The disease that killed a million piglets in China has spread to the US, and no one knows why

October 23, 2013
October 23, 2013

America’s pork industry has been gripped by an outbreak of porcine diarrhea since mid-May, the first appearance of the condition in North America. US farmers have reported 768 cases of the disease, known as porcine epidemic diarrhea virus (PEDV), through the first week of October, which implies that many more thousands of animals could be affected.

Although the disease is not transferable to humans, it has been devastating for the US pork industry. It causes severe “watery diarrhea and vomiting in nursing pigs,” according to information from the US’s National Pork Board. Almost all the piglets who get the disease die because of it, and farmers are reportedly filling “wheelbarrows of dead piglets.”

Now researchers at the Virginia-Maryland Regional College of Veterinary Medicine at Virginia Tech say they’ve traced the virus back to eastern China’s Anhui province. Anhui is one of China’s major pig-farming areas, home to companies like the fast-growing Anhui Antai Agricultural Industry Group, which slaughtered 500,000 pigs last year.

Pinpointing the origin of the virus isn’t going to provide much reassurance to US farmers. Years after it spread in China, it still hasn’t been controlled.

Reports of PEDV outbreaks in China and Europe are not new, and have been mostly controlled with vaccination over the years. But starting in 2010, China suffered a severe outbreak of PEDV that killed more than 1 million piglets in less than two years. Scientists said the Chinese death toll was thanks to new vaccine-resistant strains of the disease.

Anhui is a neighboring province to Shanghai, where thousands of dead pigs were discovered floating in the Huangpu River earlier this year, and had its own floating dead pig incidents. The Huangpu river pigs deaths have been attributed to “Porcine circovirus,” although some dead pigs found in the area also tested positive for PEDV, China’s state-run Global Times reported in March. Of the 36 samples tested by the Animal Disease Control Center in Zhejiang Province, 16 contained porcine circovirus and seven tested positive for porcine epidemic diarrhea virus, the paper reported.

In April, Shanghai Jiaotong University ‘s Agriculture Sciences School published a research paper saying piglet diarrhea was still causing serious harm to China’s pig-breeding industry, and identifying it as the cause of pig deaths in Shanghai this spring.

How the disease traveled from Anhui to North America remains a mystery. The US and Canada both ban on pork imports from China, as Nature magazine explained in July:

Although researchers know that the virus can be transported in faeces, they do not know how long it can survive outside pigs’ intestines, so it is unclear if a dirty boot, a contaminated package or an illegal import carried PEDV into the country.

Ivy Chen contributed reporting.

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