1 INTRODUCTION
Congenital tremor (CT) in neonatal piglets, also known as “dancing
piglet”, was described for the first time in 1922 (Kinsley, 1922). At
present, CT is divided into types A and B. Type A is associated with
visible histological lesions in the central nervous system (CNS) while
type B does not show any apparent lesions. Type A is further divided
into types A-I to A-V based on the causative agent, e.g., classical
swine fever virus infection (A-I), genetic defect in the Landrace
(A-III) and Saddleback (A-IV) pig breeds, and metrifonate intoxication
(A-V) (Done, 1976); however, the causal factor of type A-II CT remained
unknown for a long time. Recently, several viruses have been proposed to
cause type A-II CT, including atypical porcine pestivirus (APPV), and
only APPV has been proven to induce CT through the injection of pregnant
sows with sera containing APPV (Arruda et al., 2016; de Groof et al.,
2016).
APPV belongs to the genus Pestivirus within the familyFlaviviridae . Recently, pestiviruses were categorized into 11
different species based on phylogenetic analysis, and a new
host-independent taxonomy system for Pestivirus species was
proposed using the format Pestivirus X . APPV was categorized asPestivirus K (Smith et al., 2017). Pestivirus is a small
enveloped virus that has a single-stranded positive-sense RNA genome and
contains a large open reading frame (ORF), which encodes nearly 4,000
amino acids (aa) and is preceded by a 5′ untranslated region (UTR) and
followed by a 3′ UTR. The polyprotein is processed into four structural
proteins (C, Erns, E1, and E2) and eight
non-structural proteins (Npro, p7, NS2, NS3, NS4A,
NS4B, NS5A, and NS5B), and the gene order is
5′-Npro-C-Erns-E1-E2-p7-NS2-3(NS2-NS3)-NS4A-NS4B-NS5A-NS5B-3′
(Tautz et al., 2015).
APPV was first discovered from the serum of a pig without clinical
symptoms in the United States (Hause et al., 2015). Since then, APPVs
have been found from pigs and wild boars with or without CT worldwide on
four continents, and genomic sequence diversity among APPVs has been
reported (Beer et al., 2017; Cagatay et al., 2018; Chen et al., 2019;
Choe et al., 2020; Colom-Cadena et al., 2018; de Groof et al., 2016;
Dénes et al., 2018; Dessureault et al., 2018; Gatto et al., 2018; Mósena
et al., 2018; Muñoz‐González et al., 2017; Pan et al., 2019b; Possatti
et al., 2018; Postel et al., 2016, 2017; Schwarz et al., 2017; Shen et
al., 2018; Sozzi et al., 2019; Stenberg et al., 2020; Xie et al., 2019;
Yan et al., 2019; Yuan et al., 2017; Zhang et al., 2017; Zhang et al.,
2019; Zhou et al., 2019). However, genome sequence data of APPV have not
been reported from Japan.
In the present study, we identified the APPV genome sequence in piglets
showing CT on a Japanese pig farm, and we analyzed and compared the
complete genome sequences obtained from Japanese pigs with sequences
from the DDBJ/EMBL/GenBank databases. Furthermore, a retrospective study
to detect APPV was conducted using a total of 399 porcine samples
collected from 2005 to 2020 in Japan.