Death wriggling in your eyes

The Loa Loa ‘eye worm’ deserves more attention from the media, given the suffering it causes.


Loa Loa is a filarial nematode or ’roundworm’ that is found throughout the forests and swamps of western Africa, most commonly in Cameroon. It is sometimes known as an ‘eye worm’ and ranges from between 20mm to 70mm in length. It is a parasite whose larvae are thought to currently infect about 12 to 13 million people worldwide.

Its larvae mature beneath the skin and cause the disease Loa Loa filariasis. The symptoms include red itchy swellings in the arms and legs, called Calabar swellings. Patients may also develop cysts in connective tissue of tendons, making movement difficult and painful. However, the most disturbing feature of this parasite is its tendency when fully developed to migrate through the tissues beneath the skin and move into the eye. Here, the unfortunate patient can often clearly see the creature as well as feel its movements across the white portions of the eye (sclera). Whilst this is not normally known to affect vision, it can cause pain and irritation during the fifteen or so minutes the worm takes to travel across the eye.

So how would one become infected by this charming little creature? The infection vectors (organisms which transfer infection between hosts) for this parasite are the fruit flies, Chrysops. The initial stage in transmission is for the fly to bite an infected human and ingest a “microfilariae”, which is an early stage in the development of the parasite. This then develops into a larva within the body of the fly and travels to the proboscis (tubular mouthparts). When the fly bites another uninfected individual, the larva penetrates the skin and will develop into the mature worm, which will go on to cause its unpleasant effects.

Fortunately, treatment does exist to combat the Loa Loa. The drugs diethylcarbamazine and ivermectin can be used to treat patients or as potential preventative methods, though no vaccine has been developed. Use of insect repellents and mosquito nets can decrease the incidence of insect bites and therefore reduce transmission. However, there are currently no plans in place for long term elimination of the Chrysops fruit flies. Surgical options do exist but are not ideal due to their limited window of opportunity.

Interestingly, David Attenborough often responds to questions about his philosophical and religious outlook by giving reference to the Loa Loa, with some variation on the following quote: “My response is that when Creationists talk about God creating every individual species as a separate act, they always instance hummingbirds, or orchids, sunflowers and beautiful things. But I tend to think instead of a parasitic worm that is boring through the eye of a boy sitting on the bank of a river in West Africa, that’s going to make him blind. And I ask them, ‘Are you telling me that the God you believe in, who you also say is an all-merciful God, who cares for each one of us individually, are you saying that God created this worm that can live in no other way than in an innocent child’s eyeball? Because that doesn’t seem to me to coincide with a God who’s full of mercy.”

Regardless of your religious point of view, the Loa Loa is an example of the more gruesome creatures not often focused on by mainstream media, but causing suffering to millions worldwide. This deadly ‘eye worm’ certainly deserves more attention given its devastating impact.

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