Just imagine the life.
No more struggle, no more strife.
Your food comes right to you each day
No need for sunshine to make hay.
All right, for dog’s sake, I’ll knock off the doggerel. Sorry, I apologise. OK? Now…
Ever since student zoology days, parasites fascinated me. Considering that 80% of the human race is, at any given time, suffering from some kind of parasitic infestation, and that all of us will suffer from some kind of parasitic infestation at some time in our life, it becomes more than just of casual interest…
So, I was wondering what would go into creating the ideal parasite. What would the perfect parasite need?
Let’s think about it…and try and find a winner.
First, an ideal parasite needs to be able to find a safe and stable environment. In this respect I’d say the ideal place for the parasite would be inside the host’s body.
Advantage: It’s the host itself that protects it; the parasite can hide almost indefinitely so long as it doesn’t cause so much damage that the host notices and does something about it.
Disadvantage: If it’s inside the host, it can’t run off in a hurry when in trouble or detected, or change hosts easily if the old host sickens or dies.
Secondly, the ideal parasite needs a good way of finding its meal with the minimum of effort. In this case the tapeworms of the genus Taenia, like Taenia solium up above, take the cake and biscuit and the whole bloody bakery. They don’t even have mouths to eat…they absorb food through the entire body surface. They don’t have any way to breathe oxygen, so they respire anaerobically. All they do is lie in the intestine, with the tiny head in front attached to the wall by hooks and suckers, and absorb food, and lay eggs. Hell, they don’t even have to bother about having sex. They are self-fertilising. They literally fuck themselves.
Sweet deal, huh?
Roundworms aren’t far behind, though they do have to go to the trouble of copulating and swallowing food. They have a different system. When there is no food coming, they fall asleep and lie inert, doing nothing. When food and oxygen arrive, they wake up, gulp the food down along with whatever air there is, and then promptly go to sleep again. Another sweetheart deal…
Advantage: easy life.
Disadvantage: none, except that you’re unable to change hosts and you might, if too successful, damage the host, what with intestinal bloating and so on. If you damage the host too much, he might decide to do something about you. If you’re a hookworm, you may drink so much blood you’ll end up killing the host. Bad boy.
If you are an external parasite, like a leech or a tick for example, you need to be able to go long, long times without food in between hearty meals when the opportunity allows.
Thirdly, the parasite needs to reproduce easily. Now if you’re an internal parasite, it’s not that easy. Your eggs will pass out of the body or – if you’re a blood borne parasite - keep circulating inside, looking for an insect to suck them up. Some of the life cycles are really complicated, Taenia for example needing to be swallowed by a pig (Taenia solium) or cow (Taenia saginata) and then that animal needs to be eaten by a human for the worm to get to a new host.
The best solution for an internal parasite is probably the one used by the pinworm Entrobius. It lays eggs on the anus, and these cause such intense itching the sufferer (usually a child) scratches the anus, picks up eggs on its fingernails, and then if it puts its fingers to its mouth without washing them the eggs go right on in and begin the cycle again.
Another solution is that of the external parasite, the flea. It lays eggs on dirt around the host, not on the host itself. The disadvantage is that it needs the host to be surrounded by dirt. If it isn’t, the flea can’t breed, poor thing.
Fourthly, the parasite needs to be able to abandon a dying host quickly and move on. This is not a frivolous matter and is impossible for internal parasites, which otherwise have everything going for them. Fleas are the best in this regard. Kill a rat and watch it for a few minutes. As the body cools, the fleas are already looking for fresh abodes.
Fifthly, if a parasite can do a few services for the host, the host may overlook its depredations. Plenty of examples in other animals, not many in humans. I mean of course parasites, which cause harm, notcommensals, to which the host is indifferent, and not symbiotes, which help the host. I’m not talking of them.
Sixthly, it needs to be physically resistant to anti-parasitical medication. Worms aren’t. Lice aren’t. Fleas, so long as they can get off the body into the dirt, are.
So, do we have a winner?
You’d never find a perfect parasite with all those features, will you now? Some of them are mutually contradictory. For example, an internal parasite has good food and no effort but can’t jump ship; an external parasite needs to work for its food.
So I guess there isn’t an ideal parasite…oh, wait, there is. We have a winner.
My nominee for the Perfect Parasite: the Indian politician.
This species inhabits the body of the Indian political system and the Indian state. It works from inside. It absorbs any food (read money) that comes along; it can sleep inertly, doing absolutely nothing (certainly none of its official duties) until food and air (money and power) come along, when it suddenly wakes and gulps it all down. It is remarkably adept at causing itches and inflammations in the sense of mini-wars and crime waves to get itself re-elected, in the manner of the pinworm; it can thrive in the dirt that accrues round the system. And, like the flea, when the party to which it is attached begins faltering, it’s incredibly quick to seek a new host. It can oblige people sometimes, for a fee naturally, in illegal endeavours like setting up sham factories and human trafficking and the like. And it is incredibly tough, virtually ineradicable. If one is destroyed, two will take its place.
I believe the zoology textbooks need some modification…I wonder if they’ll credit the new classification to me.