SEOUL, South Korea (AP) — South Korea is concerned North Korea is ignoring its calls for joint efforts to stem the spread of highly contagious African swine fever following an outbreak in North Korea.

South Korea's agricultural ministry on Wednesday says blood tests of pigs from some 340 farms near the inter-Korean border conducted through Tuesday came back negative. Hundreds of fences and traps have been installed around the farms to prevent their pigs from contacting wild boars that roam in and out of North Korea.

Seoul says the North hasn't responded to proposals for joint quarantine efforts. The disease, which has decimated pig herds in China and other Asian countries, is harmless to humans but for pigs is fatal and highly contagious.