The phrase "mutated strain" refers to a version of a virus or bacteria that has changed or evolved to become different from the original form. Full definition
The rapidly mutating strains of flu virus have so far thwarted efforts to develop a vaccine that could knock out all varieties with a single injection, but recent advances suggest a synthetic solution. (scientificamerican.com)
Security analysts from Trend Micro reported that the malware has historically been a rapidly mutating strain, having gone through six different versions since it has been on the radar. (getrevue.co)
These new mutated strains of lice are supposedly resistant to the treatments often used, including all the popular brands of lice shampoos and removers. (wellnessmama.com)