Rodent health monitoring is essential for ensuring animal welfare, research integrity, and biosafety in laboratory settings. Traditionally, health surveillance has relied on soiled bedding sentinels (SBS), where rodents are exposed to soiled bedding pooled from research animals in the colony and then tested for pathogens. However, SBS has several limitations, including delayed detection, reliance on indirect pathogen transmission, and ethical concerns regarding animal use. In any given research facility, hundreds or even thousands of mice and rats may be used this way each year.

Environmental health monitoring (EHM) has emerged as a viable alternative, leveraging diagnostic sampling techniques that directly detect pathogens in the environment without using live sentinel animals. This systematic review evaluates EHM’s effectiveness compared to SBS, exploring its accuracy, feasibility, and potential for widespread adoption.

The systematic search was conducted in three major databases, initially in November 2021 and updated in October 2023. Studies included in this review had to be published in peer-reviewed journals and contain empirical data comparing EHM to SBS in rodent health monitoring. A total of 42 studies met the inclusion criteria. Data were analyzed using logistic regression and descriptive statistics to assess the sensitivity of different pathogen detection methods.

Superior Pathogen Detection Without Sentinels

Across all studies, EHM consistently demonstrated higher pathogen detection rates than SBS. SBS failed to detect pathogens in 29% of cases where EHM did detect pathogens, while EHM failed only in 3% of cases where SBS detected a pathogen.

Variability In Sampling Techniques

The review identified four primary EHM methods:

1. Exhaust dust testing (EDT): Collects dust and nucleic acids from ventilated cages
2. Sentinel-free soiled bedding (SFSB): Analyzes pooled bedding for pathogens
3. Direct colony sampling (DCS): Uses feces, fur, and oral swabs from live research animals
4. Room and equipment monitoring (REM): Assesses pathogen presence in facility air and surfaces

All methods outperformed SBS, but EDT showed the highest success rate across various pathogens.

Ethical And Economic Advantages Of Not Using Sentinels

EHM eliminates the need to euthanize thousands of sentinel rodents annually. Studies reported cost and labor savings due to reduced animal care, handling, and testing time. EHM also aligns with the 3Rs principle of refinement, reduction, and replacement, promoting more humane research practices.

Institutional Resistance To Change

Despite overwhelming evidence in favor of EHM, 89% of surveyed institutions were still using SBS as of 2021. Key barriers to adoption include skepticism regarding accuracy, compatibility with existing cage systems, and lack of institutional mandates for change. Thus, advocacy efforts should focus on increasing confidence in EHM’s effectiveness and providing clear implementation guidelines.

The evidence strongly supports transitioning away from using sentinel animals for routine rodent health monitoring. EHM provides more accurate, efficient, and humane surveillance while reducing costs. However, institutional inertia and misconceptions about EHM’s reliability hinder widespread adoption. Increasing regulatory support, providing educational resources, and demonstrating cost savings can facilitate this transition.

Additionally, further research is needed to refine best practices for EHM, particularly in optimizing sampling methods for different facility conditions and pathogen detection needs. Addressing potential concerns about sensitivity in low-prevalence infections and ensuring uniform terminology for EHM methods will also enhance adoption.

Ultimately, EHM is a superior alternative to SBS, offering enhanced pathogen detection, reduced animal use, and economic benefits. Institutions should prioritize transitioning to EHM to improve research outcomes, uphold ethical standards, and streamline laboratory operations. The findings of this review provide a compelling case for regulatory agencies, veterinary professionals, and researchers to endorse EHM as the new gold standard in rodent health surveillance.