Food-Borne Diseases

FOOD-BORNE DISEASES

Defined by the World Health Organization (WHO) as diseases "of an infectious or toxic nature caused by, or thought to be caused by, the consumption of food or water," food-borne diseases are an important cause of morbidity and economic loss worldwide. Countries that keep statistics (usually industrialized countries), may record tens of thousands of cases annually, but it is acknowledged that only a small proportion are reported centrally (see Table 1). A study in the early 1990s in England, for example, reported that only one in 136 cases of infectious intestinal diseases was recorded.

CAUSES OF FOOD-BORNE DISEASES

The agents that cause food-borne diseases include microorganisms, natural toxins, and chemical residues. Microorganisms, including bacteria, viruses,

Table 1

parasitic protozoa, and worms, are the most commonly reported causes.

The list of food-borne disease agents is expanding; the last years of the twentieth century saw the emergence of Campylobacter, now a commonly reported causes of diarrhea; verotoxin-producing Escherichia coli (VTEC), initially linked to under-cooked hamburgers and a cause of hemolytic uremic syndrome (HUS) in children; the protozoa Cryptosporidium, which is often linked to consumption of contaminated water, and Cyclospora, which has caused diarrhea in consumers of soft fruit from Central America. The most significant new agents may be "prions," which have been linked to transmissible spongiform encephalopathies.

Bacteria. The mechanisms by which food-borne bacteria cause illness include the production of toxin in food before it is eaten or the production of toxin in the intestine, which is usually linked to multiplication of the organism in that environment. Illness is usually characterized by rapid onset, within hours or days, of vomiting and diarrhea, which may last a few hours or days in healthy people. Some pathogens, or their toxins, may escape the digestive tract and cause septicaemia, meningitis, or localized internal infection. For example, the toxins of VTEC damage the tissues of the intestines and kidneys, causing hemorrhagic colitis and HUS, potentially leading to kidney failure. Common food-borne bacteria, their mode of action, and symptoms are listed in Table 2.

Viruses. Food and drink can also transport viruses, which replicate in living cells. The symptoms of viral infection reflect the tissues (organ) infected and the degree of damage caused. For example, enteric viruses (e.g., Norwalk virus) cause

Table 2

acute vomiting and diarrhea twenty-four to forty-eight hours after infection. In comparison, Hepatitis A virus targets the liver, resulting in fever and jaundice two to eight weeks after infection. Food contaminated by infected human feces is the likely source of these viruses. Outbreaks are associated with filter-feeding mollusks (e.g., oysters) harvested from sewage-contaminated seawater, infected food handlers, and fresh produce (e.g., salads and soft fruit) infected by contaminated irrigation or rinse water or during handling.

Parasites. Many parasites, including protozoa and worms, are transmitted by contaminated food or water. The risk of infection exists wherever standards of sanitation, hygiene, drinking water quality, and meat inspection are suspect. The protozoa Giardia and Cryptosporidium are important causes of diarrhea in developing and industrialized countries, and are linked particularly to contaminated water. More recently, Cyclospora has caused outbreaks of diarrhea in North America linked to contaminated berries.

Tapeworms (e.g., Taenia) and the nematode Trichinella spiralis, which causes trichinosis, are among the commonly reported food-borne worms. These parasites have complicated life cycles, and human infection usually occurs when meat containing parasite cysts or eggs is consumed. Developing larvae then migrate from the intestines to other tissues. Symptoms vary with the infecting agent, from inapparent to fatal illness, and include gastrointestinal symptoms, muscle pain, and neurological and cardiac symptoms.

Prions. In 1986, "mad cow disease" or bovine spongiform encephalopathy (BSE) was first identified in the United Kingdom. The disease spread rapidly in cattle and is characterized by behavioral changes, lack of coordination, weakness, and death. BSE was thought to infect only bovines, but increasing numbers of human cases of a variant of Creutzfeldt-Jakob disease (vCJD), first recognized in the UK in 1996, have been linked to eating meat from BSE-infected cattle in Europe, particularly in the United Kingdom. Approaches to reduce the

Table 3

risk of human infection have included depopulation of infected herds and rigid controls on the movement of cattle and bovine products. The effectiveness of these measures in limiting the spread of disease is unclear.

