AFRICA is home to so many premier-league diseases (such as AIDS, childhood diarrhoea, malaria and tuberculosis) that those in lower divisions are easily ignored. But these neglected illnesses cause suffering and death, and more subtly, when they affect children, eat away at a country's potential by reducing the human capital of its rising generation. Konzo and nodding syndrome are two particularly nasty members of this class. Both are neurological. And both do affect mainly children. But they are now yielding to investigation, and with it the possibility of prevention - though sadly not cure for those already afflicted. Nodding syndrome, which affects between 5,000 and 10,000 children in South Sudan and Uganda, was first noticed in the early 2000s, though something similar has been known from southern Tanzania since the 1960s. Konzo is older. It was identified in 1938 in what was then the Belgian Congo (now the Democratic Republic of Congo). It has since been found to occur sporadically over a wide area of central Africa. Both diseases create muscle-control and cognitive problems. Nodding syndrome causes a child (who is usually five or six when symptoms start) to lose control of his neck muscles. His head bobs repeatedly to his chest and he becomes otherwise unresponsive in what is, in essence, an epileptic fit. Those suffering from it develop slowly, both physically and cognitively, and rarely outlive their teens. Konzo does not kill, but it does disable. The name means "tied legs" in Yaka, a language widely spoken in the south-west of Congo, and that is a good description of the symptoms. It, too, generally develops in childhood, and those who have it walk as if their knees are fastened together. Like nodding syndrome, it cripples minds as well as bodies. Indeed, the latest research suggests it can also cripple the minds of those who have no physical symptoms. What causes nodding syndrome is as yet unknown. The latest suggestion is that it is an auto-immune disease triggered by the body's reaction to a parasite. Which parasite is still an unanswered question, but the most likely candidate is Onchocerca volvulus, which causes river blindness. The Onchocerca hypothesis has recently had a boost. Research by Scott Dowell of America's Centres for Disease Control and Prevention showed that the worm is much more common in people who have nodding syndrome than in those who do not. Dr Dowell's latest paper on the matter has just been published in Emerging Infectious Diseases. It is not that the worm causes the syndrome directly (there is no evidence that it gets into the brains of sufferers). Rather, the theory is that an antibody raised by the immune system to attack the worm, by an unfortunate coincidence, attacks a crucial component of the brain also. Testing that idea is hard as it means obtaining consent for autopsies and collecting samples from remote villages before the samples deteriorate. Dr Dowell has nevertheless managed to gather some in Uganda and expects to publish preliminary results soon. If Onchocerca does turn out to be the trigger, it will be good news of a sort. Infestation is easily treated by a drug called ivermectin. Merck, its manufacturer, already makes this available free for the treatment of river blindness. That would curb new cases of nodding syndrome. Mental cruelty The cause of konzo is not as mysterious. Locals have long known that the disease is a consequence of eating poorly prepared cassava, a root vegetable and staple for many. Research suggests the damage is caused by cyanide that the plant produces to ward off pests. But there are some strange wrinkles. It is, for example, unknown in South America - even though that continent has many cassava-eaters who are as poor as those of Africa. And, stranger still, though it affects children of both sexes, those who succumb in adulthood are all women. One way to avoid konzo is to prepare cassava carefully by soaking it in water for several days and then drying and fermenting it in the sun for several more. But this is time-consuming and not everyone bothers. That gave Michael Boivin of Michigan State University a chance to do a controlled experiment, to see if konzo's cognitive effects can occur in the absence of its physical ones. In a study published earlier this year he looked at three groups of children from two villages in southern Congo. One group came from a village where cassava is thoroughly processed before it is eaten. The other two came from one where it is not. Of these latter two groups, one was composed of children who showed physical symptoms of konzo and the other of those who did not. Dr Boivin tested both the blood and the mental agility of all the children. Healthy-looking children from the second village, he found, had as much cyanide in their blood as those with physical symptoms, and did almost as badly as their visibly symptomatic confrères on mental tests that the children of the first village aced. One solution to the konzo problem is to grow a variety of the crop called sweet cassava that is cyanide-free. But that brings its own problems, for its lack of cyanide means sweet cassava is far more susceptible to pests. Unlike nodding syndrome, where a drug is readily available, konzo looks like a more difficult disease to manage without tackling agricultural methods and food preparation techniques.