Zoonotic diseases including influenza, SARS, and COVID-19 often originate in systems with poor animal welfare. Improving animal welfare may be one of the most important zoonotic disease prevention strategies.
The connection between intensive animal farming welfare conditions and pandemic risk is mechanistic. Crowded, stressed animals with suppressed immune systems are more susceptible to and more efficient transmitters of respiratory and other pathogens. Influenza viruses that evolve in intensive poultry operations can acquire human transmissibility through serial passage and reassortment. Wet markets that house live wild and domestic animals in proximity create novel interspecies transmission opportunities. Improving welfare conditions in intensive farming — reducing stocking densities, improving ventilation, reducing antibiotic prophylaxis — reduces pandemic risk alongside reducing animal suffering. This creates powerful alignment between human health and animal welfare arguments for farming reform.