|Eugene H. Kaplan is the Don Axinn Distinguished Professor of Conservation and Ecology, Hofstra University and author of What’s Eating You? People and Parasites. In this original article, he writes about a phenomenon related to climate change — the movement of parasites and their hosts beyond of their traditional geographical boundaries. As Kaplan documents, this poses a dangerous threat to the rest of the world.|
A farmer is standing on a hill overlooking his parched, heat-blasted fields. He thinks, “Farmers have dealt with climate fluctuations forever. Last summer we had a lot of rain; this summer is hot and dry — those damn scientists can’t see past their noses. Common sense says that this is part of nature’s cycle.”
But he is wrong. Decade by decade, the Earth’s mean temperature has been making a jagged, but ever-ascending path to a threatening destiny — a world where all sorts of creatures are migrating from hot equatorial regions towards the ever-warming temperate zones. Unable to survive a hard freeze, the carriers of parasites are creeping north, waiting. The skeptical farmer contains a refutation inside his very body; hordes of microscopic worms slithering under his skin in an invasion of non-native parasites. He has been bitten by a blackfly, a common occurrence in his life…but this was a different kind of blackfly.
How has he become infected? In this era of increasing international air traffic, a visitor from equatorial Africa brought with him some “illegal immigrants”. At home, a tropical relative of an American blackfly bit him, sucking his blood and repaying the red gift of life, tragically, with a gift of death. Whenever a blackfly bites an infected person it will ingest, with the nourishing blood, larval worms that will develop in its body, multiply and become a horde of infective slivers. These infective larvae migrate to the salivary glands of the fly. Then it bites the traveler, salivating all the while, pouring larvae into the wound. The introduced worms will mature and reproduce inside the traveler, living in a shadowy world of thin-walled vessels that comprise the lymphatic system, becoming threadlike adults. Eventually a contorted knot of dead and calcified adults forms a bump (nodule) on his forehead or waist that brings him to the doctor. The physician will not know what it is, never having seen one before. The traveler might go blind, because the huge wormy population in his body may cause the dreaded parasitic disease, river blindness.
The tropical blackflies that are the disseminators of river blindness will spread naturally into whatever niches are available to them. As the winters that have kept them at bay become warmer, the flies will invade more northern climes, eventually finding the habitats proven hospitable to them by American blackflies, swiftly moving wooded streams. Then they move in. Once ensconced, they can pick up the infection from subsequent visitors from Africa and spread it.
Incredibly, our farmer was infected with river blindness!
However fanciful this story seems, there is a present parasitic reality:
An American tourist visits a rural village in Brazil. To him it appears to be just another picturesque native community – until he notices that there is an inordinate number of one-eyed children. The black, gaping holes where an eye should be are the result of the bite of a kissing bug, the transmitter of an ancient blood-borne parasite that causes the potentially fatal Chagas’ disease. The insect that transmits the parasite is not a tiny fly or mosquito, it is an inch-long blackish bug with a long snout. It comes out at night and, seeking a warm blood-rich area, bites the sleeping child on her lips or cheek. As it makes its painful blood-sucking bite, it defecates. The parasite is so primitive that it requires the child’s connivance to be transferred into her blood stream. Asleep, she feels the pain of the “kiss” and, rubbing the bite, sweeps the bug’s infective feces into the wound …or into her eye. Once inside the blood stream the parasite is free to attack any internal organ, even the heart, causing death.
Kissing bugs are here now. They are found in most southern states. The only reason Chagas’ disease is not common is that our temperate zone species has the peculiar habit of waiting about twenty minutes to defecate after its meal. This means when the sleeping child rubs the wound, there will be no infective feces to rub into it. But the sub-tropical species’ of kissing bugs, the immediate defecators, are spreading north with the rise in average temperature.
To compound the problem there is new evidence that the migration of animals and plants precedes the apparent increase of temperature. Invasive species begin to spread little by little, before meteorologists register the comparatively huge measurement of a rise of one degree.*
Malaria, the most dreaded parasitic disease, was once common in the United States, especially in New York State and along the Mississippi River. It was called “ague” and it killed a lot of people in the nineteenth century before it spontaneously disappeared. But hordes of tropical mosquitoes harboring the often fatal falciparum malaria are ready to migrate toward more temperate regions.
A real horror that dwarfs the current fad of vampire movies is also climate-related. Vampire bats are among the few species that can resist the mysterious disease that is rendering other bat species nearly extinct. They are increasing in number because of hamburgers. These tropical and subtropical blood-eaters prey on the herds of cattle living on huge ranches owned by Burger King and McDonalds that are carved out of rain forests in South and Central America. The three-inch bats are not dangerous to humans. They don’t even suck blood (they lap it up). But they can spread rabies. Thousands of cases a year of rabies in cattle have been reported on sub-tropical ranches, endangering production. No bat-borne rabies cases have occurred in Americans — yet. It is clear the border between Mexico and the US is porous – porous to kissing bugs and porous to vampire bats.
Global warming is only part of the problem. Current thinking is that climate change is redistributing water all over the Earth. Climate data show less frequent rain in the Middle East and North Africa than in the recent past. In these places, the future is now. In the North African Sahel customary rainy periods are sparse and inconsistent. Vast numbers of migrants crowd the borders of Kenya and Uganda waiting for a miracle to save them. They cannot survive without the rain that is the foundation of their culture. They live under filthy conditions – nurseries for parasites of all kinds. The seething population cannot be held back for long. Massive migrations will occur, and with them will come the parasites.
* For confirmation see Limnology & Oceanography 55 (4) 2010, 1478 -1484: http://www.aslo.org/lo/toc/vol_55/issue_4/1478.html
“Dip into Kaplan for a rich dose of disgust.”–Anne Hardy, Times Literary Supplement
“This is gonzo parasitology writing at its finest.”–Clint Witchalls, New Scientist
Read a sample from this humorous and grotesque book here: http://press.princeton.edu/chapters/i9136.pdf