Abstract
Enterotoxaemia (pulpy kidney) is a common bacterial disease of sheep caused by Clostridium perfringens type D epsilon toxin. It has mortality rates of up to 30% in non-vaccinated animals. Current vaccines from whole cell cultures are expensive to manufacture and can induce local inflammatory responses in sheep. They usually have reduced immunogenicity because of the difficulty of standardising the inactivation step in vaccine manufacturing. In the current study, we evaluated the safety and potency of a recombinant plant-made epsilon toxoid protein (r-Etox) as an affordable and safer alternative vaccine for developing countries. Results of injection site reactions, rectal temperature and toxin neutralisation test in single and prime–boost inoculations of mice, guinea pigs and sheep suggest that the product is not toxic to animals and could protect sheep against enterotoxaemia.
Highlights
Enterotoxaemia is a disease of economic importance in sheep, with a mortality rate of between 10% and 30% in non-vaccinated lambs
For purposes of this study, the nomenclature Etx refers to the C. perfringens type D epsilon toxin gene, recombinant C. perfringens epsilon toxin (r-Etx) is the recombinant epsilon protein produced from the plant matrix before activation by trypsinisation and recombinant plant-made epsilon toxoid protein (r-Etox) refers to the plantproduced recombinant epsilon toxin protein after trypsinisation and formalin inactivation
To assess expression of the plant-codon optimised Etx open reading frame (ORF) (Figure 1a), plant extracts from agroinfiltrated plant leaves were analysed by SDS–PAGE (Figure 1b) and western blot analysis (Figure 1c)
Summary
Enterotoxaemia (commonly known as pulpy kidney disease) is a disease of economic importance in sheep, with a mortality rate of between 10% and 30% in non-vaccinated lambs It affects calves and goats, the symptoms are less severe, causing a non-fatal subacute disease (Morris et al 2012). Available vaccines in South Africa are formalin-treated alum or oil emulsion of whole cell culture or bacterial filtrates of C. perfringens (C. welchii) type D. These vaccines usually have reduced immunogenicity because of the difficulty of standardising the inactivation step (Mathur et al 2010), and some components of the toxoids induce local inflammatory responses or allergic reactions (Jiang et al 2014). The media used for anaerobic fermentation of the bacteria are not readily available in many developing countries, including South Africa, where it has to be imported, thereby making the manufacturing process expensive
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