Rao Zihe introduces the structure of the African swine fever virus at a press conference on Friday. Photo: VCG

Chinese scientists have unlocked the unique structure of the African swine fever virus. The research published in the academic journal Science and conducted by the Institute of Biophysics of the Chinese Academy of Sciences (CAS), the Harbin Veterinary Research Institute of the Chinese Academy of Agricultural Sciences (CAAS), Shanghai Tech University, among others, lays the groundwork for the development of an effective vaccine against the disease.

China faces a great challenge in controlling the spread of African swine fever, said Bu Zhigao, the director of the Harbin Veterinary Research Institute of CAAS."The breakthrough in unveiling the fine structure of the virus is important," Bu said, adding that research will "provide clues to explore fundamental mechanisms for the infection, pathogenicity, and immunology of the African swine fever."

Scientists have isolated the epidemic strain of the African swine fever, which has spread to China. After four months, researchers collected over 100 TB of high-quality data.

The research shows the virus has a unique structure of five layers: the outer membrane, the capsid, a double-layer inner membrane, a core-shell and genome. It contains more than 30,000 protein subunits, forming a spherical particle with a diameter of about 260 nanometers.

The study identified structural proteins of the virus, revealing potential protective antigens and key information on the epitope, the part of an antigen molecule to which an antibody attaches itself.

The research also showed the complex arrangement and interaction mode of the structural proteins and proposed the possible assembly mechanism of the virus, providing an important clue as to how it invades host cells, and evades and antagonizes the host antiviral immunity.

"The size of the African swine fever virus is huge. It is the largest one among the viruses unraveled by Chinese scientists. Its diameter is 10 times longer than the diameter of the hepatitis A virus," said Wang Xiangxi, a researcher at the Institute of Biophysics of CAS. 

The five-layer structure of the African swine fever virus is very rare and more complicated than other viruses said Wang. "It has a stable structure and can survive for months under normal temperatures, posing a great challenge for prevention and control. Scientists have limited knowledge of the virus. We hope to open the door to have a better understanding of the disease."

Rao Zihe, a CAS academician and one of the leading scientists of the research, said unveiling the structure of African swine fever is the first important step in the "long march" to tackle the disease. Researchers will continue to analyze the structure of the virus's core-shell, and how the virus interacts with receptors.

Shao Feng, another CAS academician and deputy director of the National Institute of Biological Sciences, said that compared with other viruses, scientists' knowledge about African swine fever is almost zero and cooperation between scientists is needed to push forward vaccine research.

"The unveiled structure of the virus is so exquisite, and the analysis work is so beautiful. I believe it can provide help for not only developing vaccines, but also diagnosis and producing medicine for treating the disease," said Chen Xinwen, head of the Guangzhou Institutes of Biomedicine and Health of the CAS.

First documented in Kenya in 1921, African swine fever is a highly contagious viral disease of swine with mortality rates at nearly 100 percent. Over the past decade, the disease has spread to many countries, posing a serious risk of further expansion.

Between January to October, the World Organization for Animal Health was notified by 26 countries of new or ongoing outbreaks: 13 in Europe, 10 in Asia and three in Africa.

With no vaccine or treatment available, culling pigs is the most effective way to contain the outbreaks. More than 30 million pigs have been culled between 2018 and 2019.

The African swine fever pandemic has caused an estimated economic loss of $2 billion for swine production worldwide. The African swine fever virus transmits rapidly and efficiently among pigs, scientists say.

African swine fever is believed to only infect pigs. No humans or other species are known to have been infected.

China reported its first case of the disease in August in Northeast China's Liaoning Province, followed by more outbreaks in other provinces.

China is the world's largest pig producer, and it is an arduous task to control African swine fever. China has conducted lab research on a vaccine against the disease, but the vaccines under development are still not perfect, according to Bu.

Previous developments of the vaccines used traditional methods, lacking clear theoretical guidance. This research may prove beneficial for new vaccine designs, Bu said.
Newspaper headline: Cracking the code of swine flu