The Worst Human Parasites You Never Want To Have

The Worst Human Parasites You Never Want to Have

Humans have known about harmful parasites since the times of Ancient Egypt, but they’ve been around for much longer than that. Most creatures are susceptible to them and, fortunately for us, not all of them are all that interested in hitching on (or in) the human body. Take the tongue-eating louse… It makes its way into a fish via the gills, severs the fish’s tongue, and replaces it. It’s pretty grotesque stuff.

But, there are plenty of parasites out there which do have humans in their sights – and some of them are especially nasty.

The gross out antics of something like the tongue-eating louse are clearly attention grabbing, but not all parasites are quite as theatrical – not that that makes them any less horrific. Malaria is arguably the most famous parasite disease, transmitted through the bite of a mosquito carrying one of the Plasmodium parasites. The Plasmodium starts off in the mosquito’s saliva, before making its way via the bite into a human’s bloodstream. From there, it travels to the host’s liver, reproduces, infects the host’s red blood cells and causes them to explode. It’s a painful and potentially lethal process which ultimately releases yet more parasites to infect yet more red blood cells.

Another major mosquito-borne disease is lymphatic filariasis, or elephantiasis. Here, the mosquito is infected by one of three types of microscopic roundworm – which, in turn, infect the host’s lymph nodes. These worms ruthlessly block the flow of lymph (a chief transporting fluid in the body) around the lymphatic system, which causes lymphedema, a condition where unwanted fluid retention sees limbs dramatically swell. Over time, affected limbs can bulge to an enormously unnatural size and, in keeping with its ‘elephantiasis’ name, the skin hardens. In the most severe cases, the condition leaves a patient unable to perform simple day-to-day tasks like walking. Thankfully, there are treatments to stop the spread, with medicines leaving the worms to die off inside their host. It all sounds fairly stomach-churning, and in truth it really is.

Another parasite-packing insect that causes serious problems is the New World screwworm fly. While the initial screwworm is usually hatched in or near an existing wound, this worm’s maggots can (and do) eat away at live, previously healthy flesh to burrow their way into our bodies. For a carrier, the first sign of trouble is a foul-smelling, reddish-brown discharge oozing out from the bitemark. Again, if you’re infected by these then it is treatable – this time by manually removing the maggots with tweezers – but if left untreated for even a short while, it isn’t pretty… with maggots digging deeper and deeper, eating away at your muscle tissue, literally stripping the flesh from your bones. The positive is that screwworm infestation is very rare in humans, with the US completely eradicating it in 1982 – although there have been outbreaks since.

Another worm that’s today fairly rare is the Guinea worm – but it’s another that you definitely don’t want to carry! Guinea worm disease, or Dracunculiasis, is transmitted via water fleas. Contaminated water is drunk by an unsuspecting human – fleas and all – and the larvae are released, setting out to penetrate the abdominal organs. However, with the Guinea worm it takes up to a year before symptoms really start to show, meaning victims unknowingly carry it with them for months. In this way, it isn’t that dissimilar to the tapeworm – a much more common, though also pretty repulsive parasite.

Eventually though, and quite horribly, the Guinea worm shows itself by travelling under your skin (usually toward your feet) and bursting out of newly-formed blisters. The painful process is often described as being a fiery, burning sensation and, as female worms can grow up to one meter in length, removing them is not for the faint-hearted. In fact, removing them isn’t even advised – on account of the serious complications a broken or dead worm can cause. Rather, you should wait for the worm to slither its own way out, but that can take up to three months!

Theoretically, lots of parasites can be kept at bay as long as you have access to clean drinking water. But, by no means all of them. And, you don't always have to actually take a drink to run into serious trouble.

The Naegleria fowleri is otherwise known as the ‘brain-eating amoeba’, so clearly it’s extremely concerning for anyone who encounters it. Technically speaking, it is an amoeba rather than a parasite, but it’s ruthlessly parasitic in nature. And, most worryingly, you only need to get water in your nose for this thing to spread into your body, so it can be picked up while swimming or washing. Given that it’s often found in warm, fresh water (including at hot springs) and in unchlorinated swimming pools, the danger is obvious.

Once Naegleria fowleri makes contact it enters the nasal nerve tissue and heads straight for the brain. Once there, it spreads out, eats away at the victim’s nerve tissue, consumes brain cells and multiplies rapidly as Naegleriasis sets in – a rare but almost always deadly brain disease. Symptoms usually show within a week, when hosts experience headaches, fever, and a stiff neck, before suffering widespread confusion, hallucinations and a total loss of balance. Death swiftly follows, as Naegleriasis has a fatality rate of over 95%. There have only been seven recorded survivors since the 1960s.

Finally, we’ll stick with the head, but move to the eyes. Eye parasites are also extremely rare, and they’re not usually specifically aiming for your eyeball – but, in fact, they just end up there. However, for anyone who has experienced the horrendous ordeal of fishing a worm from beneath their eyelids, it surely ranks as one of the worst things that can happen. Amongst others, there have been reported cases of the cattle eyeworm plucked from human tear ducts, but as the name suggests, they’re more commonly found in other animals. The African eye worm poses a different problem, in that it does search for a human host, but its presence in the eye is more a by-product of the fact that it moves (as in, literally moves beneath the skin) all around the body – it’s just that the eye is where it’s most easily taken out. In the worst cases, eye worms can cause permanent blindness, and their presence can be indicative of wider-reaching issues leading to severe disease or death. In general, the idea of any type of organism crawling out of your eye is perhaps the clearest picture of the revulsion that these things can cause.

Overall, parasites get a pretty bad press – but for good reason. And perhaps the most frightening things about them are the variety that there is, and how easily they can be picked up – even though most are fairly rare. They’ll eat at your muscles, lodge in your stomach, or slither out of your eye sockets – proving that they really are some of the grossest but also most dangerous creatures on the planet.