Rodent health monitoring programs (also referred to as rodent health surveillance or sentinel monitoring programs) are designed to detect subclinical infections of rodents that potentially have detrimental effects to the health of the animals or the integrity of your research. Robust sentinel animal protocols are both ethically and scientifically crucial.
Sentinel Animal Protocols
A health monitoring program is designed to detect infections that may be present within the colony without having to test all the animals within the colony.There are three major types of sentinel systems:
- Dirty bedding transfer
- Direct contact
- Air-exhaust sampling
Dirty Bedding Transfer
This system involves taking bedding samples from several colony cages in the room/IVC rack/area and placing it into a cage housing sentinel animals, which allows for relatively few mice to be used to monitor multiple cages.This process is most effective for detecting pathogens transmitted primarily by fecal-oral contamination, such as Rotavirus, Mouse Hepatitis Virus, Reovirus, and Helicobacter. To ensure enough time for a putative pathogen to be transmitted, the sentinel is often exposed to the bedding for at least a month. After the determined exposure time, the sentinel animals are tested for the presence of pathogens by diagnostic methods such as serology, parasitology and PCR.
Direct Contact
For this system, live rodents are placed directly into the cage with the research animals and disease exposure/transmission is facilitated by direct contact. In this manner the program can detect adventitious agents that can infect rodents by a variety of different routes, including direct contact, aerosol, urine, and fecal-oral.A disadvantage of this system is that sentinel animals must be placed in each cage, resulting in the need for more animals. Many institutions plan to purchase or breed additional animals from the specific colony to use as sentinels. It is important to select animals for this system that are of the same sex or have been castrated to prevent unwanted pregnancies. Strains of rodents known for non-aggressiveness are preferred.
Similar to dirty bedding transfer the rodents are housed with the research animals for at least one month to provide adequate exposure time to a putative pathogen. After the required exposure time the animals are by similar diagnostic methods.
Air Exhaust
A fairly new program for rodent health monitoring of animals housed in IVCs involves monitoring the exhaust air from IVCs.There are two distinct methods for sentinel programs utilizing air exhaust:
- Exhaust air from all upstream caging in an IVC is routed to a cage housing sentinel rodents, which directly exposes the sentinel to the air processed through all cages of the rack.
- Exhaust air is routed through the IVC rack and directed through an exhaust plenum holding a collection media filter.
Rodent Sentinel Selection Criteria
With the exception of filter media air exhaust systems, all rodent health monitoring programs require the use of live rodents. Following are criteria to be considered when selecting sentinel animals1:- Source: Mice should be sourced from approved, reputable suppliers or facilities able to provide evidence of quality assurance testing.
- Strain: The stock or strain utilized as sentinels is of key importance as the strain must readily seroconvert to viral agents. Swiss or CD-1 outbred strains are acceptable for use as sentinel mice, however the Swiss strain is preferable due to their more robust immune response1. Sprague Dawley rats are recommended for the same reason.
- Sex: Female mice are preferred as sentinels over male mice as male sentinels housed together have been known to fight which may cause injury. Castrated male mice are often used.
- Age: Mice should ideally be introduced as sentinels at three-to-five weeks of age (and no older than ten weeks). This is to ensure mice remain immunocompetent and are not subject to age-related diseases at the end of a three-to-six month sentinel period.
- Replacement: Once a sentinel animal has been removed, a replacement sentinel should be added to the group within one-to-two weeks. This will maximize the potential for pathogen exposure and allow the new animal to undergo seroconversion prior to the next round of testing.
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