Almost two months after killer whale Sumar died suddenly at Sea World, the whale's cause of death was released.In an e-mail statement on Monday, Sea World announced that Sumar died of intestinal volvulus or a twisted intestinal tract, which Sea World said is in "no way related to the fact that he lived in a zoological environment." The e-mail said Sumar was "healthy and thriving" prior to his death on Sept. 7."Sometimes we know there's a cause. It's caused by parasites [or] it's caused by an infection process or something in the diet. Sometimes we have no idea," said Dr. Joe Gaydos, a wildlife veterinarian who studies orca diseases for UC Davis.Gaydos said Sumar's death was tragic because the problem doesn't happen often.Sea World said in the last 21 years, there have been five other documented sea mammal deaths due to a twisted intestinal tract.When asked if Sea World could have done anything to detect this earlier or prevent this from happening, Gaydos said, "It doesn't behoove an animal from showing another animal in the wild that it's sick, so they're very good at hiding things. So by the time the animal started showing signs, it was probably already at an end stage type of situation... I can't imagine that they could've prevented that."Gaydos said it's also hard to conclude whether the disease happens more often in captive mammals or wild ones because research in this area began four years ago.The Marine Fisheries Service said Sumar is the fourth orca to die at Sea World since 1985.