The structure of roundworms. Type Roundworms. Structure, internal systems, comparison with other types of worms

feeling of heaviness in the lower abdomen;
nausea and urge to vomit;
general malaise;
frequent diarrhea.

the helminth has a pale pink tint;

female body length - 20-40 mm, male - 15-20 mm;
dioecious individuals reproduce sexually.

With gastrointestinal infection and with the penetration of ascaris into the liver clinical symptoms expressed in the following manifestations:

Pain in the abdomen, accompanied by bouts of vomiting and constant nausea.
Diarrhea occurs with blood secretions in feces.
pressure on the liver and bile ducts contributes to the formation of obstructive jaundice.
Lack of appetite and uncontrolled weight loss.

The symptoms of pulmonary ascariasis are more problematic to recognize, since Clinical signs perceived as other diseases respiratory system, for example bronchitis, pneumonia, etc. The presence of helminths in the lungs is accompanied by the following symptoms:

dry paroxysmal cough and chest wheezing;
dyspnea;
subfebrile body temperature.

Ascariasis in the lungs, not detected in time, leads to the development of bronchial asthma.

When ascaris penetrates into the brain, a person feels severe headaches, epileptiform seizures and convulsions occur, there is a pronounced neurosis and depression.

Important! All clinical manifestations require careful diagnostic examination and related medical effects.

Piperazine;

albendazole;

Vermox, etc.

The type of roundworms or Nemathelminthes is one of the most numerous among the animal kingdom. There are over 20,000 species.

Turbellarians are considered their ancestors, but in the course of evolution, roundworms acquired special structural features, which allowed them to form a separate group.

The following classes of roundworms are distinguished:

Class Nematodes;
class ventral;
Kinoryncha class;
Hairy class;
Class Rotifers.

Features of the structure of roundworms

Sizes vary from 80 microns to 8 meters. Females are usually larger than males. All representatives have bilateral symmetry.

The body shape is often cylindrical or fusiform, characterized by the absence of segmentation. A dense cuticle completely covers the body from the outside. The body cavity of roundworms is surrounded by a skin-muscular sac. It contains a liquid that fills the space between internal organs. Serves as a support and performs a transport function.

Digestive organs

The digestive system of roundworms has a more progressive structure. Roundworms differ from flatworms in having an anus. They also have a separate hindgut.

The digestive tract is divided into three parts: anterior, middle and posterior. Food is absorbed through the mouth opening, enters the pharynx and esophagus. Digestion of the food bolus takes place in the middle section, and after absorption nutrients, the remainder is expelled.

The movement of food is now carried out only in one direction, which contributed to better digestion.

excretory system

The excretory function is performed by the cervical gland, a large unicellular formation, from which a pair of lateral tubules departs. They open outward through the excretory pore.

Ammonia is able to leave the body of roundworms through the skin by diffusion.

reproduction

Most representatives of the type are dioecious organisms. Often females and males have different appearance(phenomenon of sexual dimorphism). Development is direct, without a larval stage, and indirect with a change of hosts.

reproductive system roundworms are presented in the form of tubes. In males, this is more often one tube, which is divided into specialized departments. At the beginning, the testis is located, where the production of spermatozoa takes place, which enter the ejaculatory canal through the vas deferens. It opens into the distal part of the intestine - the cloaca. With the help of copulatory organs (cuticular needles), spermatozoa are brought out.

The female genital tract consists of two paired tubes. They are blindly closed in the initial section, here are the ovaries, where there is a constant reproduction of germ cells. The gametes travel through the oviducts and enter the uterus, where internal fertilization occurs.

Roundworm eggs are surrounded by a thin shell rare cases she's fat. There are species capable of viviparity.

Nervous system

It is represented by the peripharyngeal ring and longitudinal nerves. The ring is located in the pharynx and serves as the main associative organ. The ventral and dorsal nerves directly depart from the main ganglion and lie in the hypodermis, other nerve fibers are not connected with it.

The sense organs of roundworms are poorly developed. There is a chemical reception, organs of touch, free-living marine species have light-sensitive cells.

At the distal end of the body of roundworms are tail glands, the secreted fluid of which is necessary for attachment to the substrate.

Also roundworms in their life cycle often use intermediate hosts for full development. This is not typical for ringed worms. Annelids differ from roundworms in having a closed circulatory system, represented by the abdominal and dorsal vessels.

