Development of an oral vaccine against the ostrich-specific mycoplasma, Mycoplasma struthionis

[摘要] ENGLISH ABSTRACT: The ostrich-specific mycoplasmas Mycoplasma struthionis, Ms02 and Mycoplasma nasistruthionis, are associated with respiratory disease in ostriches, which is threatening the South African ostrich industry. Antibiotics are available to manage Mycoplasma infections, but a need to prevent infections led to an investigation into the development of vaccines against the ostrich-specific mycoplasma. After commercially available poultry mycoplasma vaccines proved to be unsuccessful in protecting ostriches against ostrich mycoplasma infections, the genome of M. struthionis was analysed and the OppA gene identified as a good vaccine candidate. The gene was isolated and used to develop the pCI-neo, VR1012 and VR1020 naked DNA vaccines. M. struthionis infects the respiratory tract of ostriches, therefore a vaccine that results in mucosal immunity is required. The use of a bacterial vector for DNA vaccines has been shown to elicit both a humoral and mucosal immune response. Salmonella enterica serovar typhimurium SL3261 was used to develop mucosal pCI-neo, VR1012 and VR1020 DNA vaccines. The pCI-neo mucosal DNA vaccine was found to be unstable in vivo and the stable mucosal VR1020 and VR1012 DNA vaccines were considered for subsequent vaccine trials. The tissue plasminogen activator (TSA) signal peptide found in the VR1020 plasmid to direct the secretion of the membrane protein, OppA, makes it a good candidate vaccine to compare against the naked DNA vaccine. A preliminary vaccine trial conducted with this vaccine was influenced by various factors including avian influenza and the statistical results proved to be invalid, but enzyme-linked immunosorbent assays (ELISAs) were developed for the successful measurement of the immune response of the ostriches. The dose of the mucosal vaccine administered in the preliminary trial might not have been enough to elicit an effective immune response in the ostriches. Different doses of the mucosal VR1012 and VR1020 DNA vaccines were therefore used in a second trial, but the trial was also influenced by a variety of factors. Even though the results of the vaccine trials were not successful, a few observations were made that could be used to improve future trials and reduce the effect of the factors on the vaccine trials, such as the effect of prior infection, as well as the stress on the ostriches.

[发布机构] Stellenbosch University