SUMMARY
Rinderpest, the legendary cattle plague, has caused devasting economic losses for centuries and it is certain to remain a threat to livestock in developing countries into the twenty first century. Strenuous efforts are now being made to achieve global eradication, a goal which became feasible with the development of the tissue culture adapted virus vaccine in the late 1950s. Today we have powerful new molecular tools which should greatly assist in this task. Second generation recombinant vaccines are available which can be used to protect animals from disease while enabling the vaccinated animals to be distinguished from the naturally infected ones. Molecular techniques have improved the speed and accuracy of disease diagnosis and it is now possible to study in very precise detail bacterial and viral pathogens which were previously difficult to isolate in the laboratory or from very poorly preserved tissue specimens from field cases. This has led to a new situation where the genomes of viruses such as rinderpest and peste des petits ruminants, which are difficult to grow to high purity in culture, can be studied even down to the nucleotide sequence level. This has enabled much more meaningful studies on the epidemiology of these viruses to be carried out and it is now possible to trace the movements of these viruses across continents. However, the most dramatic achievement of molecular biology, at the ending of a century which has seen so many startling scientific advances, is the ability to rescue infectious rinderpest virus from DNA copies of its genes. This technique has given us the potential not only to produce a genetically defined vaccine but also to understand the molecular mechanisms which determine the pathogenic nature of the virus.
1. INTRODUCTION
Rinderpest and the related virus of small ruminants, peste des petits ruminants, are morbilliviruses which constitute an antigenically related genus within the family Paramyxoviridae. These viruses are of major importance both in human and veterinary medicine. In man measles virus remains one of the most significant causes of death in young children in the less developed parts of the world. The plagues of rinderpest in Europe during the 18th and 19th centuries (Wilkinson, 1984) and the great African pandemic, following its introduction into that continent at the end of the last century (Mack, 1970), have been a great challenge to the veterinary profession. Rinderpest virus continues to cause major losses in cattle and buffalo in parts of Africa and Asia. Similarly peste des petits ruminants is currently circulating with devastating effect in sheep and goats across the Asian continent from Arabia through Pakistan, India and as far as Nepal and Bangladesh. Canine distemper, although largely controlled by vaccination in domestic dogs, is responsible for epizootics in wild carnivores and remains a threat to some endangered species. In the past decade two new species of morbillivirus have been identified which were responsible for severe epizootic diseases in marine mammals (Osterhaus et al., 1995). A morbillivirus of unknown pathogenicity was identified in American cattle by sequence analysis during the course of rinderpest cloning experiments using primary bovine lymphocytes (Baron et al., 1994) and in 1995 an unusual pulmonary infection in man and horses in Australia was ascribed to a new “equine morbillivirus” (Gould, 1996). These epizootics illustrate how “new viruses” are constantly emerging and how useful molecular techniques have been for their rapid identification and characterisation. The most recent scientific advances have enabled live virus to be rescued from DNA copies of morbillivirus genomes and this technology will soon enable us to understand the molecular determinants of pathogenicity in these viruses and will enable us to produce genetically defined and marked vaccines.
1 Institute for Animal Health, Pirbright Laboratory, Working GU24 ONF, Surrey, UK
In this paper the contribution that molecular biology has made to the understanding of rinderpest and other morbilliviruses will be outlined and prospects for the future discussed.
2. RECOMBINANT VACCINES
Advances in molecular biology have led to the development of a range of new generation vaccines, the most commonly used at present being recombinant vaccines based on various poxvirus vectors. One of the most successful has been the vaccinia recombinant rabies vaccine which is now widely used in Europe and the USA to combat the disease (Brochier et al., 1994; Pastoret and Brochier, 1996). In the case of rinderpest, vaccinia and capripox recombinant vaccines have been produced which effectively protect against challenge with virulent virus and long-term immunity trials are now in progress.
