3.2.1 Mushrooms Producing Amatoxins
By far the largest number of fatalities due to ingestion of mushrooms are caused by amatoxins. At the top of the list of amatoxin-containing mushrooms is the green death cap, Amanita phalloides, because of its wide distribution and the high content of amatoxins (5 to 8 mg per 25 g fresh tissue, corresponding to 2.5 to 4.0 mg/g dry weight). This mushroom is common all over Europe and also increasingly found in North America. Given the estimated lethal dose for humans (0.1 mg/kg body weight), a full-grown mushroom (25 g) will be sufficient to kill a human. The olive green cap of this mushroom may appear as pale or even white, prompting the classification as a separate species, A. verna, which, however, is nowadays regarded as a subspecies, A. phalloides var. verna. In the few specimens of this subspecies tested so far, the amatoxin content was lower than in A. phalloides (1 to 6 mg per 25 g fresh tissue). The white species, A. virosa, the destroying angel, is easily distinguished from this subspecies by its cone-shaped cap and by a differing toxin pattern. The overall concentration of amatoxins in A. virosa is 1 to 5 mg per 25 g fresh tissue, composed of a-amanitin, or amaninamide, with no acidic amatoxins present. Fatal cases reported for A. virosa come from areas with mild climate, such as Virginia, central France, or southern Sweden. More recently, however, there have been reports of casualties caused by A. virosa from Mexico (Perez-Moreno et al., 1994), Thailand (Chaiear et al., 1999), and Korea (Lim et al., 2000). Another white species, A. bisporigera, seems to be identical to A. virosa. In particular, the white-coloured species of the deadly Amanitas may be mistaken for edible species of Macrolepiota or Agaricus.
Amatoxins have also been found in genera other than Amanita, for example in Galerina and Lepiota. Galerinas (G. marginata, G. autumnalis) are little, brown mushrooms (LBM), with brown spores. Some grow on earth, others on rotting wood. They contain less amatoxins (0.5 to 2.4 mg per 25 g fresh tissue) than the Amanitas, but nonetheless have been reported as the cause of amatoxin poisoning in humans; a recent poisoning by G. fasciculata was reported from Japan (Kaneko et al., 2001). Small Lepiota mushrooms (L. helveola, L. brunneoincarnata, L. josserandii,) contain amatoxins in concentrations comparable with those in the Galerinas (up to 2.6 mg per 25 g fresh tissue) and are increasingly responsible for fatal cases of amatoxin poisoning in France (Ramirez et al., 1994; Meunier et al., 1995), Spain (Puig Hernandez et al., 2001), and Turkey (Paydas et al., 1990).
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