The Molecular Epidemiology of capripoxvirus in Sub-Saharan Africa
Central Research Department (now Research and Evidence Division)
To look in detail at strains of LSD virus, particularly from East Africa, to identify whether the same strains have persisted in the area, or whether the periodic epidemics are associated with the introduction of new strains from neighbouring areas.
Strains of capripoxvirus cause disease in sheep, goats and cattle, namely sheepox, goatpox and lumpy skin disease respectively. Although the strains of capripoxvirus can be distinguished by the response of the main target host, they cannot be individually identified using routine laboratory tests, such as virus neutralisation test, immunofluorescence test or agar gel immunodiffusion test. It has, however, been possible to show differences between strains of capripoxvirus by using restriction enzymes to cut the purified DNA, and then comparing the pattern of fragments generated on an agarose gel. The HinDill restriction enzyme has been used to compare isolates of capripoxvirus from sheep, goats and cattle and has shown that many of the strains can be put into groups according to the species from which each was derived. Some strains showed patterns intermediate between groups, which supported the experimental and field observation that strains of capripoxvirus are not all host specific. These intermediate strains could have arisen, for example, following recombination events between strains co-infecting mixed flocks of sheep and goats. Although some strains can be distinguished using the HinDill enzyme, others appear identical, even though they may have been collected from different countries of sub-Saharan Africa, and at intervals as long as 15 years apart. This does reflect the recognised stability of DNA viruses, and also the very close nucleotide sequence homology of all capripoxviruses so far examined. However, many small differences do exist at the nucleotide sequence level, and it should be possible to take advantage of these differences to identify individual strains to study their epidemiology. To discover whether single strains persist in an area, and periodically manifest themselves in large outbreaks of disease, and if they persist how do they evade detection; or do strains circulate from one country to another, returning when there is a sufficient population of susceptible animals. Also, it is not known how much movement of capripoxvirus takes place between species.
To take strains of capripoxvirus stored in the capripox reference section at IAH, Pirbright, particularly those isolated in sub-Saharan Africa, grow and purify each, and make DNA preparations. These will initially be compared by using HinDill restriction enzyme, and then a series of other enzymes will be used to show whether the groupings seen with HinDill remain the same. The large fragments generated by HinDill will be removed from the gels and subjected to further digestion using enszymes which are less constrained to cut the DNA. In this way it is intended to catalogue the capripoxviruses in the reference library, and develop a database to which future isolates can be added, and possibly by which their origins can be defined.
Total Cost to DFID:
Paper File Reference:
NRD 9800 958/832/001