Protozoa parasites

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

The body of a protozoan consists of only one cell. The body shape of protozoa is diverse. It can be permanent, have radial, bilateral symmetry (whip, cilia) or no permanent shape at all (amoeba). Protozoan body sizes are usually small - from 2-4 microns to 1. 5 mm, although some large individuals reach 5 mm in length, and the rhizomes of fossil shells were 3 cm or more in diameter.

the simplest human parasites

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

The organelles of protozoan movement are whips, cilia, pseudopods; or not at all. Most protozoa, like all other representatives of the animal kingdom, are heterotrophic. However, there are autotrophic ones among them.

The peculiarity of the simplest to withstand adverse environmental conditions is the ability to encistate, ie. form a cyst. With the formation of the cyst, the organelles of movement disappear, the volume of the animal decreases, it takes on a rounded shape, the cell is covered with a thick membrane. The animal goes into a state of rest and, when favorable conditions occur, returns to active life.

Encysting is a device that serves not only to protect, but also to spread parasites. Some protozoa (sporozoa) form oocysts and, in the process of reproduction, sporocysts.

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

The habitat of the simplest is diverse - it's sea, fresh water, moist soil. Parasitism is widespread. Many species of parasitic protozoa cause severe diseases in humans, domestic and wild animals and plants.

Protozoa can 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 decomposing organic matter, parasitic forms live on the surface of the body, in body cavities or tissues of host organisms.

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


Toxoplasmosis (Greek toxon - onion, onion) refers to diseases caused by the simplest single-celled organisms in various places of the human body, where they were introduced and reproduced. Cause of Toxoplasmosis - Toxoplasma Toxoplasma gondii belongs to the genus Protozoa, class flagellate.

Toxoplasma has a crescent shape 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 sliding. They penetrate the cells by rotating around the longitudinal axis.

Reproduction of Toxoplasma is asexual, occurring by longitudinal division into two parts. As a result of the repeated longitudinal division in the protoplasm of the host cell, a cluster of daughter parasites is formed, which is called "pseudocysts". Pseudocysts are found in large numbers in various organs of the infected organism during the acute stage of infection. They are surrounded by a very obscure membrane, apparently formed by the host cell, and do not have their own membrane. Cells filled with such parasites are destroyed. The released parasites penetrate new cells, where they divide again and form new pseudocysts.

When the infection becomes chronic, Toxoplasma is stored in the form of true cysts (surrounded by a special membrane). Such cysts have the ability to survive 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 the cyst ranges from a few copies to several thousand.


Giardia is the simplest parasitic animal of the flagellate class. It is pear-shaped, 10–20 inem 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 intestine. 2 oval cores, 4 pairs of flagella. It lives in the human intestine (mostly in children), mainly in the duodenum, less often in the bile ducts and gallbladder, causing giardiasis. Asymptomatic parasitic vectors are common. Infection with cysts occurs when protozoa enter the lower part of the 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 cause of the disease is lamblia - (Lamblia intestinalis). Giardia is a single-celled microscopic parasite. Giardia can withstand freezing and heating up to 50 ° C, but dies when boiled. In the United States, giardiasis is a leading gastrointestinal disease of parasitic origin. According to the INTERNET, giardiasis affects up to 20% of the world's population. Infection can occur when drinking unboiled tap water or ice made from that water when washing vegetables and fruits with unboiled water. There is a high risk of getting sick when swimming in open water bodies and in pools infected with lambia cysts. A newborn can be infected during childbirth during eruptions and head births. The contact-home route of infection is less frequent, however, with the high prevalence of the disease, it is becoming quite real, especially among segments of the population with poor general hygiene skills.


Trichomonas vaginal cysts do not form, they feed on bacteria and erythrocytes. It causes inflammation of the genitourinary system - trichomoniasis. The causative agent is sexually transmitted. Out-of-sex infection (via shared toilets, beds, etc. ) is less common. It can be passed on to a newborn baby girl from a sick mother. The transition of the disease into a chronic form is possible. When it spreads to supplements, it is difficult to treat. In trichomoniasis, the vagina is most often affected, there is a copious purulent discharge with an unpleasant odor; itching and tingling in the vagina is felt. In men, the symptom is inflammation of the urethra (urethritis), followed only by a small mucous secretion.


The amoeba lives in freshwater. The shape of the body is erratic. Performs very slow (13 mm / h) movements. Moving with the help of a pseudopod, the body flows from one part to another: either shrinking into a round lump, or spreading the "tongues-feet" to the sides.

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

There is a contractile or pulsating vacuole in the body of the amoeba. Its function is to regulate the osmotic pressure within the protozoan body. Reproduction is asexual, by mitosis, followed by division of the amoeba's body into two parts. The amoeba of the genus Entamoeba, which lives in the human digestive tract, is of the greatest importance in medicine. These include dysentery or histolytic amoebae.

Plasmodium malaria

Plasmodium malaria causes malaria, which takes place 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 suffering from malaria, and the vector is a female malaria mosquito. A female mosquito, which becomes infected while sucking a patient's blood, becomes able to transmit Plasmodium. A healthy person is infected by the bite of a mosquito infected with plasmodia, with whose saliva pathogens enter the body. Through blood flow, plasmodia enter the liver, where they pass through the first (tissue) developmental cycle, then enter the bloodstream and penetrate erythrocytes. This is where the second (erythrocyte) cycle of development ends, which ends with the breakdown of erythrocytes and the release of pathogens into the patient's blood, which is accompanied by an attack of fever.