Reptiles (Reptiles): ovoviviparity or viviparity. Reptiles (Reptiles): ovoviviparity or viviparity See what “viviparity” is in other dictionaries

Viviparity is a method of reproducing offspring in which the embryo develops inside the mother’s body and an individual is born, already free of egg membranes. Viviparous are some coelenterates, cladocerans, mollusks, many roundworms, some echinoderms, salps, fish (sharks, rays, as well as aquarium fish - guppies, swordtails, mollies, etc.), some toads, caecilians, salamanders, turtles, lizards, snakes, almost all mammals (including humans).

True viviparity is often considered only the birth of placental individuals. This viviparity is contrasted with oviparity, when the development of the embryo and its release from the egg membranes occur outside the mother’s body - after the laying of eggs. It is characteristic, for example, of insects, most fish, birds, and reptiles. The historical connection between viviparity and oviparity is proven by cases of ovoviviparity, when the embryo reaches full development in the egg located in the mother’s body, and there it is released from the egg membranes (in some fish and snakes).

In some plants, seedlings are formed on the above-ground organs, which then fall to the soil. An example of such a plant is bryophyllum, or Kalanchoe.

The development of the embryo during a live birth can occur in the ovary, oviducts, or in their extensions transformed into the uterus. The source of nutrition during a live birth is the reserve nutrients of the egg or substances coming from the mother's body. In the latter case, there is often a special organ - the placenta, through which gas exchange and nutrition of the embryo occurs (in some arthropods, salps, some species of sharks and rays, mammals, except cloacal and marsupials, and in humans).

Lifebearing sharks: (from top to bottom):
1 - angel; 2 - hammerhead fish; 3 - blue shark.

In some plants, in the axils of the leaves and in the inflorescences, instead of flowers, small shoots are formed that fall off the mother plant and take root.

Ovoviviparous aquarium fish:
1 - mollies; 2 - swordtail; 3 - guppy; 4 - Gambusia.

Such plants were called viviparous because it was mistakenly believed that they germinate seeds on the mother plant. These plants are distributed mainly in polar, high mountain or steppe places where the seeds do not have time to ripen. These include, for example, steppe bluegrass, some arctic fescue, and saxifrage. Viviparous plants also include those on whose leaves “babies” appear, which then fall off and germinate, as, for example, in indoor Bryophyllus.

P. falciparum, P. vivax.

In highly endemic areas, children under three months of age do not become infected with malaria, receiving passive immunity from a hyperimmune mother. The highest incidence of malaria in children in the second half of life is associated with weakened immunity. The disease in such children is characterized by a severe course.

Laboratory diagnostics

Diagnosis of malaria is based on an analysis of the clinical manifestations of the disease, epidemiological and geographical history data and is confirmed by the results of laboratory blood tests - thick drops and thin smears in patients. Microscopy of blood preparations stained according to Romanovsky-Giemsa remains the main method for laboratory diagnosis of malaria to this day. However, this method has certain limitations. In recent years, methods for diagnosing tropical malaria by identifying malarial antigen using immunological tests have been actively studied.

Prevention Prevention of malaria is based on three principles: prevention of infection, malarial attack and severe complications. Because a malaria vaccine is currently under development, individual prevention of malaria is carried out through measures to protect against mosquito bites and the use of antimalarial drugs for people traveling to areas where malaria is common. When traveling to these regions, it is necessary to find out whether there is a risk of malaria infection in the specific area where you are planning to travel; what season is the greatest risk of infection and what is the spectrum of resistance of the malaria pathogen to antimalarial drugs. When staying in places where malaria is common, you should take precautions to protect yourself from mosquito bites, sleep in rooms where windows and doors are covered with mesh, or under a mesh canopy, preferably impregnated with insecticide; from dusk to dawn, dress in such a way as not to leave your arms and legs exposed; Treat exposed areas of the body with repellent, especially when staying outdoors in the evening and at night. Non-immune women should not visit areas where malaria is endemic during pregnancy.

Ticket number 17

1. Class Cestoidea. Hymenolepis nana - morphology, development cycle, pathogenic effect, diagnosis and prevention of hymenolepiasis, geographical distribution.

The dwarf tapeworm is found everywhere. The disease is caused by hymenolepiasis, which most often affects children.

Rice. 8. Dwarf tapeworm ( Hymenolepis nana).

The ribbon-shaped body consists of a scolex (head), neck and strobila (Fig. 9). Length from 5 to 50 mm. The scolex is equipped with 4 hemispherical suckers and a proboscis bearing a corolla of 20–30 hooks.

The proboscis is capable of retracting into the scolex. The proboscis and suckers are organs of fixation to the mucous membrane of the host’s small intestine. With the help of suckers, the dwarf tapeworm can move along the surface of the intestinal mucosa, changing the place of attachment (Fig. 10).

Strobila has 200–300 segments. They are trapezoidal in shape, their width is greater than their length. The middle segments are hermaphroditic, and the posterior segments are mature, occupied by an enlarged uterus with eggs at different stages of development. The eggs are oval (40x53 microns), their shell is colorless, double-circuited. The oncosphere is six-hooked, has its own thin shell, from which 6 long transparent threads extend at the poles, holding the embryo in the center of the egg.

Life cycle dwarf tapeworm simplified (Fig. 11). It begins and ends in the human body, which is both its final and intermediate host. A person becomes infected by ingesting mature eggs Hymenolepis nana. In the small intestine, oncospheres are released from the egg membranes, actively penetrate into the villi, where, through a series of transition stages, they turn into cysticercoid. The latter consists of a swollen anterior part containing the scolex and neck, and a tail-shaped posterior appendage. After 4–6 days, cysticercoids destroy the villi, enter the intestinal lumen, attach between the villi, and after 14–15 days develop to the sexually mature stage. Cysticercoids can also form in the lymph nodes of the mesentery, where oncospheres can penetrate through the lymphatic vessels. When they mature, they migrate to the intestine, where they complete their development.

Rice. 10. Development cycle of the dwarf tapeworm:

1 - sexually mature individual; 2 eggs; 3 - cysticercoids.

