Flagellates: Human Parasites, General Description And Structure

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Flagellates: Human Parasites, General Description And Structure
Flagellates: Human Parasites, General Description And Structure

Video: Flagellates: Human Parasites, General Description And Structure

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Video: Parasites: Protozoa (classification, structure, life cycle) 2023, February

Flagellates, as a class of flagellates, are very diverse and number about 8000 representatives, which have a constant body shape. Flagellate protozoa are able to settle in the human body and cause various diseases.

The content of the article:

  • 1 Flagellate
  • 2 Class characteristics

    • 2.1 Subclass Plant flagellates
    • 2.2 Subclass Animals flagellates
    • 2.3 Squad Multi-flagella
  • 3 Leishmania
  • 4 Giardia
  • 5 Trichomonad intestinal (Trichomonad intestinorum)



Flagellates are a class of protozoan animals of the sarcomastigophora type, uniting 13 orders and more than 7 thousand species. A characteristic feature of all these animals is the presence of whip-like organs of movement - flagella, performing various functions. Thanks to the movement of the flagella, these microorganisms are able not only to move, but also to create currents of water that bring food. All organisms are subdivided into two main groups: phyto-flagellate (related to plants) and zoo-flagellate (similar to animals). The similarity of the two groups of microorganisms with plants and animals is determined by the structure of the cells and the type of nutrition. Thus, phyto-flagellates receive energy through photosynthesis, and zoo-flagellates - through prepared food. The cells of plant flagellates contain chlorophyll for photosynthesis. Some, such asEuglena green in the light synthesize nutrients independently in the process of photosynthesis, and in the dark they feed on ready-made organic substances like animals.

Flagellate. All plant flagellar organisms live freely in the aquatic environment. Zoo-flagellate microorganisms are devoid of chloroplasts, free-living species are rarely found among them, and the overwhelming majority of them have passed to parasitizing in plant and animal organisms. There are symbionts of animals.

The body is covered with a thin outer shell - a pellicle, sometimes with a continuous shell of chitin or a shell of cellular plates. In most species, individuals have one nucleus per cell, but some may have several dozen nuclei. Contractile vacuoles, which also carry out an excretory function, are a device for regulating osmotic pressure. Flagellates with chromatophores have a photosensitive organoid, they are characterized by positive phototaxis.

Class characteristics


One of the most important features used in the classification of protozoa are organelles of movement. In flagellates, these are bundles, or whips - thin cytoplasmic outgrowths. They are usually found at the anterior end of the body and extend from specific basal grains (basal body or kinetosome). The number of flagella in different species ranges from 1 to 8 or more. In some flagellates (leishmanias, trypanosomes), a special organoid, kinetoplast, is also placed at the base of the flagellum. In its ultrastructure, it corresponds to the mitochondria, but has a high DNA content. It is believed that energy is generated in the kinetoplast for the movement of the flagellum, which makes a rotational movement and, as it were, is screwed into the water. In some representatives of the class, the flagellum runs along the body, connecting with it with a thin outgrowth of the cytoplasm. The mentioned outgrowth,or an undulating membrane, performs wavelike movements and serves as an additional organoid of movement.

The body of the flagellates is microscopic in size, covered with a pellicle and has a relatively constant shape (oval, pear-shaped, or fusiform) characteristic of each species. The nucleus of the cell is bubble-shaped, contains one or more nucleoli. Usually flagellates have one nucleus, but there are two-core forms. Many species have contractile vacuoles, while parasitic forms do not.

By way of nutrition (assimilation), they are divided into:

  • heterotrophic - have digestive vacuoles. Parasitic forms suck up food on the entire surface of the body, mainly by pinocytosis.
  • autotrophic - chloroplasts serve as organelles of nutrition
  • mixotrophic - they can use both inorganic and organic substances for nutrition, which allows them to be classified as transitional forms from plants to animals.

Reproduction is usually asexual, by longitudinal division into two parts. Many species also have a sexual process, during which the fusion of sexual forms (copulation) occurs.

Flagellates live in fresh and sea water, less often in moist soil and play an important role in the life of water bodies, in the cycle of substances in nature. Many flagellates are parasitic. The class includes over 6,000 species.

Subclass Plant flagellates


This includes single and colonial flagellates containing chloroplasts and capable of independently providing themselves with organic compounds due to photosynthesis reactions. In the absence of light, they are able to absorb exogenous organic matter. Vegetable flagellates live in salt and fresh water, in large bodies of water they are part of the plankton.

Naturally, there are no parasitic forms among them. An interesting feature of many representatives of this subclass (euglena, dinoflagellates) is the presence of a light-sensitive eye (stigma) containing a red pigment, sometimes a kind of lens made of starch grain protrudes into it. In some dinoflagellates, this structure can reach significant sizes - up to 25 microns. The most famous representative of plant flagellates is euglena (290), as well as the colonial forms described above.

