Gibbons are capable of very rapid movement and can grab and bite with lightning speed. Even the bonobo, the smallest of the great apes, has enormous digit strength and can pull objects from or hold onto a human of much greater body size. Great caution should be used when handling unsedated apes, especially after they attain a weight of 12–15 kg (26–33 lb). Even the most reliable animals have the potential for causing serious harm to humans with whom they are in direct contact.
In addition to a general occupational-health program for people working with primates, consideration should be given to immunizing ape caregivers against hepatitis B, poliomyelitis, and influenza viruses, as well as to those currently recommended by CDC for health-care workers. Personnel with colds should not have contact with apes or they should at least wear industrial-level respirators covering the nose and mouth. Apes are susceptible to colds, and an infection with Streptococcus pneumoniae can be fatal.
Several of the great apes learn to spit and throw. Chimpanzees can spit more than a pint of water and throw feces with great accuracy. Such behavior is directed at disfavored people and strangers and sometimes is used merely to provoke a responsive person. A trusted human can usually "talk" an animal out of such behavior by a calm, gentle approach, but this is not always successful. The response of a human when being spat on might inadvertently serve to "reward" the ape and increase the likelihood of its spitting in the future.
Daily health observations by experienced persons are critical to the physical well-being of apes. Persons knowledgeable about an ape's particular personality and behavior might become aware of illness before traditional clinical signs are apparent. Veterinarians should strive to work as a team with all personnel who have contact with the apes (e.g., behaviorists, caregivers, technicians, and investigators) to develop a program to monitor the condition of the animals. Training time might be protracted, but the reward of less stress for the animals and humans can be very worth while. During treatment, drugs, especially liquid formulated ones, can be masked in flavored gelatin drinks or fruit juices, and an animal might readily accept even unusual items when they are offered by a favored person. A squeeze cage might be used as a last resort when there is no other safe way to deliver injectable medications. It is far preferable to train chimpanzees to present an arm or thigh against a wire-mesh cage wall (Laule and others 1992, 1996). They often accept injections for a small treat afterwards.