The elephant's body reacted to the T-Virus infection through increased size, strength and aggression. While this may be the only known case of an infected elephant, there is no reason against other elephants reacting in a similar way. Infected elephants may also consume flesh, suggested by Oscar's attacks on the survivors with its mouth.
The infected elephant's increased size led to a restriction of movement, slowing down the speed at which it could have run. Oscar showed visual difficulties, resorting to using his ears instead.