2.1 Vaccinia recombinant vaccines
The first recombinant rinderpest vaccines were the vaccinia recombinants made using the WR strain of vaccinia as a vector (Yilma et al., 1988; Belsham et al., 1989). An OIE. expert committee which was convened to discuss guidelines for the use of recombinant rinderpest vaccines recommended that only recombinants developed using recognised human vaccine strains as vectors should be used in the field (OIE 1989). As WR is a laboratory strain of vaccinia, other recombinants were developed in Japan (Asano et al., 1991) and in the USA (Giavedoni et al., 1991) using attenuated vaccine strains. The American vaccine is a double recombinant made using the Wyeth vaccine strain and has both the H and F genes of rinderpest inserted into the vaccinia genome. Unlike the WR strain recombinant vaccine, it does not cause pock lesions when inoculated intradermally. However, the vaccine has not yet been tested for efficacy by the sub-cutaneous route, as favoured by the OIE expert group. The Japanese recombinant vaccine was developed using the most attenuated human vaccine strain available (LC16mO strain) but contains only the H gene of rinderpest. It is totally innocuous when administered either intra dermally or subcutaneously (Yamanouchi and Barrett, 1994). To date only one long-term immunity trial has been carried out using the Japanese recombinant which proved that is effective for at least one year after a single shot vaccination (Inui et al., 1995). Longer term trials are now in progress at the Pirbright Laboratory and it is anticipated that the duration of immunity should be at least as long at that which vaccinia affords against smallpox. In addition it was shown that pre-exposure of the animals to wild type vaccinia virus did not abrogate its ability to generate an anti-rinderpest immunity (Yamanouchi et al., 1993), proving that vacciniarelated poxvirus infections in the target species would not cause interference problems. All tests on the Japanese vaccine have been carried out using the sub-cutaneous route of inoculation to minimise the possible spread of the vaccine by contact. Extensive safety and efficacy tests have been carried out on this vaccine at the Pirbright Laboratory where it was shown to conform to all the safety requirements stipulated by the OIE expert committee on rinderpest recombinant vaccines (Yamanouchi and Barrett, 1994).
2.2 Capripox recombinant vaccines
The capripox vector has two major advantages over vaccinia when it comes to developing veterinary vaccines. Firstly it is not a human pathogen and the same safety problems do not arise. Secondly it is already used as a veterinary vaccine to protect against sheep and goatpox infections (Kitching et al., 1987). Trials on the vaccine at the Pirbright Laboratory and at the Kenya Agriculture Research Institute at Muguga have shown that the capripox—rinderpest recombinant vaccine will protect cattle against lumpy skin disease as well as rinderpest, thus making it an effective dual vaccine (Ngichabe et al., 1996). It has also been shown to cross protect sheep and goats from peste des petits ruminants virus infection (Romero et al., 1995). The only drawback is the reduced protection given when animals are first vaccinated with the wild-type virus, indicating an interference due to pre-existing antibodies. This problem may be due to the use of a late rather than an early promoter to drive the rinderpest genes and new recombinants have been produced which are driven by an early promoter and which will shortly be tested in cattle.
2.3 Potential role of recombinant vaccines in GREP
Recombinant vaccines would make ideal substitutes for the conventional Plowright tissue culture adapted vaccine in situations where a country wishes to progress to a stage where it can stop vaccination and begin to follow the OIE pathway to a declaration of freedom from rinderpest. One of the major problems in such situations is the masking of disease, particularly mild strains of rinderpest, by the vaccine since vaccinated animals cannot be distinguished serologically from naturally infected recovered animals. This makes the decision to stop vaccination very difficult for many countries. By using recombinant vaccines protection can be achieved while not interfering with the ability to carry out serological monitoring for natural infection in the national herd.
3. MOLECULAR TECHNIQUES FOR DIAGNOSIS
The control of infectious disease is made easier if there is an effective vaccine but the key to success in eradication is the ability to identify the causative agent rapidly and with a very high degree of certainty. Molecular biological techniques have been successfully exploited to improve both the speed and the accuracy of disease diagnosis in human and animal medicine. The process of rapid diagnosis began a quarter of a century ago with the development of the ELISA (Engvall and Perlmann, 1971). The advent of pathogen-specific monoclonal antibodies, allied with the convenience of the ELISA, greatly eased the task of specific antigen and antibody detection in clinical specimens (Libeau et al., 1994; Anderson and McKay, 1994). However, despite their convenience, immunological techniques are limited in their sensitivity. Molecular techniques, in contrast, are extremely sensitive and can be used to characterise pathogens at the genetic level.
3.1 Nucleic acid hybridisation
Nucleic acid hybridisation is a very specific techniques for the identification of pathogenic organisms of parasitic, bacterial or viral origin. High sensitivity of detection can be achieved either on extracted nucleic acid material or in situ on histological sections. The technique is based on the ability of any nucleic acid to bind in a very stable, hydrogen-bonded duplex structure to its complementary sequence. Such a duplex is much more stable and specific than an antibody-antigen complex and, depending on the stringency with which the reaction is carried out, can be made to detect either the exact complement or a closely related sequence. DNA probes derived from the Ngenes of rinderpest and peste des petits ruminants viruses have been used to identify and differentiate the two viruses (Diallo et al., 1989) and specific probes are now available for all the morbilliviruses. The technique can be used to detect virus-specific nucleic acids even in poorly preserved field samples from which it would not be possible to recover live virus. This technique enabled us to prove early on that the morbillivirus infecting seals in Europe in 1988 was distinct from canine distemper (Mahy et al., 1988) was also used to demonstrate the presence of peste des petits ruminants in India for the first time (Shaila et al., 1990). Previously it was thought that rinderpest was the only morbillivirus present in sheep and goats on the sub-continent.
