Even though most commercially reared rodents, some rabbits, and relatively fewer dogs, cats, and nonhuman primates (NHPs) can be obtained free of certain infectious agents (ie, "specific pathogen free"), resident animal colonies must be monitored for naturally occurring disease. Investigators should have easy access to information regarding the health status of their research animals and should be alerted to changes and outbreaks right away.
Animal research facilities use a risk-based program. If vaccination could confound a study (eg, immunology, metabolism), specific-pathogen-free (SPF) animals may be left unvaccinated and protected by biocontainment. If there is exposure risk (personnel traffic, teaching use, transport, colony mingling) or a legal requirement (eg, rabies), animals are vaccinated, and this is documented in the health record/IACUC file.
In addition to monitoring for infectious disease, a quality assurance program should monitor for genetic integrity, especially for inbred mouse strains that are produced and maintained in the research facility. It should also monitor environmental factors (quality of feed, water, and bedding; efficacy of sanitation programs; air handling and quality; lighting; noise; etc) that can affect colony health.
Colony health monitoring consists of a defined program of regular physical and laboratory evaluations of animals within a unit, as well as a morbidity and mortality reporting system that enables timely identification of potential problems. Thorough investigations of illnesses, deaths, and unusual experimental outcomes in a colony are essential parts of this program. See the tables Select Physiological Data, Age of Onset of Puberty and Breeding Life, and Female Reproductive Cycles.
Select Physiological Data for Laboratory Animalsa
Species | Gestation Period, d | Litter Size | Age and Body Weight at Sexual Maturity | Typical Lifespan, yr | Average Body Temperature, °C (°F) | Heart Rate, bpm | Daily Water Consumptionb |
|---|---|---|---|---|---|---|---|
Mice | 19–21 | 4–12 | 6 wk (20–30 g) | 1–3 | 37 (98.6) | 310–840 | 4–7 mL |
Rats | 21–23 | 6–14 | 1.5−3 mo (0.2–0.3 kg) | 2–3 | 37.5 (99.5) | 300–500 | 8–11 mL/100 g |
Guinea pigs | 59–72 | 1–4 | 2–4 mo (0.4–0.6 kg) | 3–5 | 38 (100.4) | 230–380 | 10 mL/100 g |
Hamsters, golden | 15–18 | 4–10 | 2–4 mo (85–110 g) | 2–3 | 37 (98.6) | 280–410 | 30 mL |
Gerbils | 25 | 2–9 | 3 mo (60–100 g) | 2–5 | 38 (100.4) | 250–600 | 4–7 mL/100 g |
Rabbits | 30−32 | 4–12 | 5–6 mo (3–4 kg) | 5–7 | 39 (102.2) | 200–300 | 300–700 mL |
Squirrel monkeys | 150 | 1 | 2.5–3.5 yr (0.6–1.1 kg) | 16–20 | 39 (102.2) | 300–380c | 70–110 mL |
Rhesus monkeys | 165–175 | 1–2 | 4–5 yr (5–11 kg) | 15–30 | 39 (102.2) | 120–180c | 80 mL/kg |
a Also see the table Features of the Reproductive Cycle. | |||||||
b Typical ad lib water intake (baseline range) for healthy, adult, nonpregnant animals on a dry diet in thermoneutral conditions. This value varies with body mass index, number of animals per cage, moisture in feed, temperature, etc. | |||||||
c Results obtained under anesthesia. | |||||||
Age of Onset of Puberty and Breeding Life of Commonly Used Laboratory Animals
Rat | Mouse | Guinea Pig | |
|---|---|---|---|
Age at sexual maturity, wk | Males: 6–10 Females: 8–12 | Males and females: 6–8 | Males and females: 10–12 |
Breeding life, mo | Males and females: 9–12 | Males and females: 9 | Males and females: 24 |
Female Reproductive Cycles in Commonly Used Laboratory Animals
Rat | Mouse | Guinea Pig | |
|---|---|---|---|
Estrous cycle length, d | 4–5 | 4–5 | 16 |
Estrus duration, h | 10–20 | 10–20 | 6–11 |
Estrus onset to ovulation, h | 8–11 | 2–3 | 10 |
Fertilization life of ovum, h | 10–15 | 15 | 8–26 |
Fertilization life of sperm in female tract, h | 14 | 6 | 20–22 |
Presence of copulatory plug in female tract, h | 12–24 | 18–48 | 9–18 |
Ovulation rate (number of eggs) | 10–20 | 6–10 | 3–4 |
Pseudopregnancy, d | 12 | 12 | NAa |
aNA, not applicable. | |||
Although certain general principles apply, a health monitoring program must be specifically developed for each species maintained in a facility. For example, all NHPs are usually quarantined and isolated on arrival. Physical examinations, tuberculin testing (the standard is intradermal eyelid testing with mammalian old tuberculin), radiographs, and baseline hematologic and other clinical pathological tests should be performed.
