A mysterious illness, first mentioned in the media in July 2013 yet documented to be under investigation as far back as 1995, has been uncovered. Doctors in Muzaffarpur have on a yearly basis beared witness to the disease, affecting only children, and in a third of cases proving lethal only a few hours after onset.
The cause of the outbreak? According to a two year study by The Lancet published on the 30th January, the illness is caused by lychees.
For years the mystery illness had become prevalent shortly before monsoon season in July. Muzaffarpur is famous for its harvests of lychees and so naturally as part of the local diet, and with the disease seemingly focused in this area, they full under suspicion. The focus of these suspicions were never the lychees themselves, but the pesticides or pests associated with the lychee orchards.
Other avenues of investigation taking place since 1995 have included typical disease vectors such as rats, bats or sand flies. None of these investigations came close to establishing a potential cause. The illness was notorious for not following typical disease patterns, not spreading to groups of people but causing numerous isolated incidents. The illness often only affected a single child per village.
This manner of outbreak is indicative of some manner of toxicity rather than the spread of a disease. The symptoms of the disease, and the cause of deaths associated with them, are noted to occur in a manner resembling acute encephalitis. Worth noting is that only a month after the onset of this illness, mosquito numbers rise due to the wet conditions brought on by the monsoon season. With these mosquitos outbreaks of japanese encephalitis become more common, though the effects are never responsible for deaths occurring within a single day.
Locals have often attributed the deaths to superstitious beliefs, as the symptoms are often distressing and rapid. Children that were fine hours before begin screaming, suffering from seizures, then falling into a coma. Following this death can occur in a third of those affected.
The findings, by a team led by Aakash Shrivastava of the MoHFW, implicate the lychees, coupled with malnourishment in children as being the major contributing factor. This explains the seemingly random onsets, with the condition only affecting a small number of malnourished children in each village.
Specifically it was found that high levels of hypoglycin A and Methylenecyclopropylglycine (MCPG) were present, particularly in the seeds and aril of unripened lychee fruit. Both of these molecules are capable, and documented to have a degree of toxicity. MCPG has a metabolite, (Methylenecyclopropyl)formyl-CoA, which is shown to inhibit the enzymes responsible for fatty acid synthesis. Over time, dysregulation of fatty acid synthesis can disrupt proper nerve function, possibly contributing to the lychee caused illness.
An excess of hypoglycin A is also present in the ackee fruit, known to cause toxic hypoglycemic syndrome, or Jamaican vomiting sickness. The symptoms of this are very similar to that found in the toxicity following lychee consumption, including seizures, coma and death. High levels of hypoglycin A have been shown to cause hypoglycemia as well as inhibit the oxidation of long chain fatty acids.
These toxins are only dangerous at high levels. A likely explanation for the illness is that malnourished children are already prone to fall victim to illness due to weakness from malnourishment. It is likely that since the illness occurs during the season in which lychees are ripening these children may be eating large quantities of lychees to compensate for the lack of available food, leading to a build up of the toxins.