African horsesickness is caused by the AHSV, a member of the genus Orbivirus, family Reoviridae. Nine serotypes have been identified. The viral genome consists of ten double stranded (ds) RNA segments encoding at least 7 structural and 4 non¬structural proteins. The major core proteins VP3 and VP7 together with the minor core proteins VP1, VP4 and VP6 form the core particle surrounding the 10 dsRNA segments. An outer capsid, consisting of two major structural proteins VP2 and VP5 surrounds the core. VP2 is the most variable of the proteins within the AHSV serogroup and carries serotype specific epitopes which induce a protective immune response against virulent homologous AHSV challenge. The VP2 protein is therefore the antigen of choice for the development of a subunit vaccine against AHSV. It has been shown that protection against AHSV-4 can be achieved by vaccination with AHSV VP2 protein. The AHSV-3 VP2 protein has previously been cloned and expressed as baculovirus recombinant protein in our laboratory. The recombinant protein induced only a weak neutralising immune response. It has been determined in this investigation that the majority of recombinant AHSV-3 VP2 proteins expressed in Sf-9 insect cells are in an insoluble, aggregated form. This is likely to be the cause of the poor neutralising immune response induced by this protein. In order to investigate this problem two strategies were adopted. First an attempt was made to chemically solubilise the particulate VP2 protein and refold the protein into a form that may present the neutralising epitopes more appropriately. The solubilisation of the protein with 6M Guanidinium HCI was successful, but the largest percentage of the protein was again rendered insoluble during the refolding process which involves the removal of Guanidinium HCI by column chromatography. The chemical solubilisation therefore proved to be too inefficient to provide a solution to the problem. The second method for increasing the solubility and immunogenicity of the VP2 protein was by co-expression of VP2 and VP5, the two outer capsid proteins of AHSV¬3. For the dual expression of the two proteins it was necessary to characterise the AHSV-3 VP5 gene and express it as a baculovirus recombinant first. The VP5 gene was therefore sequenced. A nucleotide sequence of 1566 bp was determined encoding a peptide of 505 amino acids with a predicted size of 56K. The VP5 was expressed as baculovirus recombinant using the baculovirus Bac-to-Bac™ expression system. The yield of VP5 was low but was nevertheless better than the expression levels of AHSV-9 VP5 gene using an alternative baculovirus expression system. AHSV-3 VP2 and VP5, were cloned respectively under the polyhedrin and p10 promoters of the pFastbac dual transfer vector of the Bac-to-Bac™ baculovirus expression system. mRNA transcription of both AHSV-3 VP2 and VP5 genes in Sf-9 cells was shown. The expression of VP2 was also demonstrated but VP5 was very poorly expressed by the dual recombinant. Further research to determine the effect co-expression of AHSV-3 VP5 in the AHSV-3 VP2 antigenicity is needed. / Dissertation (MSc Agric (Genetics))--University of Pretoria, 2006. / Genetics / unrestricted

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Please read the abstract in the section 00front of this document / Dissertation (MSc (Agric): Genetics)--University of Pretoria, 2005. / Genetics / unrestricted

African horse sickness (AHS) is a non-contagious viral disease transmitted by an arthropod vector and is endemic to sub-Saharan Africa. The disease affects all equine species, but is more severe in horses and other equid species not native to Africa. Vaccination is the only demonstrated means of its prevention. The horse-owning public provides much anecdotal evidence of prophylactic strategies, such as repellents, stabling, alternate hosts, traps, paraffin, blankets, smoke or fans. The present study investigated the relationship of these strategies to the incidence of AHS, and evaluated alternate hosts, wind speed and repellents on the activity of males and females of the different Culicoides species.. Cypermethrin and citronella-containing repellents repelled the most female midges. Sheep and cattle offer an alternate blood meal to gravid and nulliparous female midges. Fans are very effective in keeping midges away from horses. Methods are summarised for the horse owner to implement in addition to vaccination to prevent AHS. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2008.

African horse sickness virus causes a non-contagious, infectious disease of equids. It is epizootic to sub-Saharan Africa and parts of the Middle East. The epizootics caused by the virus have caused widespread devastation amongst equids worldwide. Fortunately no epizootic has lasted more than 5 years outside of sub- Saharan Africa. It is vectored by species of Culicoides midges (Diptera: Ceratopogonidae) and most importantly by the two Avarita species of C. imicola Keiffer and C. bolitinos Meiswinkel. The literature pertaining to the study and research of the virus, the disease and the vectors is reviewed. Models allowing prediction of future possible outbreaks as well as details of control strategies and findings of researchers are presented and discussed. The virus needs a long term reservoir host in which to overwinter and various theories are discussed. Control measures in South Africa are suggested so that outbreaks of the disease can be reduced. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermarizburg, 2008.

African horse sickness (AHS) is a viral disease with high mortality rates, vectored by the Culicoides midge and affecting members of the Equidae family. AHS is endemic to South Africa, and, as a result, affects export and international competitiveness in equine trade, and impacts significantly on the South African racehorse and performance horse industries. AHS also has devastating consequences for rural and subsistence equine ownership. The protocol developed in this dissertation has the potential to serotype and confirm the AHS virus within a few hours at significantly less cost than current methods. It will ease the financial and time constraints of studying an outbreak in real time and has the potential to solve many of the unknown factors surrounding AHS, particularly and most importantly, the role that each serotype plays in outbreaks and the form of the disease contracted by horses. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.