Immune-based serological assays are an alternative or adjunct to screening for tuberculosis because the animals are monitored for B virus (also known as macaque herpesvirus 1, cercopithecine herpesvirus 1, and herpesvirus simiae), simian retroviruses, and other agents, depending on the NHP species and desired pathogen status.
At the time of this writing, best practices for NHPs include using PCR-based molecular assays alongside serological testing to detect key viral and bacterial pathogens. Screening panels often include simian immunodeficiency virus (SIV), simian T-cell leukemia virus (STLV), simian foamy virus, and enteric pathogens such as Shigella spp, Salmonella spp, and pathogenic Escherichia coli. Behavioral conditioning is increasingly used to decrease stress and improve the means by which samples (eg, blood, urine) are obtained. Institutions also emphasize strict use of personal protective equipment and biosecurity because of the zoonotic potential of certain infectious agents.
NHPs should be released from quarantine only after both their health status and their suitability for research have been determined. Furthermore, NHPs should undergo regular health surveillance screens, each consisting of defined elements. Depending on the nature and value of the colony and research use, screenings can range in frequency from quarterly to semiannual or annual.
For colony-maintained rats and mice, programs for disease monitoring can consist of any or all of the following:
vendor surveillance
quarantine and isolation evaluation
ongoing clinical and postmortem evaluation during a study
combination of environmental sampling and live sentinel animal programs
evaluation at termination of a study
In addition, all transplantable tumors, cells, or other biological inocula destined for animal passage should either be screened for murine and zoonotic pathogens or undergo colony management practices to appropriately isolate animals receiving these materials. Current guidance emphasizes using PCR-based pathogen screening and mycoplasma detection panels for all biological materials before transfer.
The occasional and justifiable need to obtain animals from less well defined sources, such as an investigator's colony at another institution, or from another inadequately characterized source, is of particular concern for colony health. Institutions increasingly require material transfer agreements (MTAs) and health status documentation before they accept such animals.
The presence of infectious agents in transplantable tumors, in other biological materials, or from noncommercial animal sources can seriously threaten resident colonies and personnel. Enhanced barrier protocols and rederivation by embryo transfer or cesarean section are recommended for valuable rodent lines received from noncommercial sources.
The proper use of filter-top caging technology impedes cage-to-cage transmission of infectious agents in rodent colonies, thus minimizing enzootic disease transmission and protecting naive animals from epizootics. However, filter-top cages present challenges for health surveillance programs. Because most diseases of laboratory rodents do not cause clinical signs, and because the rate of turnover of research rodents can be high and unpredictable, the standard for health monitoring was based on the premise that infectious agents were transmitted via soiled bedding to sentinels that were tested for a variety of pathogens. This indirect exposure is suboptimal for detecting many bacterial pathogens, agents transmitted by true aerosol, and fur mites.
Current trends favor direct environmental sampling (eg, exhaust-air dust PCR assay and surface swabs) over traditional sentinel soiled bedding methods for more sensitive and timely pathogen detection. Agents that are shed intermittently; those with a self-limited, single window of shedding; those that require a high dose to be infective; and those that are unstable in the environment are difficult to detect in soiled bedding.