Non-radioactive labelling techniques can be used to replace radio-isotopes allowing the technique to be used in diagnostic laboratories where radioactive material cannot be easily obtained and where facilities for its safe handling are not available (Pandey et al., 1992). However, this is not as sensitive as radioactive labelling and the technique was not successfully transferred to laboratories in developing countries. I has now been superseded in laboratories in the more advanced countries by the more sensitive and rapid polymerase chain reaction (PCR) amplification technique.
3.2 Polymerase chain reaction (PCR)
The polymerase chain reaction, first described by Saiki and colleagues in 1985, has proved to be a very powerful tool for diagnosis. It is the most sensitive molecular method yet developed for detecting nucleic acid material and there is now a very long list of pathogenic organisms for which a specific PCR test is available (Belak and Ballagi-Pordany 1993). The principle of the PCR is the repeated copying of a designated segment of DNA using specific forward and reverse primers, usually separated by 200–400 nucleotides on the genome of interest for diagnostic purposes. With the availability of thermostable DNA polymerases derived from thermophilic bacteria (Saiki et al., 1988) this repetitive copying of the DNA could be done in a single tube by repeatedly heating the DNA to high temperature (94°C) to dissociate the DNA duplex, cooling to allow annealing of the primers (37– 50°C, depending on the primers used) and finally heating to the optimum temperature (72°C) for the polymerase to copy new DNA. The cycles are repeated 25–35 times (25 cycles theoretically increases the concentration of starting DNA 107 times) to produce a DNA product which can be visualised by ethidium bromide staining on an agarose gel. The size of the DNA product is exactly defined by the location of the two primers on the virus genome.
3.3 Reverse transcription/polymerase chain reaction (RT/PCR)
The PCR technique can only be used to amplify DNA. Since the genome of all morbilliviruses consists of a single strand of RNA their genomes cannot be amplified directly by PCR but must first be copied into DNA using reverse transcriptase in a two-step reaction known as reverse transcription/polymerase chain reaction (RT-PCR). RT-PCR has been shown to be useful for the rapid detection of rinderpest-specific RNA in diagnostic samples and can be used for differentiating rinderpest from other morbillivirus infections, particularly peste des petits ruminants (Forsyth and Barrett, 1995).
The first step in RT-PCR is to make copy DNA and this is best synthesised using random hexanucleotide primers, rather than virus-specific ones. This increases the sensitivity and enables the same copy DNA product to be divided and aliquots amplified by PCR using several sets of specially designed primer sets. The amplification primers must fulfil two criteria for differential diagnosis:
They must be from a conserved region of the genome so that all strains of the virus can be detected; and
They must be type-specific to enable differential diagnosis to be made between different morbilliviruses.
Each morbillivirus has a quite distinct RNA sequence and it is easy to identify regions of the genome where the sequence is reasonably well conserved within each virus species but different enough from the other morbilliviruses to be specific; a portion of the fusion (F) protein gene fulfils these criteria.
It is also desirable to have a “universal” primer set to enable possible unknown morbilliviruses to be identified which could confuse the serological diagnosis. For this second category a gene which is highly conserved across the genus should be chosen. However, due to the redundancy of the genetic code, such sequences are not easy to find. The phosphoprotein (P) gene has some short, highly conserved regions where overlapping reading frames are used to encode the non-structural proteins and these sequences are well conserved across the genus and can be used to produce “universal” primer set (see figure 1). Such a primer set enabled amplification of nucleic acid sequences from the newly discovered infections in dolphins and porpoises in The Mediterranean in 1990 and enabled them to be characterised as new viruses before conventional cloning methods could produce results (Barrett et al., 1993a). We have since developed a second “universal” primer set based on sequences in the highly conserved central region of the N protein gene of the morbilliviruses. Because of the great potential of RNA genomes to vary it is essential to have several alternative sets of primers for detection of RNA virus genomes.
3.4 Confirming the specificity of the amplified DNA
The size of the DNA product is determined by the distance the primer sequences are separated on the primary sequence of the genome being analyzed. The position of the correct sized product can be determined by reference to the positive controls in the reactions and commercially produced DNA marker ladders. Non-specific DNA products can sometimes be produced and care is needed in interpretation of results. Usually these non-specific products are of the wrong size and are more usually found in negative samples or in samples where there is a very low concentration of the target nucleic acid. The specificity of the DNA product, particularly if it is a weak signal, should always be checked independently. This can easily be done by a rapid hybridisation probe analysis using labelled oligonucleotides. At the Pirbright laboratory we have developed a very rapid procedure based on specific digoxygenin (DIG) labelled internal primers and a commercially available anti-DIG antibody to confirm the specificity of the amplified DNA products.
