ABSTRACT
To clarify the genetic diversity of the porcine reproductive and respiratory syndrome virus (PRRSV) in Japan in recent years, we determined the nucleotide sequence of open reading frame 5 of 2482 PRRSV sequences obtained from samples collected from pigs between January 2018 and December 2020. As a result of molecular phylogenetic analysis, Cluster II represented the largest proportion (44.9−50.6%) throughout the study period, followed by Cluster IV (34.0−40.8%), Cluster III (7.8−12.1%), Cluster I (3.1−6.7%), and Cluster V (0.1−0.2%). The relative distributions between Clusters varied between geographic regions and between years: in 2018, Cluster II was the most prevalent in all regions. In 2019, Cluster II was dominant in the Hokkaido and Tohoku regions, while in other regions Cluster IV was dominant. In 2020, Cluster IV was dominant in the Kanto/Tosan and Kyushu/Okinawa regions, whilst in other regions Cluster II was predominant. Compared with a previous study, the proportions of genome sequences classified in Clusters II and IV significantly increased (p = 0.042 and 0.018, respectively) and those classified in Cluster III significantly decreased (p < 0.01). The widespread use of live attenuated vaccines using strains that belong to Cluster II might have accounted for these changes in the relative distribution between Clusters.
ABSTRACT
Using a model developed previously by the authors, a risk assessment was conducted to predict the change in the risk of ASF entering Japan as a result of the coronavirus pandemic in humans. The monthly probability of ASF entering Japan through illegal importation of pig products from China was calculated to be 4.2% (90% prediction interval: 0.0%-24.9%) in January, 0.45% (0%-2.5%) in February, 0.03% (0%-0.2%) in March and 0.0002% (0%-0.001%) in April, 0.00005% (0%-0.0003%) in May and 0.0009% (0%-0.005%) in June 2020 indicating a significant decline in the risk of ASF entry into Japan from China. The decline was attributed to a decrease in the number of air travellers from China and amount of restaurant food waste.
