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.
Lineage 1 PRRSv, the most prevalent PRRSV lineage in the U.S, can be sub-divided into eight sub-lineages
We documented the cyclic emergence and turnover of different lineages and sub-lineages (about every 3 years) based on both sequence count data and estimated past viral population sizes inferred from genetic diversity through time.
The eight sub-lineages differed in key GP5 amino acid sites that are thought to be involved in the immune response to the virus.
This week, we are sharing a report by Harmon et al. from Iowa State University regarding PCR clamping. This project was funded by AAVLD Thermo Fisher Innovation Grant in Veterinary Diagnostic Medicine and ISU-VDL.
Conventional ORF5 sequencing may not differentiate between wild-type or vaccine-like.
Blocking the amplification of vaccine-like sequences it is possible to increase the likelihood of wild-type amplification.
Clamping allows the amplification of the wild-type with mixtures containing as little as 10% of a mixture with the vaccine-like.
Occurrence of PRRS lineages is not equal in different years, systems or production types
Occurrence of specific PRRS lineages is associated with movement of animals
Continuous surveillance for PRRS occurrence is important in understanding its determinants and might be able to provide insights that can
help on its prevention
By utilizing a dataset of 1901 PRRS sequences provided by the Morrison Swine Health Monitoring Project (MSHMP) participants over 3 recent years, the spatiotemporal patterns in the occurrence of different lineages of PRRSV was described and the extent to which the network of pig movement between farms determines the occurrence of PRRS from similar lineages was investigated.
PRRS lineages occurred at different frequencies across geographically overlapping production systems. Preliminary analysis showed that the relative frequency in which specific lineages occur increase while others are decrease over time. The rate at which these changes occur appears to be system-specific. Some lineages were also more common in farms of specific production types (i.e. sow farm or nurseries). As expected, farms that were connected via pig movements were more likely to share the same lineages than expected by chance across all years.
These findings suggest that system-specific characteristics partially drive PRRS occurrence over time and across farms of different production types. Our results also
indicate that animal movement between farms is a driver of PRRS occurrence, strengthening this hypothesis of viral transmission.
Additional research is needed to quantify risks and develop mitigation measures related to animal movement.