Comparison of flat and roundworms, their similarities and differences

The nutrition of nematodes depends on the lifestyle, some consume algae and bacteria, others feed on the host's body, there are also predatory species.

Significance in nature and human life

Roundworms are an integral part of food chains. Free-living individuals absorb bacteria, protozoa, and themselves become food for fish and crustaceans.

Species living in the ground feed on decayed organic matter, thus participating in soil formation.

Roundworms can infect fungi and plants, significantly reducing yields. The nematodes enter root system and lead to the death of the rhizome, thereby inhibiting plant growth. Cereal and vegetable crops (onion, potato, wheat nematodes) are most often infected.

Common and best known affecting a person and animals, from representatives of nematodes are considered,. Vegetation-damaging worms are potato, strawberry and other nematodes.

According to their structure, nematodes are considered relatively simple organisms. An adult worm has approximately 1,000 somatic cells and hundreds of cells that are associated with the reproductive system. Roundworms can be described as "pipe within a pipe" based on the location gastrointestinal tract, which starts from the head from the mouth to the tail compartment to the anus. Nematodes have digestive, nervous, excretory, reproductive system, but they do not have a dedicated circulatory and respiratory system. The sizes of worms vary from small 0.3 mm to larger ones up to 8 meters.

It is distinguished by a well-defined skin-muscular sac, consisting of the hypodermis, cuticle and muscles. There are 4 hypodermal ridges on the back, peritoneum and sides. The dorsal and ventral chords are filled with nerve trunks, the lateral chords are needed for excretion and are filled with sensory nerves.

Nervous system

The nervous system of nematodes consists of a peripharyngeal ring, which is located at the beginning of the esophagus, six trunks branch off from it back and forth. To connect both nerve trunks, there are thin half rings on the left and right side body. They also have tactile organs and chemical sense organs.

excretory system

In the assumptions described by scientists, it is said about the excretory system of unicellular nematodes that they have intracellular channels (pseudo-coelomocytes) on the sides of the body, the cervical gland and waste products (ammonia) exit directly through the shell.

Digestive system

The digestive system consists of the intestine, which runs through the entire body in the form of a straight tube. In front of it is the esophagus, which is divided into the stoma and pharynx.

Nematode worms are heterosexual and have external sexual characteristics.

Females have a paired reproductive system. They have a uterus, vagina, oviduct and ovaries. Roundworms are fertilized internally.

At male the tail part is twisted, the reproductive system consists of a tubular testis, passing into the vas deferens and the ejaculatory canal. For fertilization in males, spicules are located in the cloaca.

reproduction

Nematodes reproduce mainly by mating, but hermaphrodites have the possibility of self-fertilization. Males are usually smaller than females or hermaphrodites, often with a curved or fan-shaped tail, which serves to capture and hold females. Mating occurs when one or more chitinous spicules exit the cloaca and enter the opening of the female. Thus, individuals transmit seminal fluid passing during the process throughout the body of the male.

Since many nematodes are not fully understood, and full information missing, their classification is considered controversial and repeatedly changed. IN different descriptions there is a conflicting classification of nematodes. Today it is considered the most modern classification international zoological journal Zootaxa and is presented in the following form:

All described suborders contain several families, they are divided into genera and, accordingly, genera into species.

Habitat

Nematodes are ubiquitous. Round worms easily adapt to any ecosystem, which makes it possible for them to live in salty and fresh water, in the soil (soil), in the tropical zone and in the polar regions.

Human infection

How roundworms enter the body

Non-compliance with the rules of personal hygiene, the use of dirty vegetables and fruits, poor-quality cooked food and the use of infected water are sources of infection with helminths.
Contact with insects can be a source of infection through the skin.

When a human is infected with nematodes, the following symptoms occur:

Violation of the stool;
Nausea and gag reflex;
Lack of appetite;
Appear dark circles under the eyes;
Discomfort (itching) in the anus.

Animal infection

Nematodes can infect all organs and tissues of an animal. Contribute to infection:

Climatic conditions (habitats of worms);
The presence of intermediate hosts in the helminth;
living conditions of the animal;
Lack of preventive measures.

