Science Page: Quarterly review of MSHMP reported PRRSv Restriction Fragment Length Polymorphism (RFLP) patterns

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 from the MSHMP team regarding reported PRRS RFLP patterns.


  •  Recording PRRSv RFLP and sequences will provide better insights into the epidemiology of the disease at local, state and national level.
  • Building a RFLP database will allow us to assess which factors could be involved or related with the emergence of a new RFLP.
  • The predominant pattern RFLP in this quarterly review is the 1-7-4.

In the first quarter of the 2018/2019 incidence year, 20 breaks affecting 12 production systems were reported. Out of these, 4 occurred in July, 13 in August and 3 in September.

Of those 20 farms, three had a break while still being status 1, one was status 2 in the process of eliminating the disease (not using any immunization protocol at that point), 6 were using field virus as the acclimatization protocol (2fvi), 8 were using vaccine (2vx), one was provisionally negative (status 3) and one broke from a status 4 after being almost 4 years completely negative (see figure below).

RFLP patterns with status at break

The distribution of the breaks is wide and affects different states. Thus, we had 6, 1, 4, 1, 4, 2, 1 and 1 break in the states of IA, IN, MN, MO, NC, NE, OK and PA, respectively. The closest 2 farms that broke were 1.2 miles apart, belonged to the same company and had the break a week from each other (no sequences was provided).

Eight out of the 20 breaks reported were accompanied by the associated RFLP. The predominant (4 out of 8) RFLP pattern since July is 1-7-4. Iowa was the state with the highest number of 1-7-4 cases.

Science Page: Remembering Professor Mike Murtaugh

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 remembering Professor Mike Murtaugh with Cheryl Dvorak.

Michael MurtaughProfessor Michael Murtaugh, PhD, passed away Tuesday September 18 from complications of pancreatic cancer. He was 67.

Mike joined the college in 1985 and spent the entirety of his University of Minnesota career in the Department of Veterinary and Biomedical Sciences. He was a consummate faculty member, excelling in teaching graduate courses and conducting research and
outreach. Mike authored more than 225 peer-reviewed journal articles, was the primary advisor for 30 Master’s and PhD students, and held three U.S. patents. His influence extended throughout the Academic Health Center at the University and throughout the world. At the time of his death, Mike was serving on the editorial boards of more than a dozen academic journals, and had successfully completed nearly 160 sponsored projects as Principal Investigator or Co-Investigator.

Mike was a respected and highly sought after mentor. He always had people coming and going from his office asking for scientific, career, and personal advice. His door was always open and he always stopped what he was doing to help others. He touched many
lives during his career. Besides his numerous graduate student advisees, he also mentored over fifteen veterinary students, thirty-six undergraduate and high school students, twelve post-doctoral researchers, twenty visiting scientists, and numerous others who came to him for advice and support. He cared about everyone not only scientifically, but also personally. He always wanted to do what was in a student’s best interests, even though it may not have been what was in his best interest. His lasting legacy is in the scientific training and education of a generation of swine health specialists and researchers.

Prof. Murtaugh was an international leader in swine immunology, and devoted considerable effort over the past 25 years in battling the Porcine
Reproductive and Respiratory Syndrome virus (PRRSv), a disease that
costs U.S. swine producers alone some $500 million annually. Mike used
molecular biological approaches to first understand the nature of PRRSv
and investigated in detail the immunological response of pigs to this pathogen.

Mike earned the B.S. degree in biology at the University of Notre Dame and
then served as a Peace Corps volunteer in Venezuela. He earned a Ph.D. in entomology at the Ohio State University. The University of Texas Medical School in Houston was his next stop— he spent four years in a post-doctoral position in the Departments of Internal Medicine and Pharmacology— before assuming a faculty position in St. Paul.

He will be remembered for his dry sense of humor and positive outlook on life, character traits that he maintained even as his battle with cancer raged. Mike cared passionately about science and derived some of his greatest personal satisfaction working on the college’s Strategic Plan and the International Conference on One Medicine and One Science (iCOMOS). Mike cared deeply about science informing policy and saw the need for scientists to be more actively involved in communicating about their research.

I am grateful to have known him, and stand in awe of the many contributions he made to our college.

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.


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.

Time-series analysis for porcine reproductive and respiratory syndrome in the United States

Today, we are sharing an open-access publication from Dr. Andreia Arruda, Dr. Ana Alba and members of the MSHMP team in the journal PlosOne.

This study was conducted using data collected from the Morrison Swine Health Monitoring Project. The main objective of this study was to use time-series analysis to investigate whether yearly patterns commonly described for PRRS were in fact conserved across different U.S. states.


