Prevalence of Linda Virus Neutralizing Antibodies in the Austrian Pig Population

Development and application of an indirect ELISA for detection of antibodies against emerging atypical porcine pestivirus

BACKGROUND

Atypical porcine pestivirus (APPV) is a newly discovered swine pestivirus, which can cause congenital tremor and high mortality in newborn piglets and subclinical infection in adult pigs, leading to significant impacts on the pig industry. Currently, there is no approved serological method to assess APPV infection status in pig farms.

METHODS

In this study, the envelope glycoprotein E2 of APPV was highly expressed in suspension HEK293 cells, and further an indirect enzyme-linked immunosorbent assay based on the recombinant E2 protein (E2-iELISA) was developed and evaluated.

RESULTS

The reaction parameters of the E2-iELISA were optimized, and the cutoff value was determined to be 0.2 by analyzing S/P values of 165 negative sera against APPV that were confirmed by virus neutralization test (VNT). Specificity test showed that the method had no cross-reaction with other common swine viruses. The E2-iELISA was evaluated using a panel of swine sera, and showed high sensitivity (113/120, 94.2%) and specificity (65/70, 92.9%), and the agreement rate with VNT was 93.7% (178/190). Subsequently, the E2-iELISA was utilized to investigate the seroprevalence of APPV in pig herds of China. When detecting 1368 pig serum samples collected from nine provinces in China, the overall seroprevalence of APPV was 73.9% (1011/1368).

CONCLUSION

Our findings suggest that the E2-iELISA is specific and sensitive, and could be a valuable tool for serological surveillance of APPV infection in pigs.

A Review on Pathological and Diagnostic Aspects of Emerging Viruses—Senecavirus A, Torque teno sus virus and Linda Virus—In Swine

Simple Summary

Worldwide demand for food is expected to increase due to population growth and swine accounts for more than one-third of meat produced worldwide. Several factors affect the success of livestock production systems, including animal disease control. Despite the importance of infectious diseases to animal health and the productivity of the global swine industry, pathogens of swine, in particular emerging viruses, such as Senecavirus A, Torque teno sus virus, and Linda virus, have gained limited interest. We performed a systematic analysis of the literature, with a focus on the main macroscopical and histological findings related to those viruses to fill the gap and highpoint these potentially hazardous pathogens.

Abstract

Swine production represents a significant component in agricultural economies as it occupies over 30% of global meat demand. Infectious diseases could constrain the swine health and productivity of the global swine industry. In particular, emerging swine viral diseases are omnipresent in swine populations, but the limited knowledge of the pathogenesis and the scarce information related to associated lesions restrict the development of data-based control strategies aimed to reduce the potentially great impact on the swine industry. In this paper, we reviewed and summarized the main pathological findings related to emerging viruses, such as Senecavirus A, Torque teno sus virus, and Linda virus, suggesting a call for further multidisciplinary studies aimed to fill this lack of knowledge and better clarify the potential role of those viral diseases in swine pathology.

DNAJC14-Independent Replication of the Atypical Porcine Pestivirus

Atypical porcine pestiviruses (APPV; Pestivirus K) are a recently discovered, very divergent species of the genus Pestivirus within the family Flaviviridae. The presence of APPV in piglet-producing farms is associated with the occurrence of so-called “shaking piglets,” suffering from mild to severe congenital tremor type A-II. Previous studies showed that the cellular protein DNAJC14 is an essential cofactor of the NS2 autoprotease of all classical pestiviruses. Consequently, genetically engineered DNAJC14 knockout cell lines were resistant to all tested noncytopathogenic (non-cp) pestiviruses. Surprisingly, we found that the non-cp APPV can replicate in these cells in the absence of DNAJC14, suggesting a divergent mechanism of polyprotein processing. A complete laboratory system for the study of APPV was established to learn more about the replication of this unusual virus. The inactivation of the APPV NS2 autoprotease using reverse genetics resulted in nonreplicative genomes. To further investigate whether a regulation of the NS2-3 cleavage is also existing in APPV, we constructed synthetic viral genomes with deletions and duplications leading to the NS2 independent release of mature NS3. As observed with other pestiviruses, the increase of mature NS3 resulted in elevated viral RNA replication levels and increased protein expression. Our data suggest that APPV exhibit a divergent mechanism for the regulation of the NS2 autoprotease activity most likely utilizing a different cellular protein for the adjustment of replication levels.

