Sequence analysis of a porcine enterovirus serotype 1 isolate: relationships with other picornaviruses

The majority of the genomic sequence of a porcine enterovirus serotype 1 (PEV-1) isolate was determined. The genome was found to contain a large open reading frame which encoded a leader protein prior to the capsid protein region. This showed no sequence identity to other picornavirus leader regions and the sequence data suggested that it does not possess proteolytic activity. The 2A protease was small and showed considerable sequence identity to the aphthoviruses and to equine rhinovirus serotype 2. The 2A/2B junction possessed the typical cleavage site (NPG/P) exhibited by these viruses. The other proteins shared less than 40% sequence identity with equivalent proteins from other picornavirus genera. Phylogenetic analyses of the P1 and 3D sequences indicated that this virus forms a distinct branch of the family Picornaviridae. On the basis of results presented in this paper PEV-1 has been assigned to a new picornavirus genus. The phylogeny of the virus in relation to other picornaviruses is discussed.

Sero- and CPE-types of porcine enteroviruses isolated from healthy and diarrheal pigs: possible association of CPE type II with diarrhea

Porcine enteroviruses (PEV) were isolated from feces of healthy and diarrheal domestic Japanese pigs, and examined for their serotypes. Each virus of the isolates corresponded not only to the Japanese version of the reference serotype, but also to its corresponding world version of the reference serotype. Twenty-two samples (75.9%) of 29 isolates from the feces of healthy pigs exhibited a characteristic of CPE I. On the other hand, 69.2% (27/39) of all diarrheal pigs showed a characteristic of CPE II. This would suggest the PEV with CPE II has a closer association with the enteric pathogenicity than that with CPE I.

General characteristics and viral susceptibility of a newborn pig kidney (NPK) continuous culture

We have developed a fibroblastic-like continuous culture of newborn pig kidney (NPK). The current cell line was serially passaged 160 times and appeared to be well suited for production and assay of a number of viruses affecting pigs, such as pig parvovirus, pseudorabies and transmissible gastroenteritis. The cell line appeared aneuploid, with a modal chromosome number of 36 and induced tumors, classified as fibrosarcoma, in athymic mice.

An enzyme-linked immunosorbent assay (ELISA) for the detection and quantification of antibodies against swine vesicular disease virus (SVDV)

A liquid phase blocking sandwich ELISA has been compared with virus neutralisation for testing pig sera for antibodies against swine vesicular disease (SVD) virus. Highest infectivity titre of SVD virus was obtained using a multiplicity of infection of 30 pfu/cell and harvesting after 21 h. Titres obtained for 300 clinically normal animals were assessed by ELISA and 89% were found to be 1/6 or less. Results were skewed and spread up to 1/45. Comparison of known positive sera resulted in a correlation between the two methods of 0.68 and showed that a virus neutralisation titre of 1/16 was equivalent to 1/40 (log10 1.61) by ELISA. Variation in results obtained by replicate testing using ELISA and virus neutralisation was almost identical. Overlap between positive and negative sera was shown to be reduced to 1-1/2 fold in ELISA. Therefore, the ELISA correlated well with virus neutralisation and has several advantages over the latter.

[Retinoic acid modification of cell culture used for reproduction of enteropathogenic viruses]

The 0.001-0.005% retinoic acid injection into the growth cultural medium of prime and continue cell cultures 12-24h before inoculation considerably raised the cell sensitivity to animal entero- and coronaviruses. The entero- and coronaviruses concentrations in cultural medium increased by 10(1.58) and 10(1.68)TCID 50/1.0 respectively. The optimized parameters of the cell culture processing for the enteropathogenic viruses reproduction improvement are proposed.

Pseudorabies virus, porcine parvovirus, and porcine enterovirus interactions with the zona pellucida of the porcine embryo

Porcine embryos (n = 93) were incubated on cell monolayers that had been previously inoculated with pseudorabies virus, porcine parvovirus (PPV), or each of 2 porcine enteroviruses. After 2, 24, or 48 hours of incubation, the embryos were fixed in glutaraldehyde and examined by electron microscopic procedures. It was found that pseudorabies virus adsorbed to the zona pellucida (ZP) and entered sperm tracks in the ZP. The PPV and both enteroviruses entered pores in the ZP and were associated with sperm that were at or near the outer surface of the ZP. In addition, PPV was seen enmeshed in cellular debris on the outer surface of the ZP. Evidence of a productive viral infection of the blastomeres of the embryos was not found.

Plaque morphology and pathogenicity for newborn mice of swine vesicular disease virus. II. Temperature-dependent mutants and their clones

From wild swine vesicular disease virus (SVDV) strains temperature-dependent (td) mutants td 27 degrees C, td 32 degrees C and td 42 degrees C were derived. Differences were noted in their pathogenicity for newborn mice. The non-homogeneity of the td populations was manifested by formation of plaques of various sizes and confirmed by differential pathogenicity of the clones derived from them. A higher pathogenicity of the td mutants and their clones was associated not only with larger plaques, but also with higher temperature permissive for the given mutant. The td 27 degrees C mutants were not virulent for newborn mice, similarly to the attenuated SVDV strain and its clones.

Plaque morphology and pathogenicity for newborn mice of swine vesicular disease virus. I. Wild strains and their clones

The population of wild swine vesicular disease virus (SVDV) strains was found non-homogeneous as manifested by varying plaque size and different pathogenicity of the clones obtained. The clones derived from large plaques (5-9 mm)--dominating among wild strains--were more virulent for newborn mice than those obtained from smaller plaques (1-2 mm). To evaluate the pathogenicity of wild SVDV strains the dose index was calculated; the clones were compared by dose index and theoretical pathogenicity index, respectively.