Error: Reference source not found Error: Reference source not found The terminal proglottids are separated from the strobila and destroyed in the intestine, and the eggs released from them enter the external environment with feces. The lifespan of a dwarf tapeworm is about 2 months.

In some cases (with dyskinesia of the digestive organs, weakening of the host’s protective mechanisms), autoinvasion can be observed, when already in the intestine oncospheres emerge from the egg membranes and, penetrating into the mucous membrane of the small intestine, give rise to a new generation of helminth.

Occasionally, the development of dwarf tapeworm can occur with a change of hosts, when larvae or adults of various insects (meal beetles, some fleas) become intermediate hosts. A person becomes infected by accidentally ingesting the above insects with food.

The optional definitive hosts of the dwarf tapeworm can be mice and rats.

2. Phylum Nemathelminthes. General characteristics of the type. Taxonomy of nematodes pathogenic to humans.

CLASS PROPER ROUNDWORMS (NEMATODA)

BODY COVERS AND MOTION APPARATUS. The skin-muscle sac of nematodes is formed by the cuticle, hypodermis and musculature. In a typical representative of roundworms, the human roundworm, the cuticle consists of 10 layers. It functions as an exoskeleton (support for muscles) and protection against mechanical and chemical factors. The hypodermis lying on it consists of a continuous mass of protoplasm: cells with rare nuclei and vacuoles, there are no boundaries between them (syncytium). The hypodermis is permeated with numerous fibrils. Metabolic processes take place in the hypodermis and intensive biosynthesis occurs. It is also a barrier that retains substances harmful to helminths.

Muscles are located under the hypodermis; it consists of individual cells grouped into 4 cords of longitudinal muscles, separated from each other by hypodermal ridges - dorsal, abdominal and two lateral.

Inside the skin-muscle sac there is a fluid-filled primary body cavity, or pseudocoel. The morphological feature of this cavity is that it is not lined with mesodermal epithelium. It contains the internal organs of nematodes. In addition, there is fluid in the cavity under high pressure, which creates support for the somatic muscles. Organs contain a small and usually constant number of cells.

The DIGESTIVE SYSTEM begins with the mouth opening located at the anterior end of the body. The mouth is surrounded by three “lips”. The digestive system is a straight tube, which is divided into three sections - anterior, middle and posterior. The anterior and posterior sections are of ectodermal origin, the middle section is of endodermal origin. The intestine ends with the anus, located at the posterior end of the body on the ventral side. In some species there is no anus.

THE CIRCULATORY AND RESPIRATORY SYSTEMS are absent, which indicates the primitive organization of nematodes. Breathing occurs through the integument or the bioenergetic process proceeds according to the type of anoxybiosis (fermentation).

The EXCRETORY SYSTEM is unique. It is represented by 1-2 unicellular skin glands, replacing protonephridia. Outgrowths extend from the gland in the form of two lateral canals, lying in the lateral ridges of the hypodermis. At the back, the canals end blindly, and at the front they unite into one unpaired canal, sometimes opening outward behind the “lips.” Special phagocytic cells located along the excretory canals also have an excretory function. Insoluble dissimilation products accumulate in the cells, as well as foreign bodies that enter the body cavity.

The NERVOUS SYSTEM consists of a peripharyngeal ring, from which nerve trunks extend - dorsal, abdominal and two lateral. The trunks are connected to each other by commissures. Sense organs are poorly developed. They are represented by organs of touch and, probably, organs of chemical sense - tubercles located mainly around the mouth, and in males, tactile tubercles at the posterior end of the body.

GENERAL SYSTEM. The genital organs have a tubular structure. In females they are usually paired, in males they are unpaired. The male reproductive apparatus consists of the testis. This is followed by the vas deferens, which turns into the ejaculatory canal, which opens into the hindgut.

The female reproductive apparatus begins with the right and left ovaries, followed by the right and left oviducts in the form of large-diameter tubes, and the right and left uterus, which have a small diameter. Both uteruses unite into a common vagina, which opens outward on the abdominal side. Reproduction is only sexual.

The question of the origin of roundworms cannot be considered completely resolved.

The peculiar organization of roundworms suggests that they are a separate branch of the phylogenetic tree of the animal world, descended from one of the classes of flatworms (turbellarians). To solve the question of the origin of the type, a small group of free-living roundworms, united in the class Gastrociliaceae, is of great interest. These are very small worms that live in water. In terms of their structure, they occupy an intermediate position between turbellaria and nematodes. They are similar to the former by the ciliary cover, excretory system in the form of protonephridia, structural features of the nervous system and reproductive apparatus, and to the latter by the structure (reduction) of the muscular system, the presence of the primary body cavity and hindgut. This suggests the origin of roundworms from turbellarians. Gastrociliates are a side branch of this evolutionary trunk.

The origin of roundworms is associated with a number of aromorphoses, which include the primary body cavity, the progressive development of the digestive system, and the appearance of male and female individuals. The biological progress of roundworms is also facilitated by a dense cuticle, which allows them to live in various environmental conditions.

Ticket number 18

The subkingdom Protozoa includes organisms from the animal kingdom, which at all stages of the life cycle exist in the form of a single cell and this differs from the multicellular animals Metazoa.

The taxonomy of protozoa from the high school course (Fig. 2) boils down to the fact that Protozoa are considered as one of the types of the kingdom Zoa with 4 main classes: Sarcodina, Flagellate, Infusoria and Sporozoa. .

The body of unicellular protozoa consists of cytoplasm bounded by an outer membrane - the plasma membrane, a nucleus, and organelles that provide the functions of nutrition, movement, osmoregulation and excretion.

Protozoa move with the help of pseudopodia (sarcodae), flagella and undulating membranes (flagellates), and cilia (ciliate ciliates).

Protozoa feed in different ways: some swallow food particles through a cellular mouth, others absorb them using pseudopodia (pseudopods), forming a digestive vacuole where food is digested (phagocytosis). In some species of protozoa, nutrition occurs by absorption of nutrients from the body surface (pinocytosis). Food consists of organic particles, microorganisms and nutrients dissolved in the environment.

In the life cycle of most protozoa, there is a trophozoite stage (vegetative form), an actively feeding form that moves in space, and a cyst stage, a resting stage. The resulting cysts are resistant to external factors. When exposed to favorable conditions, the protozoa are released from the cyst and begin to multiply.

