and G20 within the Great Plains states.

Rotaviruses B geographical distribution US
Distribution of Rotavirus B genotypes per state

Investigation of the variability within the VP7 proteins identified 8 variable regions. However, those regions did not align with the sites of high antigenicity detected in the predominant groups. Indeed, surface-exposed antigenic residues underwent negative selection more often than positive selection.


Rotavirus B (RVB) is an important swine pathogen, but control and prevention strategies are limited without an available vaccine. To develop a subunit RVB vaccine with maximal effect, we characterized the amino acid sequence variability and predicted antigenicity of RVB viral protein 7 (VP7), a major neutralizing antibody target, from clinically infected pigs in the United States and Canada. We identified genotype-specific antigenic sites that may be antibody neutralization targets. While some antigenic sites had high amino acid functional group diversity, nine antigenic sites were completely conserved. Analysis of nucleotide substitution rates at amino acid sites (dN/dS) suggested that negative selection appeared to be playing a larger role in the evolution of the identified antigenic sites when compared to positive selection, and was identified in six of the nine conserved antigenic sites. These results identified important characteristics of RVB VP7 variability and evolution and suggest antigenic residues on RVB VP7 that are negatively selected and highly conserved may be good candidate regions to include in a subunit vaccine design due to their tendency to remain stable.

Best of Leman 2017 series #3: J. Lowe – Understanding cull sow movements in North America

We launched a new series on the blog in October. Once a month, we are sharing with you a presentation given at the 2017 Allen D. Leman swine conference, on topics that the swine group found interesting, innovative or that lead to great discussions.

Our third presented is from Dr. Jim Lowe from the University of Illinois on the movements of cull sows in North America and what it implies in terms of disease transmission.

To listen to this talk, please click on the picture below.


Happy holidays to you and your loved ones!

Two UMN graduate students awarded at CRWAD

The first week-end of December was the Conference of Research Workers in Animal Diseases in Chicago. Several of the swine group graduate students were presenting their work and received an award.

NC1202 Student Award 3First, Frances Shepherd received the award for best oral presentation in the Enteric Diseases category for her presentation titled Variability and bioinformatic analysis of porcine rotavirus B and C illustrate potentially important immunological sites. Frances’ advisers are Dr. Douglas Marthaler and Dr. Michael Murtaugh.

AVEMP Student AwardsThen, Dr. Robert Valeris received the best poster award in the Veterinary Epidemiology and Preventative Medicine category for presenting Survival analysis of protocols for eradication of Mycoplasma hyopneumoniae in swine farms.

Join us in congratulating our students for their awards!


NHF: Processing fluids are effective for PRRSV diagnostics

This month in the National Hog Farmer, Drs. Carles Vilalta, Juan Sanhueza, and Montse Torremorell share a project instigated by the late Dr. Bob Morrison regarding the use of processing fluids to make a PRRSV diagnosis.

The improvement of sampling and diagnostics techniques has made sampling on the farm an easier task with the use of pooled serums or oral fluids samples for example.

One of the ways to get cheaper, more sensitive and quicker techniques would be to use routine chores, such as piglet processing, since castration and tail docking are part of the regular procedures in sow farms.

The goal of this study was to evaluate the accuracy of the processing fluids (the liquid accumulated at the bottom of the pail when farmers collect tails and testicles during routine procedures) by real-time polymerase chain reaction to assess PRRSV status in a sow herd.

The key points from the studies were:


Science page: Investigating PRRS summer outbreaks in the US

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 an investigation into PRRS summer outbreaks by Dr. Juan Sanhueza and the MSHMP team.

Key Points

  • Each year approximately 3% of the sow farms have a PRRS outbreak during the summer.
  • The incidence of summer PRRS breaks has been constant over the last 9 years.
  • There are geographical areas with higher or lower risk of summer breaks.
prevalence of summer PRRS outbreaks per year
Figure 1. PRRS summer outbreak incidence per year between 2009 and 2017.

A summer outbreak was defined as a PRRS case that happened between June 21st and September 21st of the year. The mean incidence of PRRS summer outbreaks was 3.2% between 2009 and 2017, ranging between 1.6% and 4.4%. The trend was stable among the years. (Figure 1) Not all areas are equal against summer outbreaks. Indeed, the region of Southern Minnesota – Northern Iowa is more at risk of outbreaks than others like Southern Iowa or Eastern North Carolina. (Figure 2)

areas with higer lower PRRS risk in the summer
Figure 2. Geographical areas with higher (red) and lower (blue) PRRSV incidence risk

Biosecurity measures against PRRSV should therefore be a concern all year round for swine producers!


Science Page: PRRS eradication efforts in Chile: Current situation and future prospects

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 report on PRRSV eradication efforts in Chile.

Key Points

  • After being introduced in 1999, PRRS was eradicated from the country in 2012.
  • In 2013 PRRS was again detected, sequence analysis suggested this was a new introduction to the country.
  • The Chilean swine industry and the Chilean Veterinary Services (SAG) expect to again eliminate the disease in the near future.

PRRS is a notifiable disease in Chile. It was first detected in 1999, and in 2000 both the swine industry and government joined efforts to eradicate the disease by a series of coordinated events including a mixture of herd closure and depopulation of infected premises. Vaccination was not allowed in the country to control PRRSV infection. The eradication program was completed in 2007 and as a result, Chile was declared PRRSV free in 2012. Nevertheless, on October 2013 clinical signs compatible with PRRSV were reported in a commercial sow farm. Since then, all commercial herds performed surveillance activities according to a risk score based on location and biosecurity measures. From October 2013 to October 2017, approximately 153,000 blood samples have been analyzed.

Chile eradication of PRRSVViral sequences obtained during the 2013 outbreak were compared to sequences from the early 2000s outbreak in Chile. Results showed a large genetic difference between isolates from both outbreaks. Further analyses demonstrated that the Chilean virus was closely related to a virus circulating in the state of Indiana in the US at the time of introduction. These results suggested that the latest PRRSV outbreak in Chile was most likely due to a new introduction into the country rather than a reemergence of a strain previously detected in Chile.

By October 2017, the disease was restricted to approximately 45,000 animals in six commercial farms owned by two companies that currently have eradication programs in place. These six infected commercial sites are clustered in three areas. (See figure above)