Cassava is a staple food for up to a billion people. It can also be deadly.

The children in the photo look healthy enough. There are four of them: three boys and a girl. At first glance they seem to be playing some sort of balancing game, perhaps gymnastics, rocking back and forth along a set of parallel bars. What the photo cannot show is their knock-kneed gait, their halting steps and the strained effort each is making not to fall backwards. These Mozambican children are victims of konzo, a condition that results in paralysis of the legs. They are the lucky ones, for theirs is a relatively mild version of the affliction. Those less fortunate lose all use of their legs and are reduced to dragging themselves along the ground.

It’s estimated that there are tens of thousands of people – mainly children and women of childbearing age – affected by konzo in eastern and central Africa. The condition reduces their quality of life and cuts short life expectancy. What’s worse, this grand tragedy has arisen from a basic human experience: hunger.

Konzo is caused by the ingestion of a cyanide compound that occurs naturally in cassava. This hardy plant, also known as tapioca, is a staple food for nearly a billion people in Africa, South America, Asia and the Pacific. It’s among the 2,000 plant species in the world that make cyanide as a defence mechanism to deter predators. This is the same poison favoured by spies in the form of a suicide pill.

The amount of poison produced by the plant varies from variety to variety. Many Pacific peoples prepare and eat the root much as we would cook a boiled potato, as the variety of cassava introduced into the Pacific is relatively harmless. Some African varieties produce harmful amounts of the poison, especially in times of drought when the plant is under greater stress. But periods of drought and war are also the times when more people rely on cassava for sustenance, as their alternative food sources are disrupted. Cassava flour, which is made from the dried ground roots of the plant, thus becomes a vital food source. It can also be highly toxic.

Meeting of minds

Dr Julie Cliff is an Australian doctor who’s been working in Mozambique for 30 years. The country has remained one of the world’s poorest since it gained independence in 1975, its people racked by civil war, poverty and major health problems. Working for the Mozambican Ministry of Health, Cliff was part of a team that publicised the link between the cassava harvest and konzo, bringing to light the cause of the debilitating condition. She said the motivation came from seeing thousands of people losing their only mode of transport.
“It’s a peasant society, where walking is very important,” Cliff says. “It’s nothing to have to walk tens of kilometres every day for work and school.”

But how to address the konzo problem, especially in a country where resources were so depleted? Cliff was still searching for an answer when, in 1995, she met another Australian scientist at a conference in Nigeria. Dr Howard Bradbury became interested in food analysis while working at the School of Chemistry at ANU. He led a team that made detailed chemical analyses of the root crops of the South Pacific, including cassava. He continued to pursue this interest when he retired from teaching chemistry to become a Visiting Fellow at the School of Botany and Zoology.

“As I gained a better understanding of the plant’s defence mechanism, I also became more and more concerned about its potential impacts on human health,” Bradbury says. “It was clear that something needed to be done.”

Talking at the conference, Cliff recalls Bradbury asking her what he could do to help the thousands of people crippled by cassava flour. She told him of the need for a simple field kit that would allow people to test cyanide levels in flour. He promptly set to work, designing a process that “any high school kid” could use, which was then refined for a number of applications.

“We tackled the cyanide problem by developing very simple picrate methods that could be used by workers in developing countries with no additional resources. These would determine total cyanide levels in roots, leaves and cassava products,” Bradbury says. “We developed a similar urinary thiocyanate test that would give a good measure of cyanide intake over previous days. These kits were all tested in the field with our co-workers in Mozambique and shown to be very reliable.”

The kits were based on a reaction between the cyanide compound in the cassava flour and an
enzyme that converted the poison into hydrogen cyanide gas. This would then interact with yellow picrate paper, changing its colour, which could then be compared to a colour chart to determine the amount of cyanide in the sample. The tests were simple and cheap to produce. The Australian Centre for International Agricultural Research, which had funded the work, agreed to provide kits free to developing countries in need of the technology. When taken to the field, the tests revealed some alarming findings.

“Using the kits in our study area in Mozambique we found that cyanide levels in cassava flour in normal years averaged about 45 parts per million (ppm) compared with the World Health Organisation safe level of 10ppm,” Bradbury says. “Yet in a year of low rainfall the cassava plant produces more of the cyanide compound and average amounts in cassava flour can exceed 100ppm.”

Realising that the levels of poison in some flour samples were exceptionally high, Bradbury knew there was no time to rest on his laurels. He now needed a means of removing the cyanide that, like the test kits, would be cheap to produce and simple to conduct.

