scientific objectives of individual research programs. Clearly, the requirements for a study of transmissible leukemia will differ from those of a study of chemical carcinogenesis of the respiratory tract in mice. Similarly, an elaborate program may be required to ensure the validity of research results from a project comparing the immune responses of immunodeficient mouse strains to challenge with an infectious agent, whereas a modest program might suffice for a study concerned with inheritance of a coat color gene in mice. Just as research objectives can differ greatly, health surveillance requirements also may vary over a wide range.
Indigenous infections of laboratory rodents include strong pathogens, weak pathogens, opportunists, and commensals. Therefore, in designing health surveillance programs, decisions must be made as to which agents are to be covered in the test battery. For practical reasons, it is impossible to test for all known infectious agents of rodents, or even all infectious agents that theoretically could interfere with a particular study. Therefore, testing is, of necessity, always selective. Specific justification based on pathogen significance and likelihood of interference with research is needed to include an agent in the test battery. Such information is given in Part II of this volume.
The procedures used in health surveillance generally include serologic tests, bacterial cultures, parasitologic examinations, and histopathology. Each of these may include very few or many procedures to detect different infectious agents or disease processes. Some health surveillance programs are limited to only one of these types of procedures, e.g., serologic testing.
Serologic tests are the main procedures used for detecting virus infections in rodents, but they also have been found useful for some bacterial and protozoan infections (Table 7). In recent years the enzyme-linked immunosorbent assay (ELISA) and the indirect immunofluorescent antibody (IFA) test have largely replaced the complement fixation (CF) test, and the hemagglutination inhibition (HAI) test. The ELISA and IFA tests have much greater sensitivity than the CF and HAI tests, and they give much fewer false positives than the HAI test (Smith, 1986b). False positive HAI tests have been particularly troublesome in the diagnosis of reovirus-3 and Theiler's virus infections (Kraft and Meyer, 1986; Van Der Logt, 1986). Serologic tests have the advantages of being relatively inexpensive and quickly performed in comparison to virus isolation (Balk, 1983; Smith, 1986b).