Musca sorbens is found in Sub-Saharan Africa, parts of Asia and Australia. It's actually reckoned to be a species complex rather than a single species - for those unfamiliar with the term, species complex basically means "They all look the bloody same to me, but different populations won't shag when we put them together in the lab and we can't afford to do the DNA work". I can't seem to find a good picture of them on Google images, but they look like a slightly smaller housefly with two stripes on the thorax and, on the evidence of the specimens I've seen so far anyway, they have large pins with type-written names through them.
I'm reluctant to put up the pictures I have found of the flies, partly because they're so small but mostly because they make me sad, always showing them on beautiful kids:
I try to keep this blog quite light and funny, but on a purely emotional level pictures like this show why this sort of work is important. I find it very hard to understand how I live in a world with Ikea and Facebook and Angel boxsets and hazelnut latte, and on the same planet there are people living like this, who can't spare any of their two litres of water a day for washing, let alone spare 7p to buy soap.
M. sorbens adults feed on the dissolved salts and proteins in tears and snot, and in doing so transmit the bacterium responsible for trachoma. If you like looking at pictures of manky eyes (and hey, who am I to judge?) google trachoma, if you're eating your tea then don't. At first the infection seems just like conjuntivitis (or pinkeye for my American friends - who says you never learn anything from Southpark?) and eventually clears up on its own, making it pretty low on peoples' list of priorities. Repeated infections though cause scarring of the inner eyelid, causing it to contract and rolling the eyelashes inward so that they scrape the cornea whenever the sufferer blinks. As well as being excruciatingly painful, this scarring and possibly infection of the cornea leads to blindness. As it may be several decades between the initial infection and the development of trichiasis, people rarely associate the two.
The tragedy of all this is that flies seem to prefer the eyes of children to those of adults. There may be something in the tears and snot of children that's especially attractive to these flies or it may just be that, as anyone who's ever tried to get a four year old to blow their nose will tell you, kids are mucky little bastards and probably have rather more of the relevant secretions lying around. This is one of the things I'm hoping to find out. It has also been suggested in the same way that many other infections entities have evolved strategies to maximise their distribution (the cold virus makes you sneeze out an aerosol of cold viruses, the Guinea worm induces its victims to cool their burning sores in water into which it can release its young, if you have a Britney Spears song stuck in your head chances are you'll end up humming it and infect someone else), the trachoma bacterium may cause children's' eyes to water, attracting more flies to spread it. I'll also be looking at whether secretions from kids with trachoma are more attractive to flies than those of kids without (and any child found to have trachoma in the course of the study will get antibiotic treatment).
And this is the really sad thing - if you can't afford soap, you can't afford the really simple antibiotics to cure the results. As I may have observed on a previous occasion, the world's pretty messed up really.