Flea mothers, zombie mushrooms and virus viruses - parasites like gangsters

2024 Author: Seth Attwood | [email protected]. Last modified: 2023-12-16 15:55

The parasite, like a smart gangster, does not want to kill anyone - he only needs to get his share, and in return he is even ready to provide some services. He often manipulates the host, but can also protect him from enemies. Why parasites are not an absolute evil, but a separate world and a necessary part of nature that should be protected, Maria Orlova, Candidate of Biological Sciences, Senior Researcher at Tyumen State University, explained to us.

What parasites can be in me right now and what exactly are there?

- You, most likely, belong to those 2.5 billion people who do not have parasites (in the narrow sense - worms). They have the remaining 4.5 billion, living primarily in tropical countries.

The fact that many people do not have parasites becomes a problem.

Epidemiologist David Strachan was the first to put forward this idea. According to his hygiene hypothesis, the immune system, which does not interact with parasites, does not form properly. As a result, the number of autoimmune pathologies in a person increases - diseases in which this system begins to react to the tissues of its own body as to foreign objects.

It has been noticed that those peoples for whom intestinal parasites are a normal phenomenon practically do not suffer from Crohn's disease (this is an autoimmune pathology). The causal relationship has not yet been proven, but this issue is being studied.

Aren't there mites in my face skin?

- There are - the so-called acne mites, they are present on the skin of any person. But most often outwardly they do not show themselves in any way, and they do no harm. Of course, if these ticks fail to build a normal relationship with the immune system, outwardly they manifest themselves through acne, but this happens quite rarely.

The question is precisely how to draw the line between parasitism, symbiosis, mutualism and other types of relationships. A symbiont is a roommate; that is, the parasite, strictly speaking, is also a symbiont. A mutualist is a mutually beneficial roommate. But when the roommate does not just live nearby, but also begins to harm? Unfortunately, this is still not always clear.

It is generally not clear what is considered harm and how to assess it. What looks like a negative influence to us on the surface may well suddenly turn out to be positive.

Therefore, scientists, when describing parasites, especially the microorganism level, more often use the term "opportunistic" - these are organisms that can cause harm, but have not yet done so.

Are there parasites that are perceived as pure evil?

- Outwardly, everything may look exactly like this - for a specific individual. For example, there is a dead hare - you unfold your ear, and there, like beads, there are drunk ticks hanging. The animal died from the fact that it was simultaneously attacked by a lot of parasites. It's scary to look at.

But we must understand that nature proceeds from the interests of the population and the species, and not a specific individual. The parasite is one of the factors of natural selection.

This means that the removal of a particular hare from the population was necessary for something.

But we take care of weak children, even if we admit that nature needed them to be born weak and die. So why don't we nurse hares and kill ticks?

- The parasite is not oriented towards the death of the host. It is not beneficial to him. Death from the parasite occurs in special cases. Of course, it is a pity for the bunny, but if so many ticks attacked him, it means that he had problems with the immune system, and if so, he would have died without the ticks.

The parasite's job is not to kill its host, but to adapt to it. This is one of the basic differences between a parasite and a predator. And one of the most promising ways for the parasite is to become a mutualist, that is, to move on to mutually beneficial cooperation with its owner. As I said, a symbiote is just a roommate. A mutualist is someone with whom you can live and live well. This scheme has been successfully implemented by some bacteria, intestinal, for example. Most of them started out as parasites.

But everyone is already used to bacteria. There are more interesting cases.

Once in South America, a study was carried out, during which it turned out that women infected with roundworms ascaris, on average, have two more children. Why?

Strictly speaking, the fetus is also a parasite. He is half alien, half of his DNA is non-native, and immunity, logically, should get rid of him. Of course, there are mechanisms inside the mother's body that prevent this. But sometimes a miscarriage still occurs.

When roundworms are present in the mother's body, the immune system primarily deals with them and does not attack the fetus. Helminths are also alien. Accordingly, there are fewer miscarriages. In general, it is beneficial for the parasite for the host to reproduce, because in this way it can infect the offspring.

It must be said that lately there have been more and more news about the success of helmintherapy in the treatment of autoimmune pathologies. While this method is at a semi-legal level, but still.

