COMMUNICABLE FOOD-BORNE DISEASES

As well as their involvement in the spread of viruses and the development of AMR, animal-based products also pose other direct health risks that can worsen the impact of a zoonotic pandemic. There is a host of communicable diseases that are associated with the consumption of animal-based products, creating additional risks for individual health and putting additional strain on healthcare systems. WHO estimates that, in 2010, unsafe food caused 600 million cases of food-borne diseases and more than 400,000 deaths.1 While virtually every food contains toxins or pathogens when spoiled, when it comes to food-borne infections of humans, animal-based products deserve special attention. Not only do they harbour some particularly harmful microorganisms, but the sourcing of animal-based products also increases the antimicrobial resistance of these pathogens, rendering them even more dangerous.

Campylobacteriosis – chickens as a reservoir of bacteria

Infection with Campylobacter is one of the most prevalent food-borne diseases, responsible for one out of four cases of diarrhoeal diseases, as well as being the most common cause of human gastroenteritis, globally.2 Chickens are a natural reservoir for Campylobacter. Infected birds carry a very high load of the bacteria in their gastrointestinal tract, which results in contaminated muscles, blood, and bones in the slaughtering and processing stages, which can then lead to the transmission of the pathogens to humans.3 In many parts of the world, Campylobacter shows high levels of resistance to antibiotics such as tetracyclines and fluoroquinolones. The resistance to fluoroquinolones seems to be associated with their use in poultry farming. The campylobacteriosis case-fatality rate fluctuates between <0.01 % and 8.8%.4

Infections with Campylobacter can result in serious long-term impacts on individual health. Among them are Guillain-Barré syndrome (GBS), reactive arthritis, and irritable bowel syndrome. GBS is an autoimmune response that can lead to the deterioration of the nervous system, and is quite severe, with 20% of cases requiring intensive care, and a case-fatality rate of between 3% and 10% in high-income countries.5 Globally, one in three GBS cases is triggered by Campylobacter.

Salmonellosis – eggs and excretion

A pathogen that is more familiar to the general public is Salmonella, which causes salmonellosis. Salmonellosis occurs after consumption of food or water that has been contaminated by the fecal or urinary excretions of animals that are reservoirs of Salmonella.6 7 Salmonella lives naturally in the intestines of many different animals, including rodents, poultry, pigs, and dogs.8 A recent study links the emergence of human-adapted Salmonella to the introduction and intensification of animal farming.9 Salmonella causes typhoid fever (Typhoidal Salmonella) as well as gut distress (non-typhoidal Salmonella).10

Typhoidal Salmonella is responsible for typhoid fever, which constitutes an ongoing burden on developing countries. Between 11 and 21 million people contract typhoid fever annually, and up to 161,000 people die from it.11 Its overall case-fatality rate ranges between 2.5% and 4.5%.12 Non-typhoidal Salmonella (NTS) is one of the main causes of bacterial diarrhoea worldwide and causes around 153 million cases of gastroenteritis globally anually.13 NTS is responsible for the death of more than 50,000 people each year, particularly the very young and the elderly. In 2017, the case-fatality rate for NTS was 14.5% for all ages.14

The emergence of highly virulent and antibiotic-resistant Salmonella has led to greater morbidity and mortality in humans, particularly in the last few decades. A considerable number of multiresistant strains that have emerged in animal farming show resistance to a wide variety of antibiotics, constituting a significant food-safety hazard.15 16

E. coli – friend and foe

The bacteria Escherichia coli (E. coli) normally live in the intestines of humans and other animals. While many strains are harmless and part of a healthy gut microbiome, some can produce toxins that lead to severe diseases.17 18 E. coli human infections occur when consuming food or water contaminated with faeces, with the consequences varying from mild to severe diarrhoea for most of those infected. However, in a tiny percentage of cases, infants may develop haemolytic uraemic syndrome (HUS), a life-threatening disease that causes kidney failure and the destruction of red blood cells.19 20

There are different groups of pathogenic E.coli. One of the best known groups, Shiga toxin-producing E.coli (STEC), causes abdominal cramps and diarrhoea and is primarily transmitted through the consumption of raw or undercooked animal-based products such as meat and milk. Ruminants, mainly cattle, are recognised as its primary natural reservoir.21 Some outbreaks are associated with the consumption of fruit and vegetables such as lettuce, sprouts, and spinach which have been cross-contaminated through the use of manure as fertiliser or via contaminated water.22 STEC is responsible for 90% of HUS cases in infants23 and causes about 2.8 million cases of acute illnesses, annually.24 Although STEC case-fatality ratios are low, its economic impacts are far more severe.25 As with other food-borne diseases, antibiotic resistance in E. Coli is on the rise, with animal farming at the forefront of producing antibiotic-resistant strains.26 27

Food-borne diseases – the risk of eating what is close to us

Looking closely, it is not surprising that many food-borne pathogens are derived from animal-based products. For one thing, humans are evolutionarily much closer to other animals than to plants or fungi. A virus that has adapted to infect a pig’s lung cell requires much less of a shift in its genetic material in order to be able to infect a human lung cell than would a virus originally adapted to infect a plant cell.

Additionally, the processing of animals poses a contamination risk that is difficult to control. Evisceration processes at slaughterhouses can easily lead to the cross-contamination of meat by fecal matter, which may spill when the organs are being removed, resulting in infections of a wide range of organs in humans consuming the contaminated meat. Finally, there is the risk of handling and preparing raw animal-based products at home. Even if the chicken is properly cooked, the tomatoes on the same chopping board might not be.

With every single meal containing animal-based products, the risk of contracting food-borne diseases increases. Although these food-borne diseases do not cause pandemics, they come at a considerable cost to individual health and healthcare systems – and consequently have the potential to worsen the impact of pandemics.