Rodent Health Surveillance & Disease Prevention

Colonies of research rodents are susceptible to infection with a variety of bacterial, viral and parasitic agents. In the majority of cases these agents produce no clinical signs yet result in physiologic changes that may alter and in many cases invalidate research carried out on infected animals. In addition, some of the agents may infect people working with animals. Therefore, it is important to maintain rodent research colonies free of infectious agents.

Many of these agents have the ability to spread through rodent colonies once they have been introduced. Routes of introduction of these agents include:

• Infected animals from outside the university
• Contaminated cell lines which are subsequently introduced into rodents
• Personnel who have become contaminated
• Feral rodents on campus

Once introduced into a rodent colony, an infectious agent may spread (be transmitted) rapidly through the animal facility. The ease and potential impact of such transmission has fueled the development of complicated housing systems such as barriers, microisolation systems, and positive pressure ventilated caging. Routes of transmission include:

• Direct contact between animals
• Dissemination through the room air
• Transportation of agents on equipment, instruments, and personnel

Health Surveillance

In order to minimize the chance of introducing infectious agents to our colonies, the university purchases animals only from reputable vendors who perform and report the results of extensive rodent health monitoring. Only animals that meet pre-established standards are accepted from these approved vendors. On occasion, it is necessary to import animals from a vendor or institution that is not an approved source. All animals entering from non-approved sources are quarantined on arrival and tested before release to PSU colonies. In addition, all cell lines obtained from outside the university are tested for murine pathogens before they are used in rodents.

Even with these precautions it is still possible that at some point one or more of these agents will enter a PSU rodent colony. In order to identify colonies that have become infected, the Animal Resource Program has developed a system to monitor the health of each PSU rodent colony. The effectiveness of this health surveillance system is dependant upon obtaining the most representative animals from each colony for periodic testing. At PSU, animals that are representative of the research colonies are generated by housing rodents on soiled bedding collected from the cages of research animals. These sentinel animals are therefore exposed to all the other animals they represent via this dirty bedding.

Identification of infected animals requires comprehensive testing that includes necropsy, serology, microbiologic culture, microscopic examination for parasites and in some cases molecular analysis, as by polymerase chain reaction (PCR). At PSU, sentinel animals are tested for infectious agents every 4 months.

The goal of the health surveillance system is to detect the presence of agents of concern as early as possible in the course of an outbreak. Cages containing sentinel animals are distributed at the ratio of 1 cage for each 50-75 cages of colony animals. The lower right position on each rack is designated for a sentinel cage for that rack. If a colony cage is occupying that rack position, it will be moved to a new location. The sentinel cage is clearly marked by a yellow cage card. Please do not move or disturb the animals in these sentinel cages. Their location provides a means of tracking and containing infected animals.

There are agents of concern that are not easily transmitted to sentinel animals by soiled bedding. One method to increase the sensitivity of our system is to obtain culled animals from each colony being monitored that will become the sentinels housed on soiled bedding. From time to time you are likely to be contacted by the animal resource technician who will request culls that can be used for health surveillance. One additional benefit of providing culls to act as sentinel animals is that it eliminates the need to introduce animals from outside the colony to become the sentinels. In some cases, culls from the colony are either not appropriate or not available. For instance, since we rely heavily on serologic testing, immunocompromised animals cannot be used for sentinels in our system. For those cases where no culls are available or appropriate, we will provide the sentinel.

If you have questions or comments regarding the health surveillance system, please contact the ARP office.

Animal Quarantine

All laboratory animals arriving on the PSU University Park campus from non-approved sources must undergo a period of quarantine in a protected area of the animal facility. This period allows the animal(s) to recover from the stress of shipment and to be screened for clinical health problems and infection with pathogenic organisms to prevent introduction of disease to the animal facility. The quarantine period will be dependent on the animal species, source and health status. Upon special request to the Director, acute projects approved by the IACUC may be carried out during the quarantine period.