Gorillas can get infected with most diseases suffered by humans. For this reason it is very important that tourists keep as far away from the animals as possible. The wet and cold climate highly affects gorillas since they are not friendly with such an environment. Diseases like pneumonia are the most frequent cause of death in mountain gorillas.
Most free ranging gorillas have parasites mainly intestinal parasites. Some of these parasites affect both humans and gorillas. Various malaria parasites also affect gorillas but usually are different species than those that affect humans. Many gorillas hurt themselves when they get entangled in a snare with both a hand and foot. The wound can get infected and the gorilla may die from such an injury.
Gorillas only rarely have teeth cavities, mountain gorillas in particular never suffer from it, as their food contains very little fruit and hence little sugar. Instead, in the mountain gorillas bad tartar leads to periodontitis dissolving of the jaw bones and finally to the loss of teeth.
For unknown reasons, Mountain Gorillas that have been studied appear to be naturally afraid of certain reptiles. Infants, whose natural behavior is to chase anything that moves, will go out of their way to avoid chameleons and caterpillars. Koko, the western lowland female gorilla trained in sign language, is able to understand more than 1,000 signs based on American Sign Language, and understand approximately 2,000 words of spoken English, is afraid of crocodiles and alligators, even though she was born in captivity and has never seen them. They are also afraid of water and will cross streams only if they can do so without getting wet (i.e. crossing over fallen logs). Dian Fossey observed and noted the Mountain Gorilla’s obvious dislike of rain, as well.
When the dominant silverback dies or is killed by disease, accident, or poachers, the family group may be severely disrupted. Unless he leaves behind a male descendant capable of taking over his position, the group will either split up or be taken over in its entirety by an unrelated male. When a new silverback takes control of a group family, he may kill all of the infants of the dead silverback. This practice of infanticide is an effective reproductive strategy, in that the newly acquired females are then able to conceive the new male’s offspring. Infanticide has not been observed in stable groups.
For many centuries, Africans have been hunting and killing the lowlands gorilla. For some years, gorilla meat was their only source of meat. For as long as the gorilla has been discovered, there has been considerable fear and loathing of the ape. This has lead to many attacks on the gorilla population hence to their decrease. MacDonald said that due to the increasingly wide spread firearms in rural Africa, the fear with which many locals regarded gorillas, often led to impulsive shootings (MacDonald 1985). According to MacDonald 1985, most of the hunting that is done is out of sheer fright.