Generality
Protozoa are single-celled eukaryotic microorganisms, very common in nature.
In fact, the more than 50, 000 different species of existing protozoa populate the most diverse habitats on the planet: from the ground to the deepest seas.
The protozoa live in close contact with the human being, but only on some occasions are they dangerous for the health of the latter.
Protozoa are responsible for some somewhat "famous" human infectious diseases, such as: malaria, toxoplasmosis, giardiasis, Chagas disease, etc.
What are protozoa?
Protozoa are a heterogeneous group of unicellular eukaryotic microorganisms, widespread in almost all types of habitats, from the ground and the deepest sea to freshwater basins.
They are heterotrophs, that is, organisms that draw energy and other compounds by feeding on organic substances processed by other organisms.
In the opinion of microbiologists, in nature, there would be more than 50, 000 different species of protozoa .
Meaning of eukaryotic microorganism and unicellular microorganism
According to biologists, all those microorganisms and organisms whose cellular DNA is enclosed within a structure known as the cell nucleus are eukaryotes .
The fact of possessing a cellular nucleus within which the genetic material resides is what distinguishes eukaryotes from the so-called prokaryotes: in the latter the DNA is dispersed in the cytoplasm.
A unicellular microorganism is a microorganism consisting of a single cell.
It differs from a multicellular organism, which is instead a living being formed by multiple cells.
THEY ARE PROTISTS
The protozoa represent a subnet of the kingdom of protists .
Protists are a group of eukaryotic microorganisms and organisms, difficult to classify, as they have characteristics common to animals, plants and, in some cases, even mushrooms.
According to the definitions provided by the microbiology texts, all the eukaryotic living beings that cannot be inserted into the animal, vegetable or fungal kingdom belong to the realm of protists.
Classification
The classification of protozoa has always raised considerable debate.
Without going into too much detail of the most discussed points, here it was decided to report the most common protozoa distinction, which discerns the aforementioned microorganisms based on the structures for the movement:
- Group of ciliated protozoa . The ciliated protozoa have this name because they have, around the cell that constitutes them, small mobile hairs, known as cilia .
The synchronized movement of the cilia is what guarantees the displacement of this group of protozoa.
The most important examples of ciliary protozoa are:
- Balantidium coli
- Paramecium
- Group of flagellated protozoa . The flagellated protozoa have this identifying name, because the cell that constitutes them uses one or more flagella to move. The flagella are elongated mobile structures, similar to long mobile cilia.
The most important examples of flagellated protozoa are:
- Giardia lamblia
- Trypanosoma brucei
- Trypanosoma cruzi
- Trichomonas vaginalis
- Group of prorozoa sporozoa . The protozoa sporozoa lack the structures assigned to the movement (flagellum or cilia that they are).
They have the particularity of behaving like parasites against those living beings (animals or human beings), with which they manage to make contact.
Protozoan sporozoa can pose a real threat to the health of parasitized individuals.
The most important examples of protozoan sporozoa are:
- Plasmodium knowlesi
- Plasmodium malariae (the famous causative agent of malaria in humans)
- Toxoplasma gondii (the famous etiologic agent of toxoplasmosis in humans)
- Group of amoeboid protozoa . The amoeboid protozoa move through extroflexions of the plasma membrane, extroflexions that microbiologists call pseudopodia .
The ability to create these extroflexions also allows these microorganisms to incorporate potentially nutritious substances, which are found in the environment.
The most important examples of amoeboid protozoa are:
- Entamoeba histolytica
- Acanthamoeba
History
The first person to notice the existence of protozoa was a Dutch scientist named Anton Van Leeuwenhoek, who lived between 1632 and 1723.
Van Leeuwenhoek's studies on protozoa began in 1674 and ended in 1716: in this period of time the Dutch scientist discovered a rather famous protozoan, which in the future took the name of Giardia lamblia .
To coin the term "protozoa" (singular "protozoan"), was the German zoologist Georg August Goldfuss, in 1818.
Literally, the word "protozoa" means "primitive organisms".
Features
In general, protozoa is between 10 and 50 micrometres in size .
However, there are particular protozoa that, from the point of view of size, represent real exceptions and can even reach 20 centimeters in diameter (NB: it is a protozoan that lives in the deep sea, known as Xenophyophorea ).
FILM
Some protozoa - in particular the ciliated protozoa - have an external film, which supports the entire plasma membrane (thus enveloping the entire protozoan cell).
