What is the number one killer?
Cancer remains the main cause of death in both men and women, according to the Department of Health.
It is not so much that sharks are scared of killer whales, more that they are prey of killer whales. The killer whale is the oceans number one predator but this does not mean to say that as its prey the shark is scared of it. There are thousands of types of sharks. So on the whole some sharks are quite likely to be afraid of killer whales where as others probably not.
Not by a long shot, if you're talking about causes of death in general. Search on the CDC website (http://www.cdc.gov/) for statistics on cause of death and their rankings. Generally speaking, the number one killer in the US is heart disease, followed by cancer and then "unintentional injury" of various kinds (led by "motor vehicle" accidents).