Tick Diseases

Ticks are blood-sucking parasites and tick-borne infections are an emerging disease problem worldwide. Australia is home to nearly one hundred known tick species, most of which have evolved over millennia as parasites on our wildlife and exist in unique ecologies all around the country. In addition, tick species such as Rhipicephalus (Boophilus) microplus (the cattle tick), Haemaphysalis longicornis (the bush tick), and Rhipicephalus sanguineus (the brown dog tick), introduced to the Australian continent with European settlement, are the vectors responsible for the transmission of tick fever (in its broadest sense) to cattle and dogs.

A few of the tick species in Australia also regularly bite people. Humans are most usually exposed to ticks when they or their companion animals encroach on habitats where ticks coexist with their natural wildlife hosts, which are the reservoirs for potential pathogens. People with rural occupations (farmers, foresters, rangers) and with recreational pursuits (orienteering, hunting, gardening) in areas of high tick endemicity are at particular risk of contracting tick-associated disease. Human activities contribute to the impact of vector-borne diseases by increasing vector density (urbanization, dam construction) or by introducing pathogens into areas in which they had been hitherto absent.

Ixodes holocyclus, the paralysis tick of eastern Australia, frequently bites people and is a serious pest, each year causing an estimated 100,000 cases of tick paralysis in livestock and companion animals (mainly dogs) in NSW and Queensland. In Western Australia it seems that the kangaroo tick (Amblyomma triguttatum) is most often incriminated in tick bites and reactions in people.

Ticks cause allergic reactions and two tick-borne diseases of people are well recognised in Australia; Queensland tick typhus and Flinders Island spotted fever, both rickettsial infections transmitted by native Australian tick species, including I. holocyclus. However, concern regarding the potential for other tick-transmitted infections in Australia has increased in the last few years with descriptions of new and hitherto unrecognised pathogens. New rickettsiae and Bartonella bacteria have been isolated in ticks from native and feral animals around Australia, zoonotic babesiosis (Babesia microti) known previously only in the Northern Hemisphere was reported in 2012 in a person with no travel history who had lived on the NSW south coast, and type B tularaemia was reported in September 2012 in two Tasmanians. Of concern also are recent clinical reports of Borrelia, Bartonella, Anaplasma and Ehrlichia infections among some people living in coastal New South Wales and Queensland.

Peter Irwin 2012