An Egyptian security official said police fired shots in the air and tear gas at pig owners who stoned them to prevent government workers from slaughtering the animals as a precaution against swine flu. Twelve people were injured in Manshiyet Nasr, a slum where impoverished garbage collectors live and raise pigs who feed off the refuse. The security official, who spoke on condition of anonymity because he was not authorized to talk to the media, said police were escorting government workers who came to haul the pigs away. Egypt ordered the slaughter of all the country's 300,000 pigs even though no cases of swine flu have been reported here. The World Health Organization said this was unnecessary because the virus is being spread through humans.