Natural Toxins. Toxins exist naturally in plants (e.g., haemagglutinins in haricot beans), fungi, including mushrooms and moulds (e.g., aflatoxins produced by the mold Aspergillus flavus); and animals (e.g., tetrodotoxin, a neurotoxin present in puffer fish and some amphibians). Toxic substances may result from natural decomposition processes; for example, scombrotoxins (histamines) released during decomposition of scombroid (e.g., tuna) and other fish cause flushing, sweating, headache, nausea, dizziness, and a peppery taste within minutes of consumption.

Normally safe plants and animals can pick up natural toxins, chemicals, and pollutants from their environment. Potent neurotoxins produced by algae (e.g., Gonyaulax, Pyrodinium, Gymnodinium species) accumulate in filter-feeding mollusks. Human intoxication usually coincides with algal blooms in harvesting areas, and results in sporadic cases and outbreaks of, for example, paralytic shellfish poisoning and other types of diarrhetic or neurotoxic poisoning. For example, an outbreak of amnesiac shellfish poisoning traced to mussels affected over one hundred people and caused three deaths, in Canada in 1987; memory problems and other neurologic symptoms were prolonged in severe cases. Incidents of human disease due to contaminated shellfish are reduced by regular monitoring of harvesting areas during high-risk periods. A further example, ciguatera fish poisoning, is common in tropical areas, such as the Caribbean and Pacific Islands. Algal toxins accumulate in reef fish, particularly large predators. Early gastrointestinal symptoms are followed one to two days later by neurologic symptoms.

Chemical Poisoning. Food-borne illness may result from chemical contamination of food or drink due to inappropriate use of pesticides and herbicides, contamination by cleaning agents during food preparation, leaching of chemicals from containers or the environment, or accidental or deliberate adulteration during food processing or preparation.

A devastating example of chemical poisoning followed deliberate adulteration of cooking oil in Spain in 1981 and 1982. An estimated 20,000 people were affected, about 350 died, and others suffered serious long-term illness.

PREVENTION OF FOOD-BORNE DISEASES

Food-borne diseases present public health challenges related to food-handling practices, as described by Diane Roberts, who analyzed causal factors in over 1,400 outbreaks (see Table 3). Other important factors include:

• Globalization of the food supply, resulting in rapid, international distribution of raw and processed foods and exposure to duced in less well-regulated environments.
• Economic pressures to provide products as cheaply as possible, requiring large scale production and distribution processes.
• Traditional food production and handling practices that may be inappropriate in the modern production and retailing environment.
• Public and political expectations about the safety of the food supply.
• Population-health factors that may increase risk of illness, including age (the young and elderly), existing illness (e.g., cancer), inherited traits (e.g., sickle cell disease; HLA B-27 susceptibility to reactive arthritis), and depressed immunity (from AIDS, cancer treatment, transplants, pregnancy, and poor nutrition).
• New pathogens and antibiotic-resistant strains possibly related to environmental factors and changes in farming and husbandry practices.

The response to these challenges involves government, the food industry, the public health community, and the public.

Government action encompasses legislation to regulate the conditions under which foods are produced, distributed, and retailed, and the development of codes of good practice. Governments may collect statistics to monitor the incidence and causes of food-borne disease, and they may act to protect the public by investigating disease outbreaks and withdrawing unsafe products from sale.

Modern processors and manufacturers generally adopt procedures to minimize risks of contamination, (e.g., the Hazard Analysis Critical Control Point [HACCP] approach) and to ensure product quality and safety through quality control procedures. The public health community is concerned with the development and enforcement of standards in manufacturing, processing, and retailing. Finally, the public, by becoming educated about food safety, can protect themselves by adopting appropriate hygiene practices in food preparation, and by ensuring food retailers maintain high standards of hygiene by reporting poor practices to public health authorities.

PAUL N. SOCKETT

(SEE ALSO: Bovine Spongiform Encephalopathy; Campylobacter Infection; Cryptosporidiosis; E. Coli; Foods and Diets; Pathogenic Organisms; Prions; Trichinosis; Waterborne Diseases)

BIBLIOGRAPHY

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Roberts, D. (1986). "Factors Contributing to Outbreaks of Food Poisoning in England and Wales 1970–1982." In Proceedings of the World Congress of Foodborne Infections and Intoxications 1. Berlin: Institute of Veterinary Medicine.

Scott, E., and Sockett, P. (1998). How to Prevent Food Poisoning. New York: John Wiley & Sons.

Sockett, P. N. (1995). "The Epidemiology and Costs of Diseases of Public Health Significance in Relation to Meat and Meat Products." Journal of Food Safety 15: 91–112.