A novel exogenous retrovirus isolated from koalas (Phascolarctos cinereus) with malignant neoplasias in a United States zoo
Koalas in US zoos were screened for koala retroviruses in an effort to determine the viral mechanism for koala retrovirus induced malignant neoplasias. Although the previously characterized koala retrovirus (KoRV-A) was present in all US koalas, some koalas were also infected by a novel koala retrovirus, termed KoRV-B. The genome of KoRV-B is highly related to KoRV-A; however, certain regions within the viral genome, including the envelope gene, displayed diversity. These differences are sufficient to allow KoRV-B to employ a receptor (a thiamine transporter) that differs from that used by KoRV-A (a phosphate transporter). Of great interest was the strong correlation between the presence of KoRV-B and malignant disease (lymphomas) in koalas. All koalas that died from lymphoma were KoRV-B positive as were the dead joeys ejected from the pouch of KoRV-B positive dams. We found no evidence of KoRV-B transmission from sires to offspring but did from dam to offspring through de novo infection, rather than via genetic inheritance like KoRV-A. Detection of KoRV-B in native Australian koalas should provide a history, and a mode for remediation, of leukemia/lymphoma currently endemic in this population.