A model of lineage-1 and lineage-2 rinderpest virus transmission in pastoral areas of East Africa

The development of a stochastic, state-transition model of rinderpest transmission dynamics is described using parameter estimates obtained from both laboratory and participatory research. Using serological data, the basic reproduction numbers for lineage-1 rinderpest virus in southern Sudan and for lineage-2 rinderpest virus in Somali livestock were estimated as 4.4 and between 1.2 and 1.9, respectively. The model predictions for the inter-epidemic period in Sudan and Somalia (1.2 and 4.2 years, respectively) were in agreement with analysis of livestock-owner reports (1-2 years and 5 years, respectively).

Development of a thermoresistant tissue culture rinderpest vaccine virus

The currently used Plowright's tissue culture rinderpest vaccine (RBOK strain) gives full protection and lifelong immunity, but it is highly thermolabile and requires maintenance of cold chain from vaccine production till delivery. Keeping in view the need for a thermostabile vaccine in tropical developing countries with limited refrigeration facilities, we passaged serially the RBOK strain of rinderpestvirus (RPV) at gradually elevated temperature up to 40 degrees C to obtain a thermoresistant RPV (TR-RPV) mutant. The thermoresistance (thermostability) and antigenicity of TR-RPV were compared with those of the vaccine virus by various methods, confirming the acquired properties. Thus, the infectivity titres of the TR-RPV mutant and vaccine virus were determined after incubation for various times at 37 degrees C. Regression analysis indicated that TR-RPV had a half-life of 1.81 hr and a degradation constant of 0.1656, while the parent vaccine virus had a half-life of 1.11 hr and a degradation constant of 0.2686. In capture ELISA with four different monoclonal antibodies (MAbs) to the N protein of RPV, TR-RPV showed a 10-fold higher reactivity with one MAb as compared to the vaccine virus. Although TR-RPV did react also with the other three MAbs, its reactivity was only 4-5 times higher than that of the vaccine virus. A treatment of the virus with Triton X-100 resulted in 2-4 times higher reactivity with the MAbs. The 35S-methionine-labeled vaccine virus-and TR-RPV-infected Vero cell lysates showed 6 polypeptide bands with identical pattern of migration in polyacrylamide gel electrophoresis in the presence of SDS (SDS-PAGE). Radioimmunoprecipitation assay (RIPA) of the TR-RPV and vaccine virus with a rabbit anti-RPV immune serum (RHIS) and bovine anti-RPV hyperimmune serum (BHIS) showed the presence of four identical antigenic proteins, namely H, N, F and M, for both viruses. It can be concluded that TR-RPV has indeed retained the antigenic properties of the parental vaccine virus besides acquiring thermoresistance.

Improved technique for transient expression and negative strand virus rescue using fowlpox T7 recombinant virus in mammalian cells

The suitability of recombinant T7 polymerase produced using either the highly attenuated MVA strain of vaccinia (MVA-T7) or fowlpox virus (FP-T7) for transient expression and negative strand virus rescue was compared in two mammalian cell lines (MDBK and Vero) and in primary cells of bovine, ovine and caprine origin. Such primary cells are more permissive for the growth of wild type strains of morbilliviruses, such as Rinderpest virus and Peste des petits ruminants virus. MVA-T7 was found to be highly cytopathic in the primary cells, multiplying rapidly and killing the cells within 3-5 days of infection, even when very low multiplicities of infection (MOI) were used. In contrast, FP-T7, which appeared to express similar amounts of T7 polymerase, was found to be non-cytopathic in a variety of primary and established cell lines of mammalian origin and was suitable for use in virus rescue experiments. MDBK cells and primary cells, unlike Vero cells, could not be efficiently transfected and so were unsuitable for virus rescue. Optimal conditions for rinderpest virus rescue in Vero cells were established using FP-T7 in place of MVA-T7. This system will be suitable for rescuing other viruses which grow in Vero cells.

