5/14/2009
Dear Colleagues
We finally have some data on our efforts to isolate and eradicate the parvovirus – so here is a summary of our current status:
What is parvovirus, and how widespread is the problem? Mouse parvovirus (MPV) infects the mouse for life and affects cells of the immune system causing immunomodulation, therefore is excluded from JHU research colonies. Since opening BRB in December of 2003, we have achieved an excellent record in keeping our mouse colonies parvovirus-free. Only 2 isolated cases were confirmed during the entire 6-year period, and both of those were immediately contained and eliminated. However since January 2009 we have suffered a large outbreak involving both MPV1 and MPV2. In BRB, no suite escaped infection: 26/39 rooms (67%) and 40/525 racks (7.6%) were affected. In CRB1, 5/7 rooms (71%) and 16/108 racks (14.8%) were affected, in CRB2, results to date suggest that 7/19 rooms (37%) and 13/91 racks (14.2%) are involved. Ross, Wilmer, Homewood and Bayview remain unaffected, though we have had one very recent positive in the school of Public Health that may be a cross contaminant.
How has this happened? We have been unable to definitively identify the source. However the sudden appearance at multiple locations in 3 separate buildings suggests an environmental contaminant. Initially it was suggested that sentinel mice could themselves be a source of the infection rather than signaling the existence of infected colony mice, particularly as the colony cage incidence on racks with positive sentinels was low (typically 0-3 cages per rack in BRB). However CRB and BRB buildings are both affected and they use sentinels from different vendors. Further, as more data have been collected, it is clear that most racks with positive sentinels do in fact contain infected colony cages. We examined the possibility that parvovirus-infected cells might have been injected into mice, but the nearly simultaneous widespread occurrence obviates this route. Given that the colony cage incidence in CRB is far higher than in BRB, a more realistic hypothesis is that mice in both buildings were randomly exposed, but sentinel mice and mice in CRB, are more susceptible to infection. In support of this, a much greater proportion of the mouse population in BRB is on a C57BL/6 background (genetically quite resistant to infection with MPV) compared with CRB, and sentinel mice are highly susceptible (which is why we use them).
What is the plan for eradication? Once a rack tests positive by sentinel, it is quarantined in place, surplus cages removed, and one mouse from each colony cage bled for antibodies to a panel of parvoviruses. Positive colony cages are removed to quarantine pending disposition. New sentinels are placed and exposed at 6 week intervals. Each remaining colony cage is bled a second time after a 1 month interval to identify infected cages that have not seroconverted. Two successive negative colony tests plus 3 successive negative sentinel tests are required to release the rack from quarantine. Although mice on rack quarantine may not be moved to other housing locations, work may continue – unlike with pinworm eggs, the hood disinfectants are highly effective in inactivating parvoviruses.
Where are we with this plan? To date, the entire BRB sentinel population has been evaluated once, the associated colony cages were bled (approx. 2500 cages) and all resulting positive colony cages removed. Most have been bled a second time (2500 cages) and of those, only 2 racks revealed additional positive cages. A second round of sentinel testing for the remainder of the facility is 25% complete, and of these tests, no additional positives have been identified in BRB. CRB has similarly tested almost the entire facility, quarantined positive racks, and completed initial colony testing and removal. A second round of testing is under way. Although we are not out of the woods yet, we are cautiously optimistic that the plan will be successful in eradicating MPV from our mouse colonies. Thank you everyone for helping in this enormous undertaking….we know it’s not easy to get the work done while dealing with movement restrictions and infection control SOP’s. However, it is thanks to our combined efforts that we have been successful so far. Keep up the good work!
What are we doing to prevent this happening in the future? Our sentinel systems warned us of this infection at an early stage, and our barrier caging systems have helped us avoid a much more extensive parvovirus disaster by preventing spread of infection between cages. However we did find that there was the potential for contamination during final cage assembly in the animal rooms. To close this loophole, we recently changed procedures so that each cage is now assembled and autoclaved as a complete closed unit already containing feed, so that no additional manipulation is required prior to placing the mice in the cage. In addition, strict adherence to safe handling procedures by RAR and investigators is clearly instrumental in containing the outbreak.
Please don’t hesitate to ask if you have further questions
Julie Watson 5/14/2009
