Understanding Zoonotic Diseases in Foodborne Infections

Every year, millions of people worldwide fall ill after eating food contaminated with pathogens that originally came from animals. These illnesses – known as zoonotic foodborne diseases – sit at the intersection of animal health, human health, and food safety. From the chicken on your plate to the milk in your glass, the journey of food from farm to fork carries potential risks if hygiene and safety practices break down. Understanding how these diseases spread, which pathogens are responsible, and how to prevent them is essential for anyone involved in food production, processing, or consumption.

What are zoonotic diseases? 🔗

A zoonotic disease (or zoonosis) is any infectious disease that is naturally transmitted from vertebrate animals to humans. These diseases are caused by a range of pathogens including bacteria, viruses, parasites, and fungi. According to the U.S. Centers for Disease Control and Prevention (CDC), scientists estimate that more than 6 out of every 10 known infectious diseases in humans can be spread from animals, and 3 out of every 4 new or emerging infectious diseases in people are of animal origin.

The severity of zoonotic diseases in humans varies widely – from mild gastrointestinal discomfort to life-threatening conditions. Animals that carry these pathogens often appear perfectly healthy, making detection difficult without proper testing and surveillance systems.

How zoonotic diseases spread to humans 🔗

Zoonotic pathogens can reach humans through several routes. Understanding these modes of transmission is key to preventing infections.

Direct contact 🔗

This involves physical contact with an infected animal’s body fluids – saliva, blood, urine, mucous, or faeces. Farm workers, veterinarians, and slaughterhouse employees are especially at risk. Bites, scratches, or even petting an infected animal can transfer pathogens directly to humans.

Indirect contact 🔗

Humans can pick up zoonotic pathogens from contaminated environments – barns, chicken coops, soil, water troughs, or surfaces that an infected animal has touched. This route is particularly relevant in agricultural settings where animals and humans share living or working spaces.

Foodborne transmission 🔗

This is the most significant pathway for many bacterial zoonoses. As highlighted by the European Food Safety Authority (EFSA), foodborne zoonotic diseases result from consuming food or water contaminated with disease-causing microorganisms. Common sources include unpasteurised (raw) milk, undercooked meat and eggs, and raw fruits or vegetables contaminated with animal faeces. The risk of contamination exists at every stage – from farming and slaughter to processing, distribution, and preparation at home.

Vector-borne and waterborne routes 🔗

Some zoonotic agents are transmitted by insect vectors like mosquitoes, ticks, and fleas. Others spread through contaminated water sources. While these routes are more relevant for diseases like malaria or leptospirosis, they can also play a role in the spread of certain foodborne pathogens in regions with poor sanitation infrastructure.

Major foodborne zoonotic bacteria 🔗

Bacteria are responsible for approximately two-thirds of all human foodborne diseases worldwide, with the highest burden falling on developing countries. Food animals – poultry, cattle, swine – serve as primary reservoirs, and products of animal origin such as meat, dairy, and eggs are the main vehicles of transmission. Let’s look at the most common bacterial culprits.

Salmonellosis 🔗

Salmonellosis is caused by bacteria of the genus Salmonella, one of the most widely recognised foodborne pathogens globally. Salmonella species are commonly found in the intestines of poultry, cattle, pigs, and reptiles. Humans typically become infected by consuming contaminated eggs, poultry, meat, or unpasteurised dairy products.

Symptoms usually appear 12 to 72 hours after infection and include diarrhoea, fever, and abdominal cramps. Most people recover within 4 to 7 days without treatment, but severe cases – particularly in young children, the elderly, and immunocompromised individuals – can lead to hospitalisation. According to a peer-reviewed study published in the International Journal of Environmental Research and Public Health, salmonellosis and campylobacteriosis together affect as many as 2 million people per year in the United States alone. Globally, Salmonella remains one of the top two causes of bacterial foodborne illness alongside Campylobacter.

Campylobacteriosis 🔗

Campylobacteriosis, caused by Campylobacter species (primarily C. jejuni and C. coli), is currently the most frequently reported bacterial foodborne zoonosis worldwide. This pathogen was first recognised as a cause of human disease only in 1980, but its incidence has been rising steadily since then. Campylobacter bacteria are commonly found in poultry, and contamination often occurs during slaughter when intestinal contents come into contact with the carcass.

The infection causes watery or bloody diarrhoea, cramping, nausea, and fever. In rare cases, it can lead to serious complications such as Guillain-Barré syndrome, an autoimmune condition that attacks the nervous system. Within the European Union, campylobacteriosis has been the most commonly reported foodborne zoonosis since 2005, with over 200,000 confirmed cases reported annually. The true number is believed to be significantly higher due to underreporting.