Rinderpest viruses lacking the C and V proteins show specific defects in growth and transcription of viral RNAs

Rinderpest virus is a morbillivirus and the causative agent of an important disease of cattle and wild bovids. The P genes of all morbilliviruses give rise to two proteins in addition to the P protein itself: use of an alternate start translation site, in a second open reading frame, gives rise to the C protein, while cotranscriptional insertion of an extra base gives rise to the V protein, a fusion of the amino-terminal half of P to a short, highly conserved, cysteine-rich zinc binding domain. Little is known about the function of either of these two proteins in the rinderpest virus life cycle. We have constructed recombinant rinderpest viruses in which the expression of these proteins has been suppressed, individually and together, and studied the replication of these viruses in tissue culture. We show that the absence of the V protein has little effect on the replication rate of the virus but does lead to an increase in synthesis of genome and antigenome RNAs and a change in cytopathic effect to a more syncytium-forming phenotype. Virus that does not express the C protein, on the other hand, is clearly defective in growth in all cell lines tested, and this defect appears to be related to a decreased transcription of mRNA from viral genes. The phenotypes of both individual mutant virus types are both expressed in the double mutant expressing neither V nor C.

Inhibition of replication of rinderpest virus by 5-fluorouracil

5-Fluorouracil (5FU), an analogue of uracil, was found to inhibit the production of infectious particles of rinderpest virus (RPV) in Vero cells (African green monkey kidney cells) by 99%, at a concentration of 1 microgram/ml. The levels of individual mRNA specific for five of the virus genes were also reduced drastically, while the level of mRNA for a cellular housekeeping gene-glyceraldehyde-3-phosphate dehydrogenase (GAPDH)-was unaltered by fluorouracil treatment of infected cells. Both virus RNA and protein synthesis showed inhibition in a dose-dependent manner. The virions which budded out of 5-fluorouracil-treated cells also contained reduced amounts of virus proteins compared with virus particles from untreated cells.

Adaptation of caprinised rinderpest virus to grow in Vero cells in vitro

Caprinised rinderpest virus GTV strain (GTV) was adapted to grow in Vero cells (vGTV) by polyethylene glycol-mediated fusion of infected goat spleenocytes with non-infected Vero cells. The usual methods of infection of cell culture, i.e. virus adsorption or co-cultivation, were not successful. vGTV-induced cytopathic changes in Vero cells were similar to those reported for rinderpest virus. Virus titers increased with the passage number but the virulence for goats decreased. Immunoblot analysis did not reveal any difference between vGTV and vRBOK, the tissue culture rinderprest virus RBOK strain adapted to Vero cells.

Rinderpest virus infection of bovine peripheral blood monocytes

The ability of rinderpest virus (RPV) to replicate in vitro in adherent peripheral blood monocytes and monocyte-derived macrophages under non-stimulation conditions was investigated. When flow cytometry analysis on bovine peripheral blood mononuclear cells (PBMC) was performed, monocytic cells were seen to be targets for infection by the cell culture-attenuated RBOK vaccine strain of RPV. Viral glycoprotein (H) and nucleoprotein (N) expression in adherent blood monocytes and monocyte-derived macrophages was compared with the infection in Vero cells, in which a productive infection typical of morbilliviruses is obtained. In both cell types, the infection was m.o.i.-dependent, but the rate of viral protein accumulation was slower in monocytes/macrophages. Double-labelling experiments with monoclonal antibodies against RPV and the myeloid marker CD14 confirmed that the infected blood adherent cells were monocytes and macrophages. Productive infection of monocytes was confirmed by progeny virus titration. Permissiveness to infection was not dependent on macrophage differentiation: in vitro maturation of monocytes to macrophages before infection, did not increase the susceptibility of these cells to RPV infection. With the virulent Saudi RPV isolate, similar results were obtained, although the Saudi virus apparently had a higher rate of replication compared to the attenuated virus. These observations demonstrate clearly that bovine blood monocytes and monocyte-derived macrophages serve as hosts for a relatively slow but productive infection by rinderpest virus.

