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[CAPE TOWN] Konzo — an epidemic paralytic disease resulting from the consumption of poorly processed bitter cassava — can also cause impaired cognitive functions even in children who do not show physical symptoms of the disease, a study finds.

The study was conducted in the Democratic Republic of Congo's (DRC) Bandundu Province, an area severely affected by the disease.

It discredits the previous belief by people that konzo is purely a paralytic disease, says Desire Tshala-Katumbay, the study's lead researcher and associate professor of neurology at Oregon Health and Sciences University's School of Medicine, United States.


  • Konzo can impair children's memories and problem-solving abilities
  • Even children who do not display the physical symptoms can be affected
  • Proper processing of cassava can cut the risks of catching the disease

Konzo, which means 'bound legs' in the DRC language Yaka, is caused by the almost sole consumption of insufficiently processed bitter (cyanide-rich) cassava during times of war and famine. If properly processed, the naturally-occurring cyanide is degraded. But taking shortcuts can result in severe, permanent physical effects — and much more, the study found.

Poorly processed bitter cassava can cause memory loss, affect problem solving abilities and disable other cognitive functions.

Researchers analysed 123 children with konzo, and 87 children who showed no signs of the disease but who appeared to have elevated levels of the bitter cassava toxin in their blood and urine and came from areas where konzo is endemic. They found that both groups found it much more difficult to solve problems and to organise visual and spatial information, compared with a third group from an area with little konzo.

Therefore, even children from outbreak areas who do not display the physical symptoms of the disease may be at risk of hampered mental ability by eating poorly processed bitter cassava, says Michael J. Boivin, lead author of the study and a researcher at Michigan State University, United States.

Children and adults are dependent on bitter cassava as their principal staple when there is no adequate protein intake in their diet, he adds.

Boivin says that public education on the safe preparation of the crop is essential. Poorly prepared cassava is soaked in water for less than three days and not dried in the sun following soaking.

"The fermentation from the soaking is the most important way to begin the breakdown of the toxins in the bitter cassava," says Boivin.

He adds that diversifying nutritional resources to include sources of proteins such as beans and millet is important.

Six African countries — Angola, Cameroon, Central African Republic, DRC, Mozambique and Tanzania — have reported the prevalence of konzo.

But not all researchers agree with the findings.

"It's not very conclusive," says Lumuli Mbonile, senior anatomy lecturer at the University of Western Cape, South Africa.

"The sample size was not big enough to directly suggest that there is a link between [consuming poorly processed bitter cassava] and early neuropsychological effects seen in children living in areas with a history of konzo epidemics."

He says more research needs to be done in other areas where konzo is common in order to conclude that it can first affect cognitive functions before physical presentations.

"Unless all psycho-social factors, such as the abuse of women and children, which affects their neuropsychology in areas with konzo prevalence are accounted for, then the research finding is not watertight," Mbonile says.

Link to abstract in Pediatrics

This article has been produced by SciDev.Net's Sub-Saharan Africa news desk.


Pediatrics doi: 10.1542/peds.2012-3011 (2013)