4. MOLECULAR EPIDEMIOLOGY
In addition to greater sensitivity, the main advantage that RT-PCR has over DNA probe analysis is that the resulting DNA product can be sequenced, either directly or after cloning in a suitable vector. From this data the virus can be analyzed at the genetic level and relationship of the infecting virus to other isolates can be determined. This has enabled studies on the molecular epidemiology in the case viruses which were previously difficult or impossible to isolate in the laboratory. It has been used to great advantage in human medicine to test for the newly identified hepatitis viruses in blood products. The genetic relationships between strains from different parts of the world can be established and the likely source of the new outbreak can be traced with greater accuracy. This technique has been used very successfully in the case of foot-and-mouth disease and vesicular stomatitis viruses and is now proving its value in studies on the epidemiology of the morbilliviruses.
4.1 Rinderpest virus
Initial studies showed that rinderpest virus isolates could be separated into lineages which coincided with the continent from which the viruses originated (Barrett et al., 1993b; Chamberlain et al., 1993). When historic strains were added to the database a total of five lineages could be distinguished but only two were represented in samples collected after 1983, a distinct African and a distinct Asian lineage (Wamwayi et al., 1995). The outbreak of rinderpest in wildlife (buffalo and kudu) in the Tsavo National Park in Kenya in 1994/1995 was unusual in that it was confined to wildlife and it was a complete surprise when the virus turned out to be most similar to a giraffe isolate from 1962 (RGK/1) from the same part of Kenya. Another strain of rinderpest from the same era isolated from cattle in Tanzania (RBT/1) is also in that lineage (African virus lineage 2, see figure 2). Over the previous ten years only virus of the first African lineage had been detected in Kenya and the neighbouring countries of Sudan and Ethiopia (Wamwayi et al., 1995; Abraham et al., 1996) and it was thought that the RGK/1 lineage had become extinct. The current rinderpest virus strains can thus be divided into three distinct types, an Asian and two African lineages. So far we can only speculate as to the enzootic source of this second African lineage since such a virulent virus could not have persisted unnoticed in Kenyan wildlife for over thirty years. The virus appears to be mild in cattle (Dr. H. Wamwayi, personal communication) and it is probable that there is an enzootic focus in cattle in the Kenya/Somalia border region of Africa.
4.2 Peste des petits ruminants virus
Work being carried out in parallel on peste des petits ruminants viruses has identified four distinct lineages (Shaila et al., 1996). Only three of these virus lineages have been detected since the beginning of the 1990s and the fourth may not have disappeared but may have evolved into one of the other lineages. The first lineage (now extinct?) is most closely related PPR virus lineage four which is currently causing extensive disease outbreaks across Asia from Israel to Bangladesh (see figure 3). In contrast, a virus from Ethiopia from this year was found to be most closely related to a virus isolate from Sudan in 1972 (lineage 3). The PPR viruses in lineage 2 are the most distant from the other three lineages and includes two quite recent viruses from West Africa, Ivory Coast (1989) and Guinea (1991). Since there is reported to be active PPR infection in this part of West Africa it is probable that this virus type is in circulating there. However, no recent isolates from that region have been obtained to confirm this.
4.3 Other morbilliviruses
Similar epizootiological analysis is being carried out on other morbilliviruses. In the case of recent CDV infections in lions and other big cats in the USA and in Africa, it has been shown that the likely source of the virus infecting these cats is contact with local carnivores infected with CDV and there appears to be no specially adapted feline strain of CDV (Harder et al., 1995; Haas et al., 1995). Serological and molecular analyses have confirmed that CDV continues to affect seals in Lake Baikal (Mamaev et al., 1996) and there is increasing serological evidence of widespread morbillivirus infection in cetaceans (Barrett et al., 1995).
Evidence for morbilliviruses causing persisting infections in cattle in the USA and in Europe was reported in the 1970s (Bachmann et al., 1975; Coulter and Storz, 1979). Confirmation of the presence of such a virus was obtained during a sequencing project to compare the genomes of the rinderpest vaccine and the parental virulent strain (Baron et al., 1994; Baron et al., 1996). Limo and Yilma (1990) reported the sequence of the matrix protein gene of the virulent strain of rinderpest and when we compared it to the vaccine strain sequence it only showed 65% homology in the coding region, whereas all other genes we had compared previously showed that the vaccine strain was 99% similar to the virulent parent. We then resequencing the matrix gene by PCR amplification from RNA derived from tissues from an animal infected with the virulent virus and found it to be 99% identical to the vaccine. The American group had used primary bovine cells to grow the virus and used the measles virus matrix protein gene as a probe to select the equivalent gene of rinderpest from their clone bank. The probe, being equally related to the persisting morbillivirus and to rinderpest, detected the gene from the persisting virus. These persistent morbilliviruses appear to cause mainly silent infections. Overt disease, a meningo-encephalitis, has only been associated with them in one case (Bachmann et al, 1975).
