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Blood suckers of the crawly kind

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29th Oct 2013
Professor Rick Speare   all articles by this author

PROMPT attention to leeches will minimise distress and more serious sequelae.

The discovery of the blood always comes as a shock.

The bleeding point is usually on the legs below the knees. It runs down the appendage in a wavering stream (Figure 1).

Figure 1: Twin bleeding points on the anterolateral aspect of the left lower leg of a bushwalker on the Atherton Tableland, North Queensland. Both leeches had departed the feast and were not found. Bleeding continued for at least four hours. 

If the victim is wearing shoes and long pants, the first indication of haemorrhage may be a squishy feeling as blood pools in the sock between the toes.

The inexperienced bushwalker may be horrified and mystified if no culprit is in sight. If the blood is wiped away, one finds a small lesion (about 1—2mm in diameter) that continues to bleed. Closer inspection shows it to be a V or Y shaped cut. Leeches!

Leeches are annelids that are sanguivorous micropredators, i.e. blood-sucking worms (Figure 2). Since they can imbibe up to 10 times their original weight, a meal of 1—5ml is not unusual.

Figure 2: Blood-engorged leech.

Leeches feed infrequently, one meal may do them for a year. Leeches secrete a cocktail of chemicals in their saliva to facilitate blood flow and interfere with blood clotting.

The two most interesting compounds are hirudin, which is a potent antithrombin, and calin, which prevents platelet adhesion to collagen and inhibits platelet aggregation. After the leech has dined for 10 minutes or so and departed, the wound continues to ooze blood. Bleeding can be very persistent. Ten hours is reported as the average time that oozing persists. However, there have been reports of bleeding lasting a week.

Effects are local, confined to the bite site. However, there is a case report from Turkey where a man had 130 leeches (he was immersed in a pond for an hour) and developed acute blood loss, followed by haemorrhagic diathesis.

Some people develop an itchy, erythematous papule at the bite site over several days. It persists for weeks. I suspect this is a delayed type hypersensitivity reaction. Do not scratch!

Leeches are usually found on the legs because they crawl inchworm-like along the forest floor and up low vegetation.

Transfer to a human typically occurs via the feet or legs. However, they can gain access at different points.

A spectacular site of attachment is the eye, where they feed off the conjunctiva. I still recall a terrifying experience due to a leech in my eye when I had slept in a tent in the North Queensland rainforest.

The leech was a challenge, but the worst part was my zoologist colleague’s trembling hand when he approached my eye with a pair of rat-toothed forceps in an attempt to remove the beast!

He was successful — my eye survived, but I had spectacular bloody tears for at least half a day. Subconjunctival haemorrhage will also be present. Other unusual sites include the vagina (a very rare cause of intermenstrual bleeding), the external ear canal, and in some parts of Asia the pharynx.

Leeches are not vectors for nasty pathogens.

Leeches on the skin are easy to remove — just pull them off. Leeches are tough with a rubbery feel. The mouthparts will not be torn off. The story of mouth parts being left behind after manual removal is a complete myth.

If a person is squeamish, salt can be applied directly to the leech. It rapidly contracts, disgorges your blood and falls off. Warn patients against heroic measures, particularly no burning with cigarettes, cigarette lighters or matches.

Wash the bite site, use an antiseptic if you wish (but natural bites very rarely become infected) and apply a small absorbent dressing.

The bleeding will persist until all the active salivary chemicals have gone. In the eye, apply lignocaine drops, the leech becomes paralysed, and it can be more easily removed.

Keeping the predators at bay? Trials have actually been done on leech repellents. DEET, a commercial insect repellent, is very effective. DMP, another insect repellent, works but less well. A range of plant-based products, including oil of callistemon, are comparable to DMP.

One application of DEET to cloth will keep leeches off at least seven days. When walking in rainforest, I apply DEET to my lower legs and also use it on my boots and socks.

Terrestrial leeches are widespread in rainforests in Australia and Asia. They are not confined to the tropics; even Tasmania has leeches. In endemic areas they are particularly active when it has been raining and not common when the forest floor is dry. Leeches also lurk in freshwater ponds .

And for those people contemplating self-administering natural leech therapy as a pick-me-up, count your leeches. You don’t want to end up as a case report like the Turkish gentleman!

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