The Epidemiology of Koala Retrovirus

Abstract

A novel Gammaretrovirus, named Koala retrovirus (KoRV) was identified in koalas in 2000. Subsequent testing has shown that KoRV appears to be widespread throughout the wild koala population in Australia. KoRV is apparently unique in that it is the only known example of an exogenous retrovirus which is actively undergoing the process of endogenisation. While there is currently little direct evidence that KoRV causes overt disease in koalas, it is possible or even likely that KoRV infection plays a significant role in the pathogenesis of various neoplasms and a variety of immunosuppressive disorders which are commonly diagnosed in koalas. It appears that KoRV may have arisen through the cross species transmission of a closely related retrovirus in a native Australian rodent, the grassland melomys. Both of these viruses are closely related to a third retrovirus, Gibbon ape leukaemia virus (GALV). GALV was first isolated in the late 1960＇s from captive gibbons in Thailand that were suffering from leukaemia. To date, the source of GALV remains unknown.

Identification of a Novel Subgroup of Koala Retrovirus from Koalas in Japanese Zoos

“…KoRV-A was detected in all northern koalas tested and in 4 out of 11 Victorian koalas (Fig. 3B and Table 3), consistent with previous reports that KoRV had become endogenous in koalas in northern Australia (6,7,9,10). In contrast, KoRV-J was detected in 67.5% of northern koalas but not in southern (Victorian) koalas (Fig.…”

“…A correlation between these neoplastic diseases and the plasma viral load of KoRV, the suspected causative agent, has been reported (6,7). In addition, many koalas suffer from opportunistic infectious diseases, such as chlamydiosis and cryptococcosis, indicating that KoRV may also induce immunosuppression (3,(8)(9)(10). To clarify the relationship between KoRV and these diseases, it is necessary to accumulate more epidemiological and virological data.…”

Koala immunology and the koala retrovirus (KoRV)

“…Associations with infectious disease are equivocal (Simmons, 2011;Tarlinton et al, 2005), though this might be due to the multi-factorial nature of disease, especially in populations of free-ranging animals. The most direct evidence for immunomodulatory effects of KoRV comes from the effect of purified KoRV on cytokine expression by cultured human PBMCs, whereby it induced elevated expression of interleukin-6 (IL-6), IL-10, growth-related oncogene (GRO) and monocyte chemotactic protein-1 (MCP-1) (Fiebig et al, 2006).…”

An examination of disease in captive Australian koalas (Phascolarctos cinereus) and potential links to koala retrovirus (KoRV)

“…It has previously been suggested that southern koalas suffer less from all forms of disease (including chlamydiosis) than their northern (QLD, NSW) counterparts. (Simmons et al, 2011).…”