IACUC Learning Module - Primates

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In general, primates should never be used for experiments where some other animal would do equally well, nor until it has been shown that other animals are unsatisfactory. By far the greater number of primates are used for the production and testing of viral vaccines, and for the testing of new drugs for toxicity. For these purposes primates are still essential, though, in pharmacological investigations, they normally are used only as the last step before clinical trials on humans.

Advances in AIDS research are made using nonhuman primates as subjects. Infection of macaques with simian immunodeficiency virus (SIV) has been established as an excellent animal model for studying the pathogenesis of an HIV-like virus and for evaluating newly developed antiviral drugs and vaccines. The simian immunodeficiency viruses are the closest known relatives of the human AIDS viruses, and experimental infection of macaque monkeys results in a disease remarkably similar to human AIDS. Until recently, only the chimpanzee has shown immunological changes to infection with the human immunodeficiency viruses; however, these animals have yet to develop AIDS. The pigtailed macaque (Macaca nemestrina) has recently shown promise as an AIDS model. Researchers in the state of Washington have successfully shown immunological changes due to infection with HIV and subsequent development of AIDS in a handful of these monkeys.

The similarities in genetics, physiology, and taxonomy make the nonhuman primate a particularly unique model for studies of developmental toxicity. More importantly, most of the developmental processes of the nonhuman primate resemble those of the human embryo. The rates of development (e.g., the rate at which organ differentiation occurs), the timing of implantation, the gross and ultrastructural morphology of the placenta as well as the physiology and endocrinology of the menstrual cycle and early pregnancy are much similar in the nonhuman and human primate than for any of the other laboratory animals used in developmental toxicity studies. The similarity in the rates of development (developmental stages) may be particularly important in teratogenic susceptibility. It is unknown if the longer time required for organogenesis to occur in human and nonhuman primate embryos makes them more or less susceptible to insult from exogenous sources. The longer time period required for these important events may simply increase the length of the susceptible "target" period. On the other hand, the longer period of differentiation may also allow time for tissue repair following the exogenous insult, thus decreasing the likelihood for abnormal development. In any event, primates more closely resemble each other than they do other species, making the nonhuman primate an appropriate model for the study of normal and abnormal human development. Nonhuman primates, though, should be reserved for unique situations where an animal model closely resembling the pregnant human female is required to address specific problems.

Baboons play an indispensable part in the investigations of new surgical techniques, such as organ transplants and immunosuppressive regimes. Their anatomy most closely approximates that of man as has been shown by the recent transplantations of baboons' heart and liver in human patients.

Squirrel monkeys have played an important role in the investigation of the etiology of cardiovascular diseases, especially atheroma. These diseases are responsible for more human deaths in middle age than any other.

(See Addendum 3 for further reading on the nonhuman primate's role in biomedical research.)

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Updated 01/02/2008 gea