Amanita farinosa 小托柄鵝膏菌

POISONOUS PARTS

Whole mushroom.²

TOXICITY

• Toxic Constituents

  Amanitins and phallotoxins (TRL unpublished data).

• Toxic Dose

  Intake of about 300 g mushrooms has caused liver failure in 2 local cases.³

• Mechanism

  α-Amanitin is a heat-stable bicyclic octapeptide, which inhibits RNA polymerase II. It is actively transported into hepatocytes, leading to apoptosis and liver failure. Phallotoxins are heat-stable bicyclic heptapeptides, their toxicological significance in human is unknown.^4,5

• Poisoning Features

  An asymptomatic incubation delay followed by 3 clinical phases. The first phase (6–24 hours after ingestion): vomiting, abdominal pain, diarrhoea; the second phase (12–36 hours): transient apparent clinical improvement; the third phase (>48 hours): liver failure, renal failure, coagulopathy, coma and even death.^6–9

CLINICAL MANAGEMENT

Multiple-dose activated charcoal therapy has been used for gastrointestinal decontamination in amanitin poisoning. Silibilin, penicillin G in megadoses and N-acetylcysteine have been used as antidotes. Irreversible liver failure may necessitate liver transplantation.^9–12

IDENTIFICATION FEATURES

Caps 2–4(–6) cm broad, grey-brown or grey-white, hemispherical when young, becoming flat, slightly depressed at the centre, with grey-brown mealy scales concentrated at the centre, with conspicuous striate margin. Gills free from the stem. Flesh white, thin. Stems 3–7 × 0.3–0.5 cm, enlarged at the base. Volva thin, with distinct edge. Spores 7–8.9 × 5.6–7.5 µm, hyaline.¹

CASES IN TRL

There were 6 cases of amanitin poisoning from 2013 to 2016. The mushrooms were picked in Shing Mun Country Park, Tai Mo Shan Country Park and mainland China. All patients presented with gastrointestinal symptoms, 3 of them developed acute liver failure, and 1 of them required liver transplantation. The only mushroom specimen available (photo A) was identified as A. farinosa. Laboratory analysis of amanitins and phallotoxins is available in TRL.^13–16

LABORATORY ANALYSIS

Amanitins and phallotoxins can be detected by LC-HR-MS and LC-MS/MS.^17,18

REMARK

Taxonomically, A. farinosa is classified as a fungus.