Thursday, 3 June 2010

'til death do us part

the exams are encroaching and i really should be studying (everyone says this), but i guess posting on an infectious disease topic (which i haven't done in a while) is a good compromise between doing 'work' and chilling out. so here goes.

at a dinner recently, someone had asked my friend, upon learning that she is studying i.d., 'so, what's your favourite parasite?'. this totally caught her off guard, and i'm not sure what she replied, but i think that's a pretty funny question. i mean, do you go around asking a mathematician what his favourite formula is, or a doctor what his favourite disease is? i guess as a conversation-starter, maybe some of us do. anyway, so i went home and thought about this, so that when i'm put on the spot, i'll be able to say, without a moment's hesitation, what my favourite parasite is.

schistosoma. yeap, it's a worm. but most visible parasites are, anyway, so there's not really much to choose from. i mean, it'd be a bit weird to choose something like giardia or cryptosporidium, i guess. or fungi. oh god, i hate fungi so much now. but let's not go there. schistosoma.

schistosoma eggs. 10 points to whomever can tell me the species and why. go medics.

obviously the next question would be 'why?'. well, here goes. first of all, from the scientific / micromolecular perspective, it's quite an awesome parasite. when inside your body, the adult schistosoma coats itself with tegument surface proteins that mimic your own body's antigens. basically, it's like a wolf in sheepskin, and by doing such, your body's immune response is blinded to its presence. your eosinophils and dendritic cells (kinda like your security guards) go around looking for stuff that shouldn't be there, and looks at schistosoma, then goes 'hey, nothing to see here. move along'. how fricken awesome is that? then, when your body finally figures out something is amiss, the parasite just changes its proteins and your body is fooled again. sneaky little buggers.

but, not everything's perfect: even though the adults are wiser than wary of your body's immune response, the eggs aren't really. and so, the eggs get dislodged in your intestines and maybe bladder (and also possibly other organs, but let's not go there), and your body starts to attack the eggs, causing all the pains and itches and bleeding when you pee or take a shit (OH GOD, IT BURNS!) and all that jazz. yeap, it is a parasite after all, and would only serve its name to cause you some harm.

the life cycle of schistosoma is particularly interesting. beyond going into the chicken-and-egg arguments, let's just start with schistosoma eggs in the environment, without wondering how they got there. they hatch, and become things called miracidia, which swim around in the water and infect snails. there, they develop into other things called cercariae, which are kinda like tadpoles with two tails. except they're smaller. and have no backbone. and stuff. but yeah, little mutant tadpoles of death and destruction, which go around swimming in the water, and home in on humans which happen to take a bath / swim /wash clothes / take a piss / who-knows-what in the water. then they penetrate your skin. and start moving up your veins, into your heart, then into your lungs. where they mature from the cercariae into worm-like adults. not content with having invaded your blood system like tiny vampires, they then break out of your lung alveoli, and climb up your trachea (windpipe) and then (here comes the best part) you swallow the ugly buggers into your stomach. how fricken awesome is that. and gross. yeah. it's gross. eating worms. no kidding.

this is a cercarium. yay!

anyway, moving on. now, the adults mature in your stomach (actually more like in your duodenum or small intestine) where another amazing thing happens - the male and female adults find a partner, and they mate for life. just look at this picture, where the female is in eternal, perpetual copula with the male, sitting nicely in his gynocophoral canal 'til they both die.

what says 'honey, i love you' more than eternal monogamy? and forever sitting in (spooning) embrace with your loved one? or (at least for the guy) always banging your chick, 24 - 7? aw yeah, baby, get your freak on. ahem. well, i kinda fudged things over a bit, because sometimes you do get 2 females living in one male's canal (giggity) but, isn't that more romantic? girls, if you ever let your man into a consensual threesome, trust me. he is going to find that f*cken romantic, and love you long time. especially if the threesome lasts until you both die. f*ck, yeah. ahem.

but yeah, then, obviously, with continuous, unprotected sex, the female is gonna get preggo, right? yeap. so she lays between 300 - 3000 eggs a day. no kidding. and you thought the vietnamese women who go down to the rice fields a day after giving birth were hard core. this girl just keeps on churning. and the eggs then penetrate your gut wall and find their way to various organs, from which they can cause disease, or get released into the environment all that jazz.

also, by the way, you may notice that the female is darker stained than the male. this is nothing to do with interracial preferences, but like many interesting observations, has a rationale. a very symbolic one, in fact. while both the schistosomal genders are essentially parasites, feeding on your digested food, only the female really requires blood to lay eggs. much like a mosquito. and so, females are really blood-sucking vampires of hatred and animosity (i'm talking about the schistosomes, calm down, women!). okay fine, you can argue that it's for the kids' sake, whatever helps you sleep at night. but yeah, eating blood gives a digestive by-product called haemozoin, which stains them darker. every story with a moral.

i'd go on more, but really, you don't want to read about all the intricate details of parasite worms, do you? and besides, i'm sure some people want to be able to eat lunch without throwing up, and if i were to put up some images... well. nevermind.

so. what's your favourite parasite?


Nebunu Delia said...

I love your article. Well done!!! Very personal and funny. I am still studying the parasites. When i'll be fascinated about one, i'll let you know. What species are those eggs? mansoni?

etc said...

thanks very much. i was surprised to see a comment on such an old post, but apparently this is the most viewed one (probably from links to the parasite pictures). i believe you can tell the species from the location of the spine - lateral spine for mansoni, terminal spine for haematobium, and obscure spine for japonicum. good luck with your parasitology :)