Not observing the basic rules of hygiene, people can become infected with nematodes from cats, dogs and other animals.

plant infection

The most popular are these types of nematodes:

Plant pests are absolutely harmless to humans.

Nematodes, or roundworms, are thought to have evolved from Turbellarians. In the process of evolution, they acquired a peculiar structural plan that sharply distinguishes them from flatworms. This makes us consider nematodes as a separate type of animal world. The relationship of nematodes with higher groups has not been established, and therefore nematodes are considered as a side branch of the family tree of animals. The type includes about 10,000 species.

According to the classification of V. A. Dogel (1981), the Nemathelminthes type includes 5 classes:

Class Nematoda (Nematoda).
Class Gastrociliary (Gastrotricha).
Kinorinchi class.
Hair class (Gorciiacea).
Class Rotifers (Rotatoria).

General characteristics of the type

The most characteristic external sign is a non-segmented, cylindrical or spindle-shaped body, which has a round shape in a cross section. Outside, the body is covered with a cuticle, under it only one longitudinal layer of muscles is developed. Inside the skin-muscle sac is the primary body cavity, which contains the internal organs (see Table 1). A third, posterior, section appears in the digestive tube, ending with the anus. excretory system or protonefridial, or represented by modified skin glands. The reproductive system of most nematodes is dioecious. The nervous system consists of a parapharyngeal nerve ring (or supraesophageal ganglion) and several longitudinal trunks, of which two are the most developed. The sense organs are poorly developed. Respiratory and circulatory system missing.

The mouth opening is terminally located at the anterior end of the body. The anus is located on the ventral side, near the posterior end of the body. The area behind the anus is called the tail.

Inside the skin-muscular sac is the body cavity containing the abdominal fluid and internal organs. The body cavity develops from the cavity of the blastula (blastocoel) and is called the primary body cavity. Morphologically, it is characterized by the absence of an epithelial lining and is limited directly to the muscles of the skin-muscular sac. The cavity fluid directly washes the organs and walls of the body and is under great pressure, which creates support for the muscle bag (hydroskeleton). Also, she plays important role V metabolic processes. In some nematodes, it is toxic.

Digestive system It is represented by a straight tube that begins with the mouth and ends with the anus. The mouth opening is located terminally at the anterior end and is surrounded by cuticular lips. In the digestive tube, the anterior, middle and hindgut are distinguished; the middle one develops due to the endoderm, while the anterior and posterior ones develop due to the ectoderm; the latter are lined, like the skin, with a cuticle. The foregut is often differentiated into sections: oral capsule, esophagus, bulbus, etc.

excretory system peculiar and consists of one single giant excretory (excretory) cell. The cell body is located in front of the nematode. From it, processes pierced by channels extend back and forth. The channels located posterior to the cell end blindly, while the channels extending forward are combined into common duct, opening to the outside of the excretory pore. The secretion process also involves special phagocytic cells located in the body cavity along the side excretory canals. These cells absorb decay products from the body cavity. The phagocytic nature of these cells has been proven by the experience of introducing carcass worms or other colored particles into the body cavity. Mascara is captured by phagocytic cells and accumulates in their cytoplasm.

Nervous system It is represented by a near-pharyngeal nerve ring, from which longitudinal nerve trunks depart, among which the dorsal and ventral ones are most developed. The sense organs are primitive; they are represented by tactile papillae and special organs that perceive irritants of a chemical nature (amphids). Some free-living nematodes have eyes.

reproductive system has a tubular structure. Nematodes are usually dioecious. Most males have only one (unpaired) tube, different sections of which are specialized and perform the functions of various genital organs. The narrowest, initial section - the testis - is divided into a breeding zone and a growth zone. The testicle passes into the vas deferens, after which a wide ejaculatory canal follows, opening into back department intestines.

In females, the reproductive system usually consists of two tubes. The initial, narrowest, blindly closed section of the tube is the ovary. In this part, the tube has no lumen - it is filled with multiplying sex cells. The ovary gradually passes into a wider section that performs the functions of the oviduct. The next section, the widest, is the uterus. The two uteri join together to form an unpaired vagina, or sheath, which opens outwards at the anterior end of the body. In some species, the female has only one genital tube.

Nematodes have a well-defined sexual dimorphism - males and females differ in outward signs. Males are smaller, the posterior end of the body in some of them is twisted to the ventral side.