Immunohistochemical studies of lymphoid tissues of rabbits infected with rinderpest virus

The pathogenesis of infection with the L-strain of rinderpest virus (RPV) in rabbits was investigated. Of several lymphoid tissues examined, those associated with the gut showed the most marked virus growth. The virus titres were maximal 4 days after inoculation but had declined at day 6. The distribution of viral antigen was examined immunohistochemically with the recently established anti-rabbit CD5 monoclonal antibody (MoAb), which is a pan-T-cell marker, and the anti-RPV-nucleoprotein MoAb. The virus antigen was localized in the CD5+ area at the initial stage of infection but spread to all areas of the lymphoid tissues at the later stages. By flow cytometric analysis with both rabbit CD5 and CD4 MoAbs, a decrease of the CD4+ and CD5+ subpopulations was observed in the spleen and mesenteric lymph nodes.

The growth of cell culture-attenuated rinderpest virus in bovine lymphoblasts with B cell, CD4+ and CD8+ alpha/beta T cell and gamma/delta T cell phenotypes

Cloned bovine lymphoblastoid cell lines, transformed by the protozoan parasite Theileria parva were infected with cell culture-attenuated rinderpest virus vaccine. The virus grew readily in lymphoid B cells, CD4+ and CD8+ alpha/beta T cells and gamma/delta T cells producing new infectivity, viral antigens, c.p.e. and total cell death. There did not appear to be a predilection for any particular phenotype of lymphoblast. The results imply that if the vaccine causes immunosuppression, it could do so through a variety of mechanisms.

Identification of epitope expression on the internal proteins of rinderpest virus which is dependent upon virion maturation events

Monoclonal antibodies (MAb) identified the existence of both maturation-dependent and maturation-independent epitopes on rinderpest virus antigens. The former were divided into (i) post-maturation antigenic determinants, which were dependent upon the maturation of viral antigen into complete virions; and (ii) pre-maturation antigenic determinants, which were only expressed on what appeared to be immature particles before 'budding' into the extracellular environment. Epitope expression could be related to the kinetics of virus production, with the 'post-maturation' sites requiring the production of mature/infectious virions, but the 'pre-maturation' sites being lost when mature virus was formed (these 'pre-maturation' determinants were strongly cell-associated). MAb against the different virion proteins of measles virus, when reacting with rinderpest virus did not demonstrate the same relationship to virion maturation as did the anti-rinderpest virus MAb: the anti-measles virus MAb detected maturation-independent epitopes. This work demonstrates the caution which should be taken when preparing antigens for diagnostic and epidemiological purposes, especially when MAb are being used to identify antigenic differences between isolates, and/or to compare antigenically isolates with vaccine viruses.

Improved isolation of rinderpest virus in transformed bovine T lymphoblast cell lines

Bovine T lymphoblast cell lines transformed by the protozoan Theileria parva were compared with bovine kidney (BK) and Vero cells for their ability to isolate various strains of rinderpest virus from tissues and infected secretions. All of the strains of rinderpest virus that were tested, including attenuated cell-culture, caprinised and lapinised vaccines, and both mild and virulent pathogenic strains, readily induced syncytial cytopathic effect (cpe) in T lymphoblasts. The cpe could often be detected within one day of inoculation of lymphoblasts, whereas it took three to 14 days to appear in Vero and BK cells. Using lymphoblasts it was possible to reisolate rinderpest virus from nine of 42 swabs collected from three cattle experimentally infected with an isolate from a recent outbreak of mild disease whereas the same swabs yielded only one reisolate on BK cells. It was also possible using the lymphoblasts to detect infectious virus in the ocular, nasal and oral secretions of goats and rabbits infected with caprinised and lapinised virus, respectively. Peste des petits ruminants virus appeared to grow as rapidly as rinderpest virus in the lymphoblasts whereas canine distemper virus readily induced cpe on first passage but less readily on subsequent passage. Measles virus induced relatively little cpe when inoculated into lymphoblasts and did not appear to passage in these cells. The lymphoblasts are easy to maintain in culture and since they rapidly recovered 11 isolates from 37 diagnostic samples could prove useful in laboratories carrying out rinderpest diagnosis.

