Of those, 15,000 were killed by the virus. The other 5,000 were destroyed as a precaution.
"It began with a few pigs a day, then it was hundreds," said Sun, a pig farmer and agricultural entrepreneur from Hebei province, China. "In the end, 800 pigs would die in a single day."
To put it in context, that's almost as many pigs as in the United States and Europe combined.
The virus is harmless to humans but deadly to pigs—and, so far, there is no cure or vaccine. Originating in Africa, outbreaks were recorded in eastern Europe and Russia before it first appeared in China last August.

It has since spread to other Asian countries, including Vietnam and Cambodia.
In March, the Chinese government said it had a "good control" of the epidemic. At a press conference last month, Beijing said ASF was not spreading as quickly as before.
According to the United Nations' Food and Agriculture Organization (FAO), China's central authorities have taken the right steps to bring the virus under control.
Farms Wiped Out
But the scale of the outbreak may be bigger than officials estimate, as some farmers tell CNN that the disease is not always recognized locally.Sun said initial testing by provincial officials at his Hebei farm was negative for ASF. However after he posted pictures of the dead animals online, the country's Disease Prevention and Control Center tested them and confirmed they carried the virus.
Also in Hebei, fellow farmer Zhang Haixia watched all her 600 pigs die. The official cause of death, she was told, was a regular swine influenza.

CNN has contacted authorities in Hebei for comment but has not received a response.
Martin, from the FAO, warned that it could take years before the outbreak was completely contained.
Not Enough Pork in the World
One of the main problems China faces in containing ASF is that its pig industry is fragmented. Martin said there are thousands of small farms which may not have the correct bio-security measures needed to control the spread of the disease.Another complication is that the virus can survive in pork products for months, meaning it can be reintroduced into herds by accident.
And it's not just producers who are hurting. The epidemic could also have a broader economic impact: China is the world's largest consumer of pork, a staple for the vast majority of its 1.4 billion people.

Analysts say there isn't enough pork in the world to cover China's expected shortfall and consumers are likely to turn to other meats as a substitute.
Rabobank's report predicts an "unprecedented" shift in global protein supply to China to cover the shortfall.
In the lunar calendar, 2019 is the year of the pig. It's supposed to be an auspicious year. For China's pork industry, it's anything but.
