World races to develop African swine fever vaccine

By Jessie Higgins
Some estimates say China will lose half of its pig population to African swine fever. File Photo by Stephen Shaver/UPI
Some estimates say China will lose half of its pig population to African swine fever. File Photo by Stephen Shaver/UPI | License Photo

EVANSVILLE, Ind., July 12 (UPI) -- Governments, universities and private businesses around the world are racing to develop a vaccine for African swine fever before the disease spreads around the world.

The virus, deadly to pigs, but harmless to humans, is spreading relentlessly across Asia. Half of China's pig herd might soon be gone, according to some estimates, and that's roughly a quarter of the world's pigs.


The disease also has infected pigs in Vietnam, Mongolia, North Korea, Cambodia, Laos and Bulgaria. Because of its potential to destroy a nation's pig industry, non-infected countries, including those in Europe and North America, are throwing up as many defenses as possible to keep it out.

But with no vaccine, there is only so much they can do.

"The African swine fever threat won't go away," said Dan Rock, a professor of pathobiology at the University of Illinois, who is working with colleagues in Russia to develop a vaccine. "This will be a persistent issue for a very long time. There is quite a bit of work going on in a lot of places" to create a vaccine.


There are some early signs of success.

In the last three years, scientists working for the U.S. Department of Agriculture have created three "vaccine candidates." These are vaccines that -- in a lab -- have successfully immunized pigs against the disease.

A state-run lab in China announced in May that it identified two vaccine candidates that successfully inoculated pigs, according to China Daily. The Vietnamese government announced it had similar success in June, according to View Nam News.

Promising discoveries

Other researchers in the United States, Russia, Spain and the United Kingdom say they've made promising discoveries. A New Jersey company on Monday, for example, said it made a "significant advancement" toward a vaccine, and was seeking a patent.

Even with progress, it is unlikely a vaccine will become commercially available anytime soon. In fact, in May, USDA Under Secretary Greg Ibach predicted it could be eight years before a vaccine reaches the market. Other, more progressive, predictions hover around 2 or 3 years.

"Due to the urgency, there are ways to accelerate the regulatory process and dedicate every available resource to it," said Luis Rodriguez, a USDA foreign animal disease research leader. "But even if that is the case, it is still going to be more than a year. It is not going to be in the next few months."


The same is true in other nations.

"From lab results to getting to use in the field is a long process," said Linda Dixon, a lead African swine fever virus researcher at The Pirbright Institute, a center in the United Kingdom that works to prevent and control viral disease.

This could be particularly true with African swine fever.

It is one of the largest, most complex viruses in the world. Its DNA contains 170 proteins -- many viruses have about 10. Although they've found vaccine candidates, scientists still don't have a full understanding of what all those proteins do, or how they interact with the pig.

"We don't know which of those proteins the host needs to see to develop an immune response," Rock said.

Understanding the virus' genome is not necessarily a requirement to create a successful vaccine. Humans created the first inoculations long before they knew how genes worked, Rock said.

Weakening viruses

Those early vaccines were created by deliberately weakening a virus through a process called "attenuating." Doctors and scientists would take a weak virus and pass it through a different species -- like a chicken embryo.

"As it adapts to the chicken cells, it loses its ability to infect the original host," Rock said. "So this weakened virus can multiply a little in the [host], enough for it to develop an immune response and create an immunity."


Many very successful vaccines were created this way. But, with a virus as complex as African swine fever, the chances of success shrink.

Scientists tried this particular approach in Spain and Portugal during an African swine fever outbreak in the 1960s. They inoculated pigs with a live virus that was naturally weakened. It worked, the pigs survived and they were immune to the virus. But the vaccine itself gave many of them a chronic form of the disease that was debilitating, Rock said.

Decades later, in 2010, researchers at the USDA attempted to create a vaccine by deliberately weakening the virus.

"But allowing that caused a huge amount of genetic change, and it was not useful as a vaccine anymore," said Manuel Borca, a foreign animal disease research biologist with USDA.

The other problem with that approach is that scientists don't know why the virus is weakened. They don't know what changes occurred at the genetic level.

"The new idea is we can rationally engineer attenuated viruses," Rock said. "This is based on the idea we know a lot more about the genome now. So we can identify the subset of genes [responsible for the virus' virulence]. Once we identify them, we can create a virus where we delete those critical genes."


Little funding

A handful of scientists have studied the African swine fever virus DNA for more than 20 years, in hopes of discovering those critical genes. But, until recently, there was little interest in -- or funding for -- such work.

"Nobody really thought it was much of an issue," Rock said. "African swine fever was thought to be an African thing. And Africa didn't trade much with the Americas or Europe."

The virus first escaped Africa in the 1960s, when it appeared in Spain and Portugal. But both countries were able to eradicate it without a vaccine. The virus did not make another appearance until 2007, when it infected the nation of Georgia. A few years later, it arrived in Russia.

At that time, the United Nations attempted to raise the alarm. If unchecked, the deadly disease could spread rapidly through the world's hog population.

China, with half of the world's pigs, many of which were raised in rural farms lacking biosecurity controls, was at a particularly high risk.

Those early warnings proved fatally accurate.

"Now we have an African swine fever epidemic in over half of the pigs in the world," Rock said. "It is out of Africa for good."


Since its arrival in China, interest in an African swine fever vaccine has exploded.

Many of the vaccine candidates in development -- including the three created by Borca at the USDA -- are genetically engineered to be less virulent.

The USDA is seeking a corporate partner to test its vaccine candidates on a large scale to ensure they are safe and effective. If they prove to be, that corporate partner will then set out creating a process to mass produce the vaccine -- a process that can take years.

Other scientists are trying to isolate the exact protein that is responsible for creating an immune response, and create a vaccine that uses just that protein. Such a vaccine would immunize a pig without any risk of infection.

This is they type of vaccine for which Phibro Animal Health Corp. in New Jersey is seeking a patent. Rock's team in at the University of Illinois and the Russia lab are moving in similar directions.

With this kind of research "you have priorities shift around," Rock said. "And with government, it's not always thinking strategically. They're responding to the crisis of the moment. But now, African swine fever is on the radar and it is going to stay there."


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