B95a, a marmoset lymphoblastoid cell line, as a sensitive host for rinderpest virus

We reported earlier that B95a, an Epstein-Barr virus-transformed marmoset B lymphoblastoid cell line, is more susceptible to infection with measles virus than other cells. The cell line also was found to be susceptible to infection with the lapinized Nakamura III (L) strain of rinderpest virus and various strains derived from it. The B95a cell line was therefore the only host cell system available for the propagation and quantification of the L strain. In contrast to the adaptation of the L strain to Vero cells which results in a diminution of virulence in rabbits, the propagation of the virus in B95a cells preserved the virulence and some other properties in rabbits. Furthermore, when Vero cell-adapted variants of the L strain with diminished virulence were serially passaged in B95a cells, virulence in rabbits was gradually regained.

Effects of antipyretics in rinderpest virus infection in rabbits

Administration of acetylsalicylic acid or mefenamic acid during experimental infection of rabbits with a rabbit-adapted strain of rinderpest virus did not prevent initiation of the febrile response but significantly reduced the duration of fever. Suppression of fever had a markedly deleterious effect on the course of infection, resulting in an increased content of infectious virus in the mesenteric lymph nodes, increased mortality, and retarded recovery in animals that survived the infection. Histological lesions were mainly lymphocytic depletion in lymphoid organs and lymphoid necrosis in both rabbits treated with antipyretics and those left untreated, but damage was more pronounced in the former than in the latter. More viral antigen was detected by immunofluorescence in lymphoid organs of drug-treated rabbits than in those of untreated rabbits. Antipyretic treatment resulted in higher serum interferon levels in the early phase of infection and an increased antibody response in animals that survived the infection.

Adaptation of the lapinized rinderpest virus to in vitro growth and attenuation of its virulence in rabbits

A lapinized rinderpest virus, the L strain, which is virulent in rabbits and had been grown only in rabbits, was adapted to grow in Vero cells by the fusion of Vero cells with virus-infected rabbit spleen cells in the presence of polyethylene glycol, and subsequently passaged in Vero cells by co-culture technique. After several passages, free virus was produced at high titre. The Vero cell-adapted virus acquired the ability to infect several cell lines which were non-permissive to the unadapted virus. Analysis of virus proteins by immunofluorescence using monoclonal antibodies revealed that marked changes occurred in F, P, NP and M proteins by passage in Vero cells. In parallel to the adaptation to cell culture in vitro, the virulence of the virus measured in terms of clinical signs and histological lesions in the lymphoid tissues decreased in its severity whereas its immunosuppressive capacity was maintained unaltered. Thus, rinderpest virus with different degrees of virulence is now available for study in vitro.

The differential growth of virulent and avirulent strains of rinderpest virus in bovine lymphocytes and macrophages

Rinderpest virus (RV) grew readily in cultures of purified bovine peripheral blood lymphocytes and udder macrophages. The growth of three strains of RV was compared and there appeared to be a relationship between increasing virulence and increased ability to infect lymphocytes and macrophages. The proportion of infected cells as determined by the presence of virus antigens was a better indicator of affinity between a strain and cell type than production of new infectious virus. RV grew better in populations of predominantly T lymphocytes than in T-depleted cultures. Although RV could infect 100% of cells in macrophage monolayers, it did not appear to infect more than about 30% of cells in lymphocyte cultures. Virulent RV grew more readily in bovine than caprine or ovine lymphocytes, whereas virulent peste des petits ruminants virus (PPRV) grew better in lymphocytes from sheep and goats. There was no marked difference in the growth of either virus in lymphocytes from uninfected or recently convalescent animals.

