The last time, I wrote about the toxoplasma parasite and how it changes human behaviour. Is this the only parasite that messes with the mind? No, the parasite, whether worm or bacteria, is a thinking, clever animal who will do anything for survival — like all of us. Here are some more fantastic creatures who as tenants make their hosts or landlords do what they want them to do.
The bovine lungworm, Dictyocaulus viviparous, lives in the cow’s lungs. It lays eggs, which the cow coughs up, swallows and then defecates. The egg is now in the cow dung where it hatches. This baby parasite has to get into another cow, but cows don’t eat their own dung. The parasite needs to find grass (see, how clever, it already knows that cows eat grass). This is the fantastic part. A species of fungus (Pilobolus) grows on cow dung, and when it’s ready to send out its spores, it does so in an explosive fashion. So the baby worm climbs on to the fungus, waits until it explodes, and then gets thrown out onto the grass where it waits to be eaten.
The Onchocerca parasitic worm lives in humans and causes river blindness in Africa. How does it avoid being killed by the body’s immune system? To understand its genius, you have to understand how the human body kills invaders. Parasites such as Onchocerca are attacked using a type of cell known as an eosinophil, whereas bacteria are destroyed by another type of cell, called neutrophil. These two types of cells are specific in their killing, so neutrophils are useless at killing parasites.
What the Onchocerca worm does is allow bacteria to live beneath the skin. The human body finds these bacteria and despatches neutrophils to kill them. It also notices the worm, and sends out eosinophils to kill it. But the worm is already surrounded by neutrophils which cannot get under the skin of the worm because they cannot attack worms. The neutrophils block the eosinophils from reaching their target, protecting the worm!
The liver fluke of cattle, Dicrocoelium dendriticum, is a mind controller. It is born in a cow then enters a snail. Then migrates to an ant. The ant has to be eaten by a cow to complete the cycle. The problem is that ants live either underground or on the surface of the ground, but cows tend to eat tall grass. So the parasite changes the brain of the ant to be attracted to light and climbs tall grass blades to get as close to the sun as possible. A perfect target for a cow to eat. But again, how clever, as evening approaches and the air cools, the infected ant moves away from other members of the colony and upward to the top of a blade of grass. Once there, it clamps its mandibles on to the top of the blade and stays there until dawn. Afterward, it goes back to its normal activity in the ant colony. If the host ant were to be subjected to the heat of the direct sun, it would die along with the parasite. Night after night, the ant goes back to the top of a blade of grass until a grazing animal comes along and eats the blade, ingesting the ant along with it, putting the parasites back inside their preferred host.
The Euhaplorchis californiensis is a parasitic worm that lives in the gut of shorebirds. It produces eggs that come out in the bird’s faeces and are swallowed by snails. They hatch and then leave the snail and swim out into the marshes eventually finding a fish, entering through the gills and making its way into the brain cavity. Once in the brain cavity, the parasite causes the fish to come to the surface, swim in circles, jerk around and display its silvery underside in an attempt to attract a bird’s attention. This behaviour makes the infected fish very likely to be caught and consumed by a bird. The parasite finds its way back into the bird and the process begins anew.
The larva of the hairworm, Spinochordodes tellinii, develops and grows inside grasshoppers and crickets. As it grows, the worm manipulates its host to actually seek out and dive into a large body of water committing suicide. Once in the water, the worm emerges and swims away to live out the rest of its life, leaving the host to drown.
Hymenoepimecis argyraphaga is a parasitoid wasp whose host is the spider. The adult female wasp temporarily paralyses the spider and lays an egg on its abdomen. The egg hatches into a larva which sucks the spider’s blood while the spider goes on about its normal web building and insect catching behaviour for the next two weeks. When the larva is ready to pupate, it injects a chemical into the spider, causing it to build a web whose design is completely different from any it has ever made, and then to sit motionless in the middle of this web. The wasp larva then molts, kills the spider with a poison and builds a cocoon that hangs from the middle of the web the spider has just built.
Leucochloridium Paradoxum is a parasitic flatworm that travels from birds to snails and slugs and then back to birds. But while going from bird to snail is easy, how does it go back? The worm develops hundreds of cysts or brood sacs filled with larvae. These brood sacs invade the snail’s tentacles, causing a brilliant transformation of the tentacles into a swollen, pulsating, colourful
display that mimics the appearance of a caterpillar or grub. The snail who otherwise seeks dark areas comes out into the light and is easily seen and eaten by a bird.
Plasmodium, the cause of malaria, affects both its mosquito and animal hosts. Mosquitoes that drink plasmodium-infected blood initially become more cautious about finding another victim, giving plasmodium time to replicate. Once the plasmodium is infective, mosquitoes become more likely to bite more than one person in a night, and spend more time drinking blood. In turn, once a person is infected with plasmodium, he becomes more attractive to mosquitoes, continuing the lifecycle of the parasite. What an interesting world.
