04 October 2021 - Last week, the USDA’s Agricultural Research Service (ARS) announced the imminent publication of research with the latest trials of the African Swine Fever vaccine candidate known as ASFV-G-ΔI177L.
As Dr. Douglas Gladue and Dr. Manuel Borca, the ARS researchers who discovered and patented ASFV-G-ΔI177L last year and participated in the current research, told Feedinfo, these trials were important for multiple reasons.
Firstly, because they show the vaccine candidate to be effective against a recent isolate of ASF, which was circulating in an area where the disease is causing much harm. “In our laboratory, we tested the initial outbreak strain of Georgia [in the initial work on ASFV-G-ΔI177L in 2020], and over the course of the pandemic and spread of the disease, this strain has had some small modifications or some small mutations. NAVETCO tested a recent isolate, so we can see that [our vaccine] was still protecting against this recent isolate, [with] changes that occurred over the last 10 to 12 years,” says Gladue.
“And the other important point…is having tested on pigs of a breed that was native to Vietnam,” adds Borca. “This, to our knowledge, is the first time that a scientific report shows that shows that the 2007 isolate, or a close derivative of it, like the virus that we used, is able to induce protection against viruses that, say, evolved for 12 years in the field, and it’s also to our knowledge the first report of a vaccine that has been tested in a breed of pigs that is native to Southeast Asia.”
Although the experiments documented in last week’s paper were carried out at NAVETCO in Vietnam, the ARS researchers explain that they were invited by the Vietnamese government to collaborate on the development of an ASF vaccine upon releasing their first results on ASFV-G-ΔI177L, and had been working together throughout 2020 and 2021. “All the experiments that have been performed and published in the paper published yesterday have been done at NAVETCO, with very close contact with us in terms of the design of the experiments and the evaluation of the results, and of course, writing and presentation of the manuscript,” says Borca.
What’s Next?
In Vietnam, Gladue says ASFV-G-ΔI177L will be moving on to field trials, although he cautions that the road ahead remains long. “I think it's important to point out that there's a lot of other concerns, or not concerns, but things that have to be done for commercialization, that’s approval from regulatory authorities. There’s still additional safety studies, reversion to virulence studies, that’ll have to be performed, months actually before regulatory authorities will approve it.”
Moreover, this process and the requirements involved will differ for every country, so widespread use of the technology is still not imminent.
Borca outlines some of the white spaces in the understanding of this vaccine candidate which will need to be addressed in future research: “the controlled experiments under field conditions… reversion to virulence to show genetic stability and that the attenuation phenotype stays in place…viral shedding, if a virus can be shared from an animal in the normal field conditions...the presence of any residual virulence in a specific type of pigs like, for example, the pregnant sow… that is part of the package of testing that should happen, and some of them are already [being] tested by NAVETCO.”
Meanwhile, at the ARS’s Plum Island Animal Disease Center where the two are based, work progresses on identifying genes which are involved in disease, in order to eventually produce vaccine candidates like ASFV-G-ΔI177L. “A big chunk of our activity is still in the production of information, basic information about genes that are involved in the production of disease, and the use of that information in order to produce novel or improved vaccine candidates,” explains Borca.
“The other big step that we are looking for right now is to provide them with DIVA capability. We are investing a good amount of our effort in the identification of genes that are important in the immune response…” he asserts.
Gladue, moreover, also points out that the team has made other progress beyond the identification of the important I177L gene in attenuation. These have included looking into options beyond intramuscular injection, specifically the oral-nasal route: “that’s very important for looking at [vaccination of] wild animals that we need to deliver via bait.”
They have also had breakthroughs which will be essential to cost-effective commercial production. “We have adapted our vaccine candidate to grow in a stable cell line. The importance of that is that the primary swine macrophages have to be freshly isolated from donor swine, and that poses a different regulatory concern… a stable cell line allows for easier large-scale production that will also make it easier for regulatory approval.”
Asked what the present research means when it comes to potential efficacy against the versions of the virus that have recently been detected in North America (in the Dominican Republic and Haiti), the researchers are cautiously optimistic. “We still do not have officially the identification of the genetic characteristics of the virus circulating in the Dominican Republic, but we can say, based probably on the results published yesterday, if the virus stays within the general characteristics of the Georgia virus or derivatives, we believe our vaccine should be able to [provide protection.] But these are things that can only be tested experimentally.”