Is Bovine Polyoma Virus Getting You Down?

By Dr. Ray Nims

Bovine polyomavirus (BPyV) is a double-stranded DNA virus of genus Polyomavirus. It is non-enveloped and 40-50 nm in diameter, and is a member of the same genus as SV40.

Basis of Concern. The Polyomavirus genus was so-named due to the ability of the viruses to cause tumors in susceptible host animals. Genomic sequences for the potentially oncogenic bovine polyomavirus have been detected with high frequency in bovine sera, regardless of geographic region of origin (Shuurman et al., J. Gen. Virol. 72: 2739-2745, 1991; Wang et al., New Zealand Vet. J. 53: 26-30, 2005).

Regulatory Expectations. Bovine polyomavirus is not mentioned specifically in 9CFR 113.47, Detection of extraneous viruses by the fluorescent antibody technique, as a virus of concern for raw materials of bovine origin. As a result, BPyV is not specifically probed for during most 9CFR 113.53-based raw material viral infectivity testing, and this test most likely would not be capable of detecting BPyV if present in the test material. The EMEA Note for Guidance on the use of Bovine Serum in the Manufacture of Human Biological Medicinal Products (CPMP/BWP/1793/02) states that sera users are “encouraged to apply infectivity assays for BPyV and to investigate methods for inactivation/removal of BPyV in order to limit or eliminate infectious virus from batches of serum”.

Mitigating Risk. In actual practice, the available infectivity assays for BPyV involve numerous passages using a bovine detector cell such as MDBK and are somewhat lengthy and insensitive, though more sensitive assays are under development. Cell-based infectivity testing for BPyV is not always being performed by users for each batch of bovine serum. The lack of a rapid and sensitive infectivity assay also means that viral inactivation studies for BPyV are not practically possible. While another polyomavirus such as SV40 could be used in viral inactivation/removal studies as a proxy for BPyV, in actual practice the murine parvovirus MMV (mouse minute virus) is more typically used as a worst-case model virus for such studies since it is non-enveloped and even smaller than BPyV. The few studies performed with SV40 indicate that gamma-irradiation at the dosages normally employed is not effective at inactivating this virus, as might be expected for a virus of this relatively small size (e.g., Gauvin, 2009). On the other hand, it has been shown (Wang et al., Vox Sanguinis 86: 230-238, 2004) that UVC treatment is effective in inactivating SV40. Note: since originally authoring this blog, I have come across a great number of UV-inactivation papers which indicate that polyomaviruses, and SV-40 in particular, appear to be relatively resistant to UV inactivation. The Wang et al. result may represent an outlier. I will address this in a future blog. Studies using MMV indicate that high-temperature short-time (HTST)-treatment of medium containing bovine serum is effective in inactivating this virus (Schleh et al., Biotechnol. Prog. 25: 854-860, 2009), and would by implication be effective for BPyV.

Conclusions. At the present time, infectivity screening of bovine sera for BPyV is not always being performed, and it is believed that the high frequency of detection of genomic material in bovine sera may not reflect a similarly high frequency of infectious BPyV. Risk of infection of biological products with BPyV through use of bovine-derived materials such as bovine sera may be mitigated through implementation of UVC- or HTST-treatment of media containing the sera and of viral purification processes capable of removing and inactivating an even smaller non-enveloped virus such as MMV.