The need for new tests to determine the source of Nipah outbreak deepens the mystery behind the spread of the virus.
On May 26, the medical team in its report to the ministry said samples collected from insectivorous bats in Kozhikode and Malappuram districts tested negative.
But Minister of State for Health Ashwini Kumar Choubey said today new samples of 55 fruit bats were collected two days ago and sent to National Institute of Virology (NIV) in Pune.
The test results of the fresh samples are awaited.
R R Gangakhedkar, head of Division of Epidemiology Communicable Diseases, Indian Council for Medical Research, said the previous samples were from insectivorous bats, which are not known to be Nipah carriers, and not from fruit bats.
Mr Gangakhedkar said an NIV team has collected samples of 55 fruit bats two days ago.
The Nipah virus stays for a short duration in the body of fruit bats as their system is quite capable of fighting it. So even if a bat has been infected by virus earlier, their samples may test negative later.
"Thus, there is need for a larger sample for testing," he explained.
MoS Choubey urged people not to panic as the infection has been contained.
The central medical team is examining the travel history of Mohammad Sabith, 26, the first person to die in the Moosa family that lost four members to the virus infection.
He had travelled to Saudi Arabia, where he worked as a helper, and returned to India sometime back.
The central medical team in its report last month had also ruled out pigs to be the primary source of the virus.
A total of 21 samples, including from seven species of bats, two species of pigs, one bovine and one caprine, were sent to National Institute of High Security Animal Diseases in Bhopal and National Institute of Virology in Pune.
These, included samples of bats found in the well near a house in Kerala's Perambra from where the initial death was reported.
Seventeen people - 14 in Kozhikode and 3 in Malappuram - have died due to Nipah virus so far.