Parasites

Generality

Parasites are organisms that depend on other organisms (the so-called "hosts"), as they derive from them the nutrients they need for their survival, growth and reproduction.

Some parasites are of particular medical interest, since, in addition to stealing food from guests, they are also responsible for more or less serious diseases.
According to experts, in nature, there are 3 main classes of parasites that cause disease in humans: the class of protozoa, the class of helminths and the class of ectoparasites.
Protozoa are unicellular microorganisms, which live inside the host; helminths are vermiform multicellular organisms; finally, ectoparasites are multicellular organisms that parasitize the host from the outside.

What are parasites?

Parasites are organisms that live at the expense of other organisms (the so-called "host" organisms), drawing from them the nutrients they need to survive, grow and reproduce.
Against the host organisms, some parasites are responsible for more or less serious diseases.

MEANING OF PARASITOSIS

Before describing the most important classes of parasites present in nature, it is good to draw the attention of readers to the meaning of parasitosis.
Parasitosis is the medical term for an infectious disease transmitted or caused by parasitic organisms.

ORIGIN OF THE TERM PARASITE

The word "parasite" comes from the Greek word "parasitos' (παράσιτος), which in Italian can be translated as "one who eats at another's table".
Breaking down the term parasitos, this is composed of:

• Para (παρά), which means "beside", e
• Sitos (σῖτος), which means "food".

Classes

In nature, there are three main classes of parasites that cause disease in humans.
Such classes of parasites are:

• The protozoa
• The helminths
• Ectoparasites

The protozoa and helminths that live specifically inside the host are also called endoparasites, ie "parasites of the" interior "(N.B: the prefix" endo "derives from the Greek word"éndon"which means" inside "or" inside ").

PROTOZOA

Protozoa are a heterogeneous group of unicellular eukaryotic microorganisms, widespread in almost all types of habitat possible, from the ground and the deepest sea to freshwater basins.
They are heterotrophic, that is organisms that draw energy and other compounds, feeding on organic substances processed by other organisms.
Microbiologists have estimated that, in nature, there are more than 50,000 different species of protozoa and have observed that the best criterion for distinguishing the aforementioned large number of species is the mode of movement in the environment.
Based on the modes of movement used by protozoa, these microorganisms can be divided into four large groups:

• The group of ciliated protozoa. To move, they make use of cilia, which are hair-like structures that line the outer surface of the protozoan cell.
  Some examples: Balantidium coli And Paramecium.
• The group of flagellated protozoa. To move, they use one or more flagella, which, in fact, are very large and elongated cilia.
  Some examples: Giardia lamblia,Trypanosoma brucei,Trypanosoma cruzi And Trichomonas vaginalis.
• The group of amoeboid protozoa. To make their movements, they resort to extroflexions of the plasma membrane, which in technical jargon are called pseudopodia.
  Through the pseudopods, the amoeboid protozoa are also able to incorporate the nutrients found in the environment.
  Some examples: Entamoeba histolytica And Acanthamoeba.
• The group of sporozoa protozoa. They lack structures for movement. This has made them powerful parasites, as they are forced to live off what their surroundings provide.
  Some examples: Plasmodium knowlesi,Plasmodium malariaeAnd Toxoplasma gondii.

The human being lives every day in contact with protozoa, but this does not mean that he is parasitized or is at risk of parasitosis.
In fact, in most cases, the close protozoa-human relationship has no consequences on human health; any problems that may arise from this are generally due to a decline in the immune defenses, that is, of that defensive system that protects the organism from infectious microorganisms and other threats.

Protozoa which, by behaving like parasites, can cause disease in humans are also called pathogenic protozoa.
When they manage to infect an individual, pathogenic protozoa have a general tendency to lurk in the intestine.
Among the best known diseases caused by pathogenic protozoa are:

• Malaria → causative agent: Plasmodium malariae, of the group of protozoa sporozoa.
• Amoebiasis → causative agent: Entamoeba histolytica, from the group of amoeboid protozoa.
• Amoebic dysentery → causative agent: Entamoeba histolytica, from the group of amoeboid protozoa.
• Giardiasis → causative agent: Giardia lamblia, of the group of flagellated protozoa.
• Toxoplasmosis → causative agent: Toxoplasmosis gondii, of the group of protozoa sporozoa.
• Human leishmaniasis → causative agent: Leishmania, of the group of flagellated protozoa.
• Trichomoniasis → causative agent: Trichomonas vaginalis, of the group of flagellated protozoa.
• Chagas disease → causative agent: Trypanosoma cruzi, of the group of flagellated protozoa.
• African trypanosomiasis → causative agent: Trypanosoma, of the group of flagellated protozoa.
• Primary amoebic meningoencephalitis → causative agent: Acanthamoeba, from the group of amoeboid protozoa.