IMPORTANCE DNAJC14 is an essential cofactor of the pestiviral NS2 autoprotease, limiting replication to tolerable levels as a prerequisite for the noncytopathogenic biotype of pestiviruses. Surprisingly, we found that the atypical porcine pestivirus (APPV) is able to replicate in the absence of DNAJC14. We further investigated the NS2-3 processing of APPV using a molecular clone, monoclonal antibodies, and DNAJC14 knockout cells. We identified two potential active site residues of the NS2 autoprotease and could demonstrate that the release of NS3 by the NS2 autoprotease is essential for APPV replication. Defective interfering genomes and viral genomes with duplicated NS3 sequences that produce mature NS3 independent of the NS2 autoprotease activity showed increased replication and antigen expression. It seems likely that an alternative cellular cofactor controls NS2-3 cleavage and thus replication of APPV. The replication-optimized synthetic APPV genomes might be suitable live vaccine candidates, whose establishment and testing warrant further research.

New Emergence of the Novel Pestivirus Linda Virus in a Pig Farm in Carinthia, Austria

Linda virus (LindaV) was first identified in a pig farm in Styria, Austria in 2015 and associated with congenital tremor (CT) type A-II in newborn piglets. Since then, only one more LindaV affected farm was retrospectively discovered 10 km away from the initially affected farm. Here, we report the recent outbreak of a novel LindaV strain in a farrow-to-finish farm in the federal state Carinthia, Austria. No connection between this farm and the previously affected farms could be discovered. The outbreak was characterized by severe CT cases in several litters and high preweaning mortality. A herd visit two months after the onset of clinical symptoms followed by a diagnostic workup revealed the presence of several viremic six-week-old nursery pigs. These animals shed large amounts of virus via feces and saliva, implying an important epidemiological role for within- and between-herd virus transmission. The novel LindaV strain was isolated and genetically characterized. The findings underline a low prevalence of LindaV in the Austrian pig population and highlight the threat when introduced into a pig herd. Furthermore, the results urge the need to better understand the routes of persistence and transmission of this enigmatic pestivirus in the pig population.

In the Search of Marine Pestiviruses: First Case of Phocoena Pestivirus in a Belt Sea Harbour Porpoise

Pestiviruses are widespread pathogens causing severe acute and chronic diseases among terrestrial mammals. Recently, Phocoena pestivirus (PhoPeV) was described in harbour porpoises (Phocoena phocoena) of the North Sea, expanding the host range to marine mammals. While the role of the virus is unknown, intrauterine infections with the most closely related pestiviruses— Bungowannah pestivirus (BuPV) and Linda virus (LindaV)—can cause increased rates of abortions and deaths in young piglets. Such diseases could severely impact already vulnerable harbour porpoise populations. Here, we investigated the presence of PhoPeV in 77 harbour porpoises, 277 harbour seals (Phoca vitulina), grey seals (Halichoerus grypus) and ringed seals (Pusa hispida) collected in the Baltic Sea region between 2002 and 2019. The full genome sequence of a pestivirus was obtained from a juvenile female porpoise collected along the coast of Zealand in Denmark in 2011. The comparative Bayesian phylogenetic analyses revealed a close relationship between the new PhoPeV sequence and previously published North Sea sequences with a recent divergence from genotype 1 sequences between 2005 and 2009. Our findings provide further insight into the circulation of PhoPeV and expand the distribution from the North Sea to the Baltic Sea region with possible implications for the vulnerable Belt Sea and endangered Baltic Proper harbour porpoise populations.

Characterization of a Cytopathogenic Reporter CSFV

Cytopathogenic (cp) pestiviruses frequently emerge in cattle that are persistently infected with the bovine viral diarrhea virus (BVDV) as a consequence of RNA recombination and mutation. They induce apoptosis in infected tissue cultures, are highly attenuated in the immunocompetent host, and unable to establish persistent infections after diaplacental infections. Cp strains of BVDV have been used as naturally attenuated live vaccines and for species-specific plaque reduction tests for the indirect serological detection of BVDV. Here, we present a genetically engineered cp strain of the classical swine fever virus (CSFV). Cytopathogenicity of the strain was induced by the insertion of ubiquitin embedded in a large NS3 to NS4B duplication. The CSFV RNA genome was stabilized by the inactivation of the NS2 autoprotease, hindering the deletion of the insertion and the reversion to a wild-type genome. Additional insertion of a mCherry gene at the 5'-end of the E2 gene allowed fluorescence-verified plaque reduction assays for CSFV, thus providing a novel, cost-efficient diagnostic tool. This genetically stabilized cp CSFV strain could be further used as a basis for potential new modified live vaccines. Taken together, we applied reverse genetics to rationally fixate a typical cp NS3 duplication in a CSFV genome.