Threat to U.S. Mouse Colonies

We recently identified commercial mouse serum as the source of introduction of ectromelia virus, the causative agent of mousepox, a rare and devastating murine virus, into our institution. The serum was not intended to be used in vivo; however, media supplemented with the serum was inadvertently used to feed cells that were subsequently inoculated into mice. Fortunately, we were able to contain and eliminate the virus before it spread throughout our institutional colonies. We have determined that the contaminated serum, which was obtained late last year, originated in China. The serum was imported as a batch of at least 43 liters and was filtered (0.2 μ) by the distributor. The serum has been distributed to major suppliers throughout the United States and has or may be sold as is or further processed to obtain a variety of serum-derived products. The identification of the serum source, the size of the lot from which it originated, and the distribution throughout the country by many vendors raises concerns about the potential risk to our domestic mouse colonies. Further, as tens of thousands of mice are needed to generate this quantity of serum, and considering the lack of testing of imported material for mousepox and other agents of potential concern, the likelihood is that serum contaminated with mousepox may continue to be distributed. The last major mousepox outbreak in the United States occurred in the late 1970s and early 1980s at the U.S. National Institutes of Health and a number of academic institutions. Tens of thousands of mice had to be destroyed at a cost of millions of dollars and lost research. If an outbreak of this magnitude occurs again, the impact could be considerably more devastating, as many of the gene-targeted murine models produced and used are maintained at a single institution and are irreplaceable. This incident serves as a reminder of the importance of testing all biologics, including tumors and cell lines, of rodent origin or that have been passaged in rodents, for contamination with adventitious agents. It also raises the question of whether governmental oversight of this process is sufficient to protect a critical resource.