Charles A. Mebus

African swine fever

Publisher Summary African swine fever (ASF) is a tickborne and contagious disease of swine, caused by a large icosahedral cytoplasmic DNA virus, which has been tentatively classified as an Iridouirus. ASF was first described in a comprehensive report by Montgomery in 1921. In this report he described the outbreaks of the disease in Kenya between 1909 and 1915 where 1352 (98.9%) of 1366 infected pigs died. In addition, he reported that the disease was caused by a virus, and reported the results of studies on transmission, virus survival in the environment, and host range, including the possible role of wild pigs in maintaining the virus in nature. He believed that the disease was caused by a serologic variant of the hog cholera virus (classical swine fever)a conclusion that was repeated in recent times when ASF was introduced into a previously uninfected area. Subsequent to Montgomerys report, ASF was diagnosed in many areas of southern Africa. In 1933, in an outbreak in South Africa, 8% of 11,000 infected pigs survived.

Cell culture adaptation and propagation of a reovirus-like agent of calf diarrhea from a field outbreak in nebraska

The Nebraska calf diarrhea viral (NCDV) agent was successfully adapted and propagated in several cell culture systems. Criteria of propagation were: production of a cytopathic effect, specific fluorescence, interference with cytopathogenicity of another virus, infection of neonatal calves, and identification of the NCDV agent by electron microscopy (EM) or immuno-electron microscopy (I-EM). The EM and I-EM techniques proved to be valuable diagnostic aids for detecting NCDV disease in affected calves. Morphologically, the NCDV agent resembled the reoviruses. Resistance to lipid solvents and fluorocarbon further related NCDV to this group. The NCDV agent, however, was serologically unrelated to reoviruses so a “reovirus-like” classification for this virus was suggested.

African swine fever virus specific porcine cytotoxic T cell activity

SummaryAfrican swine fever virus (ASFV) specific, cytotoxic T lymphocyte (CTL) activity has been studied in a protection model in which SLA inbred miniature swine are experimentally inoculated with a naturally occurring, non-fatal ASFV isolate (NHV). Peripheral blood mononuclear cells (PBMC) from such infected swine show significant activity in CTL assays, using cultured ASFV-infected porcine blood derived macrophages as target cells. This CTL activity is elicited from PBMC by in vitro restimulation of effector cells with low doses (multiplicity of infection=0.1) of the homologous virus isolate for 48 to 72 h. For SLAc/c effectors, this CTL activity appears to be SLA class I restricted because (1) blocking target cell antigens with monoclonal antibodies (mAb) against SLA class I antigens causes a major reduction in CTL activity; (2) there is preferential lysis of SLA class I matched, ASFV infected targets; and (3) depletion of effector cells with CD8 specific mAb and complement causes a reduction in CTL activity. The CTL activity is ASFV specific for all pigs tested in that infected macrophages are preferentially lysed as compared to normal (non-infected) cultured macrophages or macrophages infected with hog cholera virus (HCV). Lysis of macrophages infected with different ASFV isolates revealed that there is marked lysis of macrophages infected with the virulent L 60 isolate but less lysis of macrophages infected with the DR-II and Tengani isolates. In summary, our data show that ASFV specific CTL activity is triggered in swine infected with the NHV ASFV isolate.

Protection of goats against peste des petits ruminants with a vaccinia virus double recombinant expressing the F and H genes of rinderpest virus

Peste des petits ruminants (PPR) is a viral disease of goats and sheep characterized by necrotizing and erosive stomatitis, enteritis and pneumonia. The causative agent, PPRV, is a member of the family Paramyxoviridae and the genus Morbillivirus. Other members of the genus include rinderpest (RPV), measles, canine distemper and phocid distemper viruses. PPR has a very high rate of morbidity and mortality, and effective control of this disease is of economic importance in Africa, Asia and the Middle East. Currently, there is no safe and effective vaccine available against the disease. The tissue culture rinderpest vaccine (TCRV) protects small ruminants against severe disease; there are, however, clinical problems associated with vaccination. This laboratory has recently developed several effective vaccinia virus recombinant vaccines for rinderpest. These vaccines are easy to administer, inexpensive to produce and heat-stable. Goats were vaccinated with a vaccinia virus double recombinant expressing the haemagglutinin and fusion genes of RPV. Although vaccinated animals developed antibodies (neutralizing and ELISA) to RPV, and not to PPRV, they were completely protected against challenge inoculation with virulent PPRV. This would indicate that protection is most probably due to cell-mediated immunity. Use of the rinderpest double recombinant vaccinia virus in areas of the world where PPRV is endemic would aid in the control and eradication of PPR.

Analysis of sites of foot and mouth disease virus persistence in carrier cattle via the polymerase chain reaction

SummaryThis study was undertaken in order to explore possible sites of foot-and-mouth disease virus (FMDV) persistence during the carrier state. Tissue samples taken from experimentally infected animals at different times post-infection (p.i) were examined by conventional viral isolation and the polymerase chain reaction (PCR) technique. The analysis of samples from several organs taken from 17 bovines between 3 and 270 days p.i. allowed the following conclusions: 1) Virus present in oesophageal-pharyngeal fluids (OPF) during the carrier state originates in the pharynx as shown by the detection of antisense FMDV RNA by PCR, 2) PCR is more sensitive than standard virus isolation techniques and may be used for the rapid detection of FMDV in specimens obtained during the acute stage of FMD and for identification of persistently infected cattle.

