Replace Sentinel Mice
More Accurate Results
Reduce Labor & Cost
Reduce Emotional Fatigue
It is important to ensure that rodent colonies are free of adventitious infectious agents to support high quality, robust research & safety data. Over the last 50 years, health surveillance has been typically performed using sentinel animals. More recently, molecular-based diagnostics combined with environmental monitoring strategies have been adapted by many institutions to either supplement or replace the more traditional methods. These newer approaches have the possibility of significantly reducing/replacing the number of rodents used in maintaining specific-pathogen-free colonies.
We recommend starting by giving an introductory presentation to management and other stakeholders about the evidence, advantages, and practicalities of replacing sentinel rodents with environmental health monitoring. We have a 10-15 min slide deck that you are free to use and modify for your facility that you can download by clicking the image below.
Advantages = Initially less costly than exhaust plenum media holders (i.e. collars mounted media.)
Challenges = Some rack brands/designs are easier to implement environmental monitoring than others (e.g., not effective with rack designs with cage level exhaust air filtration). May not be sensitive enough for pathogens that are at low prevalence.
Advantages = Operator variability is minimized & minimal handling is required. Detects Helicobacter & MNV with similar sensitivity to swabbing. Media helps increase dust collection. Acceptable for 3-month collection. Provides a history of pathogens that were present over the previous 3 months. Presumably reduced ergonomic effort.
Challenges = Can be physically difficult to place/collect collar mounted media from single-sided racks. Collars/media must be placed AFTER racks are washed & collected BEFORE wash which requires coordination (alternatively you can wait to wash racks until they test positive and then clean once the potential outbreak is resolved). May be costly.
Exhaust air duct monitoring is not an option for static cages or racks that filter at the cage level (Bauer, 2016; Dubelko, 2018). In this case, PCR material must be collected from the cage. These methods are described in 3 key references: Dubelko, 2018; O’Connel 2021; or Hanson, 2021.
Overall, the best option is to place 10 flocked swabs inside an additional cage (where sentinel animals would usually be placed) and then transfer soiled bedding as usual. Soiled bedding should be shaken or stirred with the swabs after cage change. Flocked swabs can be tested at 1-3 months after placing them.
Research shows that PCR testing of flocked swabs was as effective or MORE effective than PCR testing from sentinel mice.
Thus far these methods have been used to detect pinworms, fur mites, mouse hepatitis virus (MHV), murine norovirus (MNV, minute virus of mice (MVM), mouse parvovirus (MPV), Theiler murine encephalomyelitis virus (TMEV), Helicobacter spp*, Syphacia obvelata, Aspiculuris tetraptera, Rodentibacter spp.*, Entamoeba muris, and Spironucleus spp.
This method is still reliant on soiled bedding transfer & dependent on personnel shaking cages or stirring. However, it is still an effective replacement for soiled bedding sentinel mice.
If animals from approved vendors will only be on-site for a short period of time (e.g., <1-2 months) then health monitoring may not be necessary. You could also consider collecting fecal samples, fur swabs +/- oral swabs directly from colony animals.
Is there really enough data on this? There are more than 20 publications supporting environmental monitoring from more than 7 years.
It’s too costly! In fact, in some cases, it may be less expensive to conduct environmental monitoring (Luchins, 2020). Be sure to factor in the cost of housing & caring for sentinel rodents.
I don’t have time to retrain my staff & develop a new program. Although there may be an initial time investment, there are time savings once implemented (Luchins, 2020).
Will other institutions accept our rodents? Reports from institutions currently using only environmental monitoring indicate that yes, other institutions will accept their rodents. In fact, other institutions recognize the increased sensitivity of this type of health monitoring program.
Will there be false positives or ambiguities? This is possible. Always investigate unexpected results further.
Will there be residual nucleic acid after rack washing? There may be some for Helicobacter spp. or MNV though may not (Mailhot, 2019). If seen, you may need to wash racks more than once or even scrub plenums to remove residual nucleic acids.
What about missing new & emerging pathogens? This problem can be helped by performing histopathology on any colony animals with unusual phenotypes/signs/illness.
Thus far we know several large academic, pharmaceutical, and government organizations have switched including University of Washington, University of Florida, and University of Chicago. However, the NA3RsC is conducting a benchmarking survey to understand further how common this practice is.
In a 2020 webinar from NA3RsC, 79% of individuals said their institution uses some form of environmental monitoring. However, 82% also said they still use sentinels.
This may depend on the pathogen. Ask your diagnostic laboratory what they recommend. They may recommend testing colony animals by cage perimeter swabs, direct fur swabs, blood, or feces to narrow down positive cages. Alternatively they may suggest pooled plenum swabbing for confirmatory testing
If you suspect a false positive or residual nucleic acid, then move cages to a clean rack & re-swab in 2-4 weeks.
Consider submitting to a different diagnostic lab for confirmatory testing.
On September 16, 2020 NA3RsC put together a panel webinar on Applications in Developing Technologies for Rodent Health Surveillance. Our speakers were Susan Dowling, DVM.; Christina Pettan-Brewer, DVM, MSC; Patricia L. Foley, DVM, DACLAM; and Chris Manuel, DVM, PhD, DACLAM.