21. "We have a really virulent strain , " he said. 22. Their work included subculturing virulent strains of the tubercle bacillus and testing different culture media. 23. However, the more virulent strain of HIV-2 could be practical for use in animal models. 24. Additionally, there is a risk that the weak strain could mutate into a more virulent strain . 25. Molds and bacteria live on the station, and one particularly virulent strain has corroded Mir's windows. 26. A virulent strain of flu hit in 1957-1958, when the Asian flu killed 70, 000 Americans. 27. Scarier still, no one knows whether virulent strains might be lurking in the next mail delivery. 28. A virulent strain of West Nile virus was isolated from the brains of eleven dead juveniles. 29. Far from having escaped the Asian flu, China has already been smitten by a virulent strain . 30. The most virulent strain , like the one in Kikwit, kills about 80 percent of its victims.
