Cassava is the staple food of more than 500 million of the poorest people in the humid tropics. The edible tubers and leaves both contain cyanogenic glucosides that are broken down by endogenous enzymes to produce hydrogen cyanide, a potent poison. Cassava cultivars containing medium-to-high amounts of cyanogenic glucosides (bitter cassava), unless treated to remove cyanide, can be a health hazard; those varieties with low amounts of cyanogenic glucosides (sweet cassava) are innocuous. In eastern and central Africa (particularly Mozambique, Tanzania and Congo) cassava is mainly processed to flour, but there have been outbreaks of a permanently crippling disease amongst children and women called ‘konzo’ due to cyanide in their food. Programs of nutritional education to avoid this problem require a way of measuring cyanogenic potential of flour, but the previously developed method for fresh cassava is not applicable to flour. This project aimed to develop a simple, semi-quantitative method suitable for cassava flour and to field-test it in Mozambique and in Indonesia, where cassava flour is used in bread as a partial substitute for wheat flour, and where village-level flour millers had no ability to measure cyanide potential in their product. A simple indicator of cyanogenic potential of tubers has generally been regarded as taste, either bitter or sweet, but previous work had shown that this was not always the case. The project ran further sets of tests to establish the relationships definitively. Additional aims included development of a simple kit for determination of thiocyanate in urine, free distribution of cyanide and thiocyanate test kits to health and agricultural workers, adaptation of the cyanide kit to determine total cyanide in cassava leaves and roots and leaves of other cyanogenic plants, and studies of the incidence and prevention of konzo in Mozambique.
The project achieved all its original objectives and more. It started as a small initiative to develop a kit for use under field conditions to determine the cyanogenic potential of cassava plant material. This developed into several kits to test different cassava materials and other plants. The kits have been used successfully to determine total cyanide in cassava roots, in cassava products such as flour, in leaves of various cyanide-containing plants including sorghum, in bamboo shoots and in flax seed meal. A kit was also developed to measure thiocyanate in human urine, which indicates recent cyanide intake in people and animals.
The cyanide-in-cassava and thiocyanate-in-urine kits were used in a four-year longitudinal study of the occurrence of konzo in Nampala Province, Mozambique. Konzo is endemic in northern Mozambique and its occurrence is linked to high cyanide levels in flour, which occurs especially after periods of low rainfall. The study has led to development of strategies for its elimination. These include introduction of low-cyanide, high-yielding, disease-resistant varieties of cassava suitable for southern and central Africa; increased agricultural production to broaden the diet by introduction of other staples, vegetables, pulses and fruit; improved processing of cassava roots to remove cyanide; and improved early warning systems of risk of konzo, based on reliable rainfall data and monitoring of cyanide levels in flour and thiocyanate in urine using the kits.
The project supplied free kits to more than 100 health workers and agriculturalists in developing countries. Demand for the kits increased steadily over the life of the project, to a level of about two kits per week (100 per year). The project also led to the establishment of a ‘Cassava Cyanide Diseases Network’, to assist all those who rely on cassava as a staple food with problems resulting from cyanide overload. Kits have been widely distributed to African countries with konzo problems, and to other parts of the world. Protocols for use of the kits have been translated into Bahasa Indonesia (with financial assistance from ACIAR for their printing), and into French (not by ACIAR).