Polypeptides and structure of African swine fever virus.

Extracellular and intracellular African swine fever virus (ASFV) was purified using a two-phase aqueous polymer system. Both the structure of the virus and the polypeptides present during the purification procedure were studied. After PEG/dextran phase separation and centrifugation through 20% (w/v) Ficoll, 79% of input infectivity was recovered as semi-purified virus. The density of the virus after equilibrium centrifugation in sucrose was 1.19 g/ml. The envelope of the virion consisting of a unit membrane was removed from the virion after centrifugation in sucrose. Removal of envelope was associated with the loss of a 230 kilodalton (kd) glycoprotein from the virion. Disruption of the viral surface structure resulted in a loss of infectivity. Eighteen of the most prominent of the 33 polypeptides of extracellular or cell free (CF) virus were those with molecular weights of 230, 195, 165, 155, 150, 125, 116, 97, 92, 73, 62, 58, 50, 45, 35, 33, 25 and 11 kd, while the fourteen most prominent polypeptides in intracellular or cell associated (CA) virus were 103, 97, 92, 84, 73, 62, 58, 54, 47, 45, 35, 33, 25 and 17 kd. The 45 kd polypeptide may be actin which copurifies with the virus. No major differences were found in the number or size of proteins among three isolates of ASFV. Electron micrographs of thin sections of ASFV show the capsid to consist of a distinct double layer of closely packed capsomeres enclosed on both sides with a semi-transparent layer. Cell associated virus measured from side-to-side 188 nm and vertex-to-vertex 212 nm. The capsid encloses an inner core composed of a dense nucleoid surrounded by a 40-48 nm layer of core protein.

Purification of african malignant catarrhal fever virus using a two-phase aqueous polymer system.

The WC11 isolate of malignant catarrhal fever virus (MCFV) was purified by a method employing phase separation of the virus in an aqueous polymer system. Virus was grown in primary bovine thyroid cells. The virus released into the extracellular medium was purified. Initial concentration and partial purification of MCFV occurred after separation of the virus into the dextran phase following the addition of 10% (w/v) polyethylene glycol and 8% (w/v) dextran T10 to the extracellular virus. Further purification was achieved by centrifugation into a 20% (w/v) ficoll cushion followed by centrifugation to equilibrium by flotation in a 15 to 36% (w/w) CsCl or 30 to 60% (w/w) sucrose gradient. Virus recovery was monitored using a plaque assay on bovine thyroid cells and ranged from 3 to 23% of the input extracellular virus.

Comparison of African and American forms of malignant catarrhal fever: transmission and clinical signs.

African and American forms of malignant catarrhal fever (MCF) infections were produced by inoculating blood from affected cattle into susceptible cattle. Ease of disease transmission, incubation period, volume of blood required for infection, and clinical signs were compared in 30 cattle with African MCF and in 19 with American MCF. American MCF was more difficult to transmit than was African MCF and required eight to ten times more blood as inoculum. American MCF incubation period was more than twice as long as that of the African MCF, but the disease course was three times shorter. Clinical signs were similar for the two forms; however, in the American form, the disease was more acute and a larger percentage of animals had severe diarrhea.

Relationship of plaque size and virulence for chickens of 14 representative Newcastle disease virus strains.

Ability of 14 Newcastle disease virus strains to produce large plaques was related to virulence for chickens. Plaque-size comparisons were made under standard conditions in chick embryo cell monolayers. All plaque-producing strains showed a range of plaque sizes modified to a degree by the overlay medium used. An increase in size was found for most strains under methyl-cellulose overlay medium. Markedly larger plaques were found under this medium for both Calif-RO and Calif-CG strains. Heterogeneity in plaque size was most pronounced in velogenic (high virulence) strains. Only populations of small plaques were found in mesogenic (intermediate virulence) strains, and plaques were rarely found in lentogenic (low virulence) strains. Statistical analysis showed that the plaque size of velogenic strains differed significantly from mesogenic strains. None of the 11 plaque-producing strains had a normal distribution of plaque sizes, owing primarily to the presence of different genotypes within the plaquing population of a strain. This was demonstrated by derivation of clones from two of the strains. The populations of the large (Herts L) and small (Herts S) clear plaque clones derived from Eng-Herts were homogenous and distinct from one another on the basis of plaque size. Herts L was more virulent than Herts S. Although Herts L became more heterogenous in respect to plaque size upon repeated passage in embryonated eggs, no decrease in virulence of the strain was observed.