“It seems germs need help,” writes Gabriel Rotello in his new book, Sexual Ecology, which examines the spread of the AIDS epidemic and draws the not very startling — but important — conclusion that wild promiscuity, be it gay or straight, provides precisely the help HIV needs to spread. (One reason marriage is so important to a healthy society is that it discourages promiscuity.)

But I knew that.

What I hadn’t known about was Egypt.

I do remember as a boy reading headlines about the Aswan High Dam, and all the controversy over building it or not building it, and whether the Soviets or we should provide the aid. This was shortly before Rachel Carson’s Silent Spring, which launched the world’s environmental consciousness in 1962. And so here I am decades later reading about this dam, and what actually happened with respect to, of all things, the snails.

I don’t think the snails had even been considered back when plans for the Aswan High Dam were under way. Yet today, reports Rotello, 58% of rural Egyptians are afflicted with schistosomiasis, a “nasty debilitating parasitic disease” which produces “weakness, weight loss, lassitude, and decreased resistance to other diseases.”

Why? The snails. And hence the dam.

“The immediate cause of schistosomiasis is a parasite called a schistosome, whose immediate hosts are snails that thrive in slow-moving streams and stagnant ponds. Each infected snail can produce thousands of male and female sporocysts that swim out into the water, free to infect any humans they come into contact with. Once those sporocysts infect their unfortunate human hosts, they migrate to the heart, lungs, and liver, where they mate and reproduce.”

For thousands of years the snails were kept in check because the Nile moved swiftly and because when it flooded each year, it deposited silt — and snails — on the land. As the water seeped into the ground and the puddles dried, the snails died. “So there was schistosomiasis throughout the ages in Egypt,” writes Rotello — they can tell that from mummies and hieroglyphs — “but apparently not very much. Indeed, it’s doubtful that Egypt could have sustained its millennial glory if a majority of its people had been stricken with such a debilitating disease.”

And then they built the dam, “the greatest engineering project in North Africa since the pyramids.” The annual floods were replaced with “thousands of miles of stagnant irrigation ditches, canals and holding ponds, covering the length and breadth of the country.” The snail population exploded and, as I say, 58% of rural Egyptians, who routinely wade in the irrigation projects as part of their work, are now debilitated.

All things considered, was the dam worth it? Conceivably, depending on how you weigh various factors and how soon, if ever, you believe a cure for schistosomiasis will be found. But to those of us who scoff at the notion that economic and population growth really could come back to haunt us — that the ozone layer really may be disappearing or the globe warming — these snails, and the 58% of rural Egyptians with parasites reproducing in their hearts, lungs and livers, are a cautionary tale.


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