Although parasite therapy has deep roots - people began to try to heal themselves by infecting themselves with parasites a long time ago. For example, in the 19th century, syphilis was fought in a similar way. The causative agent of syphilis - the treponema bacterium - dies at 40 degrees. And the temperature jumps under forty when a person is sick with malaria. Thanks to Columbus, who brought the bark of the cinchona tree from America, they already knew how to control the malaria fever. Therefore, in order to rid a person of syphilis, he was infected with malaria: he had to spend some time in a fever for treponema to die, then the temperature was brought down with quinine. The method is barbaric, of course: every third patient died. But death from syphilis was even worse.

One of the most popular parasites is Toxoplasma, which can make us love cats. Why, how does it work?

- Toxoplasma is generally something amazing. It parasitizes almost any mammal, makes no exception for anyone. She was recently discovered in seals. It is a parasite of the nervous system that loves to manipulate the owner, and he has several hosts.

First, Toxoplasma infects the rodent, and its task is to make the rodent available to its main host, the feline. For this, the cat must become attractive in the eyes of its future prey. And Toxoplasma causes such changes in the brain that the mouse begins to like the smell of cat urine, it strives for this smell. As a result, the cat eats it.

This also applies to primates. But if in nature a primate infected with Toxoplasma went to the leopard, the leopard ate it and Toxoplasma rejoiced, then in the civilized world it does not work that way. A person, having come into contact with the urine of a sick cat, falls ill, but the domestic cat cannot eat it.

Maybe Hemingway suffered from toxoplasmosis, since he was eager to hunt lions?

“If so, he would have to come and let himself be eaten. But some kind of desire for unjustified risk in people with toxoplasmosis is observed.

In the old literature, you can find the advice of pathologists, they ask students to take from those who died in a car accident, especially from those who crashed on a motorcycle, an analysis for toxoplasmosis - and almost always toxoplasma is found in the blood. Why so - the question remained open for a long time.

Today it is known that Toxoplasma, which is in the body for a long time, provokes diseases such as schizophrenia and bipolar disorder.

There is also evidence that men infected with toxoplasmosis become more aggressive, and women more docile and calm.

And this is an ordinary analysis? Can anyone get tested for toxoplasmosis?

- Yes. Moreover, for pregnant women it is mandatory, because the parasite, penetrating into the neural tube of the fetus, causes serious disturbances - the pregnancy freezes, the fetus dies. So wash your hands after cleaning the litter box.

Why is Toxoplasma so comfortable in cats?

- It's a matter of immune interaction. This is how the puzzle came together. The feline's immune system has not expelled this parasite, but she can if she wants to. As a result, they got used to each other. This process is called coevolution. Probably, this process did not go on for the rest of the owners - they got rid of the parasite.

“Okay, Toxoplasma can make a mouse become interested in cat urine, or a person to buy a bike. Or maybe some parasite set me up for a love of work and money, so that we live longer and more comfortable with him? After all, he must take care of me as a master

- Look, this is the perfect parasite! I think that over time a person will have such. Although Toxoplasma already partly does this. It has been noticed that people infected with it are eager to start their own business. Causality has not been proven, but there is a correlation.

But the one-sided cordyceps mushroom zombies ants: they attach to the leaf and die, the mushroom itself grows through them. Can parasites pump so much that some mushrooms will brainwash you and me, and then germinate through our bodies while we hang on our balconies?

- We are all already somewhat zombified to some extent. There is a wonderful book "Your second brain is the intestine", which says that intestinal bacteria manipulate us oh-oh-oh-oh how. True, we do not consider them parasites, we consider them mutualists, but nevertheless.

All our symbionts manipulate us by little things.

Strictly speaking, the very concept of "organism", scientists propose to be considered obsolete. The term "extended phenotype" is more relevant - it is an organism with all its symbionts, a certain complex.

Of course, there are organisms without symbionts, they are grown in laboratories, and such organisms are called gnotobionts. They are always clean. But they can only live in the laboratory.

We will never be as clean as gnotobionts, because we live in an open environment. We have internal symbionts and external ones. And our task is to learn to live with them.

But parasites will not germinate through us, we are arranged differently. The parasite tends to kill the intermediate host. There is a trematode that makes an ant climb on a blade of grass, freeze and wait to be eaten by its main host - a herbivorous mammal.

