Current Understanding and Health Implications of Koala Retrovirus in Zoologic Collections
Koala retrovirus (KoRV) is an RNA virus that incorporates into the host genome and has the potential to cause malignancies and immunosuppression.4 Viral particles morphologically consistent with a retrovirus were first documented in the bone marrow of a leukemic adult female koala in 1988 and subsequent nucleotide sequencing confirmed the presence of KoRV in koalas (Phascolarctos cinereus).1 KoRV is unique in that it is capable of both endogenous transmission, by incorporating into the germ line, and exogenous transmission, through horizontal spread.2,3 A newly emergent variant of KoRV (KoRVB) was recently detected in a US zoo and it may be more pathogenic than the originally isolated variant (KoRVA).5
The discovery of this variant prompted the organization of an international workshop at the San Diego Zoo (April 17–18, 2013) to facilitate discussion between basic scientists and clinicians regarding KoRV and implications for koala health and management. Through discussions on evolution, genomics, prevalence (zoo-based and free-ranging), epidemiology, disease expression, anti-retroviral drugs, vaccine development, and the zoonotic potential of KoRV, we were able to identify potential health, management, and future research strategies to reduce the impact of KoRV on koalas. The outcomes of this workshop greatly improve our understanding of KoRV, an infectious disease of emerging importance in zoo-based and free-ranging koalas.
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2. Hanger JJ, Bromham LD, MeKee JJ, O’Brien TM, Robinson WF. The nucleotide sequence of koala (Phascolarctos cinereus) retrovirus: a novel type C endogenous virus related to gibbon ape leukemia virus. J Virol. 2000;74:4264–4272.
3. Tarlinton RE, Meers J, Young PR. Retroviral invasion of the koala genome. Nature. 2006;442:79–81.
4. Worley M, Rideout B, Shima A, Janssen D. Opportunistic infections, cancer, and hematological disorders associated with retrovirus infection in the koala. Proc Am Assoc Zoo Vet Annu Conf. 1993:162.
5. Xu W, Stadler CK, Kim D, Alemaheyu M, Switzer W, Pye GW, Eiden MV. 2011. Identification of a novel gammaretrovirus in koalas (Phascolarctos cinereus) in US zoos. 23rd Workshop on Retroviral Pathogenesis, Montpellier, France; 2011.