Vaccine for African swine fever virus shows promise
US government and academic investigators have developed a vaccine against African swine fever that appears to be far more effective than previously developed vaccines, according to a study published in the Journal of Virology.
There is currently no commercially available vaccine against African swine fever, which has been devastating the swine industry in Eastern Europe and Southeast Asia. African swine fever virus (ASFV) is highly contagious and often lethal to domestic and wild pigs; humans are not susceptible. Outbreaks have been quelled — more or less — “by animal quarantine and slaughter”, according to the study.
In 2007 there was an outbreak of African swine fever in the Republic of Georgia that featured a new strain of the virus, now known as ASFV-G, and has since been spreading through Eastern Europe and East Asia. As noted by Dr Douglas P Gladue, principal investigator on the new study, “This was the first outbreak in recent history outside of Africa and Sardinia — where swine fever is endemic — and this particular strain has been highly lethal and highly contagious, spreading quickly to neighbouring countries.”
Dr Gladue serves as a senior scientist at the Plum Island Animal Disease Center, Agricultural Research Service, US Department of Agriculture. He noted that there is limited cross-protection between strains of African swine fever, likely because the antigens and degree of virulence differ among them, and that none of the historical experimental vaccines have been shown to be effective against ASFV-G. This is what the investigators at Plum Island Animal Disease Center set out to change.
Part of the process of developing whole virus vaccines involves deleting virulence genes from the virus. But when the researchers deleted genes similar to those that had been deleted in older ASFV strains to attenuate them, “it became clear that ASFV-G was much more virulent” than the other, historical isolates, because it retained a higher level of virulence, said Dr Gladue. The investigators then realised they needed a different genetic target in order to attenuate ASFV-G.
They used a predictive methodology called a computational pipeline to predict the roles of proteins on the virus. The computational pipeline predicted that a protein called I177l could interfere with the immune system of the pig. When they deleted this gene, ASFV-G was completely attenuated. Indeed, the study showed that both low and high doses of the vaccine were 100% effective against the virus when the pigs were challenged 28 days post-inoculation.
More work needs to be done to meet regulatory requirements for commercialisation, said Dr Gladue. Nevertheless, he claimed, “This new experimental ASFV vaccine shows promise, and offers complete protection against the current strain currently producing outbreaks throughout Eastern Europe and Asia.”
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