The 268 breeding herds enrolled in this project were the ones that participated in the MSHMP from July 2009 to October 2016. PPRS status of each farm was reported weekly following the AASV guidelines. The five states examined included Minnesota (MN), Iowa (IA), North Carolina (NC), Nebraska (NE), and Illinois (IL).


81 MN farms, 72 IA, 45 NC, 30 NE, 40 from IL, were enrolled in the study with a mean number of animals per site of 2,666; 3,543; 2,342; 4,041; and 4,018 respectively.

Graphs showing the prevalence (black line) and upper and lower 95% confidence intervals (grey dotted lines) of PRRS virus positive farms for the five different U.S. states participating in this study: A: Minnesota; B: Iowa; C: Nebraska, D: North Carolina and E: Illinois

The main finding of this study was that PRRS seasonality varies according to geographical region, and the commonly referred “PRRS season” is not necessarily the only time of increase in disease incidence.

Another interesting finding from this study was the presence of an alternating trend for all examined states within of the U.S., except for the state of Iowa, the largest pork producing states in the country (approximately 31.4% of the total US hog and pig inventory), which had an increasing linear trend over the examined years.

In conclusion, PRRS seasonal patterns are not homogeneous across the U.S., with some important pork producing states having biannual PRRS peaks instead of the previously reported winter peak. Findings from this study highlight the importance of coordinating alternative control strategies in different regions considering the prevailing epidemiological patterns, and the need to reinforce strict biosecurity practices beyond the typically described “PRRS season”.

You can also listen to Dr. Arruda present some of these research findings at the 2017 Leman conference.


Industry-driven voluntary disease control programs for swine diseases emerged in North America in the early 2000’s, and, since then, those programs have been used for monitoring diseases of economic importance to swine producers. One example of such initiatives is Dr. Morrison’s Swine Health Monitoring Project, a nation-wide monitoring program for swine diseases including the porcine reproductive and respiratory syndrome (PRRS). PRRS has been extensively reported as a seasonal disease in the U.S., with predictable peaks that start in fall and are extended through the winter season. However, formal time series analysis stratified by geographic region has never been conducted for this important disease across the U.S. The main objective of this study was to use approximately seven years of PRRS incidence data in breeding swine herds to conduct time-series analysis in order to describe the temporal patterns of PRRS outbreaks at the farm level for five major swine-producing states across the U.S. including the states of Minnesota, Iowa, North Carolina, Nebraska and Illinois. Data was aggregated retrospectively at the week level for the number of herds containing animals actively shedding PRRS virus. Basic descriptive statistics were conducted followed by autoregressive integrated moving average (ARIMA) modelling, conducted separately for each of the above-mentioned states. Results showed that there was a difference in the nature of PRRS seasonality among states. Of note, when comparing states, the typical seasonal pattern previously described for PRRS could only be detected for farms located in the states of Minnesota, North Carolina and Nebraska. For the other two states, seasonal peaks every six months were detected within a year. In conclusion, we showed that epidemic patterns are not homogeneous across the U.S, with major peaks of disease occurring through the year. These findings highlight the importance of coordinating alternative control strategies in different regions considering the prevailing epidemiological patterns.

NHF: PRRS is also a summer disease

Our latest collaboration with the National Hog Farmer was written by the Morrison Swine Health Monitoring Program team regarding the incidence of PRRS in the summer.

Although our understanding of disease and control methods has improved in recent years, we continue to learn new features of PRRSV epidemiology in part thanks to the Morrison Swine Health Monitoring Project. One of the most recent questions that we have addressed based on enquires from MSHMP participants is whether PRRS incidence during the summer was higher in recent years (i.e. 2016-17) compared to previous years (i.e. 2009-15). We know that PRRSV outbreaks tend to have a seasonal pattern and that they are more frequent during the fall and winter, but we know little about the breaks that happen in the summer and spring.

In order to dig into this question, we analyzed MSHMP data from 2009 to 2017 which included 1,329 outbreaks. Of these, 66% of the breaks occurred during fall and winter and 14% and 20% of the breaks occurred during summer and spring, respectively. Although there were fewer breaks in the spring and summer, the number of breaks in warmer seasons was still significant which represents an on-going frustration to producers because the “PRRSV season” is supposed to be over.

As part of the analysis we learned that between 3% and 6% of the herds break yearly during the summer and spring seasons, respectively. This represents approximately 83 herds out of the 917 reporting in the MSHMP database. If we estimate that the average sow farm has 3,000 sows, then almost a quarter of a million sows break yearly during these two seasons.

Remember, although the risk of PRRSV introduction is lower during the spring and summer, PRRSV breaks still happen, so biosecurity efforts should not be decreased. PRRSV is a sneaky virus so keep your biosecurity up, even in the summer.

All of our collaborations with the National Hog Farmer can be found here.