BANGALORE, INDIA (AFP) - The number of people sickened by a mystery ailment in a southern Indian town has fallen off sharply, officials said on Wednesday (Dec 9), as medical experts race to pinpoint the source of heavy metals in the victims' blood.

Some 578 people from Eluru in Andhra Pradesh state have been treated by authorities since Saturday, when the illness first appeared.

One man died after showing symptoms of seizures, nausea and chronic pain.

The appearance of the unexplained malady initially sparked fears in the town of 200,000 people, amid heightened health alerts over the coronavirus. India is the world's second-most infected nation with more than 9.7 million cases.

Some 471 people have been discharged from hospital so far.

Eluru Government Hospital superintendent AV Mohan said just two people were brought in with symptoms from late on Tuesday until early Wednesday, compared to the earlier rush of cases.

The state government has sampled water and air in the affected areas.

But no abnormalities, such as lead or pesticides, were found in the samples, officials said.

Mohan said on Tuesday that samples taken from 10 people stricken with the illness showed high levels of lead and nickel in their blood.

But he added that the sample was too small to be sure that the lead and nickel had caused the illness.

Vegetables, fruits and soil were also being tested, while residents in affected areas were being closely monitored by health experts. There are no major chemical factories in the region.

District officials had earlier pinpointed a possible role of chemical additives in pesticides.