A survey of ticks (Acari: Ixodidae) from an over-abundant koala (Phascolarctos cinereus) population in south eastern Australia, with an overview of the ticks and mites of koalas
Kwak, ML & Reed, J 2017, Experimental & Applied Acarology, vol. 73, pp. 109-114.
Koala health surveys undertaken at Cape Otway in Victoria in 2016 revealed that ticks are prevalent in this over-abundant koala population. A total of 1036 ticks (of the species Ixodes tasmani) were found on 159 female koalas, and every sampled female was found to have ticks present. The average infestation intensity was estimated to be 6.6 ticks per animal and there was, in general, more female ticks than male ticks found on the host. None of the animals exhibited signs of health stress or anaemia, suggesting I. tasmani may not have adverse health effects on the koalas in this region.
Parasites play a regulating role in the populations of their hosts. Ticks and mites are two ectoparasites commonly found in Australian mammals. Ticks in particular are known to be carriers of harmful pathogens, thus it is important to understand how they interact with their koala hosts, and what consequences there may be, especially where koalas are over-abundant. In the current study, all sampled koalas were found to be only infested with I. tasmani, a widely distributed Australian tick. Although this species of tick is known to carry a number of pathogens (e.g. protozoan Theileria peramelis, filarial nematode Cercopithifilaria johnstoni and Queensland tick typhus virus) and a high infestation prevalence and intensity was noted in this study, health assessments indicated that none of the sampled koalas were suffering from anaemia. To date, studies on tick-koala interactions have been very limited, and the health effects have not been clearly identified. It has been reported that other tick and mite species, if occurring in large numbers on malnourished koalas, may affect haemoglobin synthesis. In rare cases, infestation of itch mites (Sarcoptes scabeiei) may also cause sarcoptic mange in koalas.
As koala over-abundances increases in some parts of Australia, the increased dispersal and social interactions among individuals and populations may benefit the rate of parasite transmission and ultimately lead to outbreaks, which can be problematic for koala conservation. Currently, very little is known about the ecology and life cycle of ticks and mites, as well as the causes of outbreak and impact on the host. Further research will be required in order to address all the questions emerging from this study.
Summarised by Cherie Chan
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