Poland on Wednesday confirmed its first cases of deadly swine fever in domestic pigs, as the World Trade Organisation reviewed a Russian embargo on EU pork imports imposed over the disease.
"Test results showed the first outbreak of African swine fever on a farm with five pigs," in the eastern region of Bialystok bordering Belarus, Polish veterinary authorities said in a statement.
The animals were destroyed and 37 surrounding farms with 192 pigs were put under quarantine, it added.
The development comes the day after fellow EU member Latvia declared a state of emergency in a second area of the Baltic state as efforts continued to contain an outbreak of the fever among pigs.
Lithuania ordered a mass cull of wild boar earlier this year, targeting 90 percent of the estimated 60,000 living on its territory, after the disease was detected in animals thought to have come from Belarus.
Poland first imposed measures in February to safeguard its lucrative pork exports, worth 912 million euros ($1.2 billion) last year, after the disease was found in two wild boar.
China nevertheless banned Polish pork and Russia slapped its own blanket ban on pork imports from the 28-member European Union, a move Brussels criticised as "disproportionate".
African swine fever is harmless to humans but lethal to pigs and has no known cure, posing a grave threat to commercial farms.
China, home to the world's biggest pig population, is also the largest importer of Polish pork, buying 52,000 tonnes worth 68 million euros ($92 million) in 2013.
Russia absorbs a quarter of the EU's pork exports, worth around 1.4 billion euros a year.
Trade sources said the WTO's disputes settlement body has created panels to hear complaints about Moscow's ban on EU pork imports, which come at a time of heightened tension between Russia and Brussels over Ukraine.
African swine fever has spread throughout the Balkans, the Caucasus and Russia since 2007, and is endemic to areas of Africa, according to the United Nations' Food and Agriculture Organisation (FAO).
The FAO warns of "vast losses" if it migrates from Russia to China, which is home to half of the world's pigs.
Explore further: Latvia orders pig cull to stem African swine fever