Abstract
Many species of worm parasites and protozoans live in the gastrointestinal tract, but only a few are cause of serious gastrointestinal disorders. Transmission of intestinal parasites is mediated by the release of cysts, eggs or larvae, usually in stools. Some species are acquired through contaminated food or water or directly from the diseased person or animal. Gastrointestinal disorders occurring range from a mild diarrhoeal disease to an acute or chronic illness or, more rarely, to a life-threatening disease caused by spreading of parasites into the blood and organs. Planktonic and benthic algae can produce very toxic compounds which may be transported to filter-feeding shellfish or to herbivorous fish which are food for larger carnivorous fish. Along the food chain they can be concentrated, and fish caught for human consumption can be toxic. In addition, some moulds have the ability to produce toxic metabolites, such as mycotoxins, in foods and are associated with human disease, for example gastroenteritis or cancer. Mushrooms also are considered as a traditional source of food but there are a few species considered to be deadly poisonous, including Amanita phalloides and Cortinarius.