In 2005 it was discovered that H5N1 could be infecting up to half of the pig population in some areas of Indonesia, but without showing symptoms. Chairul Nidom, a virologist at Airlangga University's tropical disease center in Surabaya, East Java, did some independent research: he tested the blood of 10 apparently healthy pigs housed near poultry farms in West Java where avian flu had broken out, "Nature" reported. Five of the pig samples contained the H5N1 virus. The Indonesian government has since found similar results in the same region. Additional tests of 150 pigs outside the area were negative.