The duration of immunity in cattle following inoculation of rinderpest cell culture vaccine

The duration of immunity following a single administration of rinderpest cell culture vaccine, of 90 or more monolayer passages, was studied in E. African zebu (Boran) and grade (cross-bred European) cattle. All animals were kept for periods of 6-11 years in rinderpest-free environments; groups of them (in all 23 Borans and 10 grades) were then challenged by parenteral or intranasal inoculation of virulent virus or by contact exposure to reacting cattle. Nasal excretion of virus was studied daily over the 10-to 14-day period following challenge, and simultaneous attempts were made to detect viraemia. The neutralizing antibody response was followed at 6-month intervals over the whole post-vaccination period and then daily for 10 days and at longer intervals to 3 weeks after challenge. All 33 animals which were exposed by various routes failed to react clinically and a rinderpest viraemia was never detected. No transmission of virus from the vaccinates to susceptible in-contact controls occurred within 14 or more days, from the 20 animals which could be so tested. Clearcut serological responses to challenge were seen in six cattle (four Borans and two grades) which were challenged after 7 years or more; these reactions were all delayed to the 9th or 10th days, i.e. they were not typically 'anamnestic'. These results are discussed in relation to mass vaccination campaigns for the control of rinderpest and from the comparative viewpoint of measles vaccination in man.

Detection of rinderpest virus antigens in vitro and in vivo by direct immunofluorescence

Cell-culture attenuated and virulent strains of rinderpest virus (RV) were inoculated on to bovine kidney cell cultures. A direct immunofluorescent antibody test detected RV antigens in cell cultures within one to three days after inoculation whereas RV cytopathic effects usually took three to nine days to develop. Cells containing RV antigens were also detected in impression smears and frozen sections of tissues collected from RV infected animals at post mortem examination, and in smears of lymph node biopsies taken from cattle with clinical rinderpest. These techniques may offer additional methods for rapid diagnosis of rinderpest.

Microtitre techniques for the assay of rinderpest virus and neutralising antibody

Microtitre techniques were compared with conventional tube techniques for their ability to assay rinderpest virus and neutralising antibody to the virus. The microtitre technique was as sensitive and reliable for assaying the virus as the recommended tube technique, using cell suspensions. Both of these methods, however, were less sensitive than tube titrations on preformed cell monolayers. The microtitre test was as sensitive as the tube test for detecting and assaying virus neutralising antibody and more robust in that it was less sensitive to variations in virus dose.

The isolation of peste des petits ruminants virus from Nigerian sheep and goats

Four isolates of peste des petits ruminants virus were obtained from sick Nigerian sheep and goats. One was identical antigenically with the prototype Senegalese strain. A cross relationship was found between peste des petits ruminants virus and rinderpest virus based on neutralisation in vitro.

The isolation of adenoviruses from goats affected with peste des petits ruminants in Nigeria

Mucosal scrapings from the large intestine of two goats that had died from peste des petits ruminants (PPR) in separate outbreaks in Nigeria were examined for viruses. A mixed viral infection of PPR virus (morbillivirus) and adenovirus was confirmed in both goats. The adenoviruses did not conform to any of the ovine and bovine serotypes recognised; the two isolates were considered different serotypes. It is concluded that, although the role of adenoviruses in the epizootiology of PPR in Nigeria is difficult to appraise, they are probably commensals. This is believed to be the first report of the isolation of adenoviruses from goats.

Development of a diploid cell line from fetal calf lung for virus vaccine production

Details of isolation and replication of a fetal calf diploid cell (FCDC) is given. From the karyological point of view, the fairly large number of chromosomes existing in metaphase spreads made counting rather tedious. Lack of practical classification was another problem which made reference to individual chromosomes difficult. By increasing the population doubling of this cell, a tendency of telocentric chromosomes to undergo centric fusion was observed. Susceptibility of FCDC to different viruses is described.

The pathogenesis of rinderpest in the lymph nodes of cattle. Light and electron microscopic studies

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