Protozoan parasites

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

The body of the protozoan consists of only one cell. The body shape of protozoa is varied. It may be permanent, have radial, bilateral symmetry (flagelate, ciliate), or have no permanent shape at all (amoeba). The body sizes of protozoa are usually small - from 2-4 microns to 1. 5 mm, although some large individuals reach 5 mm in length, and the fossil shell rhizome was 3 cm or more in diameter.

the simplest human parasites

The body of the protozoan 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 in the formation of a zygote.

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

The peculiarity of the most unfavorable environmental conditions simple to endure is the ability to resist, d. m. th. form a cyst. With the formation of a cyst, the organelles of movement disappear, the volume of the animal decreases, it takes on a rounded shape, the cell is covered with a dense membrane. The animal goes into a state of rest and, when favorable conditions occur, returns to an active life.

Encysting 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 separation (asexual reproduction - approximately Biofile. Ru) to a rather complex sexual process - conjugation and union.

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

Protozoa are able to move with the help of pseudopods, flagella or eyelashes, react to various stimuli (phototax, chemotax, thermotax, etc. ). Protozoa feed on smaller animals, plant organisms and decaying organic matter, parasitic forms living on the surface of the body, in body cavities or tissues of their host organisms.

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


Toxoplasmosis (Greek toxon - bow, bow) refers to diseases caused by the simplest single-celled organisms in various parts of the human body, where their introduction and reproduction took place. The causative agent of toxoplasmosis - Toxoplasma Toxoplasma gondii belongs to the genus Protozoa, in the class of flagella.

Toxoplasma is crescent-shaped and resembles an orange slice: one end of the parasite is usually sharp, the other is rounded, up to 7 microns in length. Toxoplasma moves by sliding. They penetrate the cells by rotating around the longitudinal axis.

Reproduction of Toxoplasma is asexual, occurs with longitudinal division into two. As a result of repeated longitudinal division in the host cell protoplasm, a cluster of daughter parasites is formed, which is called a "pseudocyst". 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 filled with such parasites are destroyed. The liberated 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 true cysts (they surround themselves with a special shell). Such cysts have the ability to stay 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 flagellate class parasitic animal. It is pear-shaped, 10–20 µm long; the dorsal side is convex, the ventral side is concave and forms a suction cup for temporary adhesion to the epithelial cells of the host intestine. 2 oval nuclei, 4 pairs of flagella. Lives in the human intestine (mainly in children), mainly in the duodenum, less frequently in the bile duct and gallbladder, causing giardiasis. Asymptomatic parasitic carriers are common. 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. The incidence is sporadic. Giardiasis is common in all parts of the world.

The cause of the disease is lamblia - (Lamblia intestinalis). Giardia is a microscopic single-celled parasite. Giardia is able to withstand freezing and heating up to 50 ° C, but dies when caught. 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's population. Infection can occur when you drink uncooked tap water or ice made from this water when you wash vegetables and fruits with boiled water. There is a high risk of getting sick when swimming in open water bodies and in pools infected with lamblia cysts. A newborn baby can become infected during childbirth during the eruption and birth of the head. The rarest is the contact-family route of infection, however, with a high prevalence of the disease, it becomes quite real, especially in segments of the population with poor general hygiene skills.


Trichomonas vaginal cysts do not form, they feed on bacteria and erythrocytes. Causes inflammation of the genitourinary system - trichomoniasis. The causative agent of the disease is sexually transmitted. Infection outside sex (through shared toilet items with the patient, bed, etc. ) is less common. It can be transmitted to a newborn girl by a sick mother. Transition of the disease to a chronic form is possible. When it spreads to supplements, it is difficult to treat. With trichomoniasis, the vagina is affected more often, abundant purulent discharge appears with an unpleasant odor; feels itching and burning in the vagina. In men, the symptom is inflammation of the urethra (urethritis), accompanied only by small mucous secretions.


The amoeba lives in fresh water. The body shape is unstable. Performs very slow movements (13 mm / hour). Moving with the help of pseudopods, the body flows from one part to another: either shrinking into a round lump, or spreading "tongue-feet" to the sides.

Pseudopods also serve to catch food. In the process of feeding, the body of the amoeba flows around the food particles from all sides, and they end up inside the cytoplasm. A solvent vacuole appears. This way of eating is called fabitosis. Food consists of bacteria, unicellular algae, small protozoa. 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 body. Reproduction is asexual, with mitosis, followed by division of the amoeba body in two. Of greater importance in medicine are amoebae of the genus Entamoeba, which live in the human digestive tract. These include dysentery or histolytic amoebae.

Plasmodium and malaria

Plasmodium malaria causes malaria, which continues with fever attacks, changes in the blood, enlargement of the liver and spleen. There are four forms of malaria: three-day, four-day, 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 by sucking the patient's blood, becomes capable of transmitting plasmodium. A healthy person is infected by the bite of a mosquito infected with plasmodia, with the saliva of which pathogens enter the body. With blood flow, plasmodia enters the liver, where they undergo the first cycle of development (tissue), then pass into the bloodstream and penetrate the erythrocytes. Here they complete the second (erythrocyte) cycle of development, ending with the dissolution of erythrocytes and the release of pathogens into the patient's blood, which is accompanied by a temperature attack.