There's Something in the Air
Annual AALAS meeting showcases multiple studies on exhaust air dust testing
Six months ago, we wrote about a new trend in rodent vivarium diagnostics that could potentially eliminate the need for soiled bedding sentinels. The PCR-based surveillance of entire spaces referred to as exhaust air dust (EAD) testing administers the biological equivalent of the white-glove test. Dust samples are collected from compatible IVC racks and evaluated using PRIA® panels.
At the American Association for Laboratory Animal Science (AALAS) meeting in San Antonio, which opened on Saturday and closes Oct. 23, the growing interest in EAD as an environmental monitoring tool is apparent by the large number of posters and oral abstract presentations from academic animal research facilities and commercial animal laboratories, including Charles River’s. EAD is easily one of THE hot topics this year at AALAS—one of the largest annual gatherings of laboratory animal scientists in the world—which is surprising when you consider that few facilities were even using EAD three years ago. After developing the first comprehensive panel of PCR assays in 2008 that quickly became a successful replacement for sentinel-based quarantine, Charles River was first to initiate feasibility investigations (2011) and report (FELASA and NAALAS, 2013) the use of EAD PCR as a replacement for sentinel-based routine pathogen screening.
So what are we learning this week? Some of the latest findings address open questions regarding EAD, such as how the ventilation systems, cage designs and location affect PCR testing of EAD cage rack, and we have more data that seems to support the reliability of PCR testing of EAD over traditional or PCR sentinel bed screening (SBS). Beyond that, an animal laboratory stumbled upon an unexpected and interesting case finding in its transgenic mouse colony while conducting EAD tests while another study found the EAD method worked better at detecting fur mites than sentinels.
In the largest study thus far, preliminary data representing six academic animal research laboratories in the US compared EAD and SBS samples taken during routine health monitoring time points of individually ventilated cage (IVC) racks. The study, initiated and managed by Charles River, began in the summer of 2013 and will conclude in 2015. Thus far, the study found, that IVC type and sampling location may hamper EAD PCR testing, but that with the exception of murine norovirus (MNV), EAD plenum samples on compatible racks were better at detecting infectious agents compared to SBS testing. For instance, cage racks with high efficiency filters did not consistently detect murine parvovirus (MPV) and pinworms—which SBS testing did—because when you prevent air dust from moving outside the cage, you restrict the migration of agent-associated dust to EAD testing locations. However, PCR screening of EAD plenum samples found a number of common culprits that PCR SBS did not consistently find: C. bovis, Helicobacter, K. pneumoniae, P. pneumotropica, S. xylosis, Cryptosporidium and Entamoeba. One caveat to keep in mind with this study: The facilities did not test SBS by traditional methods for all agents, which makes it difficult to draw an apples-to-apples comparison across all the facilities. However, we plan to extract this information when the study is complete.
Julie Watson from Johns Hopkins University (one of the participants in the multi-site study referenced above) also conducted a collaborative study with Charles River which included the evaluation of IgE, traditional SBS monitoring, and EAD PCR monitoring of rack exhaust plenums for fur mite and pinworm screening Although IgE testing of sentinel mice failed to be useful for SBS monitoring, EAD testing of plenums proved to be reliable and consistent compared to traditional methods used to evaluate SBS.
An EAD study led by Kari Koszdin from the VA Puget Sound Health Care System in Seattle uncovered an interesting case finding in its transgenic mouse colony that underscores the importance of investigating unexpected results before culling animals. Not only did the PCR tests of EAD detect the same organisms found in dirty bedding—notably Helicobacter and norovirus—it also detected lymphocytic choriomeningitis virus (LCMV), a pathogen that doesn’t transfer efficiently to bedding sentinels. So why was it suddenly being detected by PCR? Charles River, which was a collaborator on this study, conducted follow-up testing and concluded that the LCMV postive finding resulted from the detection of cells shed by a transgenic mouse. This type 1 diabetes model contains a portion of the LCMV genome that is used to target and eliminate insulin expressing cells. Had there been actual LCMV infection present in the racks, this would have become a health concern for the animal facility as LCMV is a zoonotic agent that can infect humans and lead to illness or death.
Finally, another Charles River collaboration with Diane Horne from the Oregon Health and Science University in Portland evaluated whether PCR testing of EAD from a single location of an (IVC) rack was equivalent to testing sentinel animals. This study found that collecting the sample near the terminal exhaust was the best location for generation screening of animals housed in the entire rack. Like other studies, Horne’s team found EAD a viable option for collecting samples and obtaining results indirectly from animals, though they included, not surprisingly perhaps, that the amount of dust and location could have influence on the results and should be studied further. Horne’s AALAS poster presentation also included some comparative financial data. Yearly costs for the sentinel program at her facility runs around US$191,000 compared to around $27,500 for utilizing exhaust air dust samples without the use of live sentinels.
The general message from all these studies and others presented at AALAS support the idea of PCR testing of EAD samples, but there is still more work to be done as optimal testing locations are identified and IVC racks evolve to improve this method of pathogen screening.