Some species are characterized by live birth, that is, their egg develops to the stage of a larva even in the genital tract of the female, and already living larvae come out of the female's body.

Diseases caused by roundworms themselves are called nematodes. Many human nematodes are widespread and severe diseases.

Pinworm (Enterobius vermicularis)

The most widespread human helminth, which ranks first in terms of frequency of distribution among flat and round worms. Found in all areas the globe. Causes the disease enterobiasis.

Localization. lower division small intestine and early part of the large intestine.

. Ubiquitous.

Morphophysiological characteristics. small worm white color. The length of the female is 10-12 mm, the male is 2-5 mm. The posterior end of the male is twisted to the ventral side, while the female has a styloid pointed end. At the front end of the body there is a swelling of the cuticle - a vesicle that surrounds the mouth opening and participates in the fixation of the helminth to the intestinal walls. In the back of the esophagus there is a spherical swelling - the bulb, the contraction of which is supposed to play a certain role in the processes of fixation. The intestine looks like a straight tube. The reproductive system is characterized by a structure typical of nematodes. They feed on the contents of the intestines, sometimes they are able to swallow blood. The eggs are asymmetrical in shape, one side of the oval is flattened, the other is convex, the colorless shell is well expressed.

Life cycle. Fertilization takes place in the intestines. Males die immediately after fertilization. The uterus of the female, stuffed with eggs, increases so much that it occupies almost the entire body of the worm. It compresses the bulb of the esophagus, which violates the mechanism of fixation. Such females, under the influence of peristalsis, descend into the rectum. At night, they actively crawl out of the anus onto the skin of the perineum and lay eggs here (up to 13,000 eggs), sticking them to the skin. Shortly thereafter, the females die.

For the further development of the laid eggs, a special microclimate is required - a temperature of 34-36 ° C and high humidity - 70-90%. Such conditions are created in the perianal folds of the skin and perineum of a person. The eggs located here become invasive after 4-6 hours. Eggs that do not stay on the skin and fall into conditions with lower temperature and humidity do not develop. When eggs enter the human intestine, they turn into sexually mature forms without migration. Adults live in the intestines for 30 days, but it can be difficult to cure enterobiasis, since re-infection often occurs.

The female, laying eggs, causes itching, so patients comb itchy places. Eggs fall under the nails, where they also find optimal conditions for development (temperature 34-36 ° C, high humidity). Through contaminated hands, eggs easily fall into the mouth. Thus, the patient constantly infects himself again, i.e., autoreinvasion occurs, which makes it difficult to cure.

Pathogenic action. Itching, loss of appetite, diarrhea, sleep disturbance. Girls and women may inflammatory processes in the genitals when pinworms crawl into the vagina.

Laboratory diagnostics. Examination of faeces is not applicable as the eggs are deposited on the skin. The most effective scraping from the perianal folds of the skin. To do this, a match or a wooden rod is wrapped with cotton wool and moistened in glycerin, then a scraping is made and it is microscoped. Used materials are burned. You can find eggs under the nails or in nasal mucus. Sometimes pinworms are seen in the feces.

Prevention: personal - compliance with the rules of personal hygiene, especially cleanliness of hands; a sick child should be put to sleep in panties, boiled in the morning and stroked wet; public - general sanitary measures in combination with those specific for enterobiasis; systematic enterobiosis measures in children's institutions.

Vlasoglav (Trichocephalus trichiurus)

It occupies the third place in the frequency of distribution of human helminths. Causes the disease trichuriasis.

Localization. The caecum, appendix, the initial section of the large intestine.

Geographic distribution. Everywhere.

Life cycle. Pretty simple. The fertilized female lays eggs in the intestinal lumen, from where they are thrown out together with feces. In the external environment, a larva develops in the egg. Under optimal conditions (temperature 26-28 ° C), the egg becomes invasive after 4 weeks. Getting to a person through contaminated hands, vegetables, fruits, water, eggs pass into the intestines, reach the caecum and, without migration, turn into sexually mature forms. In humans, whipworms live up to 5 years.

Pathogenic action. Symptoms largely depend on the degree of infection. The presence of single instances may not cause any manifestations. With massive infection, violations are observed from the side digestive tract(pain, loss of appetite, diarrhea, constipