Prevalence of koala retrovirus in geographically diverse populations in Australia.

OBJECTIVE: To determine the prevalence of koala retrovirus (KoRV) in selected koala populations and to estimate proviral copy number in a subset of koalas. METHODS: Blood or tissue samples from 708 koalas in Queensland, New South Wales, Victoria and South Australia were tested for KoRV pol provirus gene using standard polymerase chain reaction (PCR), nested PCR and real-time PCR (qPCR). RESULTS: Prevalence of KoRV provirus-positive koalas was 100% in four regions of Queensland and New South Wales, 72.2% in mainland Victoria, 26.6% on four Victorian islands and 14.8% on Kangaroo Island, South Australia. Estimated proviral copy number per cell in four groups of koalas from Queensland and Victoria showed marked variation, ranging from a mean of 165 copies per cell in the Queensland group to 1.29 × 10(-4) copies per cell in one group of Victorian koalas. CONCLUSIONS: The higher prevalence of KoRV-positive koalas in the north of Australia and high proviral loads in Queensland koalas may indicate KoRV entered and became endogenous in the north and is spreading southwards. It is also possible there are genetic differences between koalas in northern and southern Australia that affect susceptibility to KoRV infection or endogenisation, or that environmental factors affecting transmission in northern states are absent or uncommon in southern regions. Although further studies are required, the finding of proviral copy numbers orders of magnitude lower than what would be expected for the presence of a single copy in every cell for many Victorian animals suggests that KoRV is not endogenous in these animals and likely reflects ongoing exogenous infection.

The nucleotide sequence of koala (Phascolarctos cinereus) retrovirus: a novel type C endogenous virus related to Gibbon ape leukemia virus.

A novel retrovirus, morphologically consistent with mammalian C-type retroviruses, was detected by electron microscopy in mitogen-stimulated peripheral blood mononuclear cell cultures from 163 koalas and in lymphoma tissue from 3 koalas. PCR amplified provirus from the blood and tissues of 17 wild and captive koalas, and reverse transcriptase-PCR demonstrated viral mRNA, viral genomic RNA, and reverse transcriptase activity in koala serum and cell culture supernatants. Comparison of viral sequences derived from genomic DNA and mRNA showed identity indicative of a single retroviral species-here designated koala retrovirus (KoRV). Southern blot analysis of koala tissue genomic DNA using labelled KoRV probes demonstrated banding consistent with an endogenous retrovirus. Complete and apparently truncated proviruses were detected in DNA of both clinically normal koalas and those with hematopoietic disease. KoRV-related viruses were not detected in other marsupials, and phylogenetic analysis showed that KoRV paradoxically clusters with gibbon ape leukemia virus (GALV). The strong similarity between GALV and KoRV suggests that these viruses are closely related and that recent cross-host transmission has occurred. The complete proviral DNA sequence of KoRV is reported.

The arrangement of gut-associated lymphoid tissues and lymph pathways in the koala (Phascolarctos cinereus).

Gut-associated lymphoid tissues are poorly developed in koalas. They comprise paired caecocolic lymphoid patches, and a few small mesenteric lymph nodes. The patches lie opposite one another in the lateral gut wall at the junction of the ileum, caecum and proximal colon. The lymphoid parenchyma of the patches consists of a layer of nodules and internodular parenchyma in the submucosa. Apoptosis is common in the nodules. The mucosa and lymphoid tissue of each patch is continuous over a caecocolic recess, formed by the coalescence of laminae which extend along the large intestine. Lymph sinuses between and beneath the lymphoid nodules are continuous with efferent lymph vessels in the submucosa. These then enter 2-4 small lymph nodes at the root of the mesentery. The paucity of lymphoid tissue associated with the gut may be related to germicidal activity in the Eucalypt leaves eaten by the koala.

Topography of the major superficial lymph nodes and their efferent lymph pathways in the koala (Phascolarctos cinereus).

The koala has an inguinoaxillary lymph trunk on either side of the ventral midline, and this carries efferent lymph from the superficial inguinal lymph node directly to the deep axillary lymph node. The superficial lymph nodes are large and soft compared with those of the domestic species, and each lymph centre usually contains only one or two large lymph nodes. Koalas have a rostral mandibular lymph node which has not been described in other species, but lack popliteal and subiliac lymph nodes. The superficial lymph nodes which are readily palpable in the live koala are the facial, rostral mandibular, mandibular, superficial axillary and superficial inguinal. All superficial lymph pathways terminate at the confluence of the common jugular and subclavian veins.