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.
Today’s Science Page University of Minnesota researchers Joao Paulo Herrera da Silva, Nakarin Pamornchainavakul, Mariana Kikuti, Xiaomei Yue, Cesar A. Corzo and Kimberly VanderWaal take a look at PEDV in the United States.
Alphacoronavirus porci (Porcine Epidemic Diarrhea Virus – PEDV) causes acute enteric disease in pigs, with severe symptoms in piglets, leading to economic losses. Introduced to the U.S. in 2013, it spread rapidly (1), affecting 31 states. Two strains, indel and the more virulent non-indel, have been identified in the U.S. (2). The current evolutionary status of PEDV in the U.S. remains largely unexplored. This study provides an overview of its evolution over the past decade.
Following the introduction of the virus in the U.S., a high number of cases were reported through the Morrison Swine Health Monitoring Project (MSHMP) network during the first two years (Gray bars in Fig. 1), declining in the third year and stabilizing thereafter, with slight fluctuations, except in 2021, when the incidence of PEDV was higher compared to other years of the endemic period. Sequence surveillance was also more intense during the epidemic phase (Blue line in Fig. 1), decreasing afterward. During the endemic period, approximately one sequence was generated for every 10 infected sow farms in MSHMP (Red line in Fig. 1).
To assess the evolutionary dynamics of PEDV, we analyzed 556 spike protein sequences, focusing exclusively on the non-INDEL strain, which is predominant in the U.S. Although PEDV spike protein sequences exhibit high similarity (average nucleotide identity = 99.7%), a strong pattern of genetic differentiation was detected across time. Most sequences generated after 2017 clustered into two small sub-clades (Red boxes, Fig. 2). Circulation of these clades is restricted to specific geographic regions, suggesting compartmentalized circulation within those regions with limited spread between sow farms in different regions. This insight helps determine the risk of re-introduction of PEDV if it were regionally eliminated. No descendants derived from other clades present during the epidemic period were detected, suggesting that these clades are no longer circulating in the U.S (Fig. 2).
Continued sequence surveillance is vital for the swine industry to advance toward disease eradication and is key to a) confirming the extinction of older clades, b) mapping the distribution of recent clades, and c) understanding PEDV’s evolutionary diversification. Taken together, this information can guide the strategies adopted by practitioners.
References
- Stevenson GW, Hoang H, Schwartz KJ, Burrough ER, Sun D, Madson D, Cooper VL, Pillatzki A, Gauger P, Schmitt BJ. 2013. Emergence of Porcine epidemic diarrhea virus in the United States: clinical signs, lesions, and viral genomic sequences. Journal of veterinary diagnostic investigation 25:649-654.
2. Song D, Park B. 2012. Porcine epidemic diarrhoea virus: a comprehensive review of molecular epidemiology, diagnosis, and vaccines. Virus genes 44:167-175.