Detection of koala retrovirus subgroup B (KoRV-B) in animals housed at European zoos
Fiebig, U, Keller, M & Denner, J 2016, Archives of Virology, vol. 161, pp. 3549-3553.
In addition to the common endogenous koala retrovirus KoRV-A, a second type of non-endogenous retrovirus, KoRV-B, was recently detected in animals in zoos in Japan and the United States. This study describes a different type of KoRV-B detected in koalas from zoos in Germany and Belgium.
The koala retrovirus (KoRV) is classified into two subgroups, KoRV-A and KoRV-B. KoRV-A is an endogenous provirus, while KoRV-B is an exogenous virus. All six koalas tested at either Duisburg or Antwerp zoos tested positive for KoRV-A, and two were also positive for KoRV-B. The co-infection of the two koalas with both subgroups of KoRV suggests that KoRV-A may facilitate KoRV-B, potentially with mutation or recombination having taken place for KoRV-B to emerge. Additionally, KoRV-B infected koalas had lymphoma, which suggests that KoRV-B may have been involved in the pathogenesis of lymphoma. In contrast, however, a koala that was not infected by KoRV-B in this study was also found to suffer from lymphoma. It is possible, however, that the methods employed in this study were not able to detect KoRV-B below a certain viral load threshold and that this was a false negative result. A subsequent polymerase chain reaction (PCR) analysis targeting a multimeric repeat region revealed that the infected KoRV-B koalas did not have the multimerisation of repeats seen in KoRV-B from a Los Angeles zoo. For porcine endogenous retrovirus (PERV), which is closely related to KoRV, the multimerisation of repeats was seen to increase the number of transcription factor sites and led to increased replication of PERV in human cells. This was postulated to have occurred for KoRV-B in the Los Angeles zoo but has not happened yet for the KoRV-B from the European zoos.
This study has enhanced our knowledge of the diversity and effects of retroviruses that affect koalas, which is important for the species’ conservation. It should be noted, however, that this study did not employ other methods of screening for KoRV, such as immunoblotting, which may have limited the detection of KoRV-B in the koalas tested.
Summarised by Daniel Chew
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