Analysis of the polypeptides synthesized in rinderpest virus-infected cells

We have identified, by [35S]methionine labeling, eight major induced proteins and a number of minor proteins in rinderpest virus-infected bovine kidney cells. The polypeptides ranged in molecular weight from 212 to 21.5 kDa. The majority of these polypeptides are virus specific, as demonstrated by immunoprecipitation with rabbit hyperimmune serum against rinderpest. Infected cells radiolabeled with glucosamine contained a 75-kDa polypeptide and a broad band migrating at 80 kDa, both identified as virus specific by immunoprecipitation. Phosphorylated virus-specific proteins of 65 kDa and a complex of polypeptides at 92.5 kDa were also identified. Monospecific and monoclonal antibodies against measles virus and canine distemper virus hemagglutinin, fusion protein, nucleocapsid protein, and phosphoproteins confirmed the identity of the corresponding rinderpest virus-specific polypeptides.

Further studies on the efficacy of an inactivated African horse sickness serotype 4 vaccine

The immunity induced by two inoculations of a commercial inactivated African horse sickness (AHS) serotype 4 (AHSV-4) vaccine was studied. No adverse reaction was observed in five horses following vaccination. Following challenge-inoculation, no clinical signs attributable to AHS, no viraemia indicating infection, and no anamnestic response was observed in the vaccinated ponies. Two control ponies developed clinical signs typical of AHS, high levels of viraemia, and died 7 and 8 days postchallenge-inoculation. The quality of immunity induced by the two-dose regimen was compared with a one-dose regimen from a previous study; in the one-dose study following challenge-inoculation, six of nine ponies were protected from clinical signs of AHS, seven of the nine vaccinated ponies developed an anamnestic response, and one pony had a viraemia about 10(3) 50% mouse lethal dose of AHSV-4 per ml of blood for 3 days following challenge-inoculation. The utility of an efficacious inactivated AHS vaccine in the control and eradication of AHS from a non-endemic area is discussed. The lack of viraemia following vaccination with an inactivated vaccine and the prevention of vector infection by animals exposed to field virus are important in the eradication of AHS.

Swine leukocyte antigen and macrophage marker expression on both African swine fever virus-infected and non-infected primary porcine macrophage cultures☆

Abstract Swine leukocyte antigens (SLA) and a macrophage specific marker were monitored on porcine macrophages cultured with or without macrophage colony stimulatory factor (M-CSF) and on cells infected with African swine fever virus (ASFV). SLA expression was maximal either in the total cell extract or on the cell surface at 3–4 days of culture; after 4 days these values began to decrease. Fluorescence analyses of immunostained macrophages cultured with or without M-CSF indicated a major upward shift in the number of SLA Class I molecules on individual macrophages whereas for SLA Class II both a novel expression of Class II and an upward shift in the number of molecules per cell were evident. Infection of 3-day-old macrophage cultures with three different isolates of ASFV resulted in minor changes in surface expression of SLA Class I, SLA Class II, and macrophage markers. No differences in infection with ASFV was observed whether macrophages were SLA Class II positive or negative, nor was there blocking by anti-SLA Class I or Class II monoclonal antibodies of ASFV infection of cultured macrophages.

Modulation of splenic macrophages, and swine leukocyte antigen (SLA) and viral antigen expression following African swine fever virus (ASFV) inoculation

SummaryExpression of viral and major histocompatibility complex (MHC) antigens and localization of T cells and macrophages was studied in frozen tissue sections of spleens taken from normal pigs or from pigs inoculated with highly virulent Lisbon 60 (L60), or with moderately virulent Dominican Republic 1978 (DR-II), African swine fever virus (ASFV) isolates. Splenic sections from L60 inoculated pigs exhibited a large decrease in macrophage staining, whereas DR-II infected animals appeared more intensely stained in the macrophage sheath arteries. Class I and class II MHC expression was decreased in spleens from pigs infected with either isolate at 3 day post inoculation (DPI). This was reversed in DR-II inoculated pigs at 4 DPI. Splenic tissue sections from L60 inoculated pigs exhibited only a marginal increase in SLA expression at a later time, 6 DPI. We suggest that the recovery of SLA expression during infection of pigs with ASFV is associated with survival or replacement of macrophages in the spleen leading to an effective immune response against the virus.

Survival of several porcine viruses in different Spanish dry-cured meat products

The purpose of this study was to determine the effect of the Spanish dry curing process on the inactivation of viruses of main economic importance: African swine fever virus (ASFV), classical swine fever virus (CSFV), foot and mouth disease virus (FMDV) and swine vesicular disease virus (SVDV) in Serrano cured hams and Iberian cured hams, shoulders and loins. 31 to 35 Iberian, or white pigs were infected with the respective viruses, and slaughtered at the estimated peak of viremia. The meat products were processed using the commercial procedures currently used in Spain. Samples collected at slaughter and at predetermined intervals during processing were analysed for virus survival by in-vitro and in-vivo assays. The results demonstrated that ASFV, FMDV, CSFV and SVDV are inactivated during Spanish commercial curing process in the dry-cured products studied except in the case of the Serrano ham infected with SVDV, in which the curing time required for inactivation of the virus in lymph nodes exceeded the maximum commercial curing time.