Its been some while since I posted an article on parasitic nematode worms. So, in response to almost no demand, here’s another article, on another, equally if not more so nasty, nematode worm which can, quite easily, turn your life into hell.
Onchocerca volvulus is possibly one of the more unpleasant worms out there. Its a species found in the Nematode phyla, that group of worms that live almost anywhere. Unfortunately, where O. volvulus prefers to live is inside people.
Like many parasites, the life cycle of this worm takes several stages. The bite of (usually) a fly found in the Simuliidae order of flies transmits the larvae to the host. The larvae then burrow through the flesh (which is a term which has never, ever been heard in a good context) and mature into adults into the subcutaneous tissue. A thick, collagen-rich nodule then forms around the adults, and, usually, the adults themselves do not cause much trouble, even though they can live beneath the skin for up to fifteen years, which top experts agree is fifteen years too long for a parasitic worm to be living underneath your skin. (Weirdly, I’ve been unable, to find any evidence on what the worms live on whilst living in your body; but presumably they feed on you in some way.)
The problem comes when the worms reproduce. The males wriggle through the subcutaneous tissue until they encounter one of the larger females. They mate, and then the female can produce up to 3000 larvae (technically microfilariae ) per day. (The number varies a lot depending on which source you look at, and whether they are counting total produced or total released into the host. Ed.) And, to spread to a new host, these larvae must be taken up when the Black Fly takes another blood meal. So they migrate upward, and a few of them will be taken up by the Black Fly when it next bites. They will then mature into the second larval form whilst in the fly’s gut, and then, when the fly bites another human, the larvae enter the bloodstream and the whole appalling cycle begins again.
The problem comes when the larvae don’t get taken up – and as each female can be producing 3000 microfilariae a day, there can be quite a few which are not taken up. The larvae live for just under two years, and then they die. And, ironically enough, its only when they die that the infected person’s problems really start. Similar to a really severe allergic reaction, the host’s own immune system swings into action as it detects the foreign objects within the body. What drives the severity of symptoms seems to be a) the ‘strain’ of O. volvulus you’re infected with (the ‘Savannah’ strain is, apparently, the most virulent one) and b) the characteristics of your own immune system, where a stronger immune system response leads to worsening symptoms. Weirdly, the amount of parasites inside you doesn’t appear to have much much of an effect – indeed, many people who are worst affected actually have low parasite loads compared with people with less severe symptoms. Possibly, an immune system which reacts more strongly to the parasite will kill off more of them…leading to more dead microfilariae and thus exasperating the immune response.
(There’s actually quite a bit of evidence to suggest that Wolbachia, one of the stranger symbiotic bacteria out there, doing everything from feminising male arthropod offspring to straight up killing them, is also involved. It appears that this bacteria is present in all worms, at all stages of the life cycle, and worms that have had these symbionts remove reproduce less and cause a lower immune system response inside humans. Additionally, the Savannah strain appears to have higher levels of Wolbachia in it, which could explain why this strain of the disease is more severe and more likely to lead to blindness. Ed.)
So what are these symptoms? Well, they vary considerably. Some people don’t get anything.
And then again, some people do. Itching is common; but the word ‘itching’ doesn’t really give the right impression. Think of it more as an overall burning feeling; which isn’t relieved no matter what you do, caused by your own body’s reaction to dead nematode larvae inside you. Its so bad that, frequently, people can’t get to sleep and children’s schooling is ruined as they simply can’t concentrate. It drives people to some pretty desperate measures.
Plantation workers heat up machetes until they glow red hot and press them against their bodies, whilst other people have tried pouring boiling water over themselves to get some relief. Others end up scratching themselves so badly they they bleed and become vulnerable to infection; or smash clay pots and scratch themselves with the shards. Reportedly, some people have even committed suicide over the constant itching.
This would be rather nightmarish on its own, but sadly the itching is only scratching the surface (really dude? REALLY? Ed.) of it. Depending on the severity, you can acquire a wide range of unpleasant skin diseases. These range from slight swellings of the skin, to loss or gain of pigmentation (sometimes called leopard skin), skin roughness and crustiness (also sometimes called ‘lizard skin’), the skin loosing elasticity and hanging loose from the body, leading to comparisons with cigarette or tissue paper, as well as the condition ‘hanging groin’, which frankly I do not want to think about too closely. Whilst this is certainly unpleasant on its own, it also leaves you more vulnerable to other infections, as well as, of course, leading to all the social problems which come with having a severe skin deformity.
Oh, and you can also go blind.
Yes, I probably should have started with that.
You see, the larvae are not just present in the skin – they can also migrate into the eyeball, because having worms in just your skin isn’t horrible enough, apparently. Once there, they can die, resulting in inflammation. Initially, this is temporary, but as time goes on, this inflammation leads to a loss of vision, and finally, complete and irreversible blindness. Currently, some thirty five million people are thought to be infected, and 300,000 have been permanently blinded by the disease, with another 500,000 suffering some visual impairment.
O. volvulus is mostly found in Sub-Saharan Africa, making it easily the regions 429th most pressing issue. Due to other, even worse issues facing many countries in that area, getting rid of it is not exactly easy.
Currently, the most successful treatment is Ivermectin, which doesn’t kill the adults but does cause them to stop releasing larvae, as well as actually killing the larvae themselves. In a slightly heartwarming revelation, because by this point in the article you probably need one, this drug is provided free by Merck, one of the world’s largest drugs companies.