From test to treatment

Rather than reinventing the wheel, Bradbury reasoned that there might be an existing practice around cassava production that was already, and perhaps unwittingly, neutralising the poison in the plant. Could it be the way the flour was stored? To test the hypothesis, he investigated whether the cyanide levels dropped off if the flour was kept for a long time before it was eaten. Using samples of the flour from around the world, he left them in the lab for six months. The long wait appeared to be in vain, for tests revealed that there was no noticeable decline.
Bradbury says that what happened next came as if divinely inspired. It occurred to him that Mozambique was a tropical country with high levels of atmospheric humidity. What would happen in the lab if he increased the amount of water in the air during the experiment? He repeated the experiment in a desiccator over water, recreating 100 per cent relative humidity, such as that which would be experienced on a clammy, tropical day. After 25 days roughly half of the cyanide had disappeared. The results were encouraging – moisture seemed to be essential to the process. What would happen if instead of relying on atmospheric moisture, he mixed the flour with water outright and left it to stand?

“To my surprise, after six hours the cyanide levels dropped in most samples. I’d found a way to make cassava flour safe for consumption,” Bradbury says. “It was a gift from God.”
The method involved the enzyme that occurs naturally in cassava that catalyses the breakdown of the cyanide compound to hydrogen cyanide. In the experiment described above, Bradbury saw that two of the ten samples retained a high level of cyanide even after being mixed with water. Closer analysis revealed that these samples of flour didn’t contain the catalyst enzyme. When he added this, the poison levels dropped in line with the other samples.

“Given time and moisture, the enzyme in the flour breaks down the cyanide compound to produce hydrogen cyanide gas, which diffuses into the atmosphere,” Bradbury says. “If the flour is mixed into a thick paste and then left to stand in the shade for five hours in a thin layer spread over a basket, the conversion process will reduce the amount of poison by up to five-sixths, making it safe for consumption.”

Cliff and her colleagues at Eduardo Mondlane University have successfully tested this method in Mozambique.

“People could do it easily when we demonstrated it to them. We’ve shown that it is implementable,” Cliff says.

“I think it’s a huge breakthrough, but it’s still got to be adopted. There’s often a big gap between the discovery and the implementation. Some of the major hurdles are poverty, communication and getting people to change habits.

“It’s a brilliant idea and in a sense it’s the Holy Grail, because people have been looking for a method of getting rid of the poison.”

Dr Humberto Muquingue is one of Cliff’s colleagues at Eduardo Mondlane University. The physician has been working with konzo sufferers since the early 1980s, as well as lobbying the Mozambican government to do more about the condition. He says that Bradbury’s willingness to help suffering people is commendable.

“I don’t remember any tropical disease condition that has been tackled with such bravery and stubborn persistence by a single, under-resourced person as Bradbury has done. He has kept the issue of konzo alive in Africa, even in contexts where politicians pretend such disease is not as bad as scientists proclaim.”

When asked if he thinks konzo can be dealt with once and for all, Muquingue says that outcome will depend on more government support for education.

“We know that it does not work to convince people in the north to use cassava processing techniques commonly utilised in the south. We also know that right after a konzo outbreak, the affected communities will suffer from severe famine. All this information has been made available and we just need the politicians to pay attention.”

Bradbury is keen to initiate a wide-scale grassroots education campaign so that more Mozambicans can learn how to prepare the cassava flour safely. He says getting the message out will be difficult, as the only widespread communication network in the poverty-stricken country is word of mouth. Even this technique is problematic, given that dialects differ from region to region. Advocates for the new method of cassava preparation would ideally need to be conversant in Mozambique’s official language, Portuguese, as well as the local languages for each area.

“It’s important that we get people out into the villages to explain the method to rural women, because konzo is a problem that afflicts the poorest of the poor,” Bradbury says. “Some people say, ‘Why do they eat this awful stuff? We’d never eat something like that in Australia’. But the people there have no alternative – they either eat it or starve.”

This year, Bradbury says he was “blown away” when he received a Member in the Order of Australia honour for his work. Personal accolades aside, the unassuming scientist said his motivation comes from seeing konzo victims in person. In one of his several trips to Mozambique, Bradbury visited a rehabilitation centre at Liupo. Workers there provide konzo children with vital sustenance before helping them with special exercises and crutches that could improve their mobility. Bradbury says that seeing young children forced to drag themselves along the ground fuelled his desire to assist people in developing countries.
“I knew that there were major inequalities between the first world and developing countries, but witnessing it first hand was a galvanising experience. It’s not right that children are suffering.”

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ANU Reporter 
Autumn 2007