A woman showing symptoms of epilepsy being taken to a hospital in Eluru town, during the outbreak of the ‘mystery illness’, December 6, 2020. Photo: PTI
- In December 2020, the population of Eluru town experienced an epidemic in which 600 people reported multiple neurological problems over two weeks.
- The government concluded that toxins from pesticides were the cause of the outbreak, but even after a year, definitive evidence to support this conclusion remains wanting.
- In November 2021, researchers from the National Institute of Nutrition, Hyderabad, published a paper identifying an organophosphate pesticide as the probable cause.
- For public health, we need an overhaul of Eluru’s water and sewage systems, an environmental survey to identify sources of pollution, and a household water-use survey.
Early in December 2020, the population of Eluru town in Andhra Pradesh experienced an epidemic that can only be described as bizarre. More than 600 people reported a range of neurological problems over two weeks. The epidemic ended as quickly as the epidemic began, by the middle of the month.
The dominant symptom was convulsions but also included loss of consciousness, fainting, drowsiness, nausea and vomiting, and head and limb injuries resulting from the convulsions and loss of consciousness. Some 300 people were admitted to local hospitals for treatment.
The media dubbed the cause a ‘mystery illness’, and various theories of its origins floated around.
The Andhra Pradesh government quickly swung into action and about 13 agencies, including government research institutions and private medical colleges, were assembled to investigate the epidemic. The investigations included clinical examinations, tests of water, food, air, soil and human and animal body fluids, for a range of neurotoxicants, including chemical and biological agents.
The government concluded that toxins were the cause of the outbreak, with pesticides in food or water being the most likely culprits. Some experts debated the specific pesticide that may have caused the observed illness, but even after a year, there has been no definitive evidence regarding the cause.
This being the case, some important questions still remain to be answered.
1. Was the observed illness real?
Neurologists I spoke to who treated people with the illness stated unequivocally that the convulsions were real and not mass hysteria or pseudo-seizures (or psychogenic non-epileptic seizures). Their testimony was compelling.
2. How did the toxins get into the body?
To cause illness in a wide spectrum of men, women and children, the toxins needed to be from a source common to the population. This would be from water, food or air. Since the population couldn’t all be eating the same food, and no known air pollutants cause convulsions, the likely source was water.
There are multiple anecdotal reports that the drinking water quality in the Eluru town area began deteriorating about 10 days prior to the onset of convulsions. Residents reported that the water had turned greenish-brown and emitted a bad odour, and speculated that water in the sewage and drinking-water lines could have got mixed up. They also reported that the water quality had substantially improved since the convulsion event.
Thus, the possibility that water channels were inundated by heavy rainfall from Cyclone Nivar, combined with the possibility of broken drinking-water pipes and the lack of a sewage treatment plant in Eluru, may have been important factors leading to the contamination of the town’s drinking water supply.
3. What is the probable toxin and its mechanism of action?
In November 2021, new information emerged on the epidemic. Researchers from the National Institute of Nutrition, Hyderabad, published a paper identifying triazophos, an organophosphate pesticide used for insect control, as a probable cause for the epidemic of serious neurological problems experienced by the Eluru population.
Triazophos was found in household drinking water and in the blood and urine samples of affected victims. It is efficiently absorbed by ingestion and belongs to a class of organophosphate pesticides that are well-known neurotoxins. The possibility of a mixture of chemicals interacting to enhance the neurotoxic effect must also be seriously considered. It is clear that very high concentrations of this chemical must have been present in the water to lower the seizure threshold and cause convulsions.
The inference is that contamination most likely occurred close enough to the household drinking-water supply to yield these high concentrations.
The epidemic, however, also throws up the larger question of how and why pesticides found their way into the water supply. A forensic investigation is needed to examine the source(s) and method(s) by which the pesticides could have found their way into the drinking-water supply in the area, and whether the cause was negligence or an accident. Such an exercise is vital to determine the cause of the incident, to compensate the victims, to identify those accountable and to prevent future occurrence of such episodes.
A household survey of water-use could aid a thorough exposure assessment of the affected population and is vital to determine the contaminant source and quantity of exposure to the pesticide. Such an assessment will help establish a follow-up population study to determine long-term health effects of the poisoning in the population.
4. What measures can be taken to prevent such an illness?
Eluru township’s drinking-water systems are over a hundred years old. There is open sewage visible all over the town and which drains into nearby rural areas and likely contaminates agricultural land. The drinking water and sewage systems are in urgent need of an overhaul.
India has long been known for its high production and use of pesticides in the agricultural sector. A comprehensive environmental survey of the region’s water, food, and air should be undertaken to determine the extent of pollution from industrial, agricultural and other sources. This will also throw light on whether subsequent minor outbreaks of the illness in adjacent rural areas could have been due to environmental causes.
The nearby Kolleru Lake is among the largest freshwater lakes in India and its ecology and biodiversity need to be protected from further pollution.
This epidemic of mass convulsions is unprecedented in the world, and only thorough and tough public health measures can protect the people and the environment from the untoward effects of environmental degradation.
V. Ramana Dhara is an occupational and environmental medicine physician and a former member of the International Medical Commission on Bhopal.