The recent claim that the virus responsible for fatal infections of several horses and two human cases in Australia recently, was a new morbillivirus is not borne out by the available data. The “classification” was based on comparisons of a small section of the matrix protein gene sequence, which in any case is the most conserved gene across the whole paramyxovirus family, which showed it to be most closely related to the morbillivirus genus (Murray et al., 1995; Gould 1996). No serological cross reaction could be shown with any known morbillivirus which is an antigenically closely related group of viruses. It now appears that bats are the natural hosts of the virus and it will probably will be classified in a separate genus of the paramyxoviruses because of its unusual genome and envelope structure (Gould, 1996; Hyatt and Selleck, 1996).
5. FUTURE PROSPECTS
Scientists have been able to rescue live infectious virus from DNA copies of RNA viruses with positive strand genomes for several decades, ever since polio virus was rescued from a DNA copy (Racaniello and Baltimore, 1981). However, this is a relatively simple task since the positive sense naked RNA, once it is transcribed from the DNA transfected into a suitable host cell, can act as a message to direct synthesis of the virus proteins which then can replicate the virus RNA copy. In the case of rinderpest, and other negative strand viruses such as rabies, this is not the case. Their genomes are encapsidated by the nucleocapsid protein and they must be transcribed by the virus polymerase and phosphoproteins to produce individual mRNAs for all the virus proteins before replication can be accomplished. The task of rescuing virus from the DNA copies of negative strand viruses was considered impossible until recently. However, the rapidly advancing pace of molecular technology has meant that we have now achieved this goal for rinderpest (Baron and Barrett, manuscript submitted for publication). To rescue virus a plasmid containing the full-length rinderpest genome sequence in DNA form is transfected along with three other plasmids which contain the coding sequences of the genes required for virus RNA encapsidation and replication (the nucleoprotein gene, the phosphoprotein gene and the polymerase gene). The genes in these plasmids are all under the control of a bacteriophage promoter (T7) and the transfected cells are infected with a noncytopathic strain of vaccinia virus which has been engineered to produce the bacteriophage (T7) enzyme needed to copy RNA from the plasmids. Once the messenger RNAs for the virus proteins are transcribed they will produce the required proteins to then encapsidate and copy the full-length anti-genome sense RNA that is also produced in the transfected cells.
The potential to exploit reverse genetic technology is very great. Not only will this enable more precise questions concerning the molecular determinants of pathogenicity in these viruses to be addressed, but may also be exploited to produce more precisely characterised vaccines. The vaccine “seed stock” in this case would be a DNA plasmid containing the complete coding sequence for the virus which would be distributed to the manufacturer. If, as seems likely, extra coding sequences can be introduced into the rinderpest genome, then it would be possible to produce an antigenically marked vaccine to enable vaccination to be distinguished from natural infection. This research is being actively pursued in the Pirbright Laboratory.
6. CONCLUSIONS
Recombinant vaccines have still to prove their usefulness in the fight to conquer rinderpest. While a safe and effective conventional vaccine is available, unlike the case with rabies virus, there is a reluctance to commit resources to testing a new vaccine in the field, even if it confers stability advantages and makes serological surveys for disease surveillance possible in the face of blanket vaccination campaigns. However, when the final test comes and cessation of vaccination is recommended for a country, these vaccines may provide an easy stepping stone before vaccination is finally abandoned.
Molecular biology has proved more “user friendly” in the field of morbillivirus diagnosis. Improved diagnostic capabilities have very great relevance for control programmes which are aimed at global eradication of rinderpest and other important veterinary diseases, since rapid and accurate diagnosis is the most important factor which will determine their success. These techniques are faster and easier to perform than the classic method of agent isolation followed by neutralisation tests and animal inoculation studies. In addition they can be used to characterise the pathogen in great detail, even down to the nucleotide sequence level. This results in data which are very useful for epidemiological studies on the infectious agent concerned and is essential for back tracing outbreaks which occur in non-endemic areas.
ELISA, DNA probe analysis and RT-PCR remain laboratory based techniques. With the exception of the ELISA, they have not yet been transferred to laboratories in developing countries where rinderpest and peste des petits ruminants viruses remain a problem. However, the development of microtitre plate technology for PCR, non-radioactive methods both for sequencing studies and for labelling nucleic acid probes, could make transfer of this technology to developing countries feasible in the future. Molecular biological techniques will continue to improve and they must be exploited to the full in the battle to control and conquer infectious diseases of man and his animals. To date we have only succeeded in eradicating one virus disease (smallpox) on a global basis. All the advances in modern technology will greatly aid the task of controlling diseases such as rinderpest and eventually, it is to be hoped, result in it being the first virus disease of veterinary importance to have been eradicated globally.