Comparison of proliferation and cytopathogenicity of swine vesicular virus and coxsackievirus B5

Sequential appearance of both swine vesicular disease virus and Coxsackievirus B5 antigens in a pig kidney cell line was studied by immunofluorescence and electron microscopy. The replication cycle of each virus was approximately 3-4 h. Viral antigens were demonstrable in the cytoplasm 2 h after inoculation. A compact mass of fluorescence was seen when cells showed cytopathogenic effect at 5.5 h. After 3 h, a few viral particles, seen by electron microscopy, were in the cytoplasm. Morphological changes of cells occurred at the same time. Cytoplasmic crystalline arrays of virus were first detected at 7 h.

In vivo and in vitro studies on temperature-sensitive mutants of swine vesicular disease virus

Two temperature-sensitive mutants of the Ukg 27/72 strain of swine vesicular disease virus were isolated in tissue culture and a third was derived following adaptation in mice. All three were found to have similar growth restrictive temperatures, but varied considerably in their virulence when administered to pigs. The route of inoculation appeared to exert a considerable influence on the apparent degree of attenuation, the antibody titre engendered and the transmission of disease to pigs held in contact with inoculated animals. One strain appeared almost totally attenuated when inoculated animals. One strain appeared almost totally attenuated when inoculated into pigs but spread to animals in contact causing severe disease. Virus re-isolated from one such animal was found to have retained its temperature sensitive phenotype, suggesting that virulence in this case was not directly related to temperature sensitivity. Pigs with high antibody titres were found to be susceptible when placed in contact with challenge animals, although the lesions which developed were mild.

Classification of porcine enteroviruses by antigenic analysis and cytopathic effects in tissue culture: description of 3 new serotypes

Porcine enteroviruses isolated in the United Kingdom between 1972 and 1976 were compared with the 8 serotypes previously described and with human coxsackie B virus types 1 to 6 for ability to grow in different cell lines. This allowed the classification of all strains into 3 broad groups according to type of cytopathic effect in IBRS-2 cells and further subdivision on the basis of production of cytopathic effect in BHK 21, HeLa and VERO cells. None of the porcine enterovirus strains was neutralized by antisera to human enteroviruses (Lim Benyesh-Melnick Pools) with the exception of swine vesicular disease virus, which was neutralised by coxsackie B5 antiserum. Antisera prepared either in gnotobiotic pigs or in guinea pigs against the 8 porcine enterovirus serotypes failed to neutralize 9 isolates which could be classified into 3 new serotypes, for which Nos. 9, 10 and 11 are proposed. Guinea pig sera could be used as an alternative to gnotobiotic pig sera for type differentiation.

The effect of relative humidity on swine vesicular disease virus in dried films before and during formaldehyde fumigation

Swine Vesicular Disease virus (SVDV) did not survive drying at high relative humidities (r.h.) but there was little virus loss at low r.h. Purified virus dried in films was inactivated by formaldehyde fumigation only at high r.h. Inactivation was also influenced by the suspending medium from which the virus was dried. Purified virus resuspended in distilled water and then dried, was rapidly killed, but that in tissue culture fluid survived.

The inactivation of viruses in cattle and pig slurry by aeration or treatment with calcium hydroxide

Porcine enterovirus type 2 or porcine adenovirus type 3 were seeded into samples of pig slurry, and a bovine enterovirus was seeded into cattle slurry, and samples of the slurry were aerated in the laboratory for 21 days. The viruses were inactivated more rapidly in the aerated slurry than in control slurry which was not aerated. The difference in inactivation rate was greatest for the porcine adenovirus and least for the bovine enterovirus. Inactivation of the porcine enterovirus in aerated distilled water and in aerated, autoclaved pig slurry proceeded at a similar rate as in the same materials which were not aerated. Ten samples of aerated slurry were collected from an aeration tank which received weekly additions of raw pig slurry which was sampled at the same times. Each sample yielded a porcine enterovirus after concentration with the polyelectrolyte PE-60, but in three comparative titrations the viral infectivity titre in concentrates of the raw slurry was at least 1000 times greater than in the aerated slurry. Porcine enterovirus type 2 and porcine adenovirus type 3, which were seeded into pig slurry, and a bovine enterovirus seeded into cattle slurry, were inactivated by treatment of the slurry with calcium hydroxide at pH 11.5. The inactivation rate was highest for the bovine enterovirus and lowest for the porcine adenovirus.

Scanning electron microscopical observations on the cytopathology of porcine enteroviruses in PK-14 cells

Examination by scanning electron microscopy (SEM) of PK-15 cells infected with each of the two cytopathogenic types of porcine enterovirus revealed changes similar to those observed by light microscopy. However, differences between the two types could be detected at an earlier stage of the infection. Cells infected with T80 virus (type I) were rounded, with surface microridges, while V13 (type II) infected cells were characterized by cytoplasmic protrusions.

A comparison of six methods for the concentration of a porcine enterovirus

Single-step concentration of porcine enterovirus strain T80 by adsorption to the polyelectrolyte PE60 gave virus concentration factors of 35- to 88-fold in terms of plaque-forming units, with recovery rates of 22 to 75% of total virus present in the original virus suspension. Concentration by separation in an aqueous polymer two-phase system gave virus concentration factors of 56- to 105-fold and recovery rates of 37 to 107%. In the latter procedure, sodium dextran sulfate appeared to have no effect on plaque numbers, although plaques were sharper and clearer when this substance was incorporated in the overlay. The failure of sonication of virus concentrated by either procedure to increase plaque numbers indicated the absence of virus aggregates in the concentrates. T80 virus was not effectively concentrated by cobalt chloride or polyethylene glycol precipitation or by adsorption to either aluminium hydroxide or calcium hydrogen phosphate.