Fever could kill a third of China's pigs. That's almost as many as are farmed in the US and Europe

Hebei, China(CNN) Sun Dawu's pigs started dying from a mysterious virus last December. Four months later, all 20,000 in one farm were dead.

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."

African swine fever (ASF) is decimating China's pork industry, by far the biggest in the world. Dutch bank Rabobank, which lends to the global agricultural sector, estimates the country's pig population could shrink by a third in 2019 -- up to 200 million animals -- through a combination of the disease and culling.

To put it in context, that's almost as many pigs as in the US 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.

"They've done everything they could possibly do to control the disease. They had a plan, they had a strategy, they have been responding very vigorously," said Vincent Martin, the FAO representative in China.

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.

"The local officials were afraid to be accountable," she told CNN. "They threatened us that there would be consequences if we reported to higher-ups in the government. They are afraid of losing their jobs because of this."

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.

"I'm not sure we can say it is under control because we know how complex the disease is," he said. "We have experience in other countries where it took years to get a handle on these diseases."

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.

According to government forecasts, the price of pork could rise to record levels in the second half of 2019, as demand overwhelms supply.

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.

"This shift will likely create unexpected product shortfalls in markets previously serviced by suppliers ... that will ultimately result in higher global protein prices," report author Christine McCracken wrote.

Pork producers in Europe and the US are already starting to increase shipments to China, even though US exports are subject to a 62% tariff because of the trade fight with China.

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.