THE ASSOCIATION BETWEEN CASSAVA AND THE PARALYTIC DISEASE KONZO

Konzo is the scientific name for a newly defined human disease entity characterized by the abrupt onset of a symmetrical spastic paraparesis (paralysis of both legs) in a formerly healthy person without other symptoms. Konzo affects mainly women and children and has been reported from Mozambique, Tanzania, Zaire and the Central African Republic. Studies have been carried out in several of these countries to investigate 'the cyanide hypothesis' in the etiology of konzo is caused by the combined effect of a high intake of dietary cyanogens from insufficiently processed cassava and a low intake of the sulfur amino acids necessary for the detoxification of cyanide in the body. Most studies have been observational and so the evidence for this hypothesis must be questioned. The main arguments in favor of the cyanide hypothesis are that in all areas, a strong association has been found between konzo and a number of different events which have led to a high cyanogen and low sulfur intake; these are intensive cultivation of bitter cassava varieties, a cassava dominated diet, insufficient cassava processing, and a low intake of protein-rich food. A very strong association has also been found on the individual level between high blood cyanide and konzo; a dose-response relationship has been demonstrated.

There are three important objections to the cyanide hypothesis. First, cyanide exposure from other sources has not caused konzo. Second, tropical ataxic neuropathy (TAN), a different clinical entity, has also been attributed to chronic cyanide intoxication following consumption of cassava. Third, the association is found mostly in ecological studies or in studies on aggregated level, which considered to be of weak study design.

The evidence for the cyanide hypothesis, in an etiologic role, of high cyanogen intake from insufficiently processed cassava combined with low sulfur intake, is now strong enough to urge prevention, in the short term by promotion of efficient processing of cassava roots. According to this hypothesis, there are three prerequisites for the occurrence of konzo: a farming system dominated by bitter cassava, insufficient cassava processing and a protein deficient diet. However, the cyanide hypothesis has yet to be confirmed.