2. Class Cestoidea. Taeniarhynchus saginatus - morphology, development cycle, pathogenic action, routes of infection, diagnosis, prevention, geographical distribution.

The bull or naked tapeworm reaches a length of 4–12 m, but larger individuals are also found (Fig. 2). The scolex is square-oval in shape with four well-developed suckers and a rudimentary proboscis without hooks. The neck is short. The strobila consists of 1000–2000 almost square proglottids.

Immature proglottids come first. In the middle part of the strobili there are hermaphroditic segments; they have a well-developed male and female reproductive system.

The male has numerous vesicular testes. Thin vas deferens are connected into a common ejaculatory canal, which runs across the segment and ends with the copulatory organ - the cirrus, which lies in the sac - the genital bursa. The cirrus can turn outward through an opening located on the side of the joint, in the area of ​​​​a small elevation - the genital tubercle.

The female reproductive system consists of a bilobed ovary, oviduct, ootype, vitelline, vagina, the expanded part of which forms the spermatic receptacle, and uterus. The zheltochnik lies behind the ovaries.

Mature segments of elongated shape contain the uterus. The uterus of mature segments has 17–35 lateral branches (Fig. 3) and is filled with fertilized mature eggs. Since it is a closed type, eggs with larvae can leave the host’s body only together with the last proglottids that come off. When the segments are torn off, the integrity of the uterus may be disrupted, then some of the eggs fall into the intestinal lumen and are excreted with feces into the external environment. The complete release of all eggs from a closed uterus occurs either when the segments rot, or when the latter are digested in the intestines of an intermediate host (cattle).

Rice. eleven. Scolex and segments Taeniarhynchus saginatus: A - scolex, B - hermaphroditic segment, C - mature segment; 1 - ovary, 2 - vitelline, 3 - uterus, 4 - vagina, 5 - testes, 6 - ejaculatory duct.

When the bovine tapeworm's strobila reaches 5–7 m in length, the segments begin to tear off. Then, together with feces or independently, actively crawling through the anus, the segments come out. On average, 6–8 proglottids emerge per day, each of which contains up to 175 thousand eggs. When moving, the segments squeeze mature eggs from the uterus through the anterior edge. The latter are oval or spherical in shape and have a diameter of about 28–44 µm (Fig. 4). Inside the egg there is a six-hooked embryo - the oncosphere. It is covered with a radially striated membrane, which is covered on the outside by the embryonic membrane, protected on top by the egg shell.

Rice. 3. Scolex and segmentsTaeniarhynchus saginatus

A – scolex; B – hermaphroditic segment; B – mature member

(1 – ovary, 2 – vitelline, 3 – uterus, 4 – vagina, 5 – testes, 6 – ejaculatory duct)

Rice. 12. Bovine tapeworm egg (28-44 microns).

Rice. 13. The development cycle of the bovine tapeworm.

Cyscitercus are oval-shaped vesicles with clear liquid in which the scolex and neck are located. The lifespan of ciscitercus is 8–9 months, after which they die.

Cysticerci enter the body of the final host (human) when eating insufficiently thermally processed meat from cattle. Here, in the intestine, the scolex cysticercus everts out of the finnous vesicle, attaches with suction cups to the mucous membrane of the small intestine (usually the duodenum) and the strobila begins to grow from the neck.

Ticket number 19

2. Class Cestoidea. Echinococcus granulosus - morphology, development cycle, pathogenic action, routes of infection, diagnosis, prevention, geographical distribution.

Echinococcus is a small cestode 2–11 mm long. Its body has a pear-shaped scolex, equipped with four suckers and a proboscis with two corollas of hooks (Fig. 14). Behind the neck there is a short strobila, which usually consists of three proglottids. The first segment is immature, the second is hermaphrodite, and the third is mature. The latter is the largest, occupied by a uterus filled with mature eggs. The uterus has lateral projections and contains from 400 to 800 fertilized eggs with six-hooked oncospheres. Their diameter is 30–36 microns. The eggs are similar in structure to those of other taeniaids.

Finns (larvocysts, hydatids) have the appearance of a single-chamber bladder filled with liquid. Size from a few millimeters to the size of a newborn baby's head. The walls of the finna have two shells: outer (cuticular, layered) and internal (embryonic, germinative). The outer layered shell consists of concentrically located plates, the chemical composition of which is close to hyaline and chitin. The germinal membrane has three zones: cambial (parietal), middle, containing calcareous bodies, and internal - the zone of brood capsules. In the latter, young, daughter and grandchild larvocysts are formed, containing protoscolexes, on the heads of which there is a proboscis with two rows of hooks and 4 suckers. Inside the Finns, secondary (daughter) and tertiary (grandchild) larvocysts are often formed, in which brood capsules and scolex can also develop.

Outside, around the echinococcal bladder, as a result of chronic inflammation due to the host tissues, a pronounced connective tissue capsule is formed. Between the latter and the cuticular membrane there is a narrow space filled with a polymorphocellular infiltrate.

In case of rupture of the echinococcal bladder, its germinal elements, having reached the serous membranes of the intermediate host, continue their development with the formation of secondary echinococcal cysts.

The liquid of the blisters has pronounced antigenic properties and therefore, when the blisters are opened, a powerful allergic reaction develops.

Development cycle of echinococcus. The life cycle in the development of echinococcal tapeworm (Fig. 15) includes a change of two hosts.

Ticket number 20

1. Class Flagellata. Trypanosoma brucei gambiense, Trypanosoma brucei rhodesiense - morphology, development cycles, pathogenic action, diagnosis, prevention, geographical distribution.

Species: Trypanosoma brucei gambiense

In 1902, D. Dutton discovered Trypanosoma brucei gambiense in human blood. Brucei and Nabarro identified the tsetse fly (Glossina palpalis) as the vector of the disease.

Trypanosoma brucei gambiense is the causative agent of chronic Gambian West African trypanosomiasis (sleeping sickness).

Localized in the human body and other vertebrates in the blood plasma, lymph, lymph nodes, cerebrospinal fluid, spinal cord and brain tissues.

