Parasitic protozoa

The type of protozoa (Protozoa) includes over 15, 000 species of animals that live in the seas, fresh waters and soils. In addition to free-living forms, many parasitic forms are known, which sometimes cause serious diseases - protozoanosis.

The body of the protozoa consists of only one cell. The body shape of protozoa is different. It can be permanent, have radial symmetry, bilateral (flagellates, ciliates) or have no permanent form (amoeba). The body size of protozoa is usually small - 2-4 microns to 1. 5 mm, although some large individuals reach 5 mm in length, and the fossil shell rhizomes were 3 cm or more in diameter.

the simplest human parasites

The body of the protozoa consists of the cytoplasm and the nucleus. The cytoplasm is limited by the outer cytoplasmic membrane, it contains organelles - mitochondria, ribosomes, endoplasmic reticulum, Golgi apparatus. Protozoa have one or more nuclei. The form of nuclear division is mitosis. There is also a sexual process. It consists in the formation of a zygote.

The movement organelles of the protozoa are flagella, cilia, pseudopodia; or none. Most protozoa, like all other representatives of the animal kingdom, are heterotrophic. However, among them there are also autotrophic ones.

The peculiarity of the simplest unfavorable environmental conditions to bear is the ability to engrave, eg. form a cyst. With the formation of a cyst, the organelles of movement disappear, the volume of the animal decreases, acquires a rounded shape, the cell is covered with a dense membrane. The animal enters a state of rest and, when favorable conditions occur, returns to an active life.

Engraving is a device that serves not only for protection, but also for the spread of parasites. Some protozoa (sporozoa) form an oocyst and, in the process of reproduction, a sporocyst.

Reproduction of protozoa is very diverse, from simple division (asexual reproduction - about Biofile. Ru) to a rather complex sexual process - conjugation and copulation.

The habitat of the simplest is varied: it is the sea, fresh waters, moist soil. Parasitism is widespread. Many species of parasitic protozoa cause severe disease in humans, domestic and wild animals, and plants.

Protozoa are able to move with the help of pseudopods, flagella or cilia, react to various stimuli (phototaxis, chemotaxis, thermotaxis, etc. ). Protozoa feed on the smallest animals, plant organisms and decaying organic matter, parasitic forms live on the surface of the body, in body cavities or in the tissues of their host organisms.

The pathways of food intake in the cell body are also different: pinocytosis, phagocytosis, osmotic pathway, active transport of substances across the membrane. They digest food received in digestive vacuoles filled with digestive enzymes. Some of them with photosynthetic intracellular symbionts - chlorella or chloroplasts (for example, euglena) are able to synthesize organic matter from inorganic substances using photosynthesis.


Toxoplasmosis (Greek toxon - arc, arc) refers to diseases caused by the simplest single-celled organisms in the most diverse places of the human body, where their introduction and reproduction took place. The causative agent of toxoplasmosis - Toxoplasma Toxoplasma gondii belongs to the genus of protozoa, to the class of flagellates.

Toxoplasma is shaped like a crescent and resembles an orange slice: one end of the parasite is usually pointed, the other is rounded, up to 7 microns long. Toxoplasma moves by flowing. They penetrate the cells by rotating around the longitudinal axis.

Reproduction of Toxoplasma is asexual, it occurs by longitudinal division in two. As a result of the repeated longitudinal division in the protoplasm of the host cell, an accumulation of child parasites, called "pseudocysts", is formed. Pseudocysts are found in large numbers in various organs of the infected organism during the acute phase of the infection. They are surrounded by a very dark membrane, apparently formed by the host cell, and do not have their own membrane. Cells full of these parasites are destroyed. The released parasites penetrate into new cells, where they divide again and form new pseudocysts.

When the infection turns into a chronic form, Toxoplasma is preserved in the form of real cysts (they surround themselves with a special shell). Such cysts have the ability to persist for a long time in the body of animals and humans (up to 5 years). Cysts are also found in the tissues of the eye, heart, lungs, and some other organs. The number of Toxoplasma in a cyst varies from a few copies to several thousand.


