LEFT: Australian Paralysis Tick before & after feeding.
Image: WikipediA
RIGHT: Southern Paralysis Tick. Image: iNaturalist
LEFT: Ornate Kangaroo Tick. Image: WikipediA
RIGHT: Common Marsupial Tick. Image: shire.science.uq.edu.au
LEFT: Southern Reptile Tick (Male). RIGHT: Southern Reptile Tick (Female).
Images: Tasmanian Arachnids
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