41.   When researchers found that the virus could infect human cells, clinical trials exposing people to pig cells were briefly stopped.

42.   When did the AIDS virus first infect humans?

43.   When the virus infects a cell, it must first induce the cell to divide in order to replicate and then go on to infect other cells.

44.   But scientists are worried that if the virus infects humans over a long period of time, it will adapt and begin to pass from person to person.

45.   But the Nimda virus still infected thousands of computers and files in the city, he said.

46.   Eons ago, these viruses infected the ancestors of modern pigs.

47.   In January, the virus infected hundreds of patients and staff at hospitals in Britain.

48.   Inside the mice, the virus apparently infected the target tumors and then made the angiostatin.

49.   Kew said that in Haiti and the Dominican Republic, after the introduced polio virus infected a poorly immunized population, it mutated and became even more virulent.

50.   Lee predicted the virus could infect up to half a million Taiwanese, but only a tiny number will die of complications.