KOLKATA : West Bengal has reported its first case of a mutant coronavirus strain that surfaced in the United Kingdom, a senior health official said on Wednesday.The patient, son of an official of a medical college, tested positive for the new mutated strain after returning from the UK, he added.The patient was under treatment at a government isolation facility in the city after being tested positive for Covid-19 at the Netaji Subhas Chandra Bose International Airport upon his return to Kolkata 10 days ago.His sample was further tested for the new strain. "The new strain of the coronavirus was detected during his genetic analysis.