Abstract

Herpesviruses are large enveloped double-stranded DNA viruses that have complex, highly evolved relationships with their endemic hosts, often involving latency. Using a consensus herpesviral PCR,¹ we recently discovered a novel gamma herpesvirus in a California sea lion (Zalophus californianus) with acute lymphoma or leukemia. We had previously surveyed over 50 California sea lions samples using this consensus herpesviral PCR and had not previously identified this virus. This novel virus is most closely related to two gamma herpesviruses of phocid seals and is tentatively named Otariid herpesvirus 3 (OtHV3). Although there is evidence for gamma herpesviruses causing lymphoma in endemic hosts, the most dramatic correlation between lymphoma and herpesviral infection is seen in gamma herpesviruses in aberrant rather than endemic hosts, with some aberrant host/virus systems being very reliable models of lymphoma induction.^2-4 We developed a specific OtHV3 quantitative PCR (qPCR) assay for the detection and quantitation of this virus in California sea lion tissue and buffy coat specimens. The OtHV3 qPCR assay accurately detected 10 to 10⁶ DNA copies per ng of total DNA. A total of 136 samples from 100 California sea lions from five populations were surveyed, and OtHV3 was detected in 32 animals from four of the populations, which is consistent with a virus endemic in this species. Significantly higher OtHV3 viral loads (mean ± SD = 30,214 ± 20,366) were detected in samples from the California sea lion with lymphoma suggesting active replication of the virus. It is unknown whether virus activation occurred in the animal due to immunosuppression, or if the virus was associated with the onset of acute lymphoma. The presence of significantly lower viral loads (mean ± SD = 0.13 ± 0.16) in samples from 31 sea lions surveyed suggests latency of the virus in those animals. Understanding the association of this virus with lymphoma will provide a basis for further studies assessing potential causality.

Acknowledgments

This work was funded by research grants Nos. N00014-06-1-0250 and N00014-09-1-0252 from the Office of Naval Research to HHN and JW and research contract No. N66001-08-D-0070 from the Department of Defense to PKY. We would like to thank the staff of the U.S. Navy Marine Mammal Program, The Marine Mammal Center, SeaWorld Parks and Entertainments and B. Stewart for their help with sample collection. HSWRI field sampling was conducted under authorization of Marine Mammal Permit Nos. 486-1790-00 and 486-1790-01 to Dr. Brent Stewart and was approved by the HSWRI Institutional Animal Care and Use Committee. We would also like to thank the Naval Base Ventura County and SNI/OLF for facilitating research at San Nicolas Island and Linda Archer, Jennifer Burchell and Celeste Benham for their assistance in the laboratory.

References

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