Protozoan parasites

The protozoa type (Protozoa) includes more than 15, 000 species of animals living in seas, freshwater and soil. In addition to free forms, many parasitic forms are known, which sometimes cause serious diseases - protozoanosis.

The body of protozoa is made up of a single cell. The shape of the body of protozoa is diverse. It can be permanent, have radial and bilateral symmetry (flagellates, ciliates) or have no permanent form (amoeba). The body size of protozoa is usually small - from 2 to 4 microns to 1. 5 mm, although some large individuals reach 5 mm in length, and the rhizomes of fossil shells are 3 cm or more in diameter.

the simplest human parasites

The body of protozoa consists of the cytoplasm and the nucleus. The cytoplasm is bounded 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 of the formation of a zygote.

The organelles of movement of protozoa are flagella, cilia, pseudopodia; or not at all. Most protozoa, like all other representatives of the animal kingdom, are heterotrophic. However, among them there are also autotrophs.

The peculiarity of the simplest to endure adverse environmental conditions is its ability to encyst, that is, to form a cyst. With the formation of a cyst, the organelles of movement disappear, the volume of the animal decreases, it acquires a rounded shape, the cell is covered with a dense membrane. The animal enters a state of rest and, when favorable conditions arise, returns to an active life.

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

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

The habitat of the simplest is diverse - it is the sea, fresh water, wet soil. Parasitism is widespread. Many species of parasitic protozoa cause serious disease in humans, pets, and game and plants.

Protozoa are able to move with the help of pseudopodia, flagella or cilia, react to various stimuli (phototaxis, chemotaxis, thermotaxis, etc. ). Protozoa feed on smaller 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 routes of food supply in the cell body are also different: pinocytosis, phagocytosis, osmotic route, active transport of substances across the membrane. They digest the food received in digestive vacuoles filled with digestive enzymes. Some of them with photosynthetic intracellular symbionts - chlorella or chloroplasts (for example, euglene) are able to synthesize organic matter from inorganic substances using photosynthesis.


Toxoplasmosis (Greek toxon - arc, arc) refers to the 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 crescent-shaped and looks like an orange slice: one end of the parasite is usually pointed, the other is rounded, up to 7 microns in length. The toxoplasm moves by sliding. They enter the alveoli rotating around the longitudinal axis.

Reproduction of Toxoplasma is asexual, it takes place by longitudinal division into two. As a result of repeated longitudinal divisions in the protoplasm of the host cell, an accumulation of daughter parasites is formed, called "pseudocysts". Pseudocysts are found in large numbers in various organs of the infected body during the acute phase of infection. They are surrounded by a very dark membrane, apparently formed by the host cell, and do not have their own membrane. Cells filled with these parasites are destroyed. The released parasites enter 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 in the body of animals and humans for a long time (up to 5 years). Cysts are also found in the tissues of the eyes, heart, lungs, and some other organs. The number of Toxoplasma in a cyst varies from a few specimens to several thousand.


Giardia is the simplest parasitic animal of the flagellate class. It is pear-shaped, 10 to 20 µm long; the dorsal side is convex, the ventral side is concave and forms a suction cup for temporary attachment to the epithelial cells of the host's intestine. 2 oval nuclei, 4 pairs of flagella. It lives in the human intestine (mainly in children), mainly in the duodenum, less often in the bile ducts and gallbladder, causing giardiasis. Asymptomatic parasite carriers are common. Infection with cysts occurs when protozoa enter the small 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 dies when boiled. Giardiasis is the leading parasitic gastrointestinal disease in the United States. According to the INTERNET, giardiasis affects up to 20% of the world's population. Infection can occur from drinking unboiled tap water or ice made from this water when washing vegetables and fruits with unboiled water. There is a high risk of getting sick when swimming in open bodies of water and swimming pools infected with lamblia cysts. A newborn baby can become infected during labor during the rash and birth of the head. The route of infection through household contact is rarer, however, with a high prevalence of the disease it becomes quite real, especially among segments of the population with poor general hygiene skills.


Trichomonas vaginal cysts do not form, feed on bacteria and erythrocytes. Causes inflammation of the genitourinary system - trichomoniasis. The causative agent of the disease is sexually transmitted. Infection outside of sex (by sharing toiletries, beds, etc. ) is less common. Can be transmitted to a newborn girl from a sick mother. The transition of the disease to a chronic form is possible. When it has spread to the appendages, it is difficult to treat. With trichomoniasis, the vagina is most often affected, profuse purulent discharge with an unpleasant odor appears; itching and a burning sensation in the vagina is felt. In men, the symptom is inflammation of the urethra (urethritis), accompanied by minor mucous secretions.


The amoeba lives in fresh waters. The shape of the body is inconstant. Performs very slow movements (13 mm / h). It moves with the help of pseudopods, the body flows from one part to another: either by shrinking into a round mass, or by spreading the "tongue-legs" on the sides.

Pseudopods are also used to capture food. During the feeding process, the amoeba's body circulates around food particles from all sides and they end 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. Dissolved substances from the environment are absorbed by pinocytosis.

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

Malaria Plasmodium

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