No serological evidence for the presence of swine vesicular disease virus in South Africa.

An indirect ELISA incorporating a protein A-peroxidase conjugate was developed for detecting antibodies to swine vesicular disease virus (SVDV) in pig sera. This test and a conventional virus neutralization test were found to be equally sensitive. A total of 2846 pig sera collected from various abattoirs in South Africa were tested using the indirect ELISA. No serological evidence of infection with SVDV in pigs in South Africa was found.

Failure of Haematobia thirouxi potans (Bezzi) to transmit foot-and-mouth disease virus mechanically between viraemic and susceptible cattle.

In 2 separate experiments the blood-feeding fly Haematobia thirouxi potans (Bezzi) failed to transmit foot-and-mouth disease virus when transferred from viraemic (log 2,6-log 4,3 MLD50 or TCID50/ml) to susceptible cattle. Each experiment involved 2 susceptible and 2 viraemic animals housed in separate stables and 2,000-4,000 flies of which most had fed on viraemic hosts 120 min prior to transfer. Furthermore, only minimal quantities of virus were isolated from free-living flies captured on experimentally infected buffalo (Syncerus caffer) in the acute stages of infection.

The suitability of a rolled BHK21 monolayer system for the production of vaccines against the SAT types of foot-and-mouth disease virus. I. Adaptation of virus isolates to the system, immunogen yields achieved and assessment of subtype cross reactivity.

In an examination of 34 southern African SAT-type foot-and-mouth disease viruses, all but 1 attained satisfactory levels of infectivity within 6 passages in rolled BHK21 monolayer cell cultures. However, there were marked differences between adapted viruses with respect to the mass of immunogen (146S material) produced. Several isolates which consistently produced levels greater than or equal to 2 micrograms/ml were identified. In cross neutralization tests using post-vaccinal sera, SAT-1 and SAT-2 isolates showed considerable diversity and none of the viruses tested would be expected to produce a broad-spectrum response if incorporated into a vaccine. On the other hand, when 2 of the SAT-2 isolates were incorporated into the same vaccine a distinctly broader response resulted.

African swine fever. I. Morphological changes and virus replication in blood platelets of pigs infected with virulent haemadsorbing and non-haemadsorbing isolates.

Replicating and mature viral particles were detected with the transmission electron microscope in blood platelets of pigs infected with virulent haemadsorbing and non-haemadsorbing African swine fever virus isolates. Although platelet numbers decreased terminally in infected pigs, the most noticeable morphological damage to these cells apparent in the last 2 days of the disease included cytoplasmic swelling, vacuolation, fragmentation and loss of dense granules.

Foot-and-mouth disease and the African buffalo (Syncerus caffer). II. Virus excretion and transmission during acute infection.

Three groups of young buffalo in captivity were infected by exposing them to similar buffalo in the acute stages of infection induced by needle inoculation with SAT 1 or 2 viruses. Clear foot lesions developed in most of the buffalo from which the relevant virus types were re-isolated. During the first week following infection virus was found in blood, nasal secretions, saliva, preputial secretions and faeces. Air samples collected in the immediate vicinity of acutely infected buffalo were also found to contain virus. However, the regularity of virus detection as well as the quantity of virus in buffalo specimens was generally lower than for cattle infected with viruses of the same type. Conversely, virus was detected in the nasal secretions or saliva of 3 buffalo up to 4 weeks after infection, a situation which has not been encountered in cattle. Susceptible cattle and impala (Aepyceros melampus) were penned together with or in the immediate vicinity of infected buffalo and shared feeding and watering facilities with the buffalo. The pattern of transmission which emerged indicated that transfer of these viruses from buffalo to other species probably occurs only in the acute stages of infection and where there is direct physical contact between the species.

Lesions resulting from inoculation of porcine foetuses with porcine parvovirus.

In utero inoculation of 15 sows at various stages of gestation with a local strain of porcine parvovirus (PPV) resulted in resorption, abortion or the birth of weak, dead, or mummified foetuses. Histopathological lesions observed in foetuses of sows slaughtered at various post-inoculation intervals consisted of a perivascular inflammatory reaction primarily observed in the brain and kidneys. The presence and extent of the inflammatory reaction were dependent upon the age of the foetus at the time of infection. In the sow a perivascular inflammatory reaction was found in the endometrium, while the larger blood-vessel walls were infiltrated by lymphocytes, and it is suggested that these vascular lesions may contribute to the reproductive failures associated with PPV.

Experimental infection of warthos (Phacochoerus aethiopicus) with African swine fever virus.

Although there were no obvious signs of illness following experimental infection of young warthog with African swine fever virus, the animals developed viraemias between 10(2,4) and 10(3,6) HD50/ml within the first week of infection, and virus concentrations in a number of lymphatic tissues attained high levels (greater than or equal to 10(6) HD50/g). Unlike in blood, and to some extent in the spleen, virus titres in lymph nodes did not decline appreciable during the 33-day observation period, since at the end of the period lymphatic tissues from 2 warthog were still infectious for domestic pigs to which these tissues were fed.

African swine fever: pathogenicity and immunogenicity of two non-haemadsorbing viruses.

The virulence of 2 non-haemadsorbing African swine fever virus isolates were compared with 2 haemodsorbing viruses. While 3 of these isolates usually produced acute death in pigs, 1 non-haemadsorbing virus caused either a fatal infection with an extended course, or few or no obvious signs of infection. Pigs that survived infection with the latter virus were resistant to the lethal effects of the other 3 strains as well as to a pool of 7 isolates made from Ornithodorus porcinus porcinus (senus Walton, 1964) and warthog obtained in the Northern Transvaal.