Advisor at Japan Food Research Laboratories
World Health Organization (WHO)’s World Health Day is celebrated each year on April 7th. The theme for 2015 is food safety. It is difficult to compare the food-poisoning incidents happened in each country because survey methods differ from country to country. WHO is trying to standardize the methods, and Ministry of Health, Labour and Welfare is in charge of this international effort.
Domestic food-poisoning occurrence in fiscal 2014 is released in preliminary figures which I have arranged in a table. In Japan, a doctor who gave a diagnosis of food poisoning reports to a local public health center. If the center determines it is a food-poisoning case through examination, the center reports to Ministry of Health, Labour and Welfare. The whole examination process is rather passive. In fiscal 2014, food poisoning incidents caused by bacteria and viruses occupy the large part as has happened in the past.
In the United States, epidemiological professionals perform proactive investigations of food poisoning to say nothing of reports from doctors. Through positive examinations, potential patients and numbers of infected people are estimated. If counted up by the US-style, the number of Japanese food-poisoning patients would increase considerably.
Food poisoning caused by microorganisms is divided into two broad categories. One is toxin-induced type that happens when a person eats food in which microorganisms produce toxins. The other is infection type in which food remains toxin-free but bears pathogen. Infectious food poisoning requires a precondition that pathogens get to intestine despite adversities such as gastric acid. As human intestine has immune system, arrival of pathogens sometimes does not lead to food poisoning and the person remains healthy.
Pathogens of infection types such as Enterohemorrhagic Escherichia coli O157 go through the lamina propria of intestine shown in Figure1 and attach to mucosal epithelial cells and start proliferating. If infection is established and pathogenic microorganisms start proliferating this way, even immune system sometimes cannot prevent diseases from occurring.
Pathogenic processes are different depending on agents. Some pathogens negatively affect the cellular function staying at the surface of intestine cells and cause symptoms such as diarrhea (Enteropathogenic Escherichia coli, etc.). Others produce toxins at the surface of intestine cells and the toxins go inside the cells and cause adverse effects (Vibrio cholera, Enterotoxigenic Escherichia coli). There are other types of pathogens, such as Enterohemorrhagic Escherichia coli, that have several pathogenic mechanisms and their toxins damage not only intestine cells but also tissues throughout the body by being delivered in the bloodstream. Also, some pathogens penetrate into epithelial cells of intestine and destroy the cells by proliferating inside them (Norovirus, Shigella, Salmonella, Enteroinvasive Escherichia coli). Yersinia reaches to mesenteric lymph nodes without remaining intestine cells. S. Typhi and S. Paratyphi A cause systemic infection by traveling through the bloodstream. Listeria and Vibrio vulnificus also cause opportunistic systemic infection.
Eaten food and pathogens enters the intestine in which many microorganisms live. There reside immune tissues such as Peyer’s patchs and M-cells in villus at the inner surface of intestine as shown in Figure1, and they ingest pathogens, toxins, and decomposed foods.
Macrophages and dendritic cells break down these substances further and pass these antigens onto T-cells. B-cells increase to produce IgA antibodies that bind specifically to these antigens. Dendritic cells induce activated T-cells by presenting antigens to T-cells after decomposition. B-cells residing in intestinal villus secrete IgA antibodies into intestine and pathogens and toxins become inactivated. If the antigen information requires suppression of immune response, dendritic cells will transmit the information to regulatory T-cells, which record the information, and immune response will be suppressed. Dendritic cells also induce and erase regulatory T-cells.
It is preferable that intestine’s immune system successfully responds to the invasion of food-poisoning bacteria and prevents the onset. There are health-food products advertised as “increasing immunizing power”.
This is seemingly effective against food-poisoning bacteria, but the definition of “immunizing power” is vague. The term “immunity” means avoiding a plague (epidemic). From the phenomenon that some people stay healthy or only mildly symptomatic even when many people are seriously ill, it has become recognized that human beings are equipped with a mechanism to protect ourselves from pathogens.
This phenomenon comes to be called “immunity”. Eventually it became clear that immunity is a biological defense mechanism against not only plagues but also foreign substances and toxic substances. Moreover, as shown in Figure2, it has come to be known that some immune responses are disadvantageous to human body.
It has been learned that immune system can cause inconvenience such as allergic reactions or autoimmune diseases. We should maintan a balanced life of proper food, sleep, and exercise in order not to lose resistance to food poisoning. I believe consideration toward others (Vitamin I) is also indispensable.
Ministry of Health, Labour and Welfare: The theme for World Health Day 2015 is “food safety”
Ministry of Health, Labour and Welfare: Food poisoning incidents in 2014 (preliminary report)
Hachimura. S. “Immune Response Induction by the Cell Groups Peculiar to Intestinal Immune System and Effects of Intestinal Mycobiont and Food”, Kagaku to Seibutsu, 52, 814-818 (2014)