In evolutionary biology, parasitism is a relationship between species, where one organism, the parasite, lives on or in another organism, the host, causing it some harm, and is adapted structurally to this way of life.
- It is about the most awful thing you can imagine in terms of a non-fatal ailment. It's a parasitic disease and you know you've got it when at some point you develop a blister on your skin on your leg or your arm, and it's a burning blister and soon what emerges is a worm, and it's a worm that eventually, as it comes out, could be three-feet-long. It looks like a long strand of angel hair pasta and it's excruciatingly painful as it comes out. And the way it's transmitted is through drinking water. The worm, when it comes out, you've got that burning blister, your instinct is to want to immerse the skin in water. Well, when you do that, the worm puts out thousands and thousands of larvae that infects the drinking water. If anyone drinks the water, it gets into their system and a year later they develop a blister and out comes another worm.
- David Baron, "Jimmy Carter: 'I would like the last Guinea worm to die before I do'", PRI (22 Aug. 2015)
- All infections, of whatever type, with no exceptions, are products of parasitic beings; that is, by living organisms that enter in other living organisms, in which they find nourishment, that is, food that suits them, here they hatch, grow and reproduce themselves.
- Agostino Bassi, quoted by Kevin Glynn in Gasping for Air: How Breathing Is Killing Us and What We Can Do about It (2017)
- [The parasite that causes malaria] edges through the cells of the stomach wall of the mosquito and forms a cyst which grows and eventually bursts to release hundreds of "sporozoites" into the body cavity of the mosquito [...] As far as we can tell, the parasite does not harm the mosquito [...] It has always seemed to me, though, that these growing cysts [...] must at least give the mosquito something corresponding to a stomach-ache.
- Marston Bates, The Prevalence of People (1955), p. 165
- [A] major difficulty in the parasite's life is the return to water. It is, therefore, of particular interest that the parasite appears to affect the behaviour of its hosts, and 'encourages' it to return to water. The mechanism by which this is achieved is obscure, but there are sufficient isolated reports to certify that the parasite does influence its hosts, and often suicidally for the host [...] One of the more dramatic reports describes an infected bee flying over a pool and, when about six feet over it, diving straight into the water. Immediately on impact the gordian worm burst out and swam into the water, the maimed bee being left to die.
- N. A. Croll, Ecology of Parasites (1966)
- I cannot persuade myself that a beneficent and omnipotent God would have designedly created the Ichneumonidæ with the express intention of their feeding within the living bodies of Caterpillars, or that a cat should play with mice.
- Fell Oestrus buries in her rapid course
Her countless brood in stag, or bull, or horse;
Whose hungry larva eats its living way,
Hatch'd by the warmth, and issues into day.
- The wing'd Ichneumon for her embryon young
Gores with sharp horn the caterpillar throng.
The cruel larva mines its silky course,
And tears the vitals of its fostering nurse.
- What keeps snails and flukes apart in evolution is their divergent future interests, and this is because they do not share reproductive propagules. What keeps host genes together with host genes — and parasite genes together with parasite genes - is that they do share future interests. Parasites, then, have led us to the solution to the paradox of the organism. The genes in an organism share desiderata lists. And this is simply because they submit to the same meiotic lottery and possess the same stochastic gametic destiny.
- Richard Dawkins, "Parasites, desiderata lists and the paradox of the organism", Symposia of the British Society for Parasitology, Vol. 27 (Jun. 1990), p. 72
- Let me repeat that these parasitic insects comprise ten percent of all known animal species. How can this be understood? Certainly we give our infants the wrong idea about their fellow creatures in the world. Teddy bears should come with tiny stuffed bearlice; ten percent of all baby bibs and rattles sold should be adorned with colorful blowflies, maggots, and screw-worms. What kind of devil’s tithe do we pay? What percentage of the world’s species that are not insects are parasitic? Could it be, counting bacteria and viruses, that we live in a world in which half the creatures are running from—or limping from—the other half?
