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Molecular dynamics and mode of transmission of Koala Retrovirus (KoRV) as it invades and spreads through a wild Queensland koala population.


ABSTRACT: The recent acquisition of a novel retrovirus (KoRV) by koalas (Phascolarctos cinereus) has created new opportunities for retroviral research and new challenges for koala conservation. There are currently two major subtypes of KoRV; KoRV-A, which is believed to be endogenous only in koalas from the northern part of Australia, and KoRV-B, which appears to be exogenous. Understanding and management of these subtypes requires population-level studies of their prevalence and diversity, especially when co-infected in the same population, and investigations of their modes of transmission in the wild. Towards this end, we studied a wild Queensland koala population of 290 animals over a five year period and investigated the prevalence, diversity and mode of transmission of KoRV-A and KoRV-B. We found KoRV-A to have an infection level of 100% in the population, with all animals sharing the same dominant envelope gene protein sequence. By comparison, the KoRV-B infection prevalence was only 24%, with 21 different envelope protein sequence variants found in the 83 KoRV-B positive animals. Linked to severe disease outcomes, a significant association between KoRV-B positivity and both chlamydial disease and neoplasia was found in the population. Transmission of KoRV-B was found at a rate of 3% via adult-to-adult contact per year, while there was a 100% rate of KoRV-B positive mothers transmitting the virus to their joeys. Collectively, these findings demonstrate KoRV-B as the pathogenic subtype in this wild koala population and inform future intervention strategies with subtype variation and transmission data.IMPORTANCE KoRV represents a unique opportunity to study a relatively young retrovirus as it goes through its molecular evolution in both an endogenous form, and a more recently evolved exogenous form. The endogenous form, KoRV-A, now appears to have stably and completely established itself in Northern Australian koala populations and is progressing south. Conversely, the exogenous form, KoRV-B, is undergoing continuous mutation and spread in the north and, as yet, has not reached all southern koala populations. We can now link KoRV-B to neoplasia and chlamydial disease in both wild and captive koalas, making it an imminent threat to this already vulnerable species. This work represents the largest study of koalas in a wild population with respect to KoRV-A/KoRV-B infected/co-infected animals and its linkage to chlamydial disease, neoplasia, viral evolution and spread.

SUBMITTER: Chaban B 

PROVIDER: S-EPMC5809739 | biostudies-other | 2017 Dec

REPOSITORIES: biostudies-other

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Molecular Dynamics and Mode of Transmission of Koala Retrovirus as It Invades and Spreads through a Wild Queensland Koala Population

Quigley Bonnie L BL   Ong Vanissa A VA   Hanger Jonathan J   Timms Peter P  

Journal of virology 20171213 5


The recent acquisition of a novel retrovirus (KoRV) by koalas (<i>Phascolarctos cinereus</i>) has created new opportunities for retroviral research and new challenges for koala conservation. There are currently two major subtypes of KoRV: KoRV-A, which is believed to be endogenous only in koalas from the northern part of Australia, and KoRV-B, which appears to be exogenous. Understanding and management of these subtypes require population level studies of their prevalence and diversity, especial  ...[more]

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