The bovine lungworm, Dictyocaulus viviparous, lives in the cow’s lungs. It lays eggs, which the cow coughs up, swallows and then defecates. The egg is now in the cow dung where it hatches. This baby parasite has to get into another cow, but cows don’t eat their own dung. The parasite needs to find grass (see, how clever, it already knows that cows eat grass). This is the fantastic part. A species of fungus (Pilobolus) grows on cow dung, and when it’s ready to send out its spores, it does so in an explosive fashion. So the baby worm climbs on to the fungus, waits until it explodes, and then gets thrown out onto the grass where it waits to be eaten.
The Onchocerca parasitic worm lives in humans and causes river blindness in Africa. How does it avoid being killed by the body’s immune system? To understand its genius, you have to understand how the human body kills invaders. Parasites such as Onchocerca are attacked using a type of cell known as an eosinophil, whereas bacteria are destroyed by another type of cell, called neutrophil. These two types of cells are specific in their killing, so neutrophils are useless at killing parasites.
What the Onchocerca worm does is allow bacteria to live beneath the skin. The human body finds these bacteria and despatches neutrophils to kill them. It also notices the worm, and sends out eosinophils to kill it. But the worm is already surrounded by neutrophils which cannot get under the skin of the worm because they cannot attack worms. The neutrophils block the eosinophils from reaching their target, protecting the worm!
The liver fluke of cattle, Dicrocoelium dendriticum, is a mind controller. It is born in a cow then enters a snail. Then migrates to an ant. The ant has to be eaten by a cow to complete the cycle. The problem is that ants live either underground or on the surface of the ground, but cows tend to eat tall grass. So the parasite changes the brain of the ant to be attracted to light and climbs tall grass blades to get as close to the sun as possible. A perfect target for a cow to eat. But again, how clever, as evening approaches and the air cools, the infected ant moves away from other members of the colony and upward to the top of a blade of grass. Once there, it clamps its mandibles on to the top of the blade and stays there until dawn. Afterward, it goes back to its normal activity in the ant colony. If the host ant were to be subjected to the heat of the direct sun, it would die along with the parasite. Night after night, the ant goes back to the top of a blade of grass until a grazing animal comes along and eats the blade, ingesting the ant along with it, putting the parasites back inside their preferred host.
The Euhaplorchis californiensis is a parasitic worm that lives in the gut of shorebirds. It produces eggs that come out in the bird’s faeces and are swallowed by snails. They hatch and then leave the snail and swim out into the marshes eventually finding a fish, entering through the gills and making its way into the brain cavity. Once in the brain cavity, the parasite causes the fish to come to the surface, swim in circles, jerk around and display its silvery underside in an attempt to attract a bird’s attention. This behaviour makes the infected fish very likely to be caught and consumed by a bird. The parasite finds its way back into the bird and the process begins anew.
The larva of the hairworm, Spinochordodes tellinii, develops and grows inside grasshoppers and crickets. As it grows, the worm manipulates its host to actually seek out and dive into a large body of water committing suicide. Once in the water, the worm emerges and swims away to live out the rest of its life, leaving the host to drown.
Hymenoepimecis argyraphaga is a parasitoid wasp whose host is the spider. The adult female wasp temporarily paralyses the spider and lays an egg on its abdomen. The egg hatches into a larva which sucks the spider’s blood while the spider goes on about its normal web building and insect catching behaviour for the next two weeks. When the larva is ready to pupate, it injects a chemical into the spider, causing it to build a web whose design is completely different from any it has ever made, and then to sit motionless in the middle of this web. The wasp larva then molts, kills the spider with a poison and builds a cocoon that hangs from the middle of the web the spider has just built.
Leucochloridium Paradoxum is a parasitic flatworm that travels from birds to snails and slugs and then back to birds. But while going from bird to snail is easy, how does it go back? The worm develops hundreds of cysts or brood sacs filled with larvae. These brood sacs invade the snail’s tentacles, causing a brilliant transformation of the tentacles into a swollen, pulsating, colourful
display that mimics the appearance of a caterpillar or grub. The snail who otherwise seeks dark areas comes out into the light and is easily seen and eaten by a bird.
Plasmodium, the cause of malaria, affects both its mosquito and animal hosts. Mosquitoes that drink plasmodium-infected blood initially become more cautious about finding another victim, giving plasmodium time to replicate. Once the plasmodium is infective, mosquitoes become more likely to bite more than one person in a night, and spend more time drinking blood. In turn, once a person is infected with plasmodium, he becomes more attractive to mosquitoes, continuing the lifecycle of the parasite. What an interesting world.