8. ACKNOWLEDGEMENTS
I wish to acknowledge the great contributions that members of my laboratory, both past and present, have made to this work. In particular I wish to mention Dr. Michael Baron, who has carried out the virus rescue work, and Ms Morag Forsyth and Mr Ken Inui who carried out much of the recent PCR and sequencing work. I also thank my many overseas colleagues (Dr Henry Wamwayi, Professor M.S. Shaila, Dr Adama Diallo) who have worked closely with me and have provided many of the virus samples mentioned here.
REFERENCES
ABRAHAM, G., ROEDER, P.L., FORSYTH, M., VAN'T KLOOSTER, C.G.M. AND BARRETT, T. (1996) Rinderpest occurrence in Ethiopia: Implications for control strategies. Manuscript in preparation.
ANDERSON, J. & MC KAY, J. (1994) The detection of antibodies against peste des petits ruminants virus in cattle, sheep and goats and the possible implications to rinderpest control programmes. Epidemiology and Infection, 112, 225–231.
ASANO K, TSUKIYAMA K, SHIBATA S, YAMAGUCHI K, MOMOKI T, MARUYAMA T, et al. (1991) Immunological and virological characterisation of improved construction of recombinant vaccinia virus expressing rinderpest virus haemagglutinin. Archives Virology, 116, 81–90.
BACHMANN, P.A., TER MEULEN, V., JENTSCH, G., APEL, M., IWASAKI, Y., MEYERMANN, R., KOPROWSKI, H. & MAYR, A. (1995) Sporadic bovine meningo-encephalitis - isolation of a paramyxovirus. Archives of Virology, 48, 107–120.
BARON, M.D., GOATLEY, L.G. & BARRETT, T.(1994) Cloning and sequence analysis of the matrix protein gene of rinderpest virus and evidence for another bovine morbillivirus. Virology, 200, 121–129.
BARON, M.D., KAMATA, Y., BARRAS, V., GOATLEY, L.G. & BARRETT, T. (1996) The genome sequence of the virulent Kabete ‘O’ strain of rinderpest virus: comparison with the derived vaccine. Journal of General virology, in press.
BARRETT, T., BELSHAM, G., SHAILA, M.S., EVANS, S., ANDERSON, J. (1989) Virology
BARRETT T., VISSER I.K.G., MAMAEV L., VAN BRESSEM M.-F. & OSTERHAUS A.D.M.E. (1993a) Dolphin and porpoise morbilliviruses are distinct from phocid distemper virus. Virology, 193, 1010– 1012.
BARRETT, T., AMAREL-DOEL, C., KITCHING, R.P. & GUSEV, A. (1993b) Use of the polymerase chain reaction in differentiating rinderpest field virus and vaccine virus in the same animals. Rev. sci. tech. Off. int. Epiz., 12, 865–872.
BARRETT, T., BLIXENKRONE-MØLLER, M., DI GUARDO, G., DOMINGO, M., DUIGNAN, P., HALL, A., MAMAEV, L. AND OSTERHAUS, A.D.M.E. (1995) Report on the roundtable on aquatic morbilliviruses. Veterinary Microbiology, 44, 261–265.
BELAK, S. & BALLAGI-PORDANY, A. (1993) Experiences on the application of the polymerase chain reaction in a diagnostic laboratory. Molecular and Cellular probes, 7, 241–248.
BELSHAM, G.J., ANDERSON, E.C., MURRAY, P.K., ANDERSON, J. & BARRETT, T. (1989) Immune response and protection of cattle and pigs generated by a vaccinia virus recombinant expressing the F protein of rinderpest virus. Veterinary Record, 124, 655–658.
BROCHIER B, BOULANGER D, COSTY F, PASTORET P-P. (1994) Towards rabies elimination in Belgium by fox vaccination using a vaccinia-rabies glycoprotein recombinant virus. Vaccine, 12, 1368–1371.
CHAMBERLAIN, R.W., WAMWAYI, H.M., HOCKLEY, E., SHAILA, M.S., GOATLEY, L., KNOWLES, N.J AND BARRETT, T. (1993) Evidence for different lineages of rinderpest virus reflecting their geographic isolation. Journal of General Virology, 74, 2775–2780.
COULTER, R. & STORZ, J. (1979) Identification of a cell-associated morbillivirus from cattle affected with malignant catarrhal fever: antigenic differentiation and cytologic characterisation. American Journal of Veterinary Research, 40, 1671–1677.
DIALLO, A., BARRETT, T., SUBBARAO, S.M. and TAYLOR, W.P. (1989). Differentiation of rinderpest and peste des petits ruminants viruses using specific cDNA clones. Journal of Virological Methods, 23, 127– 137.
