Characterization of the Humoral Immune Response Induced after Infection with Atypical Porcine Pestivirus (APPV)

Abstract

Atypical porcine pestivirus (APPV) is a widely distributed pathogen causing congenital tremor (CT) in piglets. So far, no data are available regarding the humoral immune response against APPV. In this study, piglets and their sows from an affected herd were tested longitudinally for viral genome and antibodies. APPV genome was detected in the majority of the piglets (14/15) from CT affected litters. Transient infection of gilts was observed. Kinetics of Erns- and E2-specific antibodies and their neutralizing capacity were determined by recently (Erns) and newly (E2) developed antibody ELISAs and virus neutralization assays. Putative maternally derived antibodies (MDA) were detected in most piglets, but displayed only low to moderate neutralizing capacity (ND50 ≤ 112). Horizontal APPV transmission occurred when uninfected and infected piglets were mingled on the flat deck. Horizontally infected piglets were clinically inapparent and showed only transient viremia with subsequently consistently high E2 antibody levels. For piglets from CT affected litters, significantly lower neutralizing antibody titers were observed. Results indicate that E2 represents the main target of neutralizing antibodies. Characterization of the humoral immune response against APPV will help to provide valuable serological diagnosis, to understand the epidemiology of this novel pathogen, and to implement tailored prevention strategies.

Atypical Porcine Pestivirus Circulation and Molecular Evolution within an Affected Swine Herd

“…In the present study, forty-five nucleotide substitutions were found along the APPV genome during the monitoring years in the farm, eleven of them causing an amino acid change. Among those, two occurred on the E2 protein-coding gene, usually recognized as the main antigen able to elicit neutralizing antibodies in infected animals [ 38 , 39 ]. Recent studies on subunit E2 vaccines from APPV have shown strong immune responses in mice [ 40 ].…”

“…The strong purifying selection we found could be explained by a lack of pressure from the host immune system, as the persistently infected animals may potentially be immunotolerant, although experimental evidence is needed to ultimately confirm this hypothesis. Regular use of ELISA systems, to monitor whether immunity is raised to the virus, would bring light to this issue [ 39 ].…”

“…Monitoring studies in APPV-infected farms during the last years showed that APPV caused persistent infections in piglets when they were infected in-utero, occasionally developing congenital tremors, while horizontal infections within the herd were transient and without visible clinical signs [ 39 ]. As aforementioned, this is similar to BVDV infections in cattle, which only causes persistent infections in the calves when the virus is transmitted in-utero before 120 days of gestation.…”

Seroprevalences of Newly Discovered Porcine Pestiviruses in German Pig Farms

“…E2 is the main surface protein of pestiviruses, normally inducing a profound serological response following infection, including neutralizing antibodies. Research on the humoral immune response against APPV shows that this is also the case for this newly discovered pestivirus [30]. Several E2 chimeric pestiviruses were shown to be able to replicate efficiently in susceptible cells [25,28].…”

“…Furthermore, the detected prevalences are high, which is also more indication that not too many samples are false negative. However, there are little data about the humoral response against APPV [30], therefore the evaluated titers cannot be put into perspective yet and an even higher seroprevalence of APPV in the German pig population might be possible.…”