This is a very sad story. Admittedly, the details about cassava safety can be a little confusing. Cassava is widely cultivated throughout the world for it’s carbohydrate-rich tuberous root. Hence, cassava is the third-largest source of food carbohydrates in the tropics (after rice and maize). Cassava is one of the most drought-tolerant crops, capable of growing on marginal soils and so is a major staple food in the developing world. Nigeria is the world’s largest producer of cassava, while Thailand is the largest exporter of dried cassava.
Doctors treating victims of cassava poisoning in Cambodia
Cassava is classified as either sweet or bitter.Farmers often prefer the bitter varieties because they deter pests, animals, and thieves. Both varieties contain cyanotoxins (the bitter varieties contain much large amounts) and it must be properly prepared before consumption, as improper preparation of cassava can leave enough residual cyanide to cause acute cyanide intoxication,goiters, and even ataxia, partial paralysis, or death.
Cassava roots, peels and leaves should not be consumed raw because they contain two cyanogenic glucosides, linamarin and lotaustralin. These are decomposed by linamarase, a naturally occurring enzyme in cassava, liberating hydrogen cyanide (HCN). Bitter cassavas may produce more than 50 times as much (1 g/kg) cyanide as the sweet (non-bitter) varieties. Cassavas grown during drought are especially high in these toxins. Excess cyanide residue from improper preparation is known to cause acute cyanide intoxication, and goiters, and has been linked to a neurological disorder affecting the ability to walk known as konzo.
Symptoms of acute cyanide intoxication appear four or more hours after ingesting raw or poorly processed cassava: vertigo, vomiting, and collapse. In some cases, death may result within one or two hours. It can be treated easily with rapid recognition and thiosulfate. Thiosulfate is very inexpensive and one can only hope that the doctors caring for these people are able to provide it although hydroxycobalamin (vitamin B12a) has been used to treat cassava-induced cyanide poisoning experimentally.
Societies that traditionally eat cassava generally understand that some processing (soaking, cooking, fermentation, etc.) is necessary to avoid getting sick.
Brief soaking (four hours) of cassava is not sufficient, but soaking for 18–24 hours can remove up to half the level of cyanide. Drying may not be sufficient, either.