A study was released this week detailing the number of creatures living in and on us as humans. (And I can't seem to find the link right now) It's more than we thought. Which is no surprise to me. I've been aware of the presence of these helpful organisms for a long time. I've been aware of the presence of the unhelpful ones almost as long. Basically, your bugs should stay your bugs. My folks and I joke that if we have an upset stomach or intestinal distress, it's because we ate someone else's E.Coli. Whether or not that's the case, a point is made: there are bugs in us and on us.
The bugs we have in our gut have important jobs to do. They help us digest our food. They help us stay healthy and fight off illness. They sometimes make things difficult for the not so helpful bugs and protect us from the "evil" ones.
But it's the bad ones that interest me. Tapeworms, hookworms, and the parasite that causes malaria, transmitted through the saliva of a mosquito. How these animals evolved into what they are now is what researchers are examining now. Any parasitic animal runs the risk of wiping itself out by being discovered. They are the cat burglars of the parasitic world, sneaking into an animal, taking what they want, and then dispersing to invade other animals.
I remember a nine year old girl telling me she had a tape worm. As I was also nine, I thought that was interesting. I asked her what it did and where she had it. After she told me it was in her insides, I admit, I didn't think it was so cool. She also told me she was taking medicine to get rid of it. And of course at that age, I had heard of worms you could get from walking barefoot in the grass or from dog poop.
But for some strange reason, I have always thought there must be some explanation of why these types of organisms live the way they do. There must be some benefit, not just to them, but to their hosts. Otherwise they couldn't have survived as long as they have. Some parasites quickly kill their host or disable them to the point that both parasite and host will suffer.
People with sickle cell anemia are not susceptible to malaria. The sickle cell structure isn't amenable to the parasite that causes malaria, so the bugs can't affect the host. Did this mutation in haemoglobin in red blood cells allow those with it to survive while others didn't and thereby allow the mutation to become an inheirited trait? Did the mutation arise because of the parasite? Or was it simply a chance event that had a slightly positive result? I say slightly because while those with sickle cell survive malaria, they often have shortened lives due to the mutation, though in malaria ridden areas they do have an advantage.
Since my diagnosis, I have often thought of MS in these terms: of what benefit is it to me to have MS? Has some virus or bacteria triggered the onset of MS? Perhaps the presence of one of those parasites keep others from settling in us. Perhaps MS evolved as a way to protect us from another, less desirable, disease. Perhaps the immune activity triggered by MS protected us from strains of plague or smallpox during the midle ages.
On a related note, recent studies in south America and in Europe/Africa show a protective action of some parasites in people with MS as compared to those with MS but no parasites. But I'm not going barefoot in the grass any time soon.
If you're really interested in parasites in general, read Parasite Rex, by Carl Zimmer. It's an absolutely fascinating look at some of the earth's most reviled creatures.