Giardia is the simplest parasitic animal of the class of flagellates. It is pear-shaped, 10-20 µm in length; the dorsal side is convex, the ventral side is concave and forms a sucker for the temporary attachment to the epithelial cells of the host's intestine. 2 oval nuclei, 4 pairs of flagella. It lives in the human intestine (especially in children), mainly in the duodenum, less often in the bile duct and gallbladder, causing giardiasis. They are common carriers of asymptomatic parasites. Cyst infection occurs when protozoa enter the lower intestine through the mouth when contaminated food or water enters the body, as well as through dirty hands, etc. The incidence is sporadic. Giardiasis is common in all parts of the world.

The causative agent of the disease is lamblia - (Lamblia intestinalis). Giardia is a single-celled microscopic parasite. Giardia is able to withstand freezing and heating up to 50 ° C, but it dies when boiled. In the United States, giardiasis is the leading gastrointestinal disease of parasitic origin. According to the INTERNET, giardiasis affects up to 20% of the world population. Infection can occur when drinking unboiled tap water or ice made from such water when washing fruits and vegetables with unboiled water. There is a high risk of getting sick when swimming in open bodies of water and in pools infected with lamblia cysts. A newborn can become infected during labor during the rash and birth of the head. Rarer is the contact-family route of infection, however, with a high prevalence of the disease, it becomes quite real, especially among segments of the population with poor general sanitation skills.


Trichomonas vaginal cysts do not form, they feed on bacteria and erythrocytes. It causes inflammation of the genitourinary system - trichomoniasis. The causative agent of the disease is sexually transmitted. Out-of-sex infection (through sharing toiletry items, bedding, etc. ) is less common. It can be passed on to a newborn from a sick mother. The transition of the disease to a chronic form is possible. When spread to the appendages, it is difficult to treat. With trichomoniasis, the vagina is most often affected, abundant purulent discharge appears with an unpleasant odor; you feel itching and burning sensation in the vagina. In men, the symptom is inflammation of the urethra (urethritis), accompanied only by minor mucous secretions.


The amoeba lives in fresh water. The shape of the body is fickle. It performs very slow movements (13 mm / h). It moves with the help of pseudopodia, the body flows from side to side: either it shrinks into a round lump, or it spreads the "tongues-legs" to the sides.

Pseudopods also serve to capture food. In the process of feeding, the body of the amoeba flows around the food particles from all sides and ends up inside the cytoplasm. A digestive vacuole appears. This way of eating is called fabitosis. Food is made up of bacteria, unicellular algae, small protozoa. The dissolved substances from the environment are absorbed by pinocytosis.

In the body of the amoeba there is a contractile or pulsating vacuole. Its function is to regulate the osmotic pressure inside the protozoan's body. Reproduction is asexual, by mitosis, followed by the division in two of the amoeba body. Of great importance in medicine are amoebas of the genus Entamoeba, which lives in the human digestive tract. These include dysentery or histolytic amoeba.

Plasmodium of malaria

Plasmodium malaria causes malaria, which proceeds with bouts of fever, changes in the blood, enlarged liver and spleen. There are four forms of malaria: three days, four days, tropical and ovalemalaria. The source of the disease is a person with malaria, and the carrier is a female malaria mosquito. The female mosquito, becoming infected while sucking the patient's blood, becomes capable of transmitting plasmodium. A healthy person becomes infected by the bite of a plasmodia-infected mosquito, with whose saliva pathogens enter the body. With blood flow, plasmodia enter the liver, where they undergo the first development (tissue) cycle, then pass into the blood and enter the erythrocytes. Here they complete the second (erythrocyte) development cycle, which ends with the disintegration of erythrocytes and the release of pathogens into the patient's blood, which is accompanied by a fever attack.