Discovery of a divergent lineage porcine pestivirus in piglets with congenital tremors

Congenital tremors is a disease of neonatal pigs characterized by action-related repetitive myoclonus. Despite early documentation (nearly 100 years ago) and worldwide distribution of the disease, the etiology of a majority of contemporary outbreaks remains a mystery but has been speculated to be an unidentified virus. This investigation describes the identification of a divergent lineage pestivirus in samples from piglets with congenital tremors and not unaffected cohorts.

Five unrelated farms located in the United States in the state of Iowa (n=4) and Illinois (n=1) reported clinical signs compatible with congenital tremor. Animal from Farm A included 15 piglets of which 11 were affected. Animals from Farm B included 5 affected piglets. Animals from Farm C included 4 affected piglets and 3 unaffected. Animals from farm D included 5 affected and 1 unaffected. Animals from Farm E included 7 affected and 6 unaffected piglets. Samples including serum, cerebrum, cerebellum, brainstem, and spinal cord were collected. Varied porcine tissues (serum, cerebrum, cerebellum, and/or spinal cord) from Farm A and Farm B were processed for MiSeq based sequencing through library generation using NextEra XT library preparation kit (Illumina) per the manufacturer’s suggested protocol, with replacement of column elution (Qiagen, MinElute) in lieu of bead normalization. A quantitative one-step RT-PCR (RT-qPCR) was developed targeting the NS3 region of the divergent lineage pestivirus and was run on tissue and/or serum samples from Farm A, B, C, D and E.

Through the use of next-generation sequence technology a divergent lineage virus originally most closely related to a Chinese bat pestivirus and now known to be more closely related to a recently reported porcine pestivirus was identified in samples from piglets with congenital tremors. The virus was detected by RT-qPCR in multiple sample types from affected piglets (31 out of 32) that originated from five unrelated farms and was not commonly detected in unaffected piglets (2 out of 14). Phylogenetic analysis of the NS3 and Npro amino acid sequences support classification of the virus identified herein as a member of the putative “atypical porcine pestivirus” species with 88.0% and 94.6% nucleotide and amino acid identity, respectively. This divergent lineage pestivirus virus is phylogenetically distinct from classical swine fever virus with an amino acid percent identity of the viral Npro ranging from 35.9 to 36.4%.

This report describes the identification of a divergent lineage porcine pestivirus in piglets with congenital tremor from five unrelated farms located in two different states in the United States.

Disclosure of Interest: None Declared.