- Whoever looks at the insect world, at flies, aphides, gnats and innumerable parasites, and even at the infant mammals, must have remarked the extreme content they take in suction, which constitutes the main business of their life. If we go into a library or newsroom, we see the same function on a higher plane, performed with like ardor, with equal impatience of interruption, indicating the sweetness of the act. In the highest civilization the book is still the highest delight.
- Ralph Waldo Emerson, Letters and Social Aims (1875), p. 177
- To choose a rough example, think of a thorn which has stuck in a finger and produces an inflammation and suppuration. Should the thorn be discharged with the pus, then the finger of another individual may be pricked with it, and the disease may be produced a second time. In this case it would not be the disease, not even its product, that would be transmitted by the thorn, but rather the stimulus which engendered it. Now supposing that the thorn is capable of multiplying in the sick body, or that every smallest part may again become a thorn, then one would be able to excite the same disease, inflammation and suppuration, in other individuals by transmitting any of its smallest parts. The disease is not the parasite but the thorn. Diseases resemble one another, because their causes resemble each other. The contagion in our sense is therefore not the germ or seed of the disease, but rather the cause of the disease. For example, the egg of a taenia is not the product of a worm disease even though the worm disease may have been the cause, which first gave rise to the taenia in the intestinal contents—nor of the individual afflicted with the worm disease, but rather of the parasitic body, which, no matter how it may have come into the world at first, now reproduces itself by means of eggs, and produces the symptoms of the worm disease, at least in part. It is not the seed of the disease; the latter multiplies in the sick organism, and is again excreted at the end of the disease.
- Friedrich Gustav Jakob Henle, "On Miasmata and Contagia", trans. G. Rosen, Bulletin of the Institute of the History of Medicine (1938), Vol. 6, p. 924
- It is only within the present epoch, that physiology and chemistry have reached the point at which they could offer a scientific foundation to agriculture; and it is only within the present epoch, that zoology and physiology have yielded any very great aid to pathology and hygiene. But within that time, they have already rendered highly important services by the exploration of the phenomena of parasitism. Not only have the history of the animal parasites, such as the tapeworms and the trichina, which infest men and animals, with deadly results, been cleared up by means of experimental investigations [...] but the terrible agency of the parasitic fungi and of the infinitesimally minute microbes, which work far greater havoc among plants and animals, has been brought to light.
- In this strange and apparently cruel operation one circumstance is truly remarkable. The larva of the Ichneumon, though every day, perhaps for months, it gnaws the inside of the caterpillar, and though at last it has devoured almost every part of it except the skin and intestines, carefully all this time it avoids injuring the vital organs, as if aware that its own existence depends on that of the insect upon which it preys!
- The facts obtained in this study may possibly be sufficient proof of the causal relationship, that only the most sceptical can raise the objection that the discovered microorganism is not the cause but only an accompaniment of the disease [...] It is necessary to obtain a perfect proof to satisfy oneself that the parasite and the disease are [...] actually causally related, and that the parasite is the [...] direct cause of the disease. This can only be done by completely separating the parasite from the diseased organism [and] introducing the isolated parasite into healthy organisms and induce the disease anew with all its characteristic symptoms and properties.
- Robert Koch, Berliner Klinische Wochenschrift (1882), p. 393
- Nowhere is it more true that "prevention is better than cure," than in the case of Parasitic Diseases.
- Rudolf Leuckart, "Author's Preface to English edition", trans. by William E. Hoyle, The Parasites of Man, and the Diseases which Proceed from Them: A Textbook for Students and Practitioners (1886), vii
- Nearly all birds build nests of some kind in which to cradle their eggs and young. The cow-bird and cuckoo (European), however, are exceptions. These birds have the rather human practice of turning their cares and labours over to somebody else. They are loafers and parasites. They lay their eggs secretly in the nests of other birds, where their eggs are hatched and their young cared for by an alien mother. I have seen a mother song-sparrow hustling about among the shrubs and grasses for an hour at a time almost, gathering food for a young cow-bird nearly twice as big as she was, while her foundling sat phlegmatically at the foot of a tree chirping and fluttering its wings, and acting as a thankless and apparently bottomless receptacle for the morsel after morsel laboriously harvested for it by its tireless little foster-mother.
