Animals maintained as microbiologically defined according to rederivation and containment principles described above, should be regularly controlled to confirm this status. Therefore, a number of animals

Figure 11.13 Examples of test performed on each sampled animal in health (microbiological) monitoring of rodents.

are sampled from the colony at frequent intervals and are subjected to a range of tests (Figure 11.13). This practice is called health monitoring, although microbiological monitoring would be a more appropriate term.

As quite a number of examinations are necessary for health monitoring, the procedures will normally be performed on animals sampled only for this purpose, and the status will be used as a picture of the population and not the individual. e.g., a mouse colony may be infected with Helicobacter hepaticus, i.e., mice from this colony may or may not have hepatic changes. The individual animal used in a research project may not even harbor the agent, and hence, health monitoring of laboratory animal colonies is based upon the principle that a few animals can be sampled for examination, but the results can be used to describe the entire colony. Therefore, if one animal is infected with a certain organism, the entire colony is considered infected with that particular organism, and if the infection is not found in any of the animals sampled, the entire colony is considered free of that organism.

It is essential to define the microbiological entity, i.e., a definition of the group of animals for which a sample is predictive, which is a complicated matter. One isolator, one individually ventilated cage, or a simple barrier-protected one-room unit used for breeding at a commercial vendor may be defined as one microbiological entity each, as the idea of the system is to keep the animals out of contact with the surroundings and due to the limited space, there is close contact between the animals, but in experimental facilities, it is often difficult to define the microbiological entity. Some bacteria easily spread from one room to another, while others do not. Under such circumstances, it would be safest but also impossible to define each cage as a microbiological entity. Therefore, individual judgments are necessary.

When the estimated number of animals have been sampled, these are subjected to a number of clinical examinations and laboratory assays, after which the microbiological status is given as a list of agents stating whether or not that agent has been found.

The commercial breeders without whom the historical process would probably have been much slower have traditionally developed most health monitoring programs. However, reports from different breeders have been difficult to compare, and, therefore, there is a need for standardization of health monitoring programs. To fulfill this, the Federation of European Laboratory Animal Science Associations (FELASA) has issued guidelines for health monitoring of various species, i.e., rodents and rabbits under breeding as well as experimental conditions,48 pigs, dogs and cats,245 primates,246 and ruminants.247 These papers set standards for which agents to test for, which methods to use, how many animals to test, how frequently this should be done and how this should be reported. Agents and methods recommended for rodents and rabbits are shown in Table 11.4. Some of these recommendations are pragmatic. If a more

Table 11.4 Agents and Methods Recommended Being Included in Health Monitoring Programs According to FELASA Guidelines for Health Monitoring

Species to be Tested

Table 11.4 Agents and Methods Recommended Being Included in Health Monitoring Programs According to FELASA Guidelines for Health Monitoring

Species to be Tested


Test Method



Guinea Pigs







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