Tuesday, March 13, 2012

East African Mystery Disease: Nodding Syndrome

I just heard about this recently, despite having considerable interest in East Africa and being a biologist. This is one of those medical mysteries that can take many years to solve and may well represent something new medically.

East African children, particularly in Uganda, Tanzania and South Sudan, are being hit with a devastating disease called "Nodding Syndrome" after one of its early symptoms. Stimuli like eating or cold seems to trigger an involuntary nodding motion of the head which often stop when the triggering stimulus stops. However, these motions can also be the precursor to much more severe seizures such as complete freezing or grand-mal seizures. Only familiar foods trigger the response. Children presented with unfamiliar foods do not go into seizures. The disorder leads to stunted brain development and atrophy and stunted overall growth and is usually ultimately fatal. Direct damage to the brain, injury during a seizure, as well as malnutrition due to difficulty in eating because of the seizures triggered by eating are main causes of death.

The cause is unknown and there is no treatment except to try and mitigate the symptoms.

This disease was first recognized in the 1960's by Dr. Louise Jilek-Aall in an isolated area of Tanzania. It got little attention until recently now that it has spread into a much wider area. In some ways the political focus on South Sudan has brought the disease wider attention and recent attempts by the CDC to identify the cause focused on South Sudan. This attempt found a high correlation between the disease and infection with a parasitic worm called Onchocerca volvulus, the nematode worm that causes "river blindness" disease. However in other villages there was no correlation between infection with this worm and nodding syndrome. To my eyes this sounds like an unlikely causative agent, but so far it remains the best candidate. If so it represents new evolution within the worm because it seems not to have caused this kind of disease before. So something in the host-parasite relationship has changed.

However, I also wonder if this might be a new manifestation of a prion disease, a type of disease (like "mad cow disease") that affects the nervous system and which can be incredibly hard to identify the causative agent. It is not clear to me if the brain pathologies have been tested for prions but it seems like it would be something that could be at least quickly ruled out. To me it sounds like it has some aspects in common, but this could easily be a superficial resemblance. I have seen prions brought up as a possible causative agent but I have seen no data related to this hypothesis. However, one aspect does not fit: most prion diseases are caused by people eating meat from an animal that had a prion disease. Since the prion protein is from another species, the change in the human nervous system is slower to develop and usually only manifests in old age. The fact that this mostly affects children suggests either that it is not a prion disease or that the source is from an animal whose prion protein is more similar to our own. Some have suggested the bushmeat trade as a source, but here why is it almost exclusively children? That is a question that all the hypotheses have trouble answering. No matter what the causative agent is it seems to mainly affect the DEVELOPING brain and not the adult brain. This is different from prion diseases and other seemingly similar disorders like Alzheimer's.

Viral causes that have been tested for have proven negative, but this probably is not an exhaustive study, so there may well be virus families that could be the causative agent.

The World Health Organization has these recommendations for treatment:

Recommendations so far made by the team include: Children with nodding syndrome be given antiepileptic drugs given that children with NS also have seizures that are responsive to antiepileptic medications. The current mass treatment program be supplemented in areas of apparent high Onchocerciasis endemnicity and Children with NS be psychologically and socially supported.

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