The B.1.617 variant of the coronavirus was first detected in India last year and has been blamed for much of a devastating Covid-19 wave that has battered South Asian nations in recent weeks.
Bangladesh, who lead the three-match series 1-0, were in trouble at 74-4 when Mushfiqur put on 87 runs for the fifth wicket with Mahmdullah Riyad (41), before they were bowled out in 48.1 overs in Dhaka.