developed. Another reason for studying the immune system in a wide variety of taxa is to find highly conserved gene segments that control vertebrate and human immune systems. Studies of the immune system of a variety of species might shed new light on the role of the immune system in cancer. When invertebrate immune systems are understood, vector-based control measures can be developed. Another reason is to find highly conserved features of vertebrate and human immune systems (Litman 1996). Studies with sharks might shed new light on the role of the immune system in cancer.
There is an urgent need to investigate infectious diseases of laboratory animals, because infectious diseases pose problems in the effective use of these animals as models. Infectious diseases, including clinically silent infections also affect the research usefulness of infected animals: Infectious diseases modify immune responses, physiology, and behavior and have been misinterpreted as phenotypic expressions of gene alterations. Infectious-disease control and diagnosis impose an unquestionable strain on maintenance costs of laboratory animals. The collective impact of infectious diseases on animal-based research is enormous.