Parasitism by Ophidascaris robertsi with associated pathology findings in a wild koala (Phascolarctos cinereus)

Abstract

Five third-stage Ophidascaris robertsi larvae, a python parasite, were recovered from a free-ranging mature male koala, Phascolarctos cinereus, from South-East Queensland. Most larval nematodes were found obstructing several hepatic blood vessels including the portal vein, causing vascular dilation. Despite the low number of parasitic larvae found, the large size of the larval third stage can lead to circulatory impairment of affected organs. Koalas may acquire O robertsi infection possibly by performing geophagy or soil ingestion, contaminated with eggs from python faeces. This is the first report of O robertsi in koalas indicating infection and subsequent pathological changes within the vasculature and liver.

A Necropsy Study of Disease and Comorbidity Trends in Morbidity and Mortality in the Koala (Phascolarctos cinereus) in South-East Queensland, Australia

“…In the current study, the use of systematic necropsies in passive surveillance increased the sensitivity of disease detection and accurately determined comorbidity patterns compared to a previous analysis using medical records where only brief notes on disease were recorded in some animals. Further, systematic necropsies allowed the characterization of several novel diseases and lower frequency etiologies of infectious, neoplastic or idiopathic disease 10,11,15,16 .…”

The ghost of hosts past: impacts of host extinction on parasite specificity

“…However, future host extinctions are likely to trim away internal branches among hosts of O. robertsi leading to increased phylogenetic distances, while all of the marsupial hosts of N. intermedium will be lost and lead to greatly increased phylogenetic specificity. Although the number of projected host extinctions is high, the ecology of O. robertsi may be relatively unimpacted as extinctions do not prune large swathes of the host tree, multiple sister taxa are projected to survive, and mammals are only intermediate hosts for this parasite which uses pythons as a definitive host [ 107 ]. However, as N. intermedium uses mammals as definitive hosts, the large phylogenetic distances between Australian eutherian rats and marsupial hosts could mean that the projected extinction of the Dasyurus hosts will dramatically shift the selective landscape of the parasite.…”

The ghost of hosts past: impacts of host extinction on parasite specificity

“…However, future host extinctions are likely to trim away internal branches among hosts of Ophidascaris robertsi leading to increased phylogenetic distances, while all of the marsupial hosts of N. intermedium will be lost and lead to greatly increased phylogenetic specificity. Although the number of projected host extinctions is high, the ecology of O. robertsi may be relatively unimpacted as extinctions do not prune large swathes of the host tree, multiple sister taxa are projected to survive, and mammals are only intermediate hosts for this parasite which uses pythons as a definitive host (Gonzalez-Astudillo et al 2019) . However, as N. intermedium uses mammals as definitive hosts, the large phylogenetic distances between Australian eutherian rats and marsupial hosts could mean that the projected extinction of the Dasyurus hosts will dramatically shift the selective landscape of the parasite.…”