Listeriosis 🔗

Listeriosis is caused by Listeria monocytogenes, a bacterium with some distinctive and dangerous characteristics. Unlike most foodborne bacteria, Listeria can grow at refrigeration temperatures (as low as 0°C), making it a particular concern in ready-to-eat foods, soft cheeses, deli meats, smoked fish, and unpasteurised dairy products.

While listeriosis is less common in terms of total cases compared to salmonellosis or campylobacteriosis, it is far more deadly. Data from the European Centre for Disease Prevention and Control shows that listeriosis has a case fatality rate of around 13.7% – the highest among all monitored zoonotic foodborne diseases. It is especially dangerous for pregnant women (where it can cause miscarriage or stillbirth), newborns, elderly people, and those with weakened immune systems.

Other notable zoonotic foodborne pathogens 🔗

While salmonellosis, campylobacteriosis, and listeriosis are among the most prominent foodborne zoonoses, several other pathogens also deserve attention.

Pathogenic E. coli 🔗

Escherichia coli O157:H7 and other Shiga toxin-producing E. coli (STEC) strains are found primarily in the intestines of cattle. Humans become infected through undercooked ground beef, contaminated raw vegetables, or unpasteurised milk and juice. Severe infections can lead to haemolytic uraemic syndrome (HUS), a potentially fatal condition involving kidney failure, especially in children.

Yersiniosis 🔗

Yersinia enterocolitica, the causative agent of yersiniosis, is primarily associated with pigs. Infection typically occurs through consumption of undercooked pork products or contaminated water. Symptoms include fever, abdominal pain, and diarrhoea, and in some cases the abdominal pain can mimic appendicitis.

Staphylococcal food poisoning 🔗

Staphylococcus aureus produces heat-stable enterotoxins in food that cause rapid-onset vomiting and diarrhoea, usually within a few hours of consumption. The bacteria are commonly transferred to food through handling by infected persons, and contaminated dairy products, meat, and bakery items are frequent vehicles.

Who is most at risk? 🔗

While anyone can contract a zoonotic foodborne illness, certain groups face a disproportionately higher risk of severe outcomes. The CDC identifies the following high-risk populations:

Children under 5 years old have immature immune systems and are more susceptible to dehydration from diarrhoeal diseases. Adults over 65 often have declining immune function. Pregnant women are particularly vulnerable to Listeria, which can cross the placental barrier. Immunocompromised individuals – such as those undergoing chemotherapy, organ transplant recipients, or people living with HIV – face heightened risk from virtually all foodborne zoonotic pathogens.

In developing countries, the burden is amplified by factors such as limited access to clean water, inadequate food storage and refrigeration, widespread consumption of raw or undercooked animal products, and poor sanitation infrastructure. A review published in Heliyon notes that in countries like India, increasing population pressure, deforestation, high demand for animal protein, and the trade of subclinically infected animals all contribute to the spread of zoonotic infections through the food chain.

The farm-to-fork risk continuum 🔗

Contamination of food with zoonotic pathogens is not a single-point event – it can happen at any stage along the food production chain. This concept is often described as the “farm-to-fork” continuum.

At the farm level, animals may harbour bacteria in their gut without showing any signs of illness. These pathogens shed through faeces can contaminate the farm environment, feed, water, and other animals. During slaughter and processing, cross-contamination can occur if intestinal contents come in contact with the carcass or processing surfaces. Pathogenic bacteria can also form biofilms on equipment and machinery, making them difficult to eliminate with routine cleaning.

At the retail and consumer level, improper storage temperatures, cross-contamination between raw and cooked foods, and inadequate cooking can all enable pathogens to survive and multiply. As a study in Current Topics in Microbiology and Immunology explains, the food production chain essentially follows the animal – and where the animal goes, the pathogen goes. Addressing contamination therefore requires intervention at every stage, not just one.

Prevention and control of foodborne zoonotic diseases 🔗

Preventing foodborne zoonoses requires a multi-pronged approach involving governments, food producers, and consumers.

Good hygiene and food safety practices 🔗

At the consumer level, safe food handling is the first line of defence. This includes cooking meat and eggs thoroughly to kill bacteria, refrigerating perishable foods promptly (below 5°C), avoiding cross-contamination by keeping raw and cooked foods separate, washing hands before and after handling food, and avoiding consumption of unpasteurised milk or raw animal products. These basic steps align with the WHO’s five keys to safer food: keep clean, separate raw and cooked, cook thoroughly, keep food at safe temperatures, and use safe water and raw materials.

