Rising African cassava production, diseases due to high cyanide intake and control measures

Abstract

Cassava is the staple food of tropical Africa and its production, averaged over 24 countries, has increased more than threefold from 1980 to 2005, and the population has more than doubled over that time compared with a 1.5 times increase worldwide. Agriculturally, cassava performs very well but the roots and leaves contain cyanogenic glucosides that are dangerous to human health. These cyanogens sometimes produce acute intoxication leading to death, they exacerbate goitre and cretinism in iodine-deficient regions, cause konzo and are implicated in the occurrence of tropical ataxic neuropathy and stunting of children. Konzo is an irreversible paralysis of the legs with many thousands of cases, mainly amongst children, in Mozambique, Tanzania, Democratic Republic of Congo, Cameroon, Central African Republic and probably other tropical African countries. Attempts to alleviate cassava cyanide toxicity have included the development of an information network and distribution in developing countries of picrate kits, which measure total cyanide in cassava and urinary thiocyanate. A simple wetting method that reduces total cyanide in cassava flour three-to sixfold has been successfully field tested and is being introduced in Mozambique. Transgenic technology shows promise in increasing the rate of loss of cyanide from roots during processing. World health and agricultural bodies should pay more attention to emerging health problems associated with toxicity of cyanogens in cassava. 1,2 It is therefore not surprising that more than 2000 plants use cyanide to protect themselves from animals and marauding insects.3 These plants produce a cyanogenic glycoside and an enzyme that catalyses its hydrolysis to a cyanohydrin, which is then hydrolysed in a second reaction to HCN. This second hydrolysis occurs spontaneously and in some cases is catalysed by a second enzyme made by the plant. The cyanogenic glycoside and the hydrolytic enzyme must occur in different parts of the plant cell, otherwise the plant itself would be poisoned. 4 With cassava the cyanogenic glucoside is linamarin (and a small amount of lotaustralin -methyl linamarin), which is located in the plant cell vacuole, and the enzyme is linamarase, which is located in the cell wall.5 If the plant cell

Straightforward rapid spectrophotometric quantification of total cyanogenic glycosides in fresh and processed cassava products

“…These illnesses include tropical ataxic neuropathy, epidemic spastic paraparesis, also known as konzo (Cliff, Muquingue, Nhassico, Nzwalo, & Bradbury, 2011;Rosling, 1988). These problems have been reported in the Democratic Republic of Congo, Nigeria, Tanzania and Mozambique (Ciglenecki et al, 2011;Mlingi, Nkya, Tatala, Rashid, & Bradbury, 2011;Nhassico, Muquingue, Cliff, Cumbana, & Bradbury, 2008).…”

Genetic Screening Identifies Cyanogenesis-Deficient Mutants of Lotus japonicus and Reveals Enzymatic Specificity in Hydroxynitrile Glucoside Metabolism

“…This is particularly problematic during years with low rainfall when the cyanide content of cassava roots increases. Acute and chronic cyanide poisoning resulting in severe neurological diseases, including paralysis and visual impairment (Konzo disease), are problems in parts of tropical Africa, especially when dietary protein levels are low (Nhassico et al, 2008). Similarly, forage grasses and legumes are also often cyanogenic and require careful agricultural management to avoid toxicity to cattle (Wheeler and Mulcahy, 1989).…”

Health factors associated with persistent konzo in four villages in the Democratic Republic of Congo (DRC)

“…Konzo epidemics also result from war when local village people are forced from their homes and gardens and forced to eat unprocessed high cyanide cassava from the bush (Cliff et al, 1997;Nhassico et al, 2008;Chabwine et al, 2011). Konzo outbreaks also occur in Central Africa when peeled cassava roots are not immersed in water for the 3 to 4 days necessary to allow the enzyme linamarase to break down fully the cyanogenic glucoside, but are short soaked for only 1 to 2 days.…”