A viral disease that killed more than 24,000 pigs last year in southern China originated in bats, Chinese scientists concluded in a study published Thursday in Nature. The paper sheds light on cross-species transmission of a highly infectious coronavirus — the same virus family that causes severe acute respiratory syndrome, or SARS — as well as the future prevention of disease in both animals and humans.
After gene-sequencing a virus found in the dead pigs in Guangdong province and a virus isolated from horseshoe bats in a cave near the farm where the epidemic originated, the scientists found that the two were 98 percent similar. The virus, identified as the swine acute diarrhea syndrome coronavirus (SADS-CoV), shares certain characteristics with the SARS-CoV, the coronavirus that causes SARS, a lung disease that originated in Guangdong and caused more than 300 deaths in China in 2002.
Zhou Peng, a researcher at the Wuhan Institute of Virology (WIV) and the lead author for the study, told Sixth Tone that the pig farm where SADS-CoV was discovered is just 100 kilometers north of Foshan, the city where the first SARS case was diagnosed. Zhou added that both of the viruses are found in horseshoe bats, which means they have ample opportunity to mingle and recombine, potentially creating new viruses that could pose health risks to animals and humans.
“Coronaviruses are badass,” Zhou said. “They [recombine] like building blocks.”
According to the scientists’ research, SADS-CoV is transmitted to pigs through the bats’ feces and has a 90 percent kill rate when it infects piglets that are less than five days old. Thus far, the disease has only been found in Guangdong, where pig farmers have managed to control the disease through close monitoring and testing carried at out at their own labs or in partnership with a local university.
Wang Linfa, a professor at Duke-NUS Medical School in Singapore and a contributor to the research, said at a news conference Wednesday that people cannot be infected with the virus by eating pork. “Our evidence is clear that the virus is not infectious to humans,” he said. “Besides, cooking and sterilization denature the viruses.”
However, the researchers’ experiments found that SADS-CoV can infect human cells in a laboratory — meaning exposure to the virus could still be risky. “Our fear is that if a virus is established in pigs and continues to spread, it will mutate and become a risk to humans,” Wang said. “This is why early-phase monitoring and long-term surveillance are important.”
Such oversight has long been in place in southern China — and the researchers say this was crucial to their quick ID of the virus. Scientists at South China Agricultural University who also participated in the research have helped to establish a surveillance system at pig farms across Guangdong. Large pig farms with more resources carry out daily testing in their own labs, while small farms send samples to the university’s laboratory in the event of a string of unnatural deaths.When the pigs got sick last year, the university acted immediately: After testing, the scientists determined that the pathogen was a previously unknown virus.
Since then, South China Agricultural University has been working on a vaccine that could eliminate the disease in pigs. “We’re making good progress,” Ma Jingyun, a professor specializing in animal immunology at the university, said. She added that the vaccine is currently in the clinical trials stage.
Scientists and health experts are best able to deal with emerging infectious diseases when there is already an early-detection system in place — such as PREDICT, a project initiated by the U.S. Agency for International Development. The Chinese researchers collaborated with PREDICT to obtain bat virus samples until they found a match and identified SADS-CoV.
International cooperation and databases of precollected samples have greatly reduced the amount of time required to identify potentially deadly viruses, said Wang. “It only took us two months to identify SADS,” he said. “That’s 10 times faster than how long it took to identify SARS a decade ago.”
“The takeaway from this research is that regardless of whether it’s animals or humans, the methodology is the same,” Wang explained. “We are confident that, in the event of human infection, we can detect and diagnose the virus at an early stage.”
Editor: David Paulk.
(Header image: Photolibrary/VCG)