The features of the film are mainly two:
- Further protect the cell e
- Maintain the shape of the cell while moving .
The protozoa film can be flexible and elastic, or rigid.
FEEDING MODES
Protozoa can take food in different ways:
- By osmosis . It means that there is a passage of nutrients through the cell membrane.
- For phagocytosis . It means that the absorption of food occurs through extroflexions of the plasma membrane (the pseudopods already discussed).
- Through cytostome . The cytostome is a mouth-like opening.
LIFE CYCLE
The life cycle of protozoa includes two stages:
- A stage of intense activity and mobility, during which the protozoa are also called trophozoites .
The trophozoites are, in fact, the protozoa in the active vital form.
- A stage of dormancy, during which protozoa are also called protozoan cysts .
Protozoa enter this stage when they are faced with periods of time when they do not have nutrients, water or oxygen at their disposal, or in which environmental conditions are inhospitable (high temperatures, exposure to toxic chemicals, etc.).
REPRODUCTION
In general, protozoa reproduce by binary fission (or binary fission ).
Binary splitting is a form of asexual reproduction, very common among simple micro-organisms such as unicellular ones.
RELATIONSHIPS WITH THE HUMAN BEING
Perhaps not everyone knows that there is a close relationship between humans and protozoa: the latter, in fact, populate our skin or live within the gastrointestinal system like many bacteria, without having particular repercussions on health.
Protozoa that live in close contact with the human being can be dangerous when the human immune defenses lose their effectiveness.
Diseases in the human being
The protozoa that can cause diseases in humans have all the characteristics of parasites and take the generic name of pathogenic protozoa .
The main pathogenic protozoa cause:
- Malaria . It is a widespread infectious disease in tropical areas, which can cause fever, chills, sweating, irritability, tiredness, decreased appetite and so on.
Cause: Plasmodium malariae, belonging to the group of protozoan sporozoa.
- Amoebiasis . It is a faecal-gold infection that generally causes intestinal symptoms.
Cause: Entamoeba histolytica, belonging to the group of amoeboid protozoa.
- Amoebic dysentery . It is an infectious disease with different analogies with amoebiasis. It is responsible for diarrhea, abdominal pain and fever.
Cause: Entamoeba histolytica, belonging to the group of amoeboid protozoa.
- Giardiasis . It is a parasitic infection that produces gastrointestinal symptoms (diarrhea, nausea, vomiting etc.).
Cause: Giardia lamblia, belonging to the group of flagellated protozoa.
- Toxoplasmosis . It is a generally asymptomatic infection. When it is symptomatic, it is responsible for a flu-like symptomatology. Very dangerous if contracted in pregnancy, as it can cause mental retardation in the fetus or abortion.
Cause: Toxoplasmosis gondii, belonging to the group of protozoan sporozoa.
- Cryptosporidiosis . It is an infection that affects the intestine and causes mainly diarrhea.
Cause: Cryptosporidium, belonging to the group of protozoan sporozoa.
- Trichomoniasis . It is an infectious sexually transmitted disease that attacks the vagina (in women), the urethra and the prostate (in men).
Cause: Trichomonas vaginalis, belonging to the group of flagellated protozoa.
- Chagas disease . It is an infectious disease that starts with fever, swollen lymph nodes and headache and culminates at the end of its course with cardiomyopathy and heart failure.
Cause: Trypanosoma cruzi, belonging to the group of flagellated protozoa.
- Human leishmaniasis . Widespread especially in tropical and subtropical areas, it can affect the skin (cutaneous leishmaniasis) or some internal organs, including spleen, liver or bone marrow (visceral leishmaniasis).
Cause: Leishmania, belonging to the group of flagellated protozoa.
- African trypanosomiasis . More known as a sleeping sickness, it is an infectious disease that can cause: joint pain, fever, swollen lymph nodes in the neck, itching, anemia (advanced stages), cardiac dysfunctions (at an advanced stage) and kidney dysfunctions (at one advanced stage).
Cause: Trypanosoma, belonging to the group of flagellated protozoa.
- Acanthamoeba keratitis . It is an infectious ocular disease, which affects mainly contact lens wearers.
Cause: Acanthamoeba, belonging to the group of amoeboid protozoa.
- Primary amoebic meningoencephalitis . It is an infectious disease responsible for an inflammatory state affecting the meninges and the brain.
Typical symptoms are: headache, fever, blindness, hallucinations and / or euphoria.
Cause: Acanthamoeba, belonging to the group of amoeboid protozoa.