Geographical distribution. It is found in a number of equatorial regions of West Africa.

Morphology. Based on morphology, trypanosomes are divided into 3 stages: trypanosomal trypomastigotes, critidial forms (epima-stigotes) and metacyclic trypomastigotes.

Invasive stage: metacyclic form.

Life cycle. The Gambian form of African trypanosomiasis is an obligate vector-borne disease with natural focality.

The vertebrate and reservoir host for the Gambian trypanosome species is primarily humans and only then domestic and some wild animals (buffaloes, goats, pigs, antelopes and rodents). In fact, Gambian trypanosomiasis is an anthroponosis, although farm animals also take some part in the transmission of its pathogen.

The vector and second invertebrate host are blood-sucking tsetse flies of the genus Glossina (species Glossina palpalis - tsetse bush fly).

A distinctive feature of the tsetse fly (Fig. 25) is a highly chitinized protruding proboscis, capable of piercing the skin of even animals such as rhinoceros and elephant. In this regard, no human clothing protects against tsetse fly bites. Both males and females drink blood.

Rice. 25. Tsetse fly is a specific carrier of African trypanosomes

The second feature of the fly is the excellent extensibility of the intestinal walls, which allows it to absorb a volume of blood that exceeds the weight of a hungry fly tens of times. These features ensure the reliability of pathogen transmission from donor to recipient.

Flies attack during daylight hours, mainly in open nature. Some anthropophilic tsetse species can enter settlements, breeding in bushes near human habitations and along the path leading to a watering hole.

Trypanosomes enter the carrier's body by feeding on the blood of an infested vertebrate animal or human. About 90% of trypanosomes consumed by the tsetse fly die. The rest reproduce in the lumen of its middle and hind intestines.

In the first days after infection, trypanosomal trypoma-stygotes are located inside a lump of absorbed blood, surrounded by a peritrophic membrane; they differ little from those found in human blood, but are somewhat shorter and with a weakly expressed undulating membrane. The trypanosomes then exit into the insect's intestinal lumen.

On days 10-12, thin forms of trypanosomes migrate into the stomach and move to the top of the proboscis. From there they move along the salivary duct to the salivary glands, where they transform into wide epimastigote stages. Trypanosomes penetrate the salivary glands

They can also pass through the myxocoel, which they enter through the intestinal wall.

Fig.26. Life cycle of Trypanosoma brucei gambiense

Epimastigotes multiply and transform into small short metacyclic stages, most trypanosomes lack a flagellum, and only a few have a short free flagellum. The metacyclic stages are capable of infecting humans, entering their blood with the saliva of the tsetse fly when sucking blood.

Path and method of infection. Trypanosomes enter the human body through the bite (inoculation) of an infested tsetse fly (Fig. 26). When bitten by a fly, metacyclic forms of trypanosomes enter the wound along with saliva.

Clinical manifestations of sleeping sickness. The acute stage of the disease is characterized by fever, headache, nausea as a consequence of intoxication, allergic swelling of the eyelids, hands and feet. The duration of the acute period when infected with Gambian trypanosome ranges from several weeks to 1 year, and then the chronic stage begins, where the first place is occupied by symptoms of inflammation of the brain and meninges. In this case, patients are in a sleepy state during the day, and at night they are excited and awake. There is marked apathy, trembling of the limbs, lack of appetite and, in the later stages of the disease, extreme exhaustion (cachexia). The disease lasts 6-10 years, and if left untreated, death occurs, although there are rare cases of recovery.

Laboratory diagnostics. In the acute stage of the disease, microscopy of blood smears (Fig. 27) stained according to Romanovsky-Giemsa is performed.

Fig.27. Trypanosomal trypomastigotes in blood smears

In the chronic stage, microscopy of the cerebrospinal fluid and immunological reactions to the presence of antibodies in the blood are performed. The method of infecting hamsters with subsequent blood microscopy after 3-4 days is also used.

Prevention. Planned identification and treatment of patients. Fighting vectors with insecticides, using mosquito nets indoors and repelling tsetse flies with repellents, taking prophylactic medications that can protect against infection when bitten by tsetse flies. Cutting down bushes near human habitations.

Species: Trypanosoma brucei rhodesiense

Trypanosoma brucei rhodesiense is the causative agent of acute Rhodesian East African trypanosomiasis. The pathogen was first discovered by G. Fantem (1910).

Localization. In the human body and other vertebrates, trypoma-stygote lives in the blood plasma, lymph, lymph nodes, cerebrospinal fluid, spinal cord and brain tissues.

Geographical distribution: savannah Africa (Eastern and Southern Africa).

Morphology. Trypanosoma brucei rhodesiense is similar in morphology to Trypanosoma brucei gambiense, but differs from it in some immunological and biological features.

Development cycle. The main hosts of Trypanosoma brucei rhodesiense are various species of antelope, zebra, hippopotamus, as well as cattle, goats, sheep and very rarely humans (Fig. 28).

The main carriers of the Rhodesian trypanosome are tsetse flies of the Morsitans group (G. morsitans, G. pallides, G. swynnertoni, G. longipalpis). They live in savannas and savannah forests, are more light-loving and less moisture-loving than Palpalis species, are more zoophilic and more willingly attack large ungulates and small warthogs than people. The fly only attacks moving objects. Tsetse flies are more likely to attack people in dark clothes.

Fig.28. Life cycle diagram of Trypanosoma brucei rhodesiense

At the site of the fly bite, a swelling appears that looks like a boil. It is surrounded by a waxy border. From here trypanosomes penetrate into the blood and lymph, and later into the cerebrospinal fluid.

In these environments, they multiply and gradually penetrate the brain tissue, causing chronic meningoencephalitis with cerebral edema and hemorrhages. During this period, trypanosomes are no longer found in the cerebrospinal fluid.

Clinical manifestations of sleeping sickness. The Rhodesian form of trypanosomiasis is more severe than the Gambian form. It lasts only 3-7 months and without treatment ends in death.

Epidemiology. The Rhodesian form of sleeping sickness is a typical anthropozoonosis. The main reservoir of infection in nature is forest antelope. Many other wildlife species and livestock serve as secondary reservoirs of the infestation. Livestock, especially those imported from other territories, can die from trypanosomiasis.

