First report of the novel atypical porcine pestivirus in Spain and a retrospective study

Abstract

This study aimed to provide information regarding viral pathogenesis and molecular epidemiology linked with recently reported atypical porcine pestivirus (APPV) strains and to determine the circulation of APPV in Spain from 1997 to 2016. Two-day-old piglets with moderate-severe congenital tremor (CT) from a Spanish farm were received for diagnostic purposes. Sera, nasal and rectal swabs and tissue samples were collected. qRT-PCR was performed in these samples, and a retrospective study to detect APPV RNA was carried out using a serum collection from 1997 to 2016. APPV genome was identified with high and moderate RNA loads in different tissues of the CT affected pigs. High APPV RNA load was detected in lymphoid organs, suggesting that these constitute a target for APPV replication. In 89 of the 642 retrospectively analysed samples (13.9%), APPV genome was detected. CT cases were related to the presence of APPV in viraemic piglets below 1 week of age, in which the viral RNA load was the highest. A considerable number of animals between 4 and 14 weeks of age and some 1-week-old piglets were viraemic in the absence of CT, which can act as carriers of the virus. The relative risk of APPV and CT was 8.5 (CI 95% 5.8-12.5). Thus, our data show that APPV infection is epidemiologically related to CT. Phylogenetic analysis from 1615 NS2-3 nucleotides showed only one defined APPV clade, grouping the most phylogenetically related strains from Europe and China. Of this clade, there are other strains from Europe, USA and China. This data confirm the high APPV genetic diversity, not being able to cluster this virus according to the geographic area. Our result showed that APPV has been circulating in Spain at least since 1997, being the earliest date of detection of this virus worldwide and suggesting that APPV may be widespread.

An emerging novel virus: Atypical porcine pestivirus (APPV)

“…In one study, 1615 nt of APPV NS2‐3 region were used to calculate the nucleotide substitutions per site per year (s/s/y) among the Spanish strain 2001, Spanish strain 2015, and German strain 2015. The results show that during the past 14 years, a mutation rate of 2.65 × 10 −3 s/s/y has occurred between the Spanish strains 2001, and 2005, while it is 3.62 × 10 −3 s/s/y between the Spanish strain 2001, and the German strain 2015 . Both high‐mutation rates were comparable with that of CSFV reported previously, suggesting that the APPV may have been evolving within the range of mutation rate as pestiviruses have.…”

“…Currently, tissue tropism of APPV was primarily determined by qRT‐PCR. In one study from the 2‐day‐old piglets, high‐APPV RNA loads were found in the tonsil, spleen, and thymus samples, while moderate RNA loads in the sera, nasal/rectal swabs, cerebrospinal fluid, and cerebrum . In another study, the APPV can be detected in nearly all tissues with the highest‐RNA levels in the submaxillary lymph nodes, and moderate RNA levels in the peripheral lymphoid organs (spleen, tonsil, and inguinal lymph node), nervous system (brain stem, brain, and cerebellum), and digestive system (duodenum) .…”

“…In comparison, CT are commonly caused by infectious agents including mild CSFV strain (Type A‐I) and previously unidentified causative agent (Type A‐II). The CT type A‐II is characterized with its sporadic and occasional occurrence in gilt litters, demyelination of the spinal cord and brain in piglets, and low‐moderate mortality of piglets caused by malnutrition . The clinical signs of CT type A‐II could be reproduced on the piglets, farrowed by sows infected with inoculum containing the potential agent 40 years ago, which has provided a powerful evidence to support the assumption that an infectious agent may be responsible for the tremor.…”

“…To date, APPV has been detected in the North America, South America, Asia, and Europe (Table ). It has been shown that APPV has been circulating in Spain as early as at least 1997, which is currently the earliest time that the APPV isolate can be tracked back to. An early study identified an APPV strain from the samples of piglets with CT and found an APPV prevalence of 6% by quantitative reverse transcriptase PCR (qRT‐PCR) in the US pig herds …”

“…Of these, APPV was first identified by next‐generation sequencing from the samples in the United States in 2015 . Shortly thereafter, it was reported in pigs with CT in the United States, Germany, the Netherlands, Spain, Austria, China, and Brazil (Table ) …”