Though a double gene-deleted vaccine being used in China may reduce mortality, it can still contribute to increased spread of the virus
By Jackie Clark
Swine health officials in North America are monitoring the use and risk of unapproved African swine fever (ASF) vaccines in China.
“We get reports from on-the-ground in China and there are a variety of different vaccines that are being tried to be used to help manage the ASF outbreak,” Dr. Paul Sundberg, executive director of the Swine Health Information Centre, told Farms.com.
These vaccines are “manufactured in a variety of different ways and they have all kinds of different effects,” he explained. “There is a double gene-deleted vaccine that’s being used fairly widely in China.”
This version is “a modified live virus vaccine,” he added.
Because the virus is live “it does cause infection, it does cause pathology, it does give the pigs ASF, but most of them at least will survive,” Sundberg explained. “That survival is something that is noteworthy. Any time that you’re losing that many pigs to a disease and you can use something to help them survive and still get to market, that’s conservation of the protein and that’s a good thing. That’s a worthy goal.”
However, “it also is not a safe and effective vaccine. It still gives pathology, it still causes infection, it still causes virus to circulate, as well as some of the pigs don’t survive,” he added.
This double gene-deleted vaccine also has the potential to make ASF detection more difficult.
“A virus that infects pigs and causes them to die is, for the most part, fairly easy to detect, because for the most part if they get that virus they’re going to die,” Sundberg explained. “It’s detectable because there’s a mortality outcome.”
However, a less virulent version of ASF that doesn’t cause mortality all the time may be more difficult to detect.
“It may just look like something else and may continue to spread,” Sundberg said. “The vaccine virus does move from pig to pig, it causes infection, it decreases the clinical signs, there’s less mortality, so therefore it might be more difficult to detect.”
However, the United States Department of Agriculture “has said that they expect that their PCR detection tests that look for antigens would be able to still find this double gene-deleted virus should it show up,” he added. “Our diagnostic test should be adequate to be able to detect it.”
It is still crucial for pork producers to remain “vigilant and attentive,” he said.
“I expect that there are other non-approved vaccines being used elsewhere, I just don’t have reports,” Sundberg added.
Scientists are administering USDA vaccines in Vietnam for clinical trials. Reports indicate “they may be available commercially as early as this fall,” he said. “In my opinion that’s probably optimistic, if you want to under-promise and overdeliver we’re still years away from a safe and effective ASF vaccine.”
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