Health status and health monitoring

The health status of the animal is also important since outbreaks of disease can have devastating effects both on programs of research, breeding programs, and on animal welfare (Mansfield et al, 2010¹). To reduce the risk of disease, most animal facilities maintain a number of barriers to prevent the introduction of infectious diseases. These will normally include control of access to the facility, use of appropriate protective clothing and equipment, incorporation of sterilisation or disinfection of cages, diet and bedding, and other measures to avoid the introduction of potentially contaminated equipment. The air supply to the unit may be filtered, and physical barriers will be in place to prevent the entry of wild rodents or birds. Cell lines and other tissue (eg tumour fragments) can be a source of pathogens, and units may require screening of this material to ensure it is free from infectious agents.

The level of barrier will vary in different facilities, and in different parts of the same facility. Some facilities will require staff to shower and change their clothing before entry, whereas others may simply require the use of protective outer clothing such as a laboratory coat, overshoes and gloves. Failure to observe these requirements can increase the risk of introducing infectious diseases since these are often present in wild rodents and birds, and hence in the environment around the facility. Pet animals can also be a potential source of infectious agents since the owner could inadvertently transfer infected material into the unit. If you have animals at home as pets, you should inform the unit manager.

One of the major sources of disease agents are animals imported from outside the research unit. Most units will have standardised procedures for importation of rodents. Some will require rederivation of the animals by embryo transfer or caesarian rederivation, whereas others may require only a period of quarantine, combined with laboratory examination for evidence of infection.

It is important to appreciate that the majority of rodent viral diseases rarely cause clinical disease. Most disease agents cause subclinical disease when animals show no detectable signs of ill health. but nevertheless may develop major alterations to their physiology. For example, immune function can be altered for very prolonged periods. These changes can have a major impact on the outcomes of research projects. Subclinical infections frequently increase the degree of variability in response to experimental treatments, and so result in the need for increased group sizes to detect a treatment effect. In some circumstances, the effects may be so marked as to completely invalidate studies. 

To monitor the effectiveness of disease control measures, and to provide reassurance to investigators that the health status of their animals is at the level required for their research, most facilities will operate a quality assurance program. This may encompass monitoring the effectiveness of sterilization and disinfection processes, and will normally assess the health status of the animals within the unit.

This can be done in a number of ways. Prior infection of animals can be assessed by looking for specific antibody responses, and this can be done either by blood sampling stock animals or by maintaining animals specifically for this purpose. These are referred to as sentinel animals, and they are housed in such a way that they come into contact with stock animals, for example by transferring soiled bedding from stock cages to sentinel cages, or by housing in the same airspace. Introduction of individually ventilated cages for rodents has made monitoring using sentinels more complex, because of the barriers provided at the level of the individual cage. Alternative or complementary approaches are to monitor using PCR assays, which can detect specific infectious agents, for example in faecal pellets taken from either sentinel or stock animals (FELASA, 2014²).

Your facility management will be able to provide details of the measures in place, what you need to do to minimise the risk of introducing infectious agents, and also give you details of the current health status of the animals that you are using.

Observing these working practices and implementing these policies not only protects animals from the introduction of disease agents but also protects the quality of scientific data that will be obtained and reduces the risk to personnel of contracting zoonotic infections.

1. Mansfield, Keith G., Lela K. Riley, and Michael L. Kent. “Workshop Summary: detection, impact, and control of specific pathogens in animal resource facilities.” ILAR journal 51, no. 2 (2010): 171-179.
2. FELASA working group on revision of guidelines for health monitoring of rodents and rabbits, M. Mähler, M. Berard, R. Feinstein, A. Gallagher, B. Illgen-Wilcke, K. Pritchett-Corning, and M. Raspa. “FELASA recommendations for the health monitoring of mouse, rat, hamster, guinea pig and rabbit colonies in breeding and experimental units.” Laboratory animals 48, no. 3 (2014): 178-192.