A project undertaken at The University of Sydney, and supervised by Prof Peter Banks.
Parasite ecology is by far least understood of the main ecological interactions in Australia. While there is much interest in the medical dimensions of problem parasites, the ecological drivers of parasite abundance and distribution are complex and poorly known. Ticks are a diverse group of ectoparasites that feed on wildlife and can cause debilitating health issues for people and pets especially in peri-urban areas. Yet, we have limited knowledge how host abundance and behaviour affects tick survival and persistence in novel urban ecosystems.
The major tick of health concern, the Australian paralysis tick (Ixodes holocyclus), is a generalist and can feed on many species. Our recent work shows that introduced black rats (Rattus rattus) are abundant in urban tick hot spots, host high numbers of juvenile Australian ticks, and may play a key role in driving urban tick dynamics.
Figure 1. An introduced black rat (Rattus rattus) in urban bushland of Sydney. Image credit: Henry Lydecker
Three decades of research into tick ecology in the Northern Hemisphere has unlocked a detailed understanding of how different wildlife hosts contribute to the tick life cycle. This has enabled targeted tick management strategies, such as population control or the use of bait boxes that administer topical repellent, that focus on the most important hosts for each tick life stage (larva, nymph, and adult). Such strategies are impossible in Australia and native bandicoots are mistakenly considered the “main” tick host to become a scapegoat for urban tick problems.
In this project, we study the role of black rats in urban tick dynamics to understand how an abundant invasive species shapes parasite ecology. Black rats are common in peri-urban bushland and backyards where residents regularly encounter ticks. However, we lack the knowledge required to make evidence-informed decisions around managing ticks.
Figure 2. A cluster of engorged nymphs (in black circle) on the neck of an anaesthetised black rat (left) and a larval Ixodes tick under the microscope (~0.8mm) (right).
Our project tests three key hypotheses:
1) That black rats amplify local tick populations (or alternatively act as ecological traps through grooming)
2) That black rats move regularly between bushland and backyards
3) That a local rat removal program will lead to a reduction in tick abundance
Solutions to prevent tick-borne public health risks are embedded in our understanding of tick ecology. By testing these hypotheses, we will definitively reveal the importance of a global commensal in maintaining urban tick populations, inform management of black rats in urban bushland by studying their movement and determine whether large-scale rat control is a viable tick management strategy.