ENGVALL, E. & PERLMANN, P. (1971). Enzyme linked immunosorbent assay (ELISA). Quantitative assay of immunoglobulin G. Immunochemistry, 8, 871–873.
FELSENSTEIN, J. (1990) Phylip Manual Version 3.3, University Herbarium, University of California, Berkley, CA.
FORSYTH, M. AND BARRETT, T. (1995) Evaluation of polymerase chain reaction for the detection of rinderpest and peste des petits ruminants viruses for epidemiological studies. Virus Research, 39, 151–163.
GIAVEDONI L, JONES L, MEBUS C, YILMA T. (1991) A vaccinia virus double recombinant expressing the F and H genes of rinderpest virus protects cattle against rinderpest and causes no pock lesions. Proc Natl Acad Sci USA, 88, 8011–8015.
GOULD, A.R. (1996) Comparison of the deduced matrix and fusion protein sequences of equine morbillivirus with cognate genes of the paramyxoviridae. Virus Research, 43, 17–31.
HAAS, L., BARON, M.D., LIESS, B. AND BARRETT, T. (1995) Editing of morbillivirus P gene transcripts in infected animals. Veterinary Microbiology, 44, 299–306.
HARDER, T.C., KENTER, M., APPEL, M.G., ROELKE-PARKER, M.E., BARRETT, T. and OSTERHAUS, A.D.M.E. (1995) Phylogenetic evidence of canine distemper virus in Serengeti's lions, Vaccine, 13, 521–523.
HYATT, A.D. & SELLECK, P.W. (1996) Ultrastructure of equine morbillivirus. Virus Research, 42, 1– 15.
INUI, K., BARRETT, T., KITCHING, R.P. and YAMANOUCHI, K. (1995) Long term immunity in cattle vaccinated with a recombinant rinderpest vaccine. Veterinary Record, 127, 669–670.
KITCHING RP, HAMMOND JM and TAYLOR WP. (1987) A single vaccine for the control of capripox infection in sheep and goats. Research in Veterinary Science, 42, 53–60.
LIBEAU, G., COLAS, F. & GUERRE, L. (1994) Rapid differential diagnosis of rinderpest and peste des petits ruminants using immunocapture ELISA. Veterinary Record, 134, 300–304.
LIMO & YILMA (1990) Molecular cloning of the rinderpest virus matrix gene: comparative sequence analysis with other paramyxoviruses. Virology, 175, 323–327.
MACK (1970) The great African cattle plague epidemic of the 1890's. Tropical Animal Health and Production, 2, 210–219
MAHY, B.W.J., BARRETT, T., EVANS, S., ANDERSON, E.C., BOSTOCK, C.J. (1988). Characterisation of a seal morbillivirus. Nature 336, 115.
MAMAEV, L., DENIKINA, N.N., BELIKOV, S.J., VOLCHKOV, V., VISSER, I.K.G., FLEMING, M., KAI, C., HARDER, T.C., LIESS, B., OSTERHAUS, A.D.M.E. AND BARRETT, T. (1995) Characterisation of morbilliviruses isolated from Lake Baikal seals (Phoca sibirica). Veterinary Microbiology, 44, 251–259.
NGICHABE, C.K., WAMWAYI, H.M., NDUNGU, E.K., BLACK, D.N., BARRETT, T. AND BOSTOCK, C.J. (1996) Trial of a capripoxvirus-rinderpest recombinant vaccine in African cattle. Epidemiology and Infection, in press.
OIE (1989) Report of the expert consultation on requirements for vaccinia-rinderpest recombinant (VRR) vaccines. Paris, 21–24 August. Reference: 58 SG/13 CS 4c, OIE, Paris, 21pp.
OSTERHAUS, A.D.M.E., DE SMART, R.L., VAS, H.W., ROBS, P.S., KENTER, M.J.H. & BARRETT, T. (1995) Morbillivirus infections of aquatic mammals: newly identified members of the genus. Veterinary Microbiology, 44, 219–227.
PANDEY, K.D., BARON, M.D. & BARRETT, T. (1992) Differential diagnosis of rinderpest and PPR using biotinylated cDNA probes. Veterinary record, 131, 199–200.
RACANIELLO, V.R. & BALTIMORE, D. (1981) Cloned poliovirus cDNA is infectious in mammalian cells. Science, 214, 916–919.
PASTORET P-P and BROCHIER B. (1996) The development and use of a vaccinia-rabies recombinant oral vaccine for the control of wildlife rabies; a link between Jenner and Pasteur. Epidemiology and Infection, 116, 235–240.
ROMERO, C.H., BARRETT, T., EVANS, S.A., KITCHING, R.P., GERSHON, P.D. AND BLACK, D.N. (1993). A single vaccine for the protection of cattle against rinderpest and lumpy skin disease. Vaccine, 11, 737–742.
