Fungi

Simple parasitic life-forms that include mushrooms, toadstools, yeasts, and moulds. Disease-causing fungi can be divided into 2 groups: filamentous fungi and yeasts. Filamentous fungi are made up of branching threads known as hyphae, which form a network called a mycelium. Mushrooms and toadstools are the reproductive structures (known as fruiting bodies) of a filamentous fungus that has spread in dead matter or soil. Yeasts are single-celled organisms. Most fungi are either harmless or beneficial to human health, but some can cause illness and disease. The fruiting bodies of some fungi contain toxins that can cause poisoning if eaten (see mushroom poisoning). Certain fungi infect food crops and produce toxins that can cause food poisoning. The best known of these is a fungus that infects cereals and produces ergot, a toxin that constricts blood vessels; and another that grows on peanuts and produces aflatoxin, a poison and carcinogen. The inhaled spores of some fungi can cause allergic alveolitis, a persistent allergic reaction in the lungs. Fungal spores are sometimes responsible for other allergic disorders such as allergic rhinitis and asthma. Some fungi are able to invade and form colonies in the lungs, in the skin, or sometimes in various different tissues throughout the body, leading to conditions that range from mild irritation to severe, even fatal, widespread infection (see fungal infections) and illness. (See also candidiasis.)