- I hope no such planet exists, but consider one where slow, painful death from parasitism is universal. How would we talk about nature on such a planet? What kind of book would Thoreau have written there?
- Arne Næss, "Should We Try to Relieve Clear Cases of Suffering in Nature?", Pan Ecology, Vol. 6 (1991), p. 131
- Some species of carpenter ants infected with metacercariae of the fluke Brachylecithutn mosquensis, are more obese than noninfected ants and, unlike the latter, they do not conceal themselves but crawl on exposed surfaces where they are easily found by birds that are the next hosts of the fluke. This behaviour seems to be a remarkable example of an animal that sacrifices its life for its parasites. The 'sacrifice', of course, is induced by the parasite.
- Elmer R. Noble and Glenn A. Noble et al., Parasitology: The Biology of Animal Parasites, 4th Edn. (1976)
- The belief is growing on me that the disease is communicated by the bite of the mosquito [...] She always injects a small quantity of fluid with her bite—what if the parasites get into the system in this manner.
- Ronald Ross, "Letter to Patrick Manson" (27 May 1896), The Great Malaria Problem and Its Solution: From the Memoirs of Ronald Ross (1988), p. 72
- I have failed in finding parasites in mosquitoes fed on malaria patients, but perhaps I am not using the proper kind of mosquito.
- Ronald Ross, "Letter to his wife" (14 Aug 1897), Memoirs: With a Full Account of the Great Malaria Problem and its Solution (1923), p. 221
- Lately, however, on abandoning the brindled and grey mosquitos and commencing similar work on a new, brown species, of which I have as yet obtained very few individuals, I succeeded in finding in two of them certain remarkable and suspicious cells containing pigment identical in appearance to that of the parasite of malaria. As these cells appear to me to be very worthy of attention [...] I think it would be advisable to place on record a brief description both of the cells and of the mosquitos.
- Ronald Ross, "On Some Peculiar Pigmented Cells Found in Two Mosquitoes Fed on Malarial Blood", British Medical Journal (18 Dec. 1897), p. 1786
- This day relenting God
Hath placed within my hand
A wondrous thing; and God
Be praised. At His command,
Seeking His secret deeds
With tears and toiling breath,
I find thy cunning seeds,
O million-murdering Death.
I know this little thing
A myriad men will save.
O Death, where is thy sting?
Thy victory, O Grave?
[Poem he wrote following the discovery that the malaria parasite was carried by the amopheline mosquito]
- Ronald Ross, In Exile (1906)
- After long pondering, I believe that I can define good and evil in terms to which even a biologist of the mechanical school can hardly take exception. At least, I fancy that I can do so for evil.
The great evil of life is parasitism.
- I can think of a few microorganisms, possibly the tubercle bacillus, the syphilis spirochete, the malarial parasite, and a few others, that have a selective advantage in their ability to infect human beings, but there is nothing to be gained, in an evolutionary sense, by the capacity to cause illness or death. Pathogenicity may be something of a disadvantage for most microbes.
- Lewis Thomas, Lives of a Cell: Notes of a Biology Watcher (1978), pp. 73–74
- The insidious lethality of a parasitic wasp, the cruelty of a cat playing with a mouse – these are, after all, just the tip of the iceberg. To ponder natural selection is to be staggered by the amount of suffering and death that can be the price for a single, slight advance in organic design. And it is to realize, moreover, that the purpose of this "advance" – longer, sharper canine teeth in male chimpanzees, say – is often to make other animals suffer or die more surely. Organic design thrives on pain, and pain thrives on organic design.