Pathogenicity of two Chinese Seneca Valley virus (SVV) strains in pigs.

Seneca Valley virus (SVV) has been identified as the causative agent of SVV-associated vesicular disease (SAVD). To investigate the pathogenicity of two newly isolated SVV strains (GD-S5/2018 and GD04/2017) in China, experimental infections of pigs were performed. In pig experiments, both SVV strains successfully infected all animals, evidenced by presence of virus shedding and robust protective antibody responses. SVV GD-S5/2018 infection resulted in characteristic clinical signs, and ulcerative lesions on the tongue and gums. However, SVV GD04/2017 did not cause any clinical symptoms except depression in pigs during the experiment. Taken together, these results demonstrate that SVV GD-S5/2018 is a virulent strain for pigs, whereas SVV GD04/2017 is nearly avirulent. The established animal models for SVV infection will be utilized to dissect the immunity and pathogenesis, and develop vaccines and antivirals.

Adaptive Immune Responses following Senecavirus A Infection in Pigs.

Senecavirus A (SVA), an emerging picornavirus of swine, causes vesicular disease (VD) that is clinically indistinguishable from foot-and-mouth disease (FMD) in pigs. Many aspects of SVA interactions with the host and the host immune responses to infection, however, remain unknown. In the present study, humoral and cellular immune responses to SVA were evaluated following infection in pigs. We show that SVA infection elicited an early and robust virus-neutralizing (VN) antibody response, which coincided and was strongly correlated with VP2- and VP3-specific IgM responses. Notably, the neutralizing antibody (NA) responses paralleled the reduction of viremia and resolution of the disease. Analysis of the major porcine T-cell subsets revealed that during the acute/clinical phase of SVA infection (14 days postinfection [p.i.]), T-cell responses were characterized by an increased frequency of αß T cells, especially CD4+ T cells, which were first detected by day 7 p.i. and increased in frequency until day 14 p.i. Additionally, the frequency of CD8+ and double-positive CD4+ CD8+ T cells (effector/memory T cells) expressing interferon gamma (IFN-γ) or proliferating in response to SVA antigen stimulation increased after day 10 p.i. Results presented here show that SVA elicits B- and T-cell activation early upon infection, with IgM antibody levels being correlated with early neutralizing activity against the virus and peak B- and T-cell responses paralleling clinical resolution of the disease. The work provides important insights into the immunological events that follow SVA infection in the natural host.IMPORTANCE Senecavirus A (SVA) has recently emerged in swine, causing outbreaks of vesicular disease (VD) in major swine-producing countries around the world, including the United States, Brazil, China, Thailand, and Colombia. Notably, SVA-induced disease is clinically indistinguishable from other high-consequence VDs of swine, such as FMD, swine vesicular disease, vesicular stomatitis, and vesicular exanthema of swine. Despite the clinical relevance of SVA-induced VD, many aspects of the virus infection biology remain unknown. Here, we assessed host immune responses to SVA infection. The results show that SVA infection elicits early B- and T-cell responses, with the levels of VN antibody and CD4+ T-cell responses paralleling the reduction of viremia and resolution of the disease. SVA-specific CD8+ T cells are detected later during infection. A better understanding of SVA interactions with the host immune system may allow the design and implementation of improved control strategies for this important pathogen of swine.

Microarray-based detection of viruses causing vesicular or vesicular-like lesions in livestock animals.

Definitive diagnosis of vesicular or vesicular-like lesions in livestock animals presents challenges both for veterinary clinicians and diagnostic laboratories. It is often impossible to diagnose the causative disease agent on a clinical basis alone and difficult to collect ample vesicular epithelium samples. Due to restrictions of time and sample size, once laboratory tests have ruled out foot-and-mouth disease, vesicular stomatitis and swine vesicular disease a definitive diagnosis may remain elusive. With the ability to test a small quantity of sample for a large number of pathogens simultaneously, DNA microarrays represent a potential solution to this problem. This study describes the application of a long oligonucleotide microarray assay to the identification of viruses known to cause vesicular or vesicular-like lesions in livestock animals. Eighteen virus isolates from cell culture were successfully identified to genus level, including representatives of each foot-and-mouth disease virus serotype, two species of vesicular stomatitis virus (VSV), swine vesicular disease virus, vesicular exanthema of swine virus (VESV), bovine herpesvirus 1, orf virus, pseudocowpox virus, bluetongue virus serotype 1 and bovine viral diarrhoea virus 1. VSV and VESV were also identified in vesicular epithelium samples, with varying levels of sensitivity. The results indicate that with further development this microarray assay could be a valuable tool for the diagnosis of vesicular and vesicular-like diseases.

