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.
In today’s Science Page the MSHMP team gives us an update on the 1H.18 PRRSV variant they’ve been monitoring.
1H.18 variant:
In May 2024, we raised attention to a new PRRSV variant being monitored, the 1H.18. This variant is typically associated with RFLP patterns 1-12-2 and 1-8-4, and can be classified as either sub-lineage 1H or 1C. Since our first communication, four additional sequences were detected. We currently have 65 1H.18 sequences identified, originating from 50 sites from nine production systems. At this moment, we have identified the 1H.18 variant in at least 5 breeding sites,12 grow-finishing sites, 16 sites classified as other (e.g. farrow to finish, show pigs) and 17 with missing information on site type. All these originated from Iowa, Minnesota, and Illinois, although no information on location was available for 17 cases. Altogether, the low number of new cases and no clear rapid geographic expansion suggest low transmissibility of this variant at this time (1).
sites based on the quarter in which the sequence was first detected in each farm.
1C.2 variant:
In 2023, we also investigated the occurrence of the 1C.2 variant (2). This variant is typically associated with RFLP pattern 1-2-4 but also included 1-2-3, 1-2-2, and others. Currently, we have identified 519 1C.2 sequences that originated from 311 sites (Figure 1). These represent 130 breeding sites and 145 grow-finishing sites, with the remaining classified as other or unknown. This variant has been identified in 21 production systems, with majority of cases originating from IA, CO, IL, and OK. The 1C.2 affected breeding sites took on average 87 weeks to reach stability when we investigated it in 2023. However, many sites had also detected the co-circulation of other PRRS viruses. Amongst the outbreaks in sites in which only the 1C.2 variant was detected during the unstable period, the median time to stability was 57 weeks, while in sites with other PRRS viruses detected, the median time to stability was 91 weeks. We also compared the average nursery mortality during the four weeks after detecting this variant to mortalities described in the 1C.5 and other PRRS viruses from a previous case-control study (3). The average nursery and finisher mortality during the four weeks after detection of 1C.2 was higher and statistically different from the controls, but no statistical differences were found to 1C.5 mortality rates.
1C.5 variant:
Lastly, we continue to monitor the occurrence of the 1C.5 variant, formerly referred to as L1C 1-4-4 variant. While the two previously mentioned variants have a much lower occurrence, the 1C.5 variant has become highly prevalent with over 3,000 sequences identified since its emergence in late 2020 from 32 production systems. It continues to occur mostly in grow-finishing sites; however, it has been identified in over 160 breeding sites. MN and IA remain the most affected states, followed by NE and SD.
MSHMP will continue to prospectively monitor these and other variants of interest, and additional reports will be issued as the situation unfolds. Do not hesitate to contact MSHMP in case you have questions.
References
1.Kikuti et al. (2024). Monitoring the detection of PRRSV variant 1H.18. Morrison Swine Health Monitoring Program. https://mshmp.umn.edu/sites/mnshmp.umn.edu/files/2024-05/SHMP%202023l24.43%20%5BMonitoring%20PRRS%20Variant%5D2.pdf
2. Kikuti et al. Monitoring of porcine reproductive and respiratory syndrome virus variant emergence. 2023 NAPRRS/NC229: International Conference of Swine Viral Diseases. Chicago, IL. 2023.
3. Kikuti et al. Emergence of a New Lineage 1C Variant of Porcine Reproductive and Respiratory Syndrome Virus 2 in the United States. Front Vet Sci. 2021 Oct 18;8:752938. doi: 10.3389/fvets.2021.752938.