No evidence of cross-species transmission of mouse retroviruses to animal workers exposed to mice James Brooks, Karly Lycett-Lambert, Kyna Caminiti, Harriet Merks, Rachel McMillan, Paul Sandstrom Article first published online: 30 DEC 2011:http://onlinelibrary.wiley.com/doi/10.1111/j.1537-2995.2011.03463.x/abstract BACKGROUND: Although recent data have brought into question the association between xenotropic murine leukemia virus-related virus (XMRV) and chronic fatigue syndrome, one group has reported evidence of human infection with distinct polytropic murine leukemia viruses (MLVs). Occult retroviral infection among humans poses a significant public health risk should it be introduced into the blood supply. To explore the possibility of cross-species transmission of MLVs to humans, we sought molecular and serologic evidence of XRMV/MLV infection among a cohort of animal workers highly exposed to mice. STUDY DESIGN AND METHODS: Before the commencement of the study, the laboratory and equipment were demonstrated to be free of XMRV/MLV DNA sequences. DNA extracted from 43 animal workers was tested using nested polymerase chain reaction (PCR) with published primer sets, targeting regions of XMRV and MLV gag. Negative controls were assayed in a 1:1 ratio with specimens. Serum specimens were tested using a validated immunoblot assay containing cross-reactive XMRV antigens. RESULTS: Initial molecular assays demonstrated that the physical space and laboratory equipment were free of MLV and XMRV DNA sequences. Nested PCR assays using multiple primer sets successfully amplified XMRV and MLV sequences from positive controls with high sensitivity. A single, nonreproducible, false-positive result from one specimen was shown to be the result of subsequent contamination. Immunoblotting of all subjects' sera failed to demonstrate any evidence of seroreactivity to XMRV proteins. CONCLUSIONS: There was no evidence of human infection with XMRV/MLV among a cohort of individuals highly exposed to mice. These data suggest that the likelihood of cross-species transmission events of MLV from mice to humans is low.