Most disgusting human parasites

For the majority of us reading this a brush with a parasite will be a fairly unremarkable episode. Hey, we’ve all had head lice, fleas and the odd case of worms – oh, maybe that’s just me. The point is these are generally just an irritation and not much more.

The collection of human parasites I’ve compiled below might start off fairly tame but soon accelerates into the realm of pure horror; there are flies that can drill into your brain, worms that can live in your eyeball and  bugs that will put you to sleep forever. In theory a parasite has evolved in such a manner as to not kill its host, this would not be good for future generations. However, it seems that some of these miniscule monsters have not read the manual.

This list is possibly enough to convince many of you that there isn’t a God; or maybe these creatures are the result of intelligent design, but that designer is one sick puppy…

Some of you may be a little disappointed that I haven’t used the absolutely most gruesome pictures I could find. I’ll leave that to you now you are armed with a few names.

10. Bedbug

Bed bug

Bed bug (Cimex lectularius)

The bedbug is on the decidedly cuddly end of our most disgusting human parasites. These little insects are about the size of an apple seed and feed exclusively on blood, preferably human. You see that big straw like thing in the photo above, that’s for plugging into you and sucking your blood.

Whist a few people don’t seem too affected by bedbug bites for many it is somewhat like having masses of mosquito bites, and for others the bug’s saliva can trigger anaphylactic shock.

The bedbug is the most likely of this list of parasites that you will encounter. It was almost eradicated from the developed world back in the 1940s but unfortunately has made a comeback. One of the problems with these critters is how hard they are to get rid of. In the daytime they can hide in the tiniest of cracks, they can also stay hidden for months on end without feeding. You think you’ve got rid of them and then they suddenly reappear.

Whilst bedbugs may be a huge irritation to people think yourselves lucky you are not a female bedbug. Mating occurs through a process called traumatic insemination in which the male basically stabs the female in the abdomen to deliver his sperm.

Bed bugs get a place on this list partly as they give us a starting point, i.e. a 1 out of 10, and also because I had a nice photo!

9. Scabies mite


Severe case of scabies

Just the word scabies alone sounds pretty unpleasant making it ideal for the skin condition it describes.  Also known as the seven-year itch scabies results in intense itching and is contagious. It can occur virtually anywhere on the body, or across the whole body.

But itch as it might, and scratch as you will, it won’t help because scabies is caused by tiny parasitic mites living under the skin. So short of scratching your skin off it will keep on itching, so that’s what some people end up doing. This excessive scratching often results in secondary, bacterial infections which are far more of a health risk than the scabies itself.

Whilst normal scabies is an unpleasant experience, it is easily treated. However, a condition known as crusted or Norwegian scabies can occur in those with weaker immune systems. This hyper-infestation of mites can mean instead of a dozen or so there are actually millions of them crawling around under the skin.

8. Loa Loa

Eye Worm

Loa Loa eye worm

The nematode Loa Loa is our first (but not last) introduction to the worms. Although these little beast may be roughly the same shape as the worms you find in the garden that help the soil, that is pretty much where the similarity ends.

If you could think of a part of the body that you really didn’t want a parasitic worm to take up residence there is a good chance a lot of you would say the face or eye. Well, they don’t call it the “African eye worm” for nothing; infection with the loa loa worm (loaiasis) is often diagnosed by the presence of a worm in the eye. That’s a pretty horrific prospect as the adult worms measure between 3 and 6 cm (1.2–2.4 inches) long.

Apparently it can be quite painful as the worm slowly moves around, just under the surface of the eyeball. Perhaps the only consolation is that when they are clearly visible like this they can be surgically removed – a process which can be seen here.

As well as crawling around the eye the loa loa worm can spend many years crawling around under the skin. In fact these worms can live up to 17 years and will spend much of this time completely undetected – until one appears traipsing across the  inner surface of the eye. This means a person may become infected many years before they realise, such as a case I read involving a woman who had visited Nigeria 6 years previously.

7. Paralysis tick

Paralysis Tick

Paralysis Tick (Ixodes holocyclus) before & after eating / Photo: ©Bjørn Christian Tørrissen – License

The Australian paralysis tick is a typically unpleasant antipodean arachnid. This is Australia of course so it shouldn’t be much of a surprise that this little nasty possesses a potentially lethal venom.

Paralysis ticks spend much of their time perched on leaves with their legs outstretched waiting for something or someone to brush past at which point they grab on. As with other ticks when a suitable host is encountered they will burrow head-first into the skin and start feeding on blood until they look fit to burst (see photo).
Like other ticks, the paralysis tick can pass on a number of nasty diseases such as Rickettsial infections or Lyme’s disease. Unlike other ticks this one secretes a neurotoxin that is capable of causing death by paralysis which progresses to the lungs causing respiratory failure.

Up until 1989 there were 20 recorded fatalities from tick paralysis in Australia. Whilst am increased awareness of the risks has eliminated much of the danger posed there is still no antivenom for this tick.

In addition to the toxin the paralysis tick often provokes an allergic reaction; this in itself can be life-threatening to some.

6. Guinea Worm

Guinea Worm

Guinea Worm (Dracunculus medinensis)

The picture of someone pulling a metre long worm out of someone’s leg should be enough to explain why this revolting parasite is on our list.

The guinea worm infects its host (humans or dogs) when they drink water that is contaminated with water fleas containing the worms larvae. Whilst the flea is digested by stomach acids, the larva is set free and begins its journey by penetrating the host’s stomach or intestine wall. It will live here in the body cavity for around 3 months where it mates with other guinea worms.

After around a year the female guinea worms will have grown to over 50cm (18ins) in length and are ready for the last stage of their journey. From the abdomen the worm makes its way down through the pelvis and along the bones of the leg towards the foot. This is usually the first sign of guinea worm infection (or dracunculiasis) and can give rise to an intensely painful burning sensation along the chosen path.

At some point they will reach the skin where the worm emerges from a blister to release hundreds of thousands of larvae when it encounters water. This stage is equally painful and associated with complications including severe allergic reaction.
Although it is very unusual for dracunculiasis to cause death it can be debilitating. There is also a risk of secondary infections if the worm dies en route.

The good news is that this parasite’s days appear to be numbered. Back in 1986 there were an estimated 3.5 million cases throughout Africa. Last year only 22 were recorded.