In early November 2022 authorities began to warn that this summer was likely to see a rise in tick numbers due to to widespread and persistent wet weather. At the same time, veterinarians were warning that the high number of domestic animals suffering tick bites was placing a strain on tick anti-venom supplies.
Now in 2023 the Australian Dept. of Heath has observed that globally in recent decades, “ticks have been expanding their geographic ranges largely due to climate change.”
Below is what might be described as a cliffs note on common ticks which bite humans in Australia.
Australian Government Dept of Health and Aging, Guidance Note: Introduction to Ticks, Australian Ticks and Tick-Borne Diseases and Illnesses, excerpt, January 2023:
Overview and summary
Ticks are parasites that feed off animal and human blood. Globally, ticks, along with mosquitoes, are recognised as the most important vectors in the transmission of bacterial and viral pathogens to humans and animals. Ticks transmit the most diverse array of infectious agents of any blood-feeding arthropod and have the potential to pose public health and biosecurity risks.
Globally, there are almost 900 species of tick, distributed into two main families: soft ticks (Argasidae) and hard ticks (Ixodidae). Of these nearly 900 tick species, only 28 species globally are recognised to transmit human pathogens, which include organisms such as bacteria, viruses and protozoa.
Hard ticks have a hard, flat body and elongated mouthparts with rows of backward pointing teeth. This group includes the most important species that bite humans. Hard ticks favour habitats with areas of vegetation, such as forests and fields where females lay eggs on the ground, however, they may also be found in urban areas if there are unoccupied patches of grass.
Soft ticks have a wrinkled leathery appearance. Only a few species of this type are found in Australia, and they rarely come into contact with people. Soft ticks generally favour sheltered habitats and will hide in the nests of hosts or areas where hosts rest.
While ticks and tick-borne diseases are often limited to specific geographical regions, they may be potentially found anywhere in the world, with international travel from endemic regions to non-endemic regions by people, animals and cargo, potentially transporting ticks.
In recent decades, ticks have been expanding their geographic ranges largely due to climate change.
Australian ticks and tick-borne illnesses
In Australia, there are over 70 species of tick, 66 of which are endemic to Australia. Five species were introduced by humans with domestic animals (‘exotic’ ticks), which result in economically important diseases restricted to domestic animal hosts. None of the exotic ticks typically bite or feed on humans.
Of the tick species endemic to Australia, 17 may attach and feed on humans, but only six of these ticks are able to act as competent vectors for the transmission of pathogens to humans. Apart from the occasional local bacterial infection at the tick bite site (eschar) the only two systemic infections that are definitely known to be transmitted by tick bites in Australia are rickettsial infections from infection with Rickettsia spp.(Queensland tick typhus (QTT), Flinders Island spotted fever (FISF), and Australian spotted fever (ASF)), and Q fever (Coxiella burnetii).
Two additional species of Rickettsia (other than those that cause QTT, FISF and ASF) have been identified in Australian ticks and may be considered potential pathogens, although their presence in febrile patients has yet to be confirmed. These new species are Rickettsia gravesii and Candidatus Rickettsia tasmanensis.
The species of Australian ticks known to bite humans and transmit bacterial infection are:
• the Australian paralysis tick (Ixodes holocyclus), which is endemic on the east coast of Australia and causes QTT due to Rickettsia australis and causes Q fever due to C. burnetii
• the common marsupial tick (Ixodes tasmani), which occurs in New South Wales, Queensland, South Australia, Western Australia, Tasmania and Victoria and causes QTT due to R. australis and causes ASF due to Rickettsia honei subsp. Marmionii
• the southern paralysis tick (Ixodes cornuatus), which occurs in New South Wales, Victoria and Tasmania and causes QTT due to R. australis
• the ornate kangaroo tick (Amblyomma trigutattum), which occurs throughout much of the central, northern and western Australia and causes Q fever due to C. burnetii
• the southern reptile tick (Bothriocroton hydrosauri), which occurs mainly in southeastern Australia and causes FISF due to R. honei
• the Haemaphysalis novaeguineae tick (no common name), which causes ASF due to R. honei subsp. Marmionii.
Three of the 66 species endemic to Australia are well-known for biting and feeding on humans - the Australian paralysis tick (I. holocyclus), the ornate kangaroo tick (A. triguttatum), and the southern reptile tick (B. hydrosauri).
In Australia, most tick bites pose no medical problems if the tick is safely removed. Tick bites can lead to a variety of illnesses in patients, with the most common being allergic reactions. The Australian paralysis tick is the most medically significant tick in Australia and is
responsible for over 95% of tick bites in humans in eastern Australia and for most tick-borne illnesses in Australia. The Australian paralysis tick can cause several illnesses, severe allergic reactions (anaphylaxis), mammalian meat allergy (MMA), paralysis, and death.
While tick bites in Australia can lead to a variety of illnesses in patients, as indicated above, much about Australian ticks and the [non-allergic] medical outcomes following tick bites remains unknown and requires further research…..
In Australia, no definite tick-borne viral infections of humans are known, although a new tick virus has recently been isolated (Graves, unpublished).2
2 Unpublished at the time of publication of this Guidance Note. Provided by Graves, S. R., April 2021
