Andrew Walker

Characterising venom toxins of veterinary importance in Australia

Several Australian invertebrates cause serious harm to pets and livestock through the production and delivery of potent venom toxins. Despite their economic importance, the mechanisms by which these toxins work are unknown. This project aims to elucidate the mechanism of action of toxins produced by two species of venomous invertebrates, the Australian paralysis tick Ixodes holocyclus and the Australian processionary caterpillar Ochrogaster lunifer, with a view to the development of strategies to limit their impact.

I. holocyclus is a major threat to our pets and livestock, affecting >10,000 dogs and numerous other animals each year, resulting in hundreds of animal deaths and massive veterinary costs. It is highly prevalent on the densely populated east coast, and it is the most common species of tick to parasitise pets and livestock in Australia. I. holocyclus injects saliva or venom containing paralytic neurotoxins that delay or prevent host detection and removal. A single tick will kill 99% of dogs if allowed to feed for more than three days, with a characteristic onset of paralysis on the fourth day, followed by limb paralysis, systemic and respiratory paralysis, and death if the tick is not removed. One group of disulphide-rich peptides, the holocyclotoxins (HCTXs), has been isolated from salivary gland extract and is proposed to constitute the relevant paralytic neurotoxins. However, the molecular mechanism by which HCTXs act is unknown.

The processionary caterpillar O. lunifer causes contact dermatitis and severe allergic reactions in mammals. The responsible structures are venom-filled urticating hairs that are tiny (~100 µm long), spear-shaped structures. These setae are also the causative agent of equine foetal loss syndrome (EAFL), a condition in which pregnant mares that ingest setae abort their foetuses. However, the function of O. lunifer venom toxins, and if they contribute to EAFL, is unknown.

This project would focus on determining the mode of action of either I. holocyclus or O. lunifer venom peptides, using techniques such as peptide synthesis or heterologous expression, electrophysiology, mass spectrometry, confocal microscopy, biolayer interferometry, and nuclear magnetic resonance.