SCRATCHING THE ITCH

It starts as an itch. The parasitic mite multiplies in a wombat’s skin, causing inflammation until fur sheds, leaving a bald patch. In the wild, where topical treatment is difficult on free-roaming animals, the disease will progress to severe skin wounds causing other health problems such as secondary bacterial infections and weight loss.

Without treatment, the outcome of sarcoptic mange is death.

Following promising field trials of a new drug in wild populations of bare-nosed wombats in New South Wales and Tasmania, University of the Sunshine Coast researchers are involved in a national effort to stop the spread of mange and save our wildlife.

Bald spots – more than skin deep

UniSC Senior Lecturer in Biomedical Science Dr Kate Mounsey has seen the terrible health impacts of the Sarcoptes scabiei mite in humans – from scalps to feet, people’s bodies covered with skin burrows, rashes, crusting, lesions. Immune systems debilitated.

For 20 years, her research in immunology, parasitology and drug resistance has focused on trying to alleviate the scourge of scabies, a tropical disease that is endemic in remote communities. Outbreaks are common in aged-care facilities, where management is difficult.

Even mild cases increase the risk of bacterial skin infections, which are linked to high rates of renal and rheumatic heart disease in Australian First Nations communities.

Scabies mite variants also cause disease in dozens of mammal species around the world, including dogs, pigs and wildlife.

When Dr Mounsey joined a ground-breaking collaboration between researchers, industry and government to improve control of the disease known as sarcoptic mange in the bare-nosed wombat of south-eastern Australia, she knew UniSC could contribute.

The collaboration, formed through an Australian Research Council Linkage Grant, includes the University of Tasmania, University of Sydney and UniSC, with partners from MSD Animal Health, WaterNSW, Bonorong Wildlife Sanctuary, Highland Conservation Pty Ltd, Hydro Tasmania and the Tasmanian Government.

Lead investigator Dr Scott Carver from the University of Tasmania says the exciting multi-disciplinary research has multiple aims, from identifying better drugs and treatment methods to examining the DNA of the mite itself, searching for ways to stop its transmission.

And that’s where UniSC is digging deep.

Mites under the microscope

For three years, Dr Mounsey and UniSC Professor of Pathophysiology Robert Harvey have been involved in the wombat project, supervising PhD student Kotaro Takano.

In the lab, they use state-of-the-art molecular techniques to analyse mite ion-channels, using biological samples of scabies mites collected from stricken wombats in the field trials down south.

“We are interested in the molecular genetics of Sarcoptes scabiei, to better understand how the mite responds to treatments used for both human and animal scabies,” says Dr Mounsey.

It is the first intensive study of these treatment receptor genes in the scabies mite, with a preliminary article led by Dr Mounsey and Professor Harvey published in the journal Parasitology Research.

The article raised concerns that high and repeat drug doses being administered to Vombatus ursinus (the bare-nosed wombat) in the wild were not proving effective in treating mange and could have negative side effects.

It concluded: “The causal factors behind treatment failures should be investigated as a matter of priority, as it is possible that moxidectin resistance is emerging in these mites infesting wombats.” Anecdotal evidence provided by wildlife carers supported this theory.

Concern about drug resistance in scabies mites is not isolated to wombats. Reports of resistance in human scabies are increasing around the world, complicating the limited treatments currently available.

Dr Mounsey says it is vital to understand the mechanisms behind any drug resistance, so new treatments and methods can be developed.

“For example, why don’t certain chemicals that kill other skin parasites work well in this instance? Are there application issues? Is drug metabolism a factor? Is something else happening in the mite at a cellular level?”

Professor Harvey, an expert in molecular neuroscience, explains that specific ion channels are the key targets of acaricides – the drugs that kill mites.

“As the ion channel genes are conserved between scabies mites isolated from different animal hosts, our research findings are directly translatable to human scabies,” he said.

“We are analysing mite ion channel sequences in the lab and are already seeing interesting variations in ion channel genes that could cause altered responses to certain drugs.”

Hope is emerging. A recently approved drug appears to be staying in wombats’ systems long enough to kill newly hatched mites and prevent them from reinfesting for a couple of months, potentially breaking the insidious cycle of mange transmission.

Clinical trials for longer acting drugs are beginning in humans as well, but counteracting drug resistance will be an ongoing issue.

For Dr Mounsey, whose own PhD examined drug resistance in human crusted scabies, it is fascinating to be applying her skills to a native marsupial species.

“The wombats with severe mange have clinical presentations that are similar to people with crusted scabies,” she says.

“Scabies is a devastating disease. The clinical progression to severe mange in both wombats and humans is still poorly understood and I think we can learn a lot by studying both.”

She pauses. “Humans in a hospital are a fair bit easier to treat than wombats in the wild, though.”

The chase is on for wombat conservation

One of the PhD students involved in the research collaboration, Kotaro Takano has witnessed first-hand the challenges of fieldwork involving stocky, clawed, possibly very sick animals that live in shared underground burrows and only forage at night.

Even for highly experienced wildlife carers, it’s not easy.

To treat a wombat with mange, the options are to creep close and use a long pole to pour medicine from a cup on to its back, or to create a false flap on its burrow that pours solution on its back as it leaves the hole.

To capture that wombat to collect mite samples for research requires more time, persistence and a really, really, big net.

But Kotaro is determined. He developed a passion for wombat conservation after moving to Australia from Japan more than a decade ago and completing a Master of Applied Science at the University of Tasmania.

He joined UniSC in September 2020 to research the genetic sequencing of ion channels involved in mange. The aim is to establish a system to directly study the responses of sequence variants in the lab.

Collaborators on the project include Cedar Creek Wombat Hospital in the NSW Hunter Valley, the University of Tasmania and The University of Queensland.

“The bare-nosed wombat is highly susceptible to mange,” he says, “and if left untreated, it causes a slow and painful death.” He points to a 94 percent decline in a population of the species in northern Tasmania’s Narawntapu National Park.

As Kotaro outlined in an interview with SBS Japanese, the key to future disease management is understanding what effects the chemicals are having on the mites’ genetic receptors, and whether that’s making them resistant to treatments.

What's Next

Since Dr Mounsey and Mr Takano presented their work at the 2022 Australian Society for Parasitology conference, the research has take a giant wombat waddle forward with a new grant from the NSW Government in June 2023 and the team publishing again, in the International Journal for Parasitology.

Preliminary findings are leading them closer to answers that could alleviate the pain of thousands of animals and improve treatments for human scabies.

“Wombats are one of Australia’s iconic animals and it’s terrible to see them suffering,” says Dr Mounsey. “UniSC’s combination of expertise in biomedical science, molecular neuroscience and animal ecology can contribute further to this major animal welfare issue.”