Brown bears are especially susceptible to human threat because their reproductive rate is so low, and anything that affects the environment or the food supply will directly affect their reproductive success. And adding to that, any female bear that is shot puts a heavy strain on the population. Many bears are killed out of fear, for sport hunting as trophies, and even taken for their body parts to be used in traditional Chinese medicine. Although safety is a big concern, brown bears rarely attack people. Brown bears get roundworm from ingesting infected fish, such as salmon, as well as any seal carcasses they may eat that wash ashore.
Humans can get roundworm from eating poorly cooked bear meat or fish.
Brown bears also harbor several external parasites, such as fleas, lice and ticks, as well as internal parasites like tapeworm, protozoans, hookworm, and flukes. Natural mortality rates for bears varies with age and sex. Their rate is so high because they have just left the care of their mother and are vulnerable to attacks by adult males. Human hunting accounts for a greater percentage. There are few recognized subspecies of brown bear, despite their incredible diversity.