Six strategies for success caring for immunodeficient mice
Aaron Rose, Ph.D.
The Jackson Laboratory offers an array of immunodeficient mice. Once you’ve selected your immunodeficient mouse you’re ready to begin…... right? Wait! Let’s run through some of the preparations you will want to go through before you bring in those new mice.
Personal Protective Equipment (PPE) is the first line of defense for the protection of your immunodeficient mouse. You need to wear it for your well-being in order to minimize the risk for allergies, mouse bites, and zoonotic disease. With immunodeficient mice we are particularly concerned about their health, so we need to carefully consider what to wear when handling them. At JAX our caretakers must wear; sterile scrubs, gloves, dedicated shoes and shoe covers, Mask, goggles, hair/beard bonnet, sterile smock, and maybe a PARP (Powered air purifying respirator). The disposable PPE should be changed with every entry to the vivarium and the dedicated equipment should be carefully stored in the vivarium to minimize exposure to contaminants.
Wearing your PPE is a good start. Now that we are all geared up let’s discuss the specifics of immunodeficient mouse handling. First, take is easy, slow and steady. There is no rush and the compromised immune systems of these mice means that skin damage can result in infection and death. It is always a good idea to consider the use of forceps when handling any strains on a regular basis. Forceps protect the technician from mouse bites but they also add another layer of protection for the mice from the microbes present on our bodies. They can easily be sanitized between handlings and this prevents cross contamination of cages with pathogens, hormones, scents, etc.. But remember: don’t over handle. Although it is important to check on the mice regularly, over-handling can be disturbing to the mice as well as increase the chances of introducing pathogens to their environment.
The sort of housing that you use will have a significant effect on your ability to manage an immunodeficient colony. We recommend that your vivarium have an entryway with limited entry, clear signage, and if you’re really serious about it, an air shower. These factors help to control the flow of researchers and workers. You may also want to consider changing the cages more often. This will help to limit the possibility of infection derived from gut flora present in the mouse feces.
It is a good idea to consider using Micro-isolator or pressurized individually Ventilated (PIV) cages. For feed and water you may use sterilization steps such as UV irradiation and acidification. At JAX, the drinking water is supplied from a local source, filtered and acidified using hydrochloric acid to pH 2.5-3.0, and autoclaved before it enters the room. We use an autoclave cycle created specifically for feed (similar to a dry cycle but shorter dry time so the feed does not dry out and harden). We sterilize for 20 minutes at 121°C and have a dry time of 5 minutes. We validate all autoclaves once a year using lots of temperature data loggers and biological indicators. On a daily basis a biological indicator is used for each load run to ensure the load has passed.
Quick Reference Guide
Monitoring the health of the mice is critical. Your most valuable tool here is your eyes. Regular (daily if possible) visual inspection of the mice will allow you to quickly catch any potential problems before they can spread to the colony. There are four major factors for any monitoring system:
- Sample size
- Frequency of testing
- Type of tests
- Interpretation of results.
The testing regime is designed around the knowledge of prevalence of infection in a population and this will help determine your sample size. The frequency of testing will ultimately be balanced by the likelihood of infection, the potential negative impact of the infection, and the cost of the test.
Sentinel mice and/or randomized sampling are typically used for diagnostic testing to determine the pathogen status of your colony as a whole. These sentinel mice may be dirty bedding sentinels (isolated from other cages in the colony), or colony integrated sentinels (taken from cages within the colony). You may also want to consider establishing a designated quarantine room or rack for the isolation of mice that have been identified by visual inspection or testing to be sick or moribund. For a more in depth discussion of monitoring see the JAX Handbook for Genetically Standardized Mice.
This cannot be overstated. A clean room of immunodeficient mice is a happy room of immunodeficient mice. What do we really mean when we say cleanliness? There are a few levels of cleaning.
Sanitization- reduction of microbial organisms on surfaces. This is what we do when we wipe down a surface with a wet cloth. Most of the organisms there have been transferred to the cloth and the surface has been sanitized. An effective sanitation program consists of cage cleaning, room cleaning and quality control.
Disinfection- destruction of most microbial organisms on surfaces. This is what we do when we spray the surface with Clidox or ethanol and wait a few minutes before wiping the surface down.
Sterilization- Complete destruction of microbial organisms on surfaces. This is when we bring out the big guns. Sterilization usually involves a step that includes heating a surface beyond a temperature at which pathogenic microorganisms can survive.
Sanitization is generally done on an as needed basis according to room use. Disinfection is an instituted process that occurs on a regular defined basis. At JAX this includes daily disinfection of changing tables, floors, tools, and more. There are other disinfection tasks performed less often that are just as crucial and you will determine these rates according to your own needs. Sterilization is critical for the care of you immunodeficient mice. The JAX sterilization of feed and water are described above. Beyond that, we sterilize bedding and any other equipment that enters the Maximum Barrier Rooms. Follow this link or a more in depth look at our animal health program.
6. Aseptic Technique
Because cleanliness can only go so far, unless you have repeated shower decontamination rooms, positive pressure suits, and hermetically sealed rooms there will be microorganisms present in any vivarium. As a result it is crucial that employees be trained in and practice aseptic technique. Aseptic technique is designed to minimize potential contamination through a strong grasp of the mechanisms of infection and the prevalence of pathogens. This means establishing training and retraining programs with verification steps to ensure that proper care is taken to minimize exposure that could jeopardize the health of immunodeficient strains
Okay, take a deep breath and relax. You’re now ready to start and maintain your immunocompromised mouse colony. Good luck and do good work.