ROMERO, C.H., BARRETT, T., CHAMBERLAIN, R.W., KITCHING, R.P., FLEMING, M. AND BLACK, D.N. (1994). Recombinant capripoxvirus expressing the haemagglutinin protein gene of rinderpest virus: protection of cattle against rinderpest and lumpy skin disease. Virology, 204, 425–429.
ROMERO, C.H., BARRETT, T., KITCHING, R.P., BOSTOCK, C. & BLACK, D.N. (1995). Protection of goats against peste des petits ruminants with recombinant capripoxviruses expressing the fusion and haemagglutinin protein genes of rinderpest virus. Vaccine, 44, 151–163.
SAIKI, R.K., SCARF, S., FELINE, F., MULLS, K.B., HORN, G.T., AIRLOCK, H.A. and ARNHEM, N. (1985) Enzymatic amplification of β-globin genomic sequences and restriction site analysis for diagnosis of sickle cell anaemia. Science, 230, 1350–1354.
SAIKI, R.K., D.H. GELFAND, S. STOFFEL, S.J. SCARF, R. HIGUCHI, G.T. HORN, K.B. MULLS & H.A AIRLOCK (1988) Primer-directed enzymatic amplification of DNA with a thermostable DNA polymerase. Science 239, 487–491.
SHAILA, M.S. PURUSHOTHAMAN, V., BHAVASAR, D., VENUGOPAL, K. and VENKATESAN R.A. (1990). Peste des petits ruminants of sheep in India. Veterinary Record, 125, 602.
SHAILA, M.S., SHAMAKI, D., FORSYTH, M., DIALLO, A., GOATLEY, L, KITCHING, P. AND BARRETT, T. (1996) Geographic distribution and epidemiology of peste des petits ruminants viruses. Virus Research, 43, 149–153.
WAMWAYI, H.M., FLEMING, M. & BARRETT, T. (1995) Characterisation of African isolates of rinderpest virus. Veterinary Microbiology, 44, 151–163.
WILKINSON L. (1984) Rinderpest and mainstream infectious disease concepts in the eighteenth century. Medical History 28, 129–150.
YAMANOUCHI, K., INUI, K., SUGIMOTO, M., ASANO, K., NISHIMAKI, F., KITCHING, R.P., TAKAMATSU, H. AND BARRETT, T. (1993) Immunisation of cattle with a recombinant vaccinia vector expressing the haemagglutinin gene of rinderpest virus. Veterinary Record, 132, 152–156.
YAMANOUCHI, K. AND BARRETT, T. (1994) Progress in the development of a heat-stable recombinant vaccine using an attenuated vaccinia virus vector. Rev. sci. tech. Off. int. Epizot., 13, 721–735.
YILMA, T., HSU, D., JONES, L., OWENS, S., GRUBMAN, M., MEBUS, C., YAMAKANA, M. & DALE, B. (1988) Protection of cattle against rinderpest with vaccinia virus recombinants expressing the HA and F genes. Science, 242, 1058–1061.
Figure 1 Use of the morbillivirus “universal” primer set, derived from conserved sequences in the phosphoprotein gene, to amplify cDNA derived from the RNA of various morbilliviruses. CDV (O): canine distemper virus Onderstepoort vaccine strain; CDV (R): canine distemper virus Rockborn vaccine strain; RPV: rinderpest virus RBOK vaccine strain; PPR: peste des petits ruminants virus Nigeria 75/1 vaccine strain; PDV1: phocid distemper virus; PMV: porpoise morbillivirus; DMV: dolphin morbillivirus; seal brain: brain from an infected Baikal seal (Phoca sibirica); M: DNA marker (123 base pair) ladder. Sequence data derived from the amplified DNA products was used to derive the phylogenetic trees shown in Figures 2 and 3.
Figure 2 Phylogenetic analysis of Asian and African strains of rinderpest virus based on sequence data derived from the fusion protein gene. The unrooted tree was derived using the PHYLIP DNADIST AND KITSCH programmes (Felsenstein, 1990).
Figure 3 Phylogenetic analysis of Asian and African strains of peste des petits ruminants virus using sequence data derived from the fusion protein gene. Analysis was carried out as described in figure 2.
Figure 4 Phylogenetic analysis of the different morbilliviruses based on sequence data derived from the phosphoprotein gene. One strain of each virus was included, except in the case of canine distemper where several strains were included to show the close similarity of these virus isolates. The unrooted tree was derived using the PHYLIP DNADIST AND FITCH programmes (Felsenstein, 1990).
Figure 5 Diagrammatic representation of the system used for rescuing live rinderpest virus from cDNA clones (Baron and Barrett, manuscript in preparation).
