Members of the genus Claviceps may infect a variety of grains, particularly rye, when they come into flower, giving rise to the condition called ergot. No great damage is caused to the crop, but as the fungus develops in the maturing grain, powerful hallucinatory compounds are produced, which cause ergotism in those who consume bread made from the affected grain. This was relatively common in the Middle Ages, when it was known as St Anthony's Fire. The hallucinatory effects of ergotism have been put forward by some as an explanation for outbreaks of mass hysteria such as witch hunts and also for the cause of the abandonment of the ship, the Mary Celeste. The effects can go beyond the psychological causing convulsions and even death. In small controlled amounts, the drugs derived from ergot can be medically useful in certain situations such as the induction of childbirth and the relief of migraine headaches.
Many fungi produce natural mycotoxins; these are secondary metabolites, which, if consumed by humans, can cause food poisoning that can sometimes be fatal. Certain species of mushrooms ('toadstools') including the genus Amanita contain substances that are highly poisonous to humans. Other examples of mycotoxin illnesses include ergotism (see Box 8.2) and aflatoxin poisoning. Aflatoxins are carcinogenic toxins produced by Aspergillus flavus that grows on stored peanuts. In the early 1960s, the turkey industry in the UK was almost crippled by 'Turkey X disease', caused by the consumption of feed contaminated by A. flavus.
It is thought likely that all animals are parasitised by one fungus or another. Extraordinary though it may seem, there are even fungi that act as predators on small soil animals such as nematode worms, producing constrictive hyphal loops that tighten, immobilising the prey.
Fungi also cause disease in plants, and can have a devastating effect on crops of economic importance, either on the living plant or in storage subsequent to harvesting. Rusts, smuts and mildews are all examples of common plant diseases caused by fungi. The effects of fungi on materials such as wood and textiles will be considered in Chapter 16.
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