Experimental Swinepox in Gnotobiotic Piglets

Congenital Suipoxvirus Infection in Newborn Piglets in an Austrian Piglet-Producing Farm

In February 2020, a fourth parity sow gave birth to a litter of piglets with four piglets presenting pox-like skin lesions. Lesions were distributed over the whole skin surface and ulcerative lesions were also observed on the mucosa of the oral cavity. The skin lesions were described as looking like pox lesions. Virological and histopathological investigations confirmed congenital suipoxvirus infection. Since there is no effective treatment available, the farmer was recommended to improve hygiene. No further cases occurred after this single event. In the past, suipoxvirus infections were mainly related to improper hygiene conditions and to pig lice as vectors. Today, conventional pigs are usually kept under good hygienic conditions and pig lice are not reported anymore to occur in Austrian conventional pig farming systems. Therefore, we speculate, that other living vectors, such as the stable fly, may play a role in the transmission of suipoxvirus between and within farms and in the occurrence of congenital suipoxvirus infections in neonatal piglets.

Swinepox Virus Strains Isolated from Domestic Pigs and Wild Boar in Germany Display Altered Coding Capacity in the Terminal Genome Region Encoding for Species-Specific Genes

Swinepox virus (SWPV) is a globally distributed swine pathogen that causes sporadic cases of an acute poxvirus infection in domesticated pigs, characterized by the development of a pathognomonic proliferative dermatitis and secondary ulcerations. More severe disease with higher levels of morbidity and mortality is observed in congenitally SWPV-infected neonatal piglets. In this study, we investigated the evolutionary origins of SWPV strains isolated from domestic pigs and wild boar. Analysis of whole genome sequences of SWPV showed that at least two different virus strains are currently circulating in Germany. These were more closely related to a previously characterized North American SWPV strain than to a more recent Indian SWPV strain and showed a variation in the SWPV-specific genome region. A single nucleotide deletion in the wild boar (wb) SWPV strain leads to the fusion of the SPV019 and SPV020 open reading frames (ORFs) and encodes a new hypothetical 113 aa protein (SPVwb020-019). In addition, the domestic pig (dp) SWPV genome contained a novel ORF downstream of SPVdp020, which encodes a new hypothetical 71aa protein (SPVdp020a). In summary, we show that SWPV strains with altered coding capacity in the SWPV specific genome region are circulating in domestic pig and wild boar populations in Germany.

Research Relevant Background Lesions and Conditions: Ferrets, Dogs, Swine, Sheep, and Goats

Animal models provide a valuable tool and resource for biomedical researchers as they investigate biological processes, disease pathogenesis, novel therapies, and toxicologic studies. Interpretation of animal model data requires knowledge not only of the processes/diseases being studied but also awareness of spontaneous conditions and background lesions in the model that can influence or even confound the study results. Species, breed/stock, sex, age, anatomy, physiology, diseases (noninfectious and infectious), and neoplastic processes are model features that can impact the results as well as study interpretation. Here, we review these features in several common laboratory animal species, including ferret, dog (beagle), pig, sheep, and goats.

Recombinant swinepox virus expressing beta-galactosidase: investigation of viral host range and gene expression levels in cell culture

Swinepox virus (SPV) has been proposed as a potential vector for generating recombinant vaccines for swine. However, little is known about important aspects of SPV biology, such as the functionality of SPV promoters or the host range of SPV. Using a transient expression assay, well-characterized vaccinia virus promoters were shown to be active in cells infected with SPV. A recombinant SPV expressing beta-galactosidase (beta-gal) was constructed and characterized. The E. coli LacZ gene was placed under the control of a strong vaccinia synthetic early/late promoter and was inserted by homologous recombination in a noncoding region of the SPV genome. The recombinant SPV expressing beta-gal was used to characterize the host range of the virus by measuring protein expression and virus production in different cell lines. In general, SPV expressed more protein and grew more efficiently than vaccinia virus in porcine cell lines. Surprisingly, the recombinant SPV was able to infect and replicate in several cell lines of nonswine origin. The virus directed regulated early and late gene expression of beta-gal in those cells and formed blue plaques in cell monolayers in the presence of X-gal. Upon infection with the recombinant SPV, there was a significant level of viral replication, and the virus can be serially passaged in some nonswine cell lines. The data presented suggest that despite the strict host tropism of SPV, the virus exhibits a relatively broad host range in cell culture.

The molecular biology of swinepox virus. II. The infectious cycle

Studies based on low-stringency hybridizations of radiolabeled swinepox virus (SPV) DNA to Southern blots containing DNA of representative members of the Orthopoxvirus, Leporipoxvirus, and Avipoxvirus genera and the Entomopoxvirus subfamily have revealed no DNA homology at this level of resolution. Antigenic relatedness between SPV and vaccinia was also analyzed using immunoprecipitations and revealed little if any cross-reactivity. The growth characteristics of SPV in tissue culture were examined by light microscopy and revealed both a delayed and a different cytopathology than that of vaccinia virus. SPV causes foci in pig kidney cells that are not evident until at least 4 days postinfection, whereas vaccinia rapidly generates plaques on these cells. The kinetics of DNA accumulation, protein expression, and RNA transcription of SPV have been examined and indicate that each of these facets of the SPV growth cycle is also considerably delayed when compared to vaccinia virus. Our data indicate that swinepox virus is unique from other poxviruses characterized to date and supports the classification of swinepox virus into a separate genus, Suipoxvirus, within the poxvirus family.

The molecular biology of swinepox virus. I. A characterization of the viral DNA

Swinepox virus (SPV), the prototype member of the Suipoxvirus genus, is uncharacterized at the molecular level. We have analyzed the DNA of SPV and demonstrate that the genome is 175 kb in size and like the more commonly studied Orthopoxvirus, Avipoxvirus, and Leporipoxvirus genera, is terminally cross-linked and contains inverted terminal repetitions (ITRs). In addition, the ITRs are unstable, probably due to the presence of a variable number of direct repeats of approximately 70 bp in length. Restriction enzyme cleavage maps for the enzymes HindIII, AvaI, HaeII, KpnI, BglI, SalI, and XhoI are also presented.

Swinepox. Virus isolation, experimental infections and the differentiation from vaccinia virus infections

The isolation of swinepox virus in primary pig kidney cell cultures is reported. The differentiation from vaccinia virus was possible with challenge infections of convalescent pigs and the use of the agar gel diffusion precipitation (AGDP) test and immuno-electroosmophoresis (IEOP). Using both immune precipitation tests reactions of identity were obtained between the heterologous antigens of swinepox and vaccinia viruses. A total of 829 pig sera from the field were tested for precipitating antibodies with the IEOP. Antibodies were detected in 65 (=7.8 per cent) of these serum samples.

The etiology of swine dysentery. I. Oral inoculation of germ-free swine with Treponema hyodysenteriae and Vibrio coli

Germ-free swine varying in age from 5 to 20 days were inoculated orally with cultures of either a spirochete (B-78), Vibrio coli, or a combination of the two. Both agents readily colonized the intestinal tracts of the exposed pigs without producing clinical or pathologic signs of swine dysentery. Acute disease and deaths occurred only when piglets were exposed to whole, ground colonic material reportedly from animals with swine dysentery. Disease and deaths were associated with Salmonella infantis.