And it is difficult for a person to be an intermediate owner, because there are not so many predators that hunt him. Toxoplasma is practically an exception. So a person is not threatened that a mushroom will sprout through him. We will simply continue to be manipulated.

But how do parasites manage to manipulate us? And how do parasites control the ant's behavior so that it goes out onto the path, lies down there and dies?

- It's not that difficult. There is such a parasite - Rishta, once very widespread in the tropics and subtropics. Rishta enters the human body through water, after a while she needs to go outside and re-enter the water. Therefore, Rishta causes a sensation of heat in the extremities - it acts on the receptors. A man runs to the water, sticks his feet in there, and she comes out safely.

Probably, initially it came out of the skin when a person was just bathing. It is clear that in hot climates people generally swim a lot. And individuals secreting a substance that additionally caused a feeling of heat in a person selectively survived. Conventional natural selection. And this has transformed into the fact that now the rishta necessarily causes a sensation of heat in the limbs.

This is how most parasites develop their skills. And with the mushroom, trematode and ant there was about the same story.

When you talked about Toxoplasma, you mentioned co-evolution. So parasites help to evolve?

- Of course, the eternal struggle of the parasite with the host significantly moves evolution. Parasites contribute significantly to biodiversity and reproductive potential.

Roundworms make the host more fertile, other parasites, on the contrary, castrate their host.

Some crustaceans, sacculina for example, destroy the host's reproductive system, replacing it with its own, and the host looks after the offspring of the parasite, thinking that this is his offspring.

This arrangement prevents the host population from growing.

And some parasites guard their host. They do this due to their capabilities: they destroy a new species with similar ecological requirements, which appeared in the given territory and began to compete. Conventionally, certain deer live in the forest, they have their own parasites, once people bring other deer into this forest to increase biodiversity, and then the battle of parasites begins.

A parasite is always more pathogenic for a new host than for an old one, since their immune relationships have not yet been established. And in the end, either local animals or invaders with their parasitic co-invaders will win. This was overlooked for a very long time by wildlife experts who tried to introduce species and suddenly suffered inexplicable (at that time) setbacks.

Co-invaders have played an important role in the history of mankind. Syphilis appears to have come to Europe from America. And the Europeans, on the contrary, brought smallpox to the New World, which is why the Indians began to die en masse. Here you are, the co-invaders in action.

I'll keep up the conversation about the invaders. Swift has a poem "Basilio Leopoldovich the Cat". He is short: “The microscope revealed to us that there is a biting flea on a flea; / There is a tiny flea on the toy flea, / But the flea, too, bites into it angrily / The flea, and so ad infinitum. " The poem describes the phenomenon of superparasitism. Could you explain how it happened that some parasites have their own parasites? How can you be so lazy as to be a parasite?

“Only a select few have such parasites. First, the arthropods. Arthropods are often parasites, but they often become hosts of other parasites - fungi. Mushrooms are very fond of arthropods, because they contain chitin in their integuments, and chitin is in fungi. As you can imagine, it is very convenient to absorb someone else's chitin.

And so, for example, blood-sucking flies of bats carry on themselves the spores of fungi, and these fungi from time to time germinate on them, which is very conducive to the humid microclimate of the caves.

It is believed that there are practically no parasites higher than the second order, and the second order is already an extremely rare phenomenon. But this is only in multicellular organisms.

So that you understand, the chain is as follows: a host, a parasite, a first-order hyperparasite, and if there is a parasite on it, then a second-order hyperparasite. But viruses are different. Viruses are, in principle, a completely parasitic group, they do not have their own metabolism, all the master's, therefore, hyperparasitism of the second and even third order is quite possible for them. For example, acanthamoeba is an amoeba that sometimes gets caught in liquid for contact lenses, parasitizes on humans, it has a first-order virus, it has a second-order virus, and on it there is a parasitic substance - mobile genetic elements. In general, yes, everything is like in Swift's rhyme.

If I neglect the tests and decide to have a baby when I have parasites in me, will I pass them on too? If so, is there a possibility that my great-grandmother passed on these parasites to me?

- This is what is happening, and very successfully. In general, for higher vertebrates there is a pattern: the higher the level of sex hormones, the lower the immune status. And during pregnancy, the level of these hormones increases, so the pregnant female is often attacked by external parasites: ticks, lice, fleas, while she, on the contrary, becomes resistant to some parasites. By the way, for the same reason, dominant males are also often more fleas than ordinary males - high testosterone levels suppress immunity.

