sentence1: First identified in 1930, swine flu is a common and sometimes fatal respiratory disease in pigs caused by type A influenza virus. The disease does not normally spread to humans, though infections are sporadically recorded, especially among people who have been directly exposed to pigs. The recent cases in Mexico and the United States, however, appear to have spread through human contact. From December 2005 through February 2009, only 12 cases of swine influenza were reported in the United States. In 1988 a pregnant woman died after contact with sick pigs. In 1976, swine flu at an U.S. military base at Fort Dix, New Jersey killed one soldier. Four were hospitalized with pneumonia. At first, experts feared the strain was related to the Spanish Flu of 1918, which killed millions, but the strain never spread beyond the base.
sentence2: Swine flu spreads to humans through contact with infected pigs.