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| The Death Cap Mushroom |
The
Death Cap mushroom, Amanita phalloides is reported to have resulted in
more than 50% of all mushroom-related deaths in humans. Apart from containing
the deadly compound, alpha amatoxin, the relatively innocuous appearance of the
Death Cap also appears to be a contributing factor to this alarming statistic.
Two
recent fatalities in Australia, for instance, have highlighted the tendency
among people of Asian origin to mistake this deadly fungus for the harmless
straw mushroom, a culinary delicacy in Asia. Both mushrooms are a
yellowish-green in colour and have white gills.
Identifying Death Caps
One
method of distinguishing the two mushrooms is to search for remnants of a ‘universal
veil’, a thin film that covers the death cap when young. As the mushroom
matures, the lower remains of the veil can be observed as a swelling at the
base of the fungus.
This
swelling, however, may be below ground level, and can therefore often only be
detected by digging under the soil. Other indicators can be used to infer the
identity of Death Caps, including the fact that they are often found near oak
and other European tree species.
This
is due to the mycorrhizal association that occurs between the underground
filaments of the mushroom and the roots of these plants. In such an
association, nutrients pass between the fungus and the plant roots in a
mutually beneficial relationship.
Amatoxin and its Effects
Amatoxins,
a group of cyclic octapeptides, are responsible for most of the toxic effects
of the Death Cap and its relatives. Alpha amatoxin, in particular, targets the
liver and kidneys by inactivating the enzyme RNA polymerase II. This inhibits
protein synthesis and ultimately leads to cell death.
A
sinister feature of alpha amatoxin is that a patient may not experience any
symptoms for up to twelve hours after ingesting a poisonous mushroom. Vomiting,
cramping and diarrhoea may then be experienced. Following this, the patient may
feel as though he or she is recovering, but over the next two or three days the
toxin continues to destroy the liver and kidneys and can result in death.
Other Mushrooms Containing Amatoxins
Amatoxins
also occur in other members of the Amanita family, including the Destroying
Angel (Amanita ocreata), the Fool’s Mushroom (Amanita verna), the
European Destroying Angel (Amanita virosa), the Death Angel (Amanita
bisporigera) and the East Asian Death Cap (Amanita subjunquilea).
In
addition, amatoxins can be found in several related species such as the Deadly
Galerina (Galerina autumnalis), the Deadly Parasol (Lepiota
josserandii) and the Deadly Conocybe (Conocybe filaris). All of
these species are considered to be extremely poisonous, and although injections
of milk thistle extract may alleviate symptoms in some cases, there is no
effective antidote to amatoxin poisoning.
As
a consequence, although many Amanitas and their relatives are edible,
mycologists advise avoiding all of them to avoid the risk of incorrectly
identifying individual specimens.
The Fly Agaric and the Hallucinogenic Effects of Muscimol
Another
member of the Amanaita family, the Fly Agaric (Amanita muscaria),
pictured below, can produce severe vomiting and diarrhoea when ingested, along
with mildly hallucinogenic effects. Often confused with the ‘magic mushrooms’
of the Psilocybe genus, Fly Agarics resemble the red and white spotted
mushrooms of fairytale books.
Unlike
the Death Cap, the damaging compound in the Fly Agaric is ibotenic acid, which
can be converted in the body to the even more toxic muscimol. Muscimol affects
the central nervous system and can result in confusion, convulsions, chills,
sweating and delusions. Although these symptoms usually disappear after 24
hours, death from respiratory failure can occur in rare instances.
How to Avoid Amanita Poisoning
Identification
is the key to avoiding the more toxic members of the Amanita family. The pale
gills, white spores and basal collar, common to all Amanita species, should
alert the mushroom collector to any potential culinary disasters.
Galerinas,
which also contain deadly amatoxins, have a small, brown cap, tan gills and
rusty-brown spores. Possessing a thin stalk, they may be found growing in small
groups on rotting
wood. Together with the Amanitas, they provide a persuasive
argument for restricting one’s mushroom collecting to the supermarket.
References
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