Controls in food production 🔗

At the industry level, implementing Good Manufacturing Practices (GMP), Hazard Analysis and Critical Control Points (HACCP) systems, and standard sanitation operating procedures is essential. Pasteurisation of milk and proper heat treatment of processed foods are proven methods for eliminating zoonotic bacteria. In the EU, coordinated control programmes targeting Salmonella in poultry production have led to significant reductions in human salmonellosis cases over the past two decades.

Animal health surveillance 🔗

Monitoring livestock health, vaccinating animals where applicable, and controlling antibiotic use in animal husbandry are all critical. The growing issue of antimicrobial resistance (AMR) – fuelled in part by the overuse of antibiotics in farming – makes zoonotic infections harder to treat and represents one of the most pressing global health challenges.

The One Health approach 🔗

Zoonotic diseases cannot be effectively addressed by human health professionals alone. This is where the One Health approach comes in. As defined by the World Health Organization (WHO), One Health is an integrated approach that recognises the interconnection between the health of people, animals, plants, and their shared environment.

The CDC’s One Health Office promotes collaboration among physicians, veterinarians, ecologists, and public health professionals to address threats at the human-animal-environment interface. Key organisations – including the WHO, the Food and Agriculture Organization (FAO), the World Organisation for Animal Health (WOAH), and the United Nations Environment Programme (UNEP) – have jointly developed the One Health Joint Plan of Action (2022-2026) specifically to reduce risks from emerging and re-emerging zoonotic epidemics.

In practice, the One Health approach means joint disease surveillance across human and animal health sectors, coordinated outbreak response, shared laboratory diagnostic resources, and integrated data systems. For countries like India, where human-animal contact is intensive due to farming practices and a large livestock population, adopting One Health is especially urgent. As a study in the Indian Journal of Community Medicine highlights, India needs systematic zoonotic surveillance, a national zoonotic disease registry, and stronger collaboration between veterinary and public health institutions to combat these threats.

Global burden and why it matters 🔗

The scale of foodborne zoonotic disease is staggering. The WHO estimated that in 2010, approximately 600 million people fell ill from contaminated food, with nearly 350 million of those cases caused by pathogenic bacteria. In the European Union alone, over 350,000 human cases of foodborne zoonoses are reported every year, though the actual figure is believed to be much higher. In the United States, foodborne illness affects roughly 48 million people annually.

Beyond the human toll, the economic impact is enormous – encompassing healthcare costs, lost productivity, trade disruptions, and food recalls. Estimates suggest that foodborne illnesses cost the US economy tens of billions of dollars each year. For developing nations, where healthcare systems are already strained, the burden of foodborne zoonoses adds further pressure on limited resources.

Climate change, increasing global trade in food products, urbanisation, and the expansion of intensive animal farming are all expected to increase the risk of zoonotic foodborne diseases in the coming decades. Understanding these diseases and building robust prevention systems is not just a food safety issue – it is a global public health priority.

Key takeaways for food safety 🔗

To sum up the critical points about zoonotic diseases in the context of foodborne infections: zoonoses are infections transmitted naturally between animals and humans, and the foodborne route is one of the most important pathways. The leading bacterial agents – Salmonella, Campylobacter, and Listeria – are commonly found in healthy food-producing animals and can contaminate meat, dairy, eggs, and fresh produce at any point in the supply chain. Prevention requires a combination of proper food handling, industrial safety protocols, animal health monitoring, and cross-sector collaboration through the One Health framework.

What do you think? How aware are consumers in your region about the risks of foodborne zoonotic diseases, and what role do you think education plays in reducing the incidence of these infections?

References

1. https://www.cdc.gov/one-health/about/about-zoonotic-diseases.html
2. https://www.efsa.europa.eu/en/topics/topic/foodborne-zoonotic-diseases
3. https://pmc.ncbi.nlm.nih.gov/articles/PMC7341400/
4. https://pmc.ncbi.nlm.nih.gov/articles/PMC5981902/
5. https://pmc.ncbi.nlm.nih.gov/articles/PMC10742679/
6. https://www.sciencedirect.com/science/article/pii/S2405844024172714
7. https://pmc.ncbi.nlm.nih.gov/articles/PMC7121890/
8. https://www.who.int/news-room/fact-sheets/detail/one-health
9. https://www.cdc.gov/one-health/about/index.html
10. https://pmc.ncbi.nlm.nih.gov/articles/PMC7232973/