Protozoal parasites

The type of protozoa (Protozoa) comprises over 15, 000 animal species that live in the seas, freshwater 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 the protozoa is diverse. It can be permanent, have radial, bilateral symmetry (flagellates, ciliates) or have no permanent shape at all (amoeba). The body sizes of protozoa are usually small - from 2-4 micrometers to 1. 5 mm, although some large individuals reach 5 mm in length, and fossil clam roots were 3 cm or more in diameter.

the simplest human parasites

The body of the protozoa consists of the cytoplasm and the cell nucleus. The cytoplasm is delimited 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 locomotor organelles of protozoa are flagella, cilia, pseudopodia; or none at all. Most unicellular organisms, like all other representatives of the animal kingdom, are heterotrophic. However, among them there are also autotrophs.

The peculiarity of the most easily endured adverse environmental conditions is the ability to encystatize, i. H. form a cyst. With the formation of a cyst, the locomotor organelles 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 dormant state and, under favorable conditions, returns to an active life.

Encysting is a device that is used not only to protect but also to spread parasites. Some protozoa (sporozoa) form an oocyst, and in the process of reproduction, a sporocyst.

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

The habitat of the simplest is diverse - it is the sea, fresh water, moist soil. Parasitism is common. Many types of parasitic protozoa cause serious disease in humans, domestic animals, wild animals, and plants.

Protozoa can move with the help of pseudopodia, flagella or cilia and 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 body surface, in body cavities or tissues of their host organisms.

The ways in which food is taken up in the cell body are also different: pinocytosis, phagocytosis, osmotic path, active substance transport through the membrane. They digest the food they eat in the digestive vacuoles filled with digestive enzymes. Some of them with photosynthetic intracellular symbionts - chlorella or chloroplasts (e. g. euglena) - can synthesize organic material from inorganic substances through photosynthesis.


Toxoplasmosis (Greek Toxon - bow, bow) describes diseases that are caused by the simplest single-celled organisms in the most varied of parts 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 sickle-shaped and resembles a slice of orange: 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.

The multiplication of Toxoplasma is asexual, it takes place by dividing it longitudinally into two parts. As a result of repeated longitudinal division in the host cell's protoplasm, an accumulation of daughter parasites is formed, which are referred to as "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 dark membrane, apparently formed by the host cell, and do not have a membrane of their own. Cells filled with such parasites are destroyed. The released parasites invade new cells, divide again there and form new pseudocysts.

When the infection turns into a chronic form, Toxoplasma remains 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 eye, heart, lungs, and some other organs. The number of toxoplasmas in a 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 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 duct and gallbladder, and causes giardiasis. Asymptomatic parasitic carriers are common. Cyst infection occurs when protozoa enter the lower intestines through the mouth, contaminated food or water enter the body, 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 unicellular microscopic parasite. Giardia can withstand freezing and heating up to 50 ° C, but 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's population. Infection can occur when drinking unboiled tap water or ice from such water, when washing vegetables and fruits with unboiled water. There is a high risk of disease when swimming in open water or in pools infected with lamblic cysts. A newborn baby can become infected during labor during the outbreak and head birth. The contact-household route of infection is less common, but with a high prevalence of the disease it becomes quite real, especially among population groups with poor general knowledge of hygiene.


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 transmitted sexually. Extra-sexual contamination (from toiletries shared with the patient, bed, etc. ) is less common. Can be transmitted from a sick mother to a newborn baby girl. The transition of the disease into a chronic form is possible. If it gets carried over to the appendages, it is difficult to treat. With trichomoniasis, the vagina is most often affected, there is an abundant purulent discharge with an unpleasant odor; Itching and burning sensation can be felt in the vagina. In men, the symptom is inflammation of the urethra (urethritis), accompanied by only a small amount of mucus secretions.


Amoebas live in fresh water. The body shape is inconsistent. Performs very slow (13 mm / h) movements. It moves with the help of pseudopodia, the body flows from one part to the other: either it shrinks into a round lump or spreads the "hyoid bones" to the sides.

The pseudopods are also used to capture food. When eating, the amoeba's body washes the food particles from all sides and they get into the cytoplasm. A digestive vacuole is created. This type of food is called fabitose. Food consists of bacteria, unicellular algae and small protozoa. Dissolved substances from the environment are absorbed through pinocytosis.

There is a contractile or pulsating vacuole in the body of the amoeba. Its function is to regulate the osmotic pressure inside the protozoal body. Reproduction occurs asexually, through mitosis, followed by the division of the body of the amoeba into two parts. Of greatest importance in medicine are the amoebas of the genus Entamoeba, which live in the human digestive tract. These include dysentery or histolytic amoeba.

Malaria plasmodium

Plasmodium malaria causes malaria, which occurs with fever attacks, blood changes, and 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 vector is a female malaria mosquito. The female mosquito that becomes infected by sucking the patient's blood will be able to transmit Plasmodium. A healthy person becomes infected through the bite of a mosquito infected with plasmodia, with the saliva of which pathogens enter the body. With the blood flow, plasmodia reach the liver, where they go through the first (tissue) development cycle, then pass into the blood and penetrate the erythrocytes. Here they complete the second (erythrocyte) development cycle, which ends with the breakdown of the erythrocytes and the release of pathogens into the patient's blood, which is accompanied by an attack of fever.