A person usually becomes infected during various work outside populated areas. Men get sick more often. Epidemiological outbreaks are sometimes observed.

Laboratory diagnostics. Detection of trypanosomal trypomastigotes in blood smears, and later in the cerebrospinal fluid.

Prevention. Identification and treatment of patients, control of vectors - tsetse flies, protection from bites.

They are characterized (Fig. 2) by fixation organs - suckers (oral and abdominal). The oral cavity is located at the anterior end of the body, and in its center there is a mouth opening. The ventral sucker serves only for fixation. The digestive and excretory systems have a structure typical of flatworms. The nervous system consists of a peripharyngeal nerve ring with two ganglia and three nerve trunks (dorsal and two lateral). Fertilization is cross-fertilization; self-insemination occurs less frequently.

Trematode eggs have a dense shell. Their size varies from 27x11 microns in the cat fluke to 130-145x70-80 microns in the liver fluke. At one pole of the egg there is a cap, at the other there is a thickening of the shell: called a tubercle or spine. The spine may occupy a central position at the pole, but may be displaced to the side.

Trematodes develop with two intermediate hosts (Fig. 3). The first intermediate host is always a mollusk, the second is various species of vertebrate and invertebrate animals. In all flukes, at the first stage after being released from the body of the final host, the egg must enter the environment, most often the input. Only there is contact with the intermediate host – mollusks – possible. Already when the fluke is released from the uterus, the egg contains an embryo covered with cilia - miracidium. This is a young larva that contains germ cells that ensure their parthenogenetic reproduction. After the lid opens, the miracidium leaves the egg membranes and enters the water. Then it is swallowed or actively introduced into the body of the mollusk. Miracidium can also enter the body of a mollusk passively, through its digestive tract. In its body, the miracidium sheds its cilia and turns into the next larval stage - the sporocyst, which is sac-shaped and contains germ cells from which redia develop. Asexual reproduction also occurs in them and more mature larvae, cercariae, are formed. The latter, in many structural features (presence of suckers, digestive tract), resemble sexually mature flukes. Cercariae of all fluke species have a muscular tail appendage. They actively leave the body of the mollusk

Another way: cercariae enter the body of the second intermediate host and turn into the next stage - metacercariae. Second (additional) intermediate hosts are various species of fish and crustaceans. Together with their tissues, metacercariae enter the body of the final host and there they reach sexual maturity (feline, pulmonary flukes).

Thus, adolescaria and metacercariae enter the body of the final host through the mouth. Cercariae - penetrate through the skin and mucous membranes, that is, they do not undergo further larval metamorphosis.

The general name for diseases caused by flukes is trematodes.

The main causative agents of trematodes and the ways of their penetration into the human body

Ticket number 21

1. Class Flagellata. Trypanosoma cruzi - morphology, development cycle, pathogenic effect, routes of infection, diagnosis, prevention, geographical distribution.

Species: Trypanosoma cruzi

Trypanosoma cruzi, the causative agent of American trypanosomiasis (Chagas disease), is a transmissible natural focal protozoan disease.

In 1909, the Brazilian physician Carlos Chagas isolated the pathogen from the blood of a patient and described the disease it caused, which was named Chagas disease in his honor.

Localized in blood plasma, cardiomyocytes, endothelial cells of the liver, lungs, lymph nodes, cerebrospinal fluid, tissues of the spinal cord and brain.

Geographical distribution: in South and Central America.

Morphology. Trypanosoma cruzi differs from the causative agents of African trypanosomiasis by its shorter body length (13-20 µm) and larger kinetoplast of trypomastigote forms. In fixed blood products Tr. cruzi often has a curved shape, like the letters C or S (C- and S-shapes).

The development cycle of Trypanosoma cruzi includes a vertebrate host (humans and more than 100 species of animals) and a specific

carrier - triatomine flying bugs (Fig. 29).

The invasive stage for the bedbug is trypomastigotes in the blood of a sick person or animal. Since the piercing mouthparts of bedbugs, unlike the tsetse fly, are very weak and are not able to pierce even human skin, they find abrasions or mucous membranes, conjunctiva, nasal membranes, lips (for which they received the name “kissing bugs”).

Fig.29. Life cycle diagram of Trypanosoma cruzi

Trypomastigotes, entering the body of triatomine bugs, reach the stomach, here they turn into epimastigotes and multiply within several days. They then pass to the hindgut, where they revert to the trypomastigote form (metacyclic trypomastigote). From this moment on, bedbugs become infectious.

Thus, the invasive stage for the vertebrate host

is a metacyclic trypomastigote. After entering the body of a vertebrate animal (natural reservoir) or a person, trypo-mastigotes remain in the peripheral blood for some time, become trypanosomal trypomastigotes, but do not reproduce.

A human or animal cell filled with amastigotes increases in size and turns into a pseudocyst, the shell of which is the host cell wall. Before rupture and immediately after rupture of such a pseudocyst, the amastigote (bypassing the promastigote, epimastigote stage) turns into trypomastigote. The latter invade neighboring cells and multiply in the amastigote stage with the formation of new pseudocysts.

Thus, amastigotes are purely intracellular parasites. Some of the trypomastigotes that are released from the pseudocyst and do not enter neighboring cells enter the blood, where they circulate, and from there they can enter the carrier’s body.

Cases of congenital trynosomosis have also been reported in humans. It has now been established that transplacental transmission is also possible, but its level is relatively low: on average, 2-4% of infected children are born to sick mothers. There is no transovarian transmission. Infection with trypanosomiasis is also possible through the nutritional route (including through mother's milk) and through blood transfusions.

ranges from 25–60%.

Clinical manifestations of Chagas disease. At the site of trypanosome penetration, a tissue reaction is noted, swelling - “chagoma” - a dense inflammatory infiltrate. The lymph nodes become enlarged, fever, chills, headache, and often an allergic skin rash appear.

Later, trypanosomes (amastigote stage) penetrate various tissues and organs: heart, spleen, liver, kidneys, adrenal glands, intestinal muscle layer, brain and spinal cord, and other organs.

