Five members of a family died mysteriously in the last 15 days at Bhandardah Nayabari village in Baliadanga upazila, creating panic among local people.
Villagers said Taher Ali, 55, son of Fazar Ali of the village, died on 9 February after falling sick with symptoms of breathing problem.
Later, his son-in-law Habibur Rahman, 35, died on 20 February while Taher's wife Hosne Ara, 45, died the following day the same way.
Taher's elder son Yousuf Ali, 30, and younger son Mehedi Hasan, 24, fell sick on Sunday. Yousuf died on the way to Rangpur Medical College Hospital while Mehdi died while he was undergoing treatment.
Being informed by the local people, Mosabberul Haque, officer-in-charge of Baliadangi police station, visited the house.
The OC said doctors at Rangpur Medical College and Hospital told him that 'brain virus' might be the reason behind their death. The disease spread from cough and sneezing, he quoted the doctors as saying.
"A probe panel is coming from Dhaka today to investigate the cause behind the death," said physician Shahjahan Newaj, civil surgeon of Thakurgaon, adding that viral attack might be a reason behind the death.