Pigs from two North Carolina farms have tested positive for the H1N1 flu virus in a federal laboratory, though officials report all animals have recovered and likely contracted the virus from humans.

The pigs showed signs of mild illness and were tested in a U.S. Department of Agriculture lab in Ames, Iowa, said State Veterinarian David Marshall. He added that this case shows the state’s monitoring system is working.

Herd owners said workers who had contact with the pigs showed flulike symptoms in the days before the animals’ illness, said Tom Ray, director of livestock health at the N.C. Department of Agriculture and Consumer Services. Pigs at both farms must have caught the virus from them, he said.