The clinical picture often depends on the age of the patients. In adults and adolescents, cardiac muscle cells are often affected. Inflammation of the myocardium leads to disturbances in the functioning of the heart, which in some cases causes death.

A severe manifestation of trypanosomiasis is the development of meningoencephalitis, which is very common in children due to the failure of the blood-brain barrier.

The acute form of trypanosomiasis either ends in death or becomes chronic. Only children die from the acute form, which is sometimes caused by meningoencephalitis or myocarditis. Mild atypical forms of trypanosomiasis also occur.

Laboratory diagnostics: microscopy of blood smears, cerebrospinal fluid preparations, punctures from lymph nodes. However, due to the fact that these studies do not always give a positive result, immunological tests (complement fixation test, intradermal test) and cultivation of trypanosomes in nutrient media are used.

Prevention: timely diagnosis, treatment and isolation of patients, improvement of living conditions and destruction of bedbugs.

2. Class Cestoidea. Dipylidium caninum - morphology, development cycle, pathogenic action, routes of infection, diagnosis, prevention, geographical distribution.

The pumpkin tapeworm is a white or slightly yellowish cestode, 20–50 cm long and 3 mm wide. The front part of the strobila is narrow and thin, and at the back it gradually thickens. The posterior mature segments resemble cucumber seeds. The scolex is equipped with four oval suckers and a club-shaped retractable proboscis with 4–8 transverse rows of hooks (Fig. 12).

The hermaphroditic segments, occupying the middle part of the strobila, have 150–200 vesicular testes. On the sides of each segment there are genital tubercles with a genital opening. Behind the latter, in the posterior part of the segments, there are tubular ovaries, and behind them are paired vitelline ovaries. At the end of the strobila there are mature segments occupied by a loop-shaped uterus filled with cocoons - capsules with mature eggs. Since mature eggs have an oncosphere surrounded by membranes of a reddish hue, mature segments are also pink.

Life cycle of the pumpkin tapeworm (Fig. 13). Mature segments, breaking away from the strobila, actively go out into the external environment, where they are destroyed, and the capsules accumulate in the perianal folds and disperse in the external environment (they end up on the ground and animal fur).

Dogs and other definitive hosts become infected by ingesting cysticercoid-infected fleas and lice-eaters. Once in the small intestine, cysticercoids attach to the mucous membrane and reach sexual maturity after 15–20 days.

Ticket number 22

1. Non-pathogenic amoebas - taxonomy. Acanthamoeba - taxonomy, routes of infection, pathogenic action, diagnosis, prevention, geographical distribution.

Species: Entamoeba gingivalis (Аmoeba buccalis)

The oral amoeba is a commensal. This is the first amoeba to be found in humans. It was described by G. Gross in Moscow (1849) and, independently

from him, S.I. Steinberg in Kyiv (1862). Oral amoebas are found in more than 25% of people who do not follow the rules of oral hygiene.

Localized in the oral cavity.

Geographical distribution is widespread.

Morphology. In the life cycle of the oral amoeba (Fig. 8), one stage is distinguished: trophozoite (vegetative form).

The average size of the trophozoite is 10-12 microns. Oral amoebae usually form many pseudopodia, wider than those of dysenteric amoebae. The cytoplasm is divided into light granular ectoplasm and darker, highly vacuolated endoplasm. Digestive vacuoles contain bacteria, fungi, and epithelial cells.

In stained preparations, the nucleus is visible; it contains a small karyosome, from which several achromatin filaments extend to the nuclear membrane. Peripheral chromatin has the appearance of separate clumps, not identical in shape and size.

Life cycle. Oral amoebas enter the human body through airborne droplets (with droplets of saliva or sputum), through the sharing of toothbrushes, tableware, and also through kissing. In the oral cavity they are found between the teeth, in gum pockets and carious cavities of the teeth. They can cause bad breath and also contribute to increased tartar deposits. Often oral amoebas are localized in the lacunae of the palatine tonsils in chronic tonsillitis. Amoebas reproduce by binary fission. Cysts do not form.

Laboratory diagnostics. Detection of the vegetative form in smears from the carious cavity of the tooth, white plaque on teeth.

Prevention. Compliance with personal hygiene rules: do not use other people’s toothbrushes, shared mugs, glasses, etc.

▪ Intestinal amoeba

Species: Entamoeba coli

Intestinal amoeba is a commensal. Amoebas are found equally often in the stool of healthy individuals and in patients suffering from intestinal diseases.

Localized in the large intestine.

Geographical distribution is widespread. In some regions of the world, the detection rate of intestinal amoebas reaches 40%.

Morphology. In the life cycle of the intestinal amoeba (Fig. 9), there are 2 stages: the trophozoite (vegetative form) and the round octanuclear cyst 15-17 μm in diameter (the largest of the intestinal amoeba cysts).

Rice. 9. Stages of the life cycle of intestinal amoeba

The average size of the trophozoite is 20-30 microns. Pseudopodia in the form of wide bulges are formed slowly on different sides of the body. There is no distinction between ectoplasm and endoplasm. The cytoplasm is highly vacuolated. Some of the vacuoles have a characteristic oblong or slit-like shape. Digestive vacuoles are usually round and contain absorbed bacteria, fungi, and starch grains. The nucleus in the cell is clearly visible even in living, unstained amoebas. The large karyosome is located eccentrically. Peripheral chromatin in the form of coarse clumps is unevenly distributed.

Laboratory diagnostics. Detection of 8-core cysts in fecal smears.

Prevention. Compliance with personal hygiene rules (washing hands, fruits, vegetables), combating mechanical carriers of cysts (flies and cockroaches).

Class: Lobosea

Order: Acanthopodida

Genus: Acanthamoeba

Species: Acanthamoeba castellani

Acanthamoebiasis is a protozoan disease caused by various types of free-living amoebas, manifested by damage to the eyes, skin and central nervous system.

Etiology. For humans, 6 species of amoebas belonging to the genus Acanthamoeba are pathogenic: A. astronyxis and A. palestinensis affect the central nervous system, A. hatchetti - the eyes, A. polyphaga, A. culbertsoni and A. castellani - the central nervous system and eyes. Some of them cause skin damage.

Geographical distribution. Acanthamoebas are distributed everywhere. Most often, cases of the disease are recorded in countries with tropical and subtropical climates.