But back to the females.

When a female is pregnant, her life cycle and the life cycle of the parasite are often synchronized, and eventually the parasite also becomes pregnant.

So he conquers new territory - a cub appears, and new parasites are already ready for him.

So pregnant, lactating females and newborns are highly infected in many species. And sometimes you can observe what scientists call sexual segregation - males during this period keep themselves apart so as not to get infected themselves. At least there is such a version. In reality, we see, for example, in bats, that at this time the females form a so-called brood colony, and here they sit, covered with ticks and fleas, and the neat males just look at them. From afar.

Also synchronous with parasites. I only heard about the synchronization of menstruation

- This is a very common phenomenon. It is convenient for parasites to reproduce at this time, because, firstly, the host's immune system is suppressed by a high level of hormones, and secondly, sex hormones, steroids, have a rather simple transformation process. The parasite, consuming steroids in the blood, quickly metabolizes them into its own - and immediately becomes pregnant, gives birth to offspring, and it successfully undergoes metamorphosis into an adult.

And we can talk about a dynasty of parasites if the species has specific parasites, life-long. If they are passed from parent to child, then their evolutionary history developed in parallel. And if we build an evolutionary tree for a given parasite, it will reflect the evolution of the host.

The phylogeny of the parasite very often helps to complete some links in the host's phylogeny, or at least to figure out some small facts, for example, this is how migration processes can be established. For example, with the help of parasites, it was found that some species of lemmings crossed Beringia several times and populated the New World several times.

If you and I drew posters with the phrase “equal rights for parasites” and went out with them to the square, what would we say to journalists who would come up to us for a comment?

- First of all, we would demand the right to study and protection. Parasites, like all biological objects, have the right to be perceived as a necessary part of the biosphere and to protect it.

According to the latest data, among all organisms of the biosphere are parasitic - half, if not more. We cannot say more precisely yet, because many groups of parasites are still very little studied. But this already demonstrates that parasites are an integral component of the ecosystem, and our task is to understand why it is necessary. The good news is that the role of parasites in the ecosystem has been revisited lately. Abroad, this process began about 20 years ago, in Russia we are doing this now.

The data obtained will help us better understand the biology of the host and find out who the parasite is. For example, it was previously believed that lichen is a kind of symbiotic relationship between fungi and algae, but now it seems that the fungus parasitizes there.

And if we talk about the protection of parasites, now in the Red Data Books you can find only some leeches and a louse of a pig-eared pig. The latter ended up there, because the pig itself was an endangered species, as a result, its specific louse was also brought there. But it's good that they did it.

If the host species has a low abundance, then its specific parasite, for which it is the only host, should be automatically entered into the protected list.

And sometimes it needs to be entered earlier, because there is a high probability that it has already become extinct. The fact is that to maintain the number of the parasite, a certain minimum number of hosts is needed. And when it falls below this limit, that's it, the parasite dies out.

Why? Here we have two pigs, each with several parasites. Let them breed for health

- Parasites also need genetic diversity. If we can still maintain this genetic diversity in the host population, then we simply cannot with parasites. Or it may happen that these parasites are necessary for the hosts.

Scientists have this rule: the more species there are in a community, the more stable it is. And we never thought about whether this rule applies to parasites. And it spreads. The more parasites in a community, the more resistant it is.

What is your favorite parasite?

- I love mites of the genus Spinternix, they live on the wings of bats and are incredibly beautiful. They have a tiled cuticle with shields of various shapes - completely alien creatures! You look at them and get aesthetic pleasure.

And if we talk about properties, then most of all I am interested in rhinonisids - these are ticks that live in birds in the lungs. The fact is that these are ectoparasites, that is, external parasites that have passed to endoparasitism. And for this it was necessary to contrive. In this sense, they are unconditional good fellows.

In general, parasitic arthropods, especially ticks, should be considered as some kind of parallel to us and approximately the same intelligent form of life. It is different, but no less intelligent than we are, just intelligent in its own way. We have adapted to live in the Arctic Circle, and ticks are in the pulmonary sacs, in the stomach and in a thousand other places with an aggressive environment.