PRRSv RFLP pattern changes in the USA

Key Points

  • MSHMP continues monitoring PRRSv RFLP patterns associated with outbreaks in participant systems.
  • The proportion of reported 1-7-4 outbreaks decreased significantly from July 2018 compared to that from January 2017 to June 2018.
  • The proportions of reported 1-8-4, 1-4-4, 1-3-4, 1-10-2, and 1-1-2 outbreaks have not changed significantly in recent years.
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Detection of PRRSV RFLP type 1-7-4 over time

This week, Dr. Mariana Kikuti from the MSHMP team shares information about the PRRS RFLP type 1-7-4 prevalence in the MSHMP data.

Key Points

  • PRRSV RFLP type 1-7-4 was first identified in our MSHMP dataset in 2003.
  • An increasing trend up to 2014 has been observed and is now on a decreasing trend.
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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.