ELMINTI

Visible to the naked eye in their adult stage, helminths are worm-like multicellular organisms, which, like parasites, live inside the host organism (usually in the intestine).
In living at the expense of the host, helminths always cause limited damage to the organism that hosts them. By adopting this strategy, they derive maximum benefits from their parasitic behavior: the survival of the host organism, in fact, also guarantees their survival.
Moreover, if helminths caused the death of those who supply them with food, they would face death themselves.
The typical consequences of helminth parasites consist of: debilitation of general health, presence of diseases and / or a state of malnutrition.
The classification of helminths is a matter of debate and discussion. Without going into too much detail of the most discussed points, here it was decided to report the most common classification, which recognizes the existence of three main groups of helminths:

• The group of flatworms or flat worms.
  Capable of living both as free forms and as parasitic forms, the Platelminti are organisms with bilateral symmetry, with a flattened and depressed body in the dorsal-ventral sense, and without respiratory organs and a real circulatory system.
  They have a digestive cavity, with an "opening for the ingestion of food and another" opening for the expulsion of waste substances.
  In nature, there are two subgroups of Platelminti that can nest inside the human body: the Trematodi Platelminti and the Cestodi Platelminti.
• Trematodes: These are leaf-shaped or elongated worms, which can parasitize the intestinal tract, liver, lungs and blood vessels.
  Examples of Trematodi: Schistosoma mansoni, Schistosoma japonicum And Fasciola hepatica.
  Examples of Trematode parasitosis: schistosomiasis and swimmer's dermatitis.
• Cestodes: they are ribbon-shaped worms with a segmented body, characterized by the presence of a particular adhesion organ, known as scolice.
  They can lodge in the digestive tract or in the tissues.
  Examples of Cestodes: Taenia solium, Taenia saginata And Hymenolepis.
  Examples of Cestode parasitosis: solitary worm.
• The group of Nematodes or cylindrical worms. They are bilaterally symmetrical, non-metameric, cylindrical, thread-like or fusiform worms, which can measure a few millimeters or even several decimeters.
  Like the Platelminti, they are able to live in both free and parasitic form.
  Inside the human body, they can parasitize the intestinal tract, blood, lymph or subcutaneous tissues.
  Examples of Nematodes: Ascaris, Trichuris, Necatur americanus And Rhabditis.
  Examples of Nematode Parasitosis: ascariasis, necatoriasis, trichinosis, trichuriasis, elephantiasis, enterobiasis, etc.
• The group of Acanthocephals or hookworms or, again, gods worms with hooked heads. They are bilaterally symmetrical worms, with a cylindrical body and a color tending to white.
  The peculiarity of the Acanthocephali is the presence of a spiny retractable proboscis at the level of the head: this proboscis (from which the name of hookworms depends) is an organ that serves for adhesion.
  Of average length between 4 and 5 centimeters, they lack mouth, intestines and anus. To take in the nutrients, they use osmosis.
  They are of little interest to the human being, as they do not seem capable of infecting the latter.

Most important features of helminths

Life cycle

The life of helminths varies from group to group: some helminths live on average one year, others can survive for up to 8 years.
The lifespan of a helminth depends on how it affects the host's immune system.

Cestodes and Trematodes are, as a rule, hermaphrodites; Nematodes tend to differentiate into males and females.

Reproduction and Eggs

To reproduce, all helminths produce eggs.
Helminth eggs have a tough, multi-layered casing, which protects them from threats from the external environment.

Generally, the total number of eggs laid by a helminth, during the reproductive phase, is in the thousands or hundreds of thousands.

Adult helminths lay their eggs at least once a day; Taenia solium it also lays eggs six times a day.

Larval state and larvae

From the hatching of the helminth eggs, the larvae arise.
The maturation process of the eggs, which leads to the birth of the larvae, varies from helminth to helminth: there are helminths whose egg maturation process takes a couple of weeks and helminths whose egg maturation process takes up to 4 months.

ECTOPARASITES

Ectoparasites are all those parasitic organisms that live and grow outside the host, binding, for example, in the case of humans, to the skin.
The bond established by the ectoparasites can also be very long, in the order of weeks if not months.
The ability of ectoparasites to stabilize outside the host organism is generally due to specific organs and the mouth apparatus, which therefore has a double function: to allow the binding and to take nutrients from the host.
Ectoparasites of human interest belong to the phylum of the Arthropods and are: ticks, lice, mites, mosquitoes and fleas.
Some of the aforementioned parasites can cause very serious, sometimes fatal diseases (for example ticks).

Ectoparasite meaning
The term ectoparasite has the prefix "ecto", which derives from the Greek word "ektós", whose Italian meaning is" out "or" external ".
In light of this, therefore, ectoparasites are "the parasites of the" outside ".