Epidemiology. The incidence is sporadic, infection is possible in all seasons of the year.

Morphology. The life cycle of Acanthamoeba includes two stages (Fig. 13): trophozoite (10 – 45 µm) and a mononuclear cyst (7 – 25 µm) with a multilayered shell.

Rice. 13. Stages of the Acanthamoeba life cycle

The trophozoite is oval, triangular or irregular in shape. Inside the cytoplasm there is one nucleus with a large karyosome, there is an extra-nuclear centosphere. Narrow pseudopodia resemble spinous projections.

Life cycle. Acanthamoeba are aerobes that live in soil and warm fresh water bodies, mainly in bottom silt. There are especially many of them in reservoirs formed by discharges from power plants and polluted by wastewater. The presence of a large amount of organic matter and high water temperature (+ 28˚C and above) in these reservoirs contribute to a sharp increase in amoeba populations. When the water temperature decreases, the pH changes, or the substrate dries out, Acanthamoebas encyst. Their cysts are resistant to drying, cooling and the action of many antiseptics in standard concentrations. Due to their small size, they can spread aerogenously. Acanthamoeba cysts have been isolated from the tissues and excrements of many species of fish, birds and mammals

Invasive stages and routes of invasion. Acanthamoebas are often found in nasopharyngeal swabs and in the feces of healthy people.

▪ In case of eye lesions (Fig. 14), drops of water containing trophozoites or their cysts enter the conjunctival cavity. Very often, Acanthamoeba keratitis develops in people who use soft contact lenses and do not follow the hygienic rules of wearing and caring for them.

▪ With primary skin lesions, amoebas or their cysts fall on open wounds on the surface of the skin with contaminated water or through household contact.

▪ When the central nervous system is damaged, amoebas are introduced into the brain by the hematogenous route from primary lesions in the cornea of ​​the eye or in the respiratory tract.

Rice. 14. Eye lesions (keratitis) due to acanthamoebiasis

Laboratory diagnosis of acanthamoeba keratitis is carried out on the basis of the results of microscopic examination for the presence of vegetative and cystic forms of amoebae in tear fluid, washings and scrapings from ulcerative lesions of the cornea and sclera. Native preparations are examined in a conventional microscope under low light or using phase contrast. Permanent preparations, stained using the Romanowsky-Giemsa method, are first carried out by microscopy at low and medium magnifications, and then examined in more detail under an immersion lens. Sometimes they resort to cultivating Acanthamoeba on the medium of Robinson et al. In some cases, a bioassay is used for diagnosis by infecting laboratory animals.

The diagnosis of acanthamoeba skin lesions is established on the basis of the detection of amoebas and their cysts in native and colored preparations prepared from the substrate of infiltrates and biopsy samples of affected tissues.

The most effective method for diagnosing amebic encephalitis is the study of native cerebrospinal fluid preparations, in which motile trophozoites are determined.

Prevention. To prevent acanthamoeba keratitis when using contact lenses, careful adherence to the rules of hygiene and sterilization of lenses, periodic instillation of bactericidal agents (albucid, chloramphenicol, etc.) are recommended.

Prevention of Acanthamoeba skin lesions and encephalitis involves observing personal hygiene rules and limiting contact with Acanthamoeba habitats.

Live birth

Viviparity is a method of reproduction in which an animal does not carry eggs, but directly gives birth to young or larvae at different stages of development; The development of the embryo from the egg occurs still inside the mother’s body. Essentially, fertilization is only a special modification of the usual method of reproduction through eggs, since in this case, too, the embryo develops from the egg itself, from the egg cell of the mother’s body. Regarding the method of development of the embryo during pregnancy, two cases should be distinguished: 1) the development of the embryo, which occurs in some parts of the female reproductive apparatus, occurs exclusively due to the supply of nutritional material (nutrient yolk) contained in the egg itself; 2) during its development, the embryo draws nutritional material directly from the mother’s body. Nutrition of the developing embryo at the expense of the mother’s body is possible not only under one condition: under certain conditions, it is carried out even when the female carries the laid eggs with her on various parts of her body. Thus, in water fleas (Daphnia and others), the female carries her so-called “summer” eggs, which develop without preliminary fertilization, in a special space between the shell and the back of the body (brood chamber, Brutraum). The eggs lie here outside the body, in a space filled with water, but well protected from the environment. In summer Daphnia eggs, there is a greater or lesser depletion of the nutritious yolk and, accordingly, a greater or lesser replacement of it with nutritious material coming from the mother’s body into the brood chamber. For this purpose, the blood filtrate protrudes from the walls of the shell into the brood chamber; in those forms where the small egg is almost completely devoid of a nutritious yolk, at the bottom of the brood chamber, during the development of the eggs, a special organ is formed that serves to release nutrients into the cavity of the chamber - it can be compared to the afterbirth of mammals. The American pipa (Pipa dorsigera) carries its eggs on its back, where they adhere to the skin; the skin begins to thicken, and each egg becomes overgrown with an annular ridge, a special capsule or cell is formed, closed by a thin gelatinous lid. In this cell, the development and complete metamorphosis of the embryo takes place, which is nourished by the secretion of the mother’s skin glands. Similar modifications in the processes of development of the embryo from the egg are also observed during pregnancy, that is, in cases where embryonic development occurs in the ovaries or the excretory tract of the reproductive apparatus. The simplest case is when the mother’s body, which contains the eggs, serves solely to protect the eggs. In this case, the eggs are so rich in nutritious yolk that the embryo finds in the egg itself enough material for its development. An example is the scorpion, whose round eggs, very rich in yolk, remain in the ovarian cavity, where they undergo a full development cycle, so that small scorpions are born, quite similar to adults. In some snakes and lizards, the development of eggs surrounded by a dense shell occurs while they are in the oviducts, and when the animals lay eggs, the latter contain already fully developed young that immediately emerge from the eggshell (the so-called ovoviviparous animals). Then, in a number of viviparous forms, we see more or less complete adaptation to the nutrition of the embryo directly at the expense of the maternal organism.

