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Masters Degrees (Animal and Poultry Science)

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Browsing Masters Degrees (Animal and Poultry Science) by Subject "African horse sickness."

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    Molecular diagnosis of African horse sickness.
    (2018) McColl, Evan Saul.; Laing, Mark Delmege.; Burgdorf, Richard Jörn.; Young, Marion Belinda.
    African horse sickness (AHS) is a viral disease of equids caused by the African horse sickness virus (AHSV), a double-stranded RNA virus of the genus Orbivirus. The disease had a devastating effect on the sporting horse industry, and many communities who rely on equids for subsistence farming. In this study, which started in 2016, blood samples were collected from 81 horses in the KwaZulu Natal province of South Africa. Six horses (7%) were identified as AHSV positive and had their viral load quantified using a standard RT-qPCR assay. A semi-quantitative method, using digital gel image analysis, was evaluated as an alternative to qPCR in resource-limited settings. A significant correlation was found in the quantification data obtained using qPCR and digital gel analysis (P < 0.01), demonstrating the potential for its use in under-equipped diagnostic laboratories. Vaccination is currently the main tool for control of AHS in endemic areas. Live attenuated vaccines (LAV) have the potential to disrupt effective disease monitoring by being a source of the detectable virus. The sensitivity of nucleic acid diagnostic assays allows for the detection of low levels of AHSV prior to the onset of clinical signs. A study was conducted on the effect that this vaccine has on viraemia levels and the disruptive effect this may have is discussed. Routinely vaccinated miniature mares (n=9) had their AHSV viraemia levels monitored following the use of a commercial polyvalent LAV. No AHSV was detected in the horses following vaccination. The absence of AHSV in the mares supports the concept that multiple vaccinations reduce the risk of vaccine-induced viraemia. Flinders Technology Associates® filter paper cards (FTA® cards) are designed to store nucleic acid from fresh sample material in a stable matrix and may be a practical solution to disease surveillance in resource-limited settings, where conventional sampling methods are not always suitable. Storage and elution conditions of AHSV RNA from these cards have yet to be investigated. This study compared the efficacy of two elution reagents for AHSV RNA extraction from blood applied to FTA® cards. Cards with AHSV positive blood applied were stored at room temperature for one week. Amplified products were extracted using TE-buffer with an elution time of 24 hours. This study shows that FTA® cards are feasible for AHSV nucleic acid assays but further investigation into standardised procedures for the storage and recovery of AHSV RNA from FTA® cards is required. The AHSV genome is made up of ten double-stranded RNA segments with nine antigenically different serotypes of AHSV identified so far. However, there is limited information on the serotype prevalence of AHSV in endemic areas. Therefore, multivalent vaccines remain the mainstay for disease control in these regions. Improved epizootiological information can improve vaccination programs and control mechanisms. In this experiment, a novel approach was investigated for the assessment of AHSV nucleic acid variations using high-resolution melt analysis (HRMA). Blood infected with a wild strain of AHSV was used in a PCR that targeted regions of Segment 10 (S10) and Segment 2 (S2). Following this, high-resolution melting curves were generated from these PCR products. S10 primers amplified the expected 181 bp product but the other primer sets failed to amplify the S2 gene segment, warranting further evaluation and optimisation of the primer sets used to detect currently circulating AHSV strains.
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    Testing for passive transfer of immunity in foals, and an evaluation of the African horse sickness vaccination schedule.
    (2005) Crow, Linnet Jean Isobel.; Young, Marion Belinda.; Bradford, Gail Smith.
    This thesis comprises an introductory review of the literature, followed by reports of two experiments which are presented in the form of scientific papers. For this reason, there may be some repetition between chapters, particularly in terms of experimental procedure. To avoid unnecessary repetition, a single list of references is given at the end of the thesis. For the sake of completeness , several appendices are attached to Chapters Two and Three which would not ordinarily be included in a scientific paper. The literature review looks at the passive transfer of immunity from the mare to the foal, the consequences of failure of passive transfer of immunity and different methods of testing whether the transfer of passive immunity has occurred. The review concludes with a discussion of vaccination programmes against African horse sickness. Trial One evaluated different tests for determining whether the transfer of passive immunity from mare to foal has occurred in order to determine which of these tests should be used preferentially. A single radial immunodiffusion test was used as the reference standard. A series of samples .was taken from a group of foals and tested using four methods: single radial immunodiffusion , glutaraldehyde coagulation, zinc sulphate turbidity and protein refractometer tests. Trial Two explored African horse sickness vaccination programmes, focusing on when to vaccinate foals for the first time. A series of samples was taken from a group of foals from birth until two months after their second set of African horse sickness vaccinations (one year old). The samples were tested for the presence of African horse sickness antibodies for each of the nine serotypes to determine when maternal immunity fades and to evaluate the effect of each vaccination on the level of immunity.