Chicken and turkey factory farms are so crowded and filthy they are perfect reservoirs for disease.
Tens of thousands of birds are packed in sheds teeming with bacteria and ammonia fumes and many become ill from the unsanitary environment.
Laying hens are crammed in battery cages stacked tier upon tier.
Faeces from the birds on top fall on those below, providing ideal conditions for diseases such as bird flu to spread.
According to the World Health Organization, people can become infected with bird flu by eating undercooked infected chicken or by eating food prepared on the same cutting board as contaminated chicken or eggs.
Even touching the broken eggshells of infected eggs puts consumers at risk.
And flu vaccination is no guarantee of safety, as 25 per cent of children who died of influenza from 2010 to 2014 had been immunised.
The best way to prevent bird flu – and save billions of animals from pain and suffering – is by eating a vegan diet.