Cyanide poisoning, cyanide diseases and stunting of children
Cyanide is very poisonous because it binds to an enzyme called cytochrome oxidase and stops its action in respiration, which is a key energy conversion process in the body. The lethal dose for an adult depends on body weight and is between 30 and 210 mg of hydrogen cyanide. Sometimes these limits are exceeded by persons eating a cassava meal and deaths occur due to cyanide poisoning. Smaller (non-fatal) amounts of cyanide cause acute intoxication with symptoms of dizziness, headache, stomach pains, vomiting and diarrhea.
Konzo
In East and Central Africa excessive cyanide intake from cassava
produces "konzo", a local name which means "tied
legs". It was first described in 1928 in the Democratic
Republic of Congo (D.R. Congo), formerly called Zaire, and konzo causes irreversible
paralysis of the legs in children and women of child bearing age.
The onset of paralysis of both legs occurs abruptly, as for example
after manual work or a long walk or in bed during the night. Konzo
is an upper motor neuron disease which has not been fully characterised.
About one half of those with konzo need assistance with sticks
or from another person in order to be able to stand or walk. Epidemics
of konzo occurred in Nampula Province in northern Mozambique as
a result of drought in 1981-2 and war in 1992-3. In D.R. Congo in 2004 konzo was reported from four Provinces due to the prolonged war and there is an estimated 100,000 cases. In Mozambique in 2005 there were more than 100 cases in Nampula and Zambezia Provinces due to drought.
The disease is persistent in some areas and is associated with
large amounts of cyanide in cassava flour and high levels of urinary
thiocyanate in school children (Ernesto,
et al. 2002). Konzo occurs in Mozambique,
Tanzania, Democratic Republic of Congo, Central African Republic,
Cameroon and probably in Uganda, Angola and other countries of East and Central
Africa.
We have developed a wetting method that reduces by up to 5/6 ths the cyanide content of cassava flour and has recently been successfully field tested by rural women in Mozambique. We hope that this will eventually lead to the elimination of konzo in Africa.
(see Simple wetting method to remove cyanide from flour).
Tropical Ataxic Neuropathy
(TAN)
TAN is a condition that has been known for more than a century
and occurs in many countries of Africa, the West Indies and India (see Madhusudanan et al., CCDN News No 11, p3).
It is a chronic condition of gradual or insidious onset, which
is commonest amongst poor males and females in their 50's and
60's and is rare in children under 10. Patients are usually poor
and consume a monotonous cassava diet. Symptoms include loss of sensation in hands, a sensation
of something smeared on the soles of the feet which cannot be
removed by trying to wipe it off (paresthesia and dysesthesia),
blurring or loss of vision, ataxia of gait, deafness and weakness
and thinning of the legs. The disease is persistent in Nigeria
and its incidence can be up to 18-26 persons per 1000 in villages
where the diet is nearly all cassava. By comparison in yam-eating
villages there is no incidence of TAN. It was considered that TAN was due solely to chronic cyanide intoxication but recent studies by Rosling and coworkers have shown that the situation may be more complex. By contrast konzo is due to acute cyanide exposure and levels of
blood cyanide in konzo patients were found to be about 20 times
as high as those in TAN patients. The onset of TAN is usually
slow over months or years, whereas the onset of konzo is abrupt
and its course is non-progressive. The mean age of people affected
by TAN is greater than 40 years whereas konzo is primarily a disease
of children and females in the fertile age group.
Goitre and Cretinism
Low dietary intake of iodine causes
insufficient production of iodine-containing hormones in the thyroid
gland and this causes goitre (enlargement of the thyroid gland)
and cretinism (shortness of stature and severe mental impairment).
Iodine deficiency disorders including goitre and cretinism are
a major global health problem which affects about 500 million
people. Ingested cyanide from cassava consumption is converted
in the body to thiocyanate which is removed in the urine. The
thiocyanate is a goitrogen, because it inhibits the uptake of
iodine by the thyroid gland. Cyanide intake from cassava consumption
thereby aggravates goitre and cretinism, but only if the iodine
supply is below the recommended daily intake. Thus the effect
of cassava in exacerbating the effect of goitre and cretinism
may be corrected by increasing the intake of iodine.
Stunting of Children
Children in the Democratic Republic of Congo who ingested large amounts of cyanide from cassava were found to be stunted. This may be due to the fact that ingested cyanide is converted into thiocyanate by a reaction that uses up sulphur-containing amino acids which are essential in the diet, because they can only be obtained from the food consumed (Cardoso et al., 2004). A shortfall of these amino acids would limit protein synthesis that could cause stunting.