Subclass Animals flagellates

This subclass unites exclusively heterotrophic flagellates. The various members of the subclass are solitary or colonial. Many animals flagellates are parasites, including humans, causing a number of serious diseases. For this reason, this subclass is of particular interest from a medical point of view. The greatest number of human parasites is included in the orders of kinetoplastid and multi-flagella.

The order Kinetoplastid is distinguished by the presence in its representatives of a special organelle located near the basal corpuscle of the flagellum - the kinetoplast. In fact, it is a large mitochondria with a high DNA content.

African trypanosomes are the causative agents of the most severe sleeping sickness. Depending on the geographic region, there are East African Rhodesian and West African Gambian trypanosomes. The parasite is carried by the blood-sucking tsetse flies from the glossin genus, and the natural reservoir is wild ungulates, more recently, primarily humans, as well as domestic animals.


The parasite is characterized by a complex development cycle. The first stage takes place in the digestive system of the tsetse fly, and the second in a large vertebrate animal or person. With the saliva of a carrier fly, when bitten, a pathogenic microorganism enters the blood and lymph of a person, after which the brain is affected. Symptoms initially appear as mild fever, but then muscle weakness, fatigue, and drowsiness appear. A deep depletion of the body develops, drowsiness is replaced by prolonged periods of coma, during which the patient's body is often seized by convulsions. The West African variant of sleeping sickness can develop for years (up to 10 years) and without treatment is usually fatal, although spontaneous recovery has been reported.East African trypanosomiasis develops much faster and ends with death as early as the sixth month of the disease.

Flagellate. The disease, unfortunately, is still widespread in the countries of tropical Africa (about 10,000 people are infected with Gambian trypanosomes annually, and 1500 with Rhodesian ones). Vaccines are ineffective or ineffective at all, since the parasite, during its development in the human body, changes its antigenic properties after each reproduction. However, at present, relatively effective medications have been found, which have significantly reduced mortality.

An American trypanosomiasis called Chagas' disease occurs in South and North America. The causative agent first infects macrophages, and then striated muscle tissue (including cardiomyocytes) or brain neuroglia, where it loses flagella and multiplies. Cases of detection of the parasite in the human spleen and liver are described.


The course of the disease is accompanied by weakness and high fever; in children, it often ends in death. Carriers are triatomaceous bugs, which are also called "kissing bugs" for their tendency to drink blood by biting the skin of the lips. In the intestines of the bug, trypanosomes multiply and become invasive (capable of infecting humans). Defecating on the skin, bugs leave numerous parasites in the feces, which, through minor skin lesions, penetrate the bloodstream and are carried throughout the human body.

In addition to humans, some trypanosomes can cause disease in camels and cattle. These parasites enter the body of animals through bloodsucking flies. But the infection of horses with trypanosomes occurs sexually, as a result of which the disease is called "coining disease".

Among the kinetoplastid pathogens that are pathogenic for humans, an important role belongs to Leishmanias, which received the generic name in honor of the English physician W. Leishman, who was one of the first to describe these parasites.

They have complex developmental cycles and are carried by blood-sucking insects (mosquitoes). Leishmanias are intracellular parasites that infect the mononuclear phagocyte system. Inside cells (primarily blood monocytes and tissue macrophages), the parasite is in an amastigotic state (i.e., without flagella), but flagella are formed in the mosquito's body or on a nutrient medium. Depending on the localization, human leishmaniasis are of two types - dermatotropic (affecting the skin) and viscerotropic (affecting internal organs).

Detachment Multi-flagella

The order of the Multi-flagella is composed exclusively of parasitic microorganisms, they all have several flagella. Human parasites are Trichomonas and Giardia. Vaginal trichomoniasis is widespread and is caused by Trichomonas vaginalis. The parasite causes inflammation of the female and male genital organs. Also known is the intestinal Trichomonas, which lives in the large intestine and feeds on bacteria.

Since the pathogenic effect of this protozoan on the human body has not yet been identified, there is no reason to consider it a parasite. But a completely obvious parasite is lamblia, the causative agent of giardiasis. This simplest was named in honor of the professor of Kharkov University D.F. Lyambl, who opened it in 1859.

The microorganism has a pronounced bilateral symmetry, two nuclei and eight flagella. The presence of a suction cup on the ventral side of the body allows lamblia to attach to the epithelial lining of the small intestine.

The microorganism usually colonizes the upper parts of the small intestine, primarily the duodenum, and absorbs food from the chyme. Intensive reproduction of the parasite leads to the fact that a significant part of the surface of the mucous membrane is covered with a layer of microorganisms, as a result of which the absorption function of the small intestine is impaired. The disease most often develops in children. Trophozoids trapped in the colon are encystised and excreted in feces.


