Cassava and Konzo: When Your Food Paralyzes You

Well that short break I decided to take became a much longer break than I had anticipated. But I’m back. So let’s jump right into the interwoven story of cassava, konzo and poverty facing folks in some African countries.

Most people in the West have probably never heard of konzo before. I know I hadn’t until a couple months ago. Konzo is a neglected disease that causes polio-like paralysis in affected persons. However konzo is not caused by an infectious disease but is instead caused by improperly prepared cassava, which naturally contains cyanide. So perhaps a bit out of scope for this blog but I through the subject matter warranted attention. However, it’s not enough just to say that konzo is only caused by improperly prepared cassava, it’s more complicated than that.

Image of three African children suffering from mild, moderate, and severe konzo.

Image of three African children suffering from mild, moderate, and severe konzo. Courtesy H. Nzwalo and J. Cliff, PLOS.

History of konzo

Konzo was first described by an Italian doctor eighty or so years ago in what is now the Democratic Republic of Congo. Epidemics have been reported throughout cassava-eating areas of rural Africa. Because konzo often impacts people living in very rural areas, the number of reported cases is probably far less than the actual number of cases. If you live very far from a hospital, how are you going to report your case of paralysis?

How cassava causes paralysis

Cassava is a root vegetable that forms the staple diet of more than 600 million people around the world. The 1-3 meter high tropical shrub can grow in poor soil and is drought-resistant. The cassava root provides carbohydrates and the leaves of the plant provide some protein. The plant is relatively easy to cultivate and requires much less work than other crops. Additionally, the roots can be kept in the ground for a long time, thereby allowing families to use cassava to bridge the seasonal food gap.

However, cassava contains naturally occurring cyanide which is a neurotoxin. It is thought that cassava’s high cyanide production is a defense mechanism to keep the plant from being eaten by insects or animals. In humans, high consumption of cyanide coupled with a diet low in protein causes konzo and its irreversible polio-like paralysis. So you might be wondering why, if cassava contains a neurotoxin and is the main diet food for 600 million people, we don’t have more cases of konzo. This is where the interplay of konzo, cassava and poverty come into play.

Woman washing cassava in a lake.

Woman washing cassava in a lake. Courtesy FAO.

Interplay of forces to cause konzo

Cassava is the main food staple for people living in very rural and very poor areas. The cyanide content of the cassava plant depends on environmental factors such as drought. This is because the cyanide content within the plant is water dependent. So the cassava can be more or less dangerous depending upon how wet the ground is. 

Normally, the way the cassava plant is processed helps decrease its cyanide levels so that cases of konzo do not occur. Cassava can be processed in a variety of ways but common methods include soaking, sun drying, heap fermentation and grating plus roasting. All of these methods allow for the cyanide to be released from the cassava plant before it is eaten.

Interestingly, konzo is associated with a diet high in cyanide and low in protein. The lack of protein is key because the presence of sulfur amino acids (SAA) makes the neurons less susceptible to cyanide. This means that if you are eating protein you are helping protect your neurons from the negative effects of cyanide. Now this isn’t a permanent solution where eating a chicken every day means you can eat as much improperly prepared cassava as you want. It merely emphasizes the fact that being undernourished is a serious contributing factor to konzo.

Epidemics of konzo frequently occur in areas of high poverty undergoing challenges such as political instability, wars, drought, crop failure, population displacement, etc.. Places where people don’t have the time to properly prepare the cassava before eating it. They can’t wait weeks for the cassava to be soaked, dried and made into flour before eating it, or they will starve. 

The impact of konzo is devastating and much more widespread than we realize. As someone who, until recently, had never heard of konzo I can’t help but wonder why this isn’t getting more attention? I’m sure it’s because the affected population is rural, poor and from non-Western countries. But what responsibility do intergovernmental organizations like the UN have to try to address konzo and its devastating effect on families and communitites?


If you’d like to learn more about konzo check out this feature from Global Health Now. 

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