Detection and investigation of atypical porcine pestivirus in a swine production system

Abstract

A commercial farrow-to-finish farm was suspicious of atypical porcine pestivirus (APPV) after observing clinical signs of congenital tremors (CT) and splay leg (SL) of newborn pigs. If introduced onto the farrow-to-finish, the two potential routes of introduction could be through replacement gilts or incoming semen doses. Therefore, this study aimed to determine the prevalence of clinical APPV within the sampled population, identify the route of APPV introduction to this system, and determine prevalence of detectable APPV RNA within a population of gilt multiplication farm offspring through an isolation nursery and finisher barn. Farrowing records were analyzed for the presence of CT or SL and corresponding parity of the dam. Overall, prevalence of clinically affected litters within batch farrowing groups ranged from 0 to 31%. Phylogenetic analysis was conducted on a serum sample from a gilt at the isolation nursery, semen dose for the farrow-to-finish farm, and serum of a CT piglet. Results indicated that the virus circulating in clinically affected piglets was most similar to an incoming semen dose (98.9% nucleotide identity). Blood samples were collected at four time points and revealed APPV clinical prevalence was 37.5–77.5% during the nursery phase and 0–26% during the finisher phase. Oral fluids were also collected during the finisher phase and APPV clinical prevalence was 100% for all sampling time points. In summary, introduction of APPV into naïve herds is associated with increased clinical CT and SL cases and is detectable in asymptomatic pigs during the nursery and finisher production phases. This study found that potential screening tests for APPV could include oral fluids or qRT-PCR analysis of semen doses especially when trying to identify prevalence levels on naïve farm.

Congenital tremor and splay leg in Swedish piglets : a study of the viral causes and routes of transmission

“…In the literature, there are reports of co-morbidity between CT type A-II and splay leg following infection with APPV Gatto et al 2018b;Houston et al 2022). Thus, APPV has by some been suggested as one causative agent of splay leg, but the causality between APPV and splay leg is to this date not established .…”

“…Studies have shown that APPV may be transmitted transplacentally as well as horizontally Folgueiras-González et al 2020b;Houston et al 2022). However, the exact routes of horizontal transmission are not yet fully understood.…”

“…An orofecal transmission route has been suggested, given the prolonged detection and shedding of APPV in salivary glands, saliva, the gastrointestinal tract, and faeces (de Groof et al 2016;Folgueiras-González et al 2020b) as well as venereal transmission via semen, through both natural mating and artificial insemination (de Groof et al 2016;Folgueiras-González et al 2020b;Houston et al 2022). The pathogenesis is currently not described, but lymphatic tissue, the cerebellum, and serum stand out with high viral loads following both vertical and horizontal transmission (Pan et al 2018;Buckley et al 2021;Ren et al 2022) Transplacental infection with APPV is associated with signs of congenital tremor in the off-spring through both experimental infections Buckley et al 2021) and natural infections Gatto et al 2018b;Pan et al 2018;Folgueiras-González et al 2020b;Guo et al 2020;Pedersen et al 2021;Shi et al 2021;Houston et al 2022;Ren et al 2022). A litter born to an APPVinfected dame may consist of a mix of uninfected, healthy piglets, infected and healthy piglets, and infected, diseased piglets.…”

“…There are also some reports of co-morbidity of congenital tremor and splay leg following infection with APPV Gatto et al 2018b;Houston et al 2022) but the causality between APPV and splay leg are not established Stenberg et al 2022). Further, there are no reports of piglets with APPV infection and solely splay leg as the clinical outcome.…”

“…Based on the current knowledge, there are two suggested routes of transmission of extra importance: 1) Into farms from breeding boars via AI-semen. APPV is readily transmitted via AI-semen from clinically healthy boars (Houston et al 2022), and farmers are relying on pathogen-free semen to maintain good health status at their farms. 2) Between wild boar and domestic pigs (or vice versa).…”