Most infectious diseases originate from animals, and covid-19 is no exception. Improved disease monitoring on farms, as well as improved safety measures along the food chain, could help prevent another pandemic, scientists say.

About 60% of human pathogens are of animal origin, including HIV, severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS) and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), more commonly known as covid-19. Of the five new human diseases that emerge each year, three come from other animal species.

As farms have become larger and more industrialised over recent decades, scientists have warned that, unchecked, our farming systems invite the emergence and spread of disease.

Large poultry and pork farms housing thousands of animals are two recognised reservoirs of influenza A viruses (IAVs), scientists say. IAVs are the only influenza viruses known to cause flu pandemics, and animal vaccination safeguarding measures vary widely between countries.

“Worldwide, the variety of IAVs in swine farms is increasing and surveillance for IAVs with pandemic potential is woefully neglected,” researchers in the US and China said in a joint paper last November. The US and China are the world’s largest producers of pork and poultry.

The researchers warn that in many countries, animals, workers and farm infrastructure need better monitoring for disease, and farmers need rapid and accurate diagnostics so they can quickly detect the emergence of a novel IAV.

Food safety

Food safety is vital at every stage of the food chain, from farm to fork. Farmers, manufacturers, buyers, packagers, distributors, regulators and consumers all have a role to play, according to a 2018 food sustainability report produced by The Economist Intelligence Unit and Barilla Center for Food & Nutrition Foundation.

Every year 420,000 people die and 600m fall ill from eating contaminated food. The majority develop diarrhoeal diseases. Indeed, certain strains of norovirus and salmonella have also caused pandemics.

There is currently no evidence that the virus behind covid-19 is being spread through food. But there is evidence that other coronaviruses can exist in food—the virus causing MERS was found in the milk of infected camels, for example.

Avian influenza viruses are usually transmitted to people through direct contact with an infected animal, but there is a risk of people becoming infected after eating raw poultry blood, the World Health Organisation (WHO) warns.

As Jeffrey LeJeune, food safety and quality officer at the Food and Agriculture Organisation (FAO), puts it: “Pathogens don’t read history textbooks—they write them.”

“They are dynamic and they are continually evolving. We need to take environmental precautions,” he says, “so that they don’t become foodborne.”

People infected with covid-19 can shed the virus in their stool even if they are asymptomatic. As such, personal hygiene, handwashing and sanitation are vital forms of protection against its spread.

Wildlife

The origin of the virus behind covid-19 is still unknown. There is no evidence of it coming from food-producing domestic animals, though some say it may have come from wild animals on sale in a food market in Wuhan, China.

Bats are a possible source, but with no evidence of direct transmission from bats to humans the virus may also have jumped to humans via a third animal.

Wild animals are an important source of food and income for millions living in rural areas—but regulating the safety of wild meat is difficult because most of its trade is either informal or illegal.

China temporarily banned the trade and consumption of wildlife in January, and in April Wuhan officials announced planned upgrades to its farmers’ markets in a bid to improve hygiene. 

Also in April, the WHO received an open letter from 241 animal welfare groups arguing that the virus behind the 2002-03 SARS outbreak may have emerged from wildlife markets in China before spreading to more than 25 countries.

“Failure to enforce permanent bans on all wildlife markets then allowed for a similar, but more severe, disease to emerge,” they said.

Other diseases associated with wildlife include Ebola, HIV and rabies.

The FAO says experts in agriculture, medicine and veterinary science need to work together to prevent the spread of infections from animals. That includes strengthening food control systems, increasing diagnostic capacity and practising food safety during processing and cooking.

“We know that contamination can occur anywhere along the food chain from the farm right to the table,” comments Mr LeJeune, “[so] prevention can also occur at any of those steps”.

“Complacency is a real problem in all areas—so don’t let your guard down, wash your hands, keep your food preparation environment safe, and be safe.”