Live birth- this is a method of reproducing offspring in which the embryo develops inside the mother’s body and an individual is born, already free of egg membranes. Viviparous are some coelenterates, cladocerans, mollusks, many roundworms, some echinoderms, salps, fish (sharks, rays, as well as aquarium fish - guppies, swordtails, mollies, etc.), some toads, caecilians, salamanders, turtles, lizards, snakes, almost all mammals (including humans).

True viviparity is often considered only the birth of placental individuals. This viviparity is contrasted with oviparity, when the development of the embryo and its release from the egg membranes occur outside the mother’s body - after the laying of eggs. It is characteristic, for example, of insects, most fish, birds, and reptiles. The historical connection between viviparity and oviparity is proven by cases of ovoviviparity, when the embryo reaches full development in the egg located in the mother’s body, and there it is released from the egg membranes (in some fish and snakes).

The development of the embryo during a live birth can occur in the ovary, oviducts, or in their extensions transformed into the uterus. The source of nutrition during a live birth is the reserve nutrients of the egg or substances coming from the mother's body. In the latter case, there is often a special organ - the placenta, through which gas exchange and nutrition of the embryo occurs (in some arthropods, salps, some species of sharks and rays, mammals, except cloacal and marsupials, and in humans).

The next proposed stage in the origin of life is protocells. A.I. Oparin showed that in standing solutions of organic substances, coacervates are formed - microscopic “droplets” bounded by a semi-permeable shell - the primary membrane. Organic substances can be concentrated in coacervates, reactions and metabolism with the environment occur faster in them, and they can even divide like bacteria. Fox observed a similar process when dissolving artificial proteinoids; he called these balls microspheres.

Female meerkat with baby (Suricata suricatta)

In protocells like coacervates or microspheres, nucleotide polymerization reactions took place until a protogen was formed from them - a primary gene capable of catalyzing the emergence of a certain amino acid sequence - the first protein. Probably the first such protein was the precursor of the enzyme that catalyzes the synthesis of DNA or RNA - DNA or RNA polymerase. Those protocells in which the primitive mechanism of heredity and protein synthesis arose divided faster and “pumped” into themselves all the organic substances of the “primary broth”. At this stage, natural selection was already underway for the speed of reproduction; any improvement in biosynthesis was picked up, and new protocells replaced all previous ones.

The phenomenon of asymmetry of organic molecules still remains mysterious. The fact is that asymmetric molecules of amino acids, sugars and other substances can exist in two forms, looking like mirror images of each other. They were called right and left. During abiogenic synthesis, they arise in equal quantities. But the amino acids that make up the proteins of all terrestrial organisms are always left-handed, and the sugars (ribose and deoxyribose) of nucleic acids are always right-handed. The reason for this phenomenon is unclear. Probably, the asymmetry accelerated the process of synthesis of proteins, nucleic acids and the growth of protocells. This was reproduced in model experiments on a computer: “protocells” from right-handed or left-handed elements “grew” faster and replaced symmetrical ones. The fact that our amino acids are left-handed and sugars are right-handed can be explained by chance.

The final steps in the origin of life—the origin of ribosomes and transfer RNAs, the genetic code, and the cell's energy machinery using ATP—have not yet been replicated in the laboratory. All these structures and processes are already present in the most primitive microorganisms, and the principle of their structure and functioning has not changed throughout the history of the Earth. Therefore, for now we can only reconstruct the final scene of the grandiose spectacle of the origin of life only tentatively - until it can be recreated in an experiment. Perhaps such protocells still exist on one of the planets in space, where life began to develop later or developed more slowly.

For now, we can only say that the emergence of life on earth took relatively little time - less than 1 billion years. Already 3.8 billion years ago, the first microorganisms existed, from which all the diversity of forms of earthly life originated.

Embryonization of ontogeny- this is the emergence in the process of evolution of the ability to pass through some stages of development under the protection of the mother’s body or special (sperm or egg) membranes. Embryonic development is not an original property, but the result of evolution. Embryonization at the same time reflects the tendency of development to become increasingly complex in a more protected and constant internal environment (Table 14.2). In this case, functions take place in ontogenesis and are the result of a similarly directed selection action (A.A. Zakhvatkin).

The adaptive significance of embryonication can be seen from the example of the evolution of different types of embryonic development in animals: primary larval, non-larval and secondary larval. The starting point in evolution is the primary larval type of development, characteristic of animals that lay small eggs with a small supply of yolk (sponges, polychaetes, crustaceans, freshwater teleosts). The larva of these animals is free and can exist independently. During the transition to the formation of large eggs containing more yolk, the larval type is replaced by non-larval development (cephalopods, sharks, hagfish, some amphibians, reptiles, birds, oviparous mammals, etc.). During non-larval development, the embryo remains for a long time under the protection of the egg membranes, consuming food reserves from the egg. In the adaptation of vertebrates to terrestrial conditions, the transition to non-larval development was of great importance. In reptiles and birds, compared to amphibians, embryonic ontogenesis is enhanced by the addition of a fertile period and leads to the release of the initial stages of development from the aquatic environment by creating the necessary conditions for the development of the embryo in the egg. Food reserves in the egg (and) increase, the amnion, yolk sac, allantois, chorion-serosa are formed, the method of crushing and the type of embryogenesis change. All this determines the possibility of development of eggs on land and the emergence from them of an individual immediately capable of active independent life.

In general, embryonic ontogenesis is accompanied by many changes in plants and animals and leads to an increased role of the internal environment in the development of the embryo and its emancipation from the external environment. One of the important results of embryonication is supplying the embryo with the necessary food and achieving its rapid development. In connection with the protection of the embryo, with increased embryonication, selection goes to reduce the number of eggs and embryos and increase the survival rate of embryos. The highest stage of embryonication is viviparity, associated with placentation and feeding the cubs with milk. Due to the increased protection of the embryo and the strengthening of the system of morphogenetic correlations, embryonic development in mammals becomes especially conservative compared to that of other animals (including reptiles and birds). The conservatism of embryonic stages apparently neutralizes the effect of small mutations, and when mutations occur that go beyond acceptable threshold levels, it contributes to the elimination of their carriers. Thus, embryonication contributes to strengthening the integrity of ontogenesis in evolution, the phenomena of neoteny and fetalization.