Leishmania is found in the tropics. Causes a group of diseases - leishmaniasis, occurring with lesions of the skin and mucous membranes (cutaneous leishmaniasis or pendin ulcer) or internal organs (visceral leishmaniasis or kalaazar). Leishmaniasis is carried by mosquitoes, which become infected by sucking the blood of a sick person or animal. The pathogen enters the human body when bitten by a mosquito.

Cutaneous leishmaniasis (pendino ulcer). Leishmanias penetrate human skin, in the cells of which they multiply; an inflammatory process occurs, followed by tissue necrosis (necrosis) and the formation of ulcers. There are two types of cutaneous leishmaniasis: urban and rural.

In urban cutaneous leishmaniasis, infection occurs through sick people and, probably, dogs; the pathogen, having entered the human body, within 2-8 months (rarely 3-5 years) does not cause visible manifestations of the disease (incubation period).

Then a brownish nodule (leishmanioma) appears at the site of the mosquito bite (most often on the face or hands), gradually increasing. After 5-10 months, a round ulcer with dense edges and purulent discharge develops at the site of the nodule. More often 1-3 ulcers occur. The disease lasts 1-2 years.

With rural cutaneous leishmaniasis, infection occurs from the great and midday gerbils, the small-toed ground squirrel, etc. The incubation period for rural cutaneous leishmaniasis is from 1 week to 2 months. The disease begins acutely. On the skin (face, hands, often legs), leishmaniomas appear, resembling an abscess (furuncle). Ulcers form in the first weeks of the illness: irregular,

with dense edges, a yellow bottom and purulent discharge. Healing begins in 2-4 months, followed by scarring. The duration of the disease is 3-6 months.

Flagellate. Visceral leishmaniasis (kalaazar). Infection occurs from a sick person, dogs, wild animals (wolves, foxes, etc.). The incubation period lasts from 10-21 days to 1 year and rarely longer, most often 3-6 months. The disease develops gradually. Weakness, lethargy appear, the temperature rises, the spleen and liver enlarge. The skin acquires a peculiar color - waxy, pale green or dark ("kala-azar" - black disease). There are changes in the heart, blood, adrenal glands, kidneys.

Treatment of leishmaniasis is stationary

Prevention consists in destroying rodent burrows (both rodents and mosquitoes living in these burrows die), trapping stray dogs, examining the entire population of dogs in the outbreak and eliminating animals with leishmaniasis, as well as destroying mosquito breeding sites.



Giardia (Giardia) cause a disease called giardiasis. They parasitize in the small intestine, sometimes in the gallbladder; exist in two forms: mobile (vegetative) and motionless (cyst form). The mobile form of lamblia has four pairs of flagella and a suction disc, with its help it is attached to the mucous membrane of the small intestine. Infection occurs through the use of food and water contaminated with cysts, as well as through hands and household items. Once in the gastrointestinal tract in persons with low acidity of gastric juice and even in a healthy person, lamblia multiply in the small intestine, sometimes in large quantities, causing irritation of the mucous membrane. Pains appear in the upper abdomen or in the navel area, bloating, rumbling, and nausea are noted. There may be constipation followed by diarrhea (mixed with mucus). Most often, children are sick.

Treatment: diet is recommended

Prevention: Personal hygiene, food protection from contamination, fly control.

Trichomonas Intestinal (Trichomonad intestinorum)

small flagellate (length - 5-15 microns), living in the large intestine. It has 3-4 flagella, one nucleus, an undulating membrane and an axostyle. It feeds on bacteria of the intestinal flora. Cyst formation has not been established.

Infection occurs through food and water contaminated with Trichomonas. If it enters the intestines, the parasite multiplies rapidly and can cause diarrhea.

Intestinal Trichomonas creates a lot of problems related to the activity of the intestines to a person, including colitis, enterocolitis, cholecystitis. In addition, according to some researchers, signs of intestinal Trichomonas activity may be edema, erosion, polyps, ulcers; pallor of the skin, anemia, muscle weakness. It is also found in the intestines of healthy people, i.e., carriage is possible.

Diagnosis: Based on the detection of vegetative forms in the feces.


1.Personal. Compliance with the rules of personal hygiene, heat treatment of food and water, thorough washing of vegetables and fruits (especially those contaminated with soil).

2. Public. Sanitary arrangement of public places, monitoring of public water supply sources, sanitary and educational work with the population.

Find out more:

  • Intracellular parasites: types, diagnosis and treatment
  • Giardiasis (lamblia) in adults - signs, symptoms, treatment
  • Giardia in adults - symptoms, diagnosis and treatment

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