Induction of apoptotic cellular death in lymphatic tissues of cattle experimentally infected with different strains of rinderpest virus.

The presence, type, and extent of cellular death in lymphatic tissues of cattle experimentally infected with rinderpest virus strains of different virulence was investigated morphologically. Cells with DNA strand breaks were identified in histological sections of palatine tonsil, spleen, and mesenteric and mandibular lymph nodes by the TUNEL (terminal desoxynucleotidyl transferase-mediated dUTP nick end labelling) assay. In addition, representative samples of lymphatic tissues were examined by transmission electron microscopy. The results indicated that cellular disassembly in lymphatic tissues was caused by both apoptosis and oncosis. Cells with DNA strand breaks were observed in follicular and parafollicular areas of lymphatic tissues and their numbers were determined. A significant correlation was found between the number of TUNEL-positive cells and viral virulence. These results suggest that, in addition to oncosis, apoptotic cellular death in lymphatic tissues contributes substantially to the pathogenesis of rinderpest.

Trial of a capripoxvirus-rinderpest recombinant vaccine in African cattle.

Cattle were vaccinated with differing doses of an equal mixture of capripox-rinderpest recombinant viruses expressing either the fusion protein (F) or the haemagglutinin protein (H) of rinderpest virus. Animals vaccinated with 2 x 10(4) p.f.u. or greater of the combined viruses were completely protected against challenge, 1 month later, with both virulent rinderpest and lumpy skin disease viruses. Vaccination with any of the doses did not induce any adverse clinical response in the animals or transmission of the vaccine virus between animals. All cattle challenged 6 or 12 months after vaccination with 2 x 10(5) p.f.u. of the mixture of recombinant viruses were protected from severe rinderpest disease. Ten out of 18 were completely protected while the remaining 8 developed mild clinical signs of rinderpest. Cattle vaccinated with the recombinant vaccines after prior infection with the parental capripox virus showed more marked clinical signs of rinderpest after challenge with virulent rinderpest, but 9 out of 10 recovered, compared with 80% mortality in the unvaccinated controls.

Evidence for different lineages of rinderpest virus reflecting their geographic isolation.

Sequence analysis of part of the fusion protein gene from recent isolates of rinderpest virus revealed that distinct lineages of the virus exist which reflect the geographical location of their isolation in Africa and Asia. Current strains circulating in Kenya and Sudan were most similar, both in terms of nucleotide sequence and pathogenic nature, to viruses isolated in Egypt and in Nigeria in 1983/1984 and they were quite distinct from an East African isolate (RBT-1) from the 1960s. Two older isolates of the virus, the Japanese avianized/lapinized vaccine strain dating from the 1930s and the Old Kabete strain dating from 1911, each differed considerably from the other viruses. The sequence data were derived from the region where the precursor protein is cleaved to yield the biologically active F1/F2 heterodimer; all strains analysed had a highly basic connecting peptide which is required for efficient cleavage by endogenous host cell proteases. No correlation was found between amino acid changes at this site and the rinderpest virus pathogenicity unlike the association reported for Newcastle disease virus.

Confirmation of rinderpest in experimentally and naturally infected cattle using microtitre techniques.

Virulent rinderpest virus was detected by immunoperoxidase staining of microtitre bovine kidney cell cultures within 24 to 48 hours of inoculation with prescapular lymph node and spleen homogenates from experimentally infected steers. Rinderpest virus specific cytopathic effects were evident from 48 hours in microtitre plates and from 72 hours in rolled tube cultures. Nasal and ocular secretions collected from cattle naturally infected with rinderpest and inoculated into bovine kidney cell cultures did not readily yield cytopathic virus in both tubes and microtitre plates, but immunoperoxidase staining of microtitre cultures on the fourth day of inoculation detected replication of virus in cultures inoculated with ocular and nasal secretions from seven of 17 cattle tested.

Use of Vero cells for the isolation and propagation of malignant catarrhal fever virus.

Vero cells were compared with primary bovine thyroid (BTh) cultures for the isolation of malignant catarrhal fever virus from infected blood and tissues. Comparative titrations showed Vero cells detected only two-fold less infectivity in rabbit spleen suspensions than BTh cells. Twenty three of 32 bovine buffy coat cell preparations which were positive on BTh cells were also positive on Vero cells. The cytopathic effects (CPE) of virus isolates in Vero cells consisted of syncytia and refractile cytomegalic cells which were as easy to recognise and developed as rapidly as CPE in BTh cells. Two laboratory strains of malignant catarrhal fever virus were readily adapted to and maintained by passage in Vero cells.