Use of automated real-time reverse transcription-polymerase chain reaction (RT-PCR) to monitor experimental swine vesicular disease virus infection in pigs.

Automated real-time RT-PCR was evaluated as a diagnostic tool for swine vesicular disease virus (SVDV) infection on a range of samples (vesicular epithelium, serum, nasal swabs, faeces) from four inoculated and three in-contact pigs over a period of 28 days. Traditional diagnostic procedures (virus isolation, and ELISAs for antigen and antibody) were used in parallel. Each inoculated pig developed a significant viraemia and clinical disease, and excreted virus, which was transmitted to the in-contact animals. The latter, however, developed only a short-lived, low-level viraemia and no clinical disease. The RT-PCR and virus isolation were generally comparable in detecting SVDV in the serum and nasal swabs from inoculated and in-contact pigs up to day 6 after infection; it was possible, however, to isolate virus for a longer period from the faeces of a few pigs. This suggested that further optimization of the template extraction method was required to counteract the effects of RT-PCR inhibitors in faeces. It was concluded that the automated real-time RT-PCR is a useful diagnostic method for SVD in clinically or subclinically affected pigs and contributed to the study of the pathogenesis of SVD in the pigs.

Swine vesicular disease: an overview.

Swine vesicular disease (SVD) is a notifiable viral disease of pigs included on the Office International des Epizooties List A. The first outbreak of the disease was recognized in Italy in 1966. Subsequently, the disease has been reported in many European and Asian countries. The causative agent of the disease is SVD virus which is currently classified as a porcine variant of human coxsackievirus B5 and a member of the genus enterovirus in the family picornaviridae. From a clinical point of view, SVD is relatively unimportant, rarely causing deaths and usually only a minor setback to finishing schedules. However, the clinical signs which it produces are indistinguishable from those caused by foot-and-mouth disease, and its presence prevents international trade in pigs and pig products. This article reviews recent findings on all aspects of the virus and the disease which it causes.

Electron microscopy of cells cultured in serum-free medium after inoculation of swine vesicular disease virus.

Morphological alterations of IB-RS-2 cells cultured in serum-free maintenance medium after inoculation of swine vesicular disease virus (SVDV) were studied electron-microscopically. Cells harvested 0 to 3 hours after inoculation showed no alterations. Cellular alterations were observed from 4 to 7 hours after inoculation. Many vacuoles appeared just beneath the cytoplasmic membrane and were separated by thin cytoplasm. Narrow pathways were sometimes seen in the degenerative cells. They occasionally ran from the vacuole just beneath the cytoplasmic membrane to the nuclear cistern. Ribosome-like granules were seen along the narrow pathway or diffusely in the cytoplasm, or accumulated to form an islet. Membrane-bound bodies were frequently noticed in the central region of the cell. Cytoplasmic blebs were sometimes seen projecting from the cell surface. Vacuoles, narrow pathways and cytoplasmic blebs were absent in cells cultured in the medium with serum. So serum might exert some effects on the cytoplasmic membrane or cytoskeletal framework. Crystalline arrays of SVDV were found in the cytoplasm of degenerative cells harvested from 4 to 7 hours after inoculation. They were near the ribosome-like granules and membrane-bound bodies, but had no relationship with vacuoles just beneath the cytoplasmic membrane and narrow pathway. Their size and morphology were the same as those seen in the cells cultured in the medium with serum.

Swine vesicular disease viruses isolated from healthy pigs in non-epizootic period. II. Vesicular formation and virus multiplication in experimentally inoculated pigs.

An infection experiment was carried out on pigs with swine vesicular disease virus isolated from healthy pigs (SVDV-H). Inoculation was done by two routes, intradermal in the coronary band of the foot and oral. Observation was made on the formation of vesicles and their spread, the virus contents of serum, swab of the oral cavity, and feces, the vicissitude of neutralizing antibody titers, and the distribution of virus in the body. From its results the pathogenicity of virus was judged. In the pigs inoculated intradermally there was a difference in the extension of the area involved in vesicular formation between any two strains of virus. That is, vesicular formation was restricted to the site of inoculation, involved the site of inoculation and the sole of the hoof, or spread over the oral and nasal regions. In every pig, however, vesicles developed only for 2 approximately 5 days after inoculation. After that, repair progressed rapidly. Some strains caused viremia, which was mild. The virus was detected from the site of vesicular formation, but not from any organ. Neutralizing antibody began to be detected 3 days after inoculation. Its titer reached a plateau about 10 days later. In the pigs inoculated perorally, no vesicles were formed. The virus was only detected from the tonsils and the intestinal contents. These findings made it clear that SVDV-H was less pathogenic than swine vesicular disease virus isolated from diseased pigs.

