Last year, I went on a fungi foray near Pennyroyal Creek, north of Lorne.
At the bottom of a steep gully in a dense, ferny forest we found a couple of uncommon fungi species. When I arrived home I found something else uncommon – a tick on my leg. It was easily brushed off I wanted to identify it, but there were no reports of human-infecting ticks in the Otways, so I sent pictures to the Museum.
They asked for the specimen, which I sent, and I received the following reply:
I showed it to one of the Curators in Entomology and he said it is a male. The hypostome (mouthpart) is broken but he believes it is most likely Ixodes holocyclus, which would be unusual for the Otways. Had you recently been to the east of the state or had anyone visited?
The answer was ‘No’, so it appears that we have an unrecognised population here, and an adult male targeting a human (see edited Wikipedia information below).
Ixodes holocyclus, the Australian Paralysis Tick, is one of about 75 species of Australian ticks and is considered the most important medically. It can cause paralysis by injecting neurotoxins into its host. It is usually found in a 20-kilometre wide band following the eastern coastline of Australia, as far west as Lakes Entrance.
There are reports of paralysis ticks from inland Victoria, including north-eastern suburbs of Melbourne. This may reflect general movement of insects and ticks from equatorial to polar latitudes which in turn may be related to global warming. They are found in many types of habitat, particularly areas of high rainfall such as wet sclerophyll forest and temperate rainforest. The native hosts for the paralysis tick include koalas, bandicoots, possums and kangaroos.
The life cycle of Ixodes holocyclus consists of 4 stages – egg, larva, nymph, adult. The larvae and nymphs are neither male nor female. Ticks hatch as six-legged larvae after an incubation period of 40 to 60 days. Larvae search for a blood meal from a host, feed for four to six days, then drop from the host and moult to become an eight-legged nymph. Nymphs require a second blood meal before they can moult again to become an adult. Female adults then require a further blood meal of up to ten days before dropping off to lay up to 3000 eggs in leaf litter. The female tick dies 1–2 days after egg laying is complete. Male adults will search for females on the host for mating, and to parasitise the females for blood meals. Adult male ticks rarely blood-feed on a host. The male dies after fertilising the female although some males can endure for longer if they parasitise the engorging female. The whole cycle takes around a year to complete.
Ixodes holocyclus has no eyes. To find a host, the ticks climb onto vegetation and wave their forelegs slowly until a host comes within reach. When on the host, they may not attach immediately, but wander for up to two hours until attaching on the back of the host’s head or behind an ear. Certain stimuli, such as carbon dioxide, heat and movement initiate questing behaviour. A fully engorged tick may be anywhere from 200 to 600 times their unfed body weight and may stay on a host for up to three weeks without the tick being significantly engorged or causing paralysis.
To feed, the tick cuts the skin and a small pool of blood is formed. The hypostome is inserted, which also anchors the tick by its reverse barbs. It can break off during tick removal, causing a local reaction (I still had a red mark on my leg after 6 weeks). During feeding, the liquid portion of the meal is first concentrated and then injected back into the host. The kinds of effects caused by bites of Ixodes holocyclus vary in their frequency according to the type of host and whether the tick is at the stage of larva, nymph or adult.
- Humans are most notably affected by local irritation, allergic reactions and tick-transmitted infectious diseases. Tick paralysis is possible but now uncommon.
- Domestic animals (pets and livestock) are most notably affected by tick paralysis. Allergic reactions and tick-transmitted infectious diseases are possible but rarely diagnosed.
- Native animals are most notably affected by anaemia caused by carrying heavy burdens of ticks drawing large quantities of blood. Tick paralysis may occur, but is mainly recognised in captive animals following a discontinuity in exposure and so a drop in immunity.