Before the widespread use of filter-top caging, dedicated sentinels in open cages were readily exposed to airborne fomite particles and true aerosols from infected animals in the colony. Sentinels themselves can add confounding factors if their age or genetic background make them relatively resistant to some infections. Sentinel-free monitoring strategies and digital dashboards that integrate health metrics are increasingly used in high-barrier facilities. For small fish in aquatic systems, the sump provides useful information for health monitoring.
The primary contemporary challenges to research rodent health—particularly for mice—are noroviruses, parvoviruses, Helicobacter spp, pinworms, and fur mites that infect or infest colonies. These agents can disrupt biological processes and introduce variation into research data. For the most part, these agents, along with mouse hepatitis virus, are thought to have gained entry to research colonies largely via the trading of live mice of unique genotypes between institutions. The situation is complicated by the inability of quarantine programs to reliably detect and exclude these agents. However, a body of substantial, compelling, anecdotal evidence suggests that nonsterilized diets might be a source of introduction for some pathogens (eg, mouse parvovirus).
Pearls & Pitfalls
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Murine norovirus is the most widespread virus in domestic mouse colonies. The virus was described in 2003, but it likely existed in research mice for decades before that. Mouse parvovirus was definitively discovered 10 years earlier. New agents, such as mouse kidney parvovirus and murine astrovirus, continue to be detected. These agents cause subclinical infection among immunocompetent mice but can cause disease or have unknown effects in mice with immune dysfunction.
Infections can vary between institutions and within individual rooms, requiring more localized health assessments. Next-generation sequencing, along with untargeted shotgun metagenomic analysis, is increasingly used to detect and characterize previously undocumented microbial agents in rodent colonies. These methods enable high-resolution microbial community profiling, which detects microbiota shifts that might confound experimental outcomes, latent infections, and virus discovery, even in colonies designated as specific pathogen free.
The use of mice with increasingly extreme levels of immunosuppression has been associated with a resurgence in morbidity and mortality rates caused by Corynebacterium bovis. C bovis can cause substantial skin disease, including alopecia and hyperkeratosis, in immunodeficient mice and can be transmitted via fomites, aerosols, and contact, making strong biosecurity measures critical. This bacterium, along with certain nonenveloped viruses, such as murine norovirus and parvoviruses, can persist for long periods in healthy mice and can contaminate and remain infectious in the environment for months, making them ideally suited to survive even in colonies kept in filter-top cage systems.
Embryo transfer by in vitro fertilization or more traditional cesarean section is an important tool in pathogen exclusion; however, it can also contribute to the narrowing of genetic and microbiome diversity, with potential reverberations across many biological processes, behaviors, and experimental repeatability. The loss of native microbiota can influence immune system development and metabolic phenotypes. Strategies to restore microbiome complexity, such as embryo transfer to surrogate dams with defined microbial communities, are gaining traction in colony management.
For More Information
Albers TM, Henderson KS, Mulder GB, et al. Pathogen prevalence estimates and diagnostic methodology trends in laboratory mice and rats from 2003 to 2020. J Am Assoc Lab Anim Sci. 2023;62:229-242.
Sorzano COS, Sanchez I, Naranjo A. Statistical design for health monitoring in laboratory animal facilities using sentinel animals. Lab Anim. 2024;58:345-353.
Balansard I, Cleverley L, Cutler KL, Spångberg MG, Thibault-Duprey K, Langermans JAM. Revised recommendations for health monitoring of non-human primate colonies (2018): FELASA Working Group Report. Lab Anim. 2019;53(5):429-446.
Lupini L, Bassi C, Guerriero P, Raspa M, Scavizzi F, Sabbioni S. Microbiota and environmental health monitoring of mouse colonies by metagenomic shotgun sequencing. World J Microbiol Biotechnol. 2022;39(1):37.
Lee VK, David JM, Huerkamp MJ. Micro- and macroenvironmental conditions and stability of terrestrial models. ILAR J. 2020;60:120-140. doi:10.1093/ilar/ilaa013