Experimental swine vesicular disease, pathology and immunofluorescence studies.

Two day old piglets were inoculated intravenously with 1 ml of swine vesicular disease virus UK-G 27-72 isolate. Using infectivity tests, immunofluorescent staining and gross and histopathological examination, pathogenesis of the infection was studied in tissue specimens collected daily from one through seven days postinoculation. Swine vesicular disease virus had a strong affinity for the epithelia of the tongue, snout, coronary band and lips, the myocardium and the lymphoid elements of the tonsil and the brain stem. The virus had the greatest affinity for the epithelium of the tongue. However, there was no evidence that the tongue was the initial replication site for swine vesicular disease virus. Prickle cells in the stratum spinosum appear to be the primary targets for the virus. The necrotic foci in the stratum spinosum appeared first, followed the next day by reticular degeneration and multilocular intraepidermal vesicular formation. In the digestive tract and most of the other visceral organs the short duration and sudden drop of the virus titres and the negative fluorescence and pathological findings suggest that these are not important sites for the replication of swine vesicular disease virus in this experiment. The virus was recovered from most of the central nervous tissue specimens. Although the piglets had significant central nervous system lesions, signs of impaired central nervous system function were not detected. However, subtle nervous signs could have been obscured by difficulties in locomotion resulting from severe lesions of the feet.

Neuropathology of experimental swine vesicular disease in pigs.

A total of 26 young pigs were inoculated intracerebrally, intravenously or intradermally with the UKG27/72 strain of SVD virus, grown in tissue culture, and killed two, four, eight or 16 days after exposure. Overt nervous symptoms were seen only in pigs inoculated intracerebrally, but all pigs of all groups showed a non-suppurative meningitis and panencephalomyelitis principally affecting the mid- and fore-brain. Ganglioneuritis with intranuclear inclusion bodies in perineuronal amphicytes were found to be the most consistently useful characters for distinguishing SVD from other virus encephalitides of pigs. Spinal radiculitis was a feature of the early stages of CNS involvement and lesions were found also in the optic nerve, retina and cornea.

General pathology of experimental swine vesicular disease.

Twenty-four minimal disease pigs were inoculated intracerebrally, intravenously or intradermally with an English strain of swine vesicular disease virus. In the skin, snout, tongue and tonsil the main lesion was a full-thickness coagulative necrosis of the stratified squamous epithelium. In the renal pelvis, bladder, tonsillar crypts and the collecting ducts of salivary glands and pancreas, epithelial degeneration with the formation of periodic acid-Schiff-positive material were consistent features of this disease. Histopathological examination alone could not be relied upon to differentiate between well-established skin lesions caused by swine vesicular disease and foot and mouth disease. The relationship between vesicular disease and Coxsackie B5 is discussed briefly.

Brain and spinal cord lesions in pigs inoculated with swine vesicular disease (UKG strain) virus and coxsackievirus B5.

Pigs inoculated intravenously with swine vesicular disease virus (UKG strain), those inoculated with coxsackievirus B5, and other pigs exposed by pen contact to the same viruses developed diffuse encephalomyelitis. Perivascular cuffing, with lymphocytes and formation of neuroglia cell foci, were most prominent in telencephalon, diencephalon, and mesencephalon. Encephalitis was of mild to severe intensity. Severity of lesions was more extensive and severe in the pigs exposed to swine vesicular disease virus. Pen contact exposure to either of the 2 viruses caused a more severe central nervous system reaction than did intravenous inoculation. The type and the distribution of lesions produced by the 2 viruses indicate that they may be related.

[Swine vesicular disease: pathological study (author's transl)]. / La maladie vésiculeuse du porc: étude anatomo-pathologique

Seventy-eight pigs inoculated with swine vesicular disease virus are autopsied at reaction times staged from day I to day 44. Two viral strains of different pathogenicity are studied. Non pathognomonic histological lesions of this disease are identical to those observed in foot and mouth disease. This confirms the relationship of the two viruses.