No, they don't suffer. They get better within a few weeks. The disease has been compared to having a bad cold in humans. No, they can't harm humans. Why does it matter? Because during the period of the illness, they stop gaining weight, and lose weight. Thus, big business which now owns over 90% of farm animals, would lose some of their profit. That's why they're killed. Another statistic worth remembering is that while about 500,000 animals have been 'culled' during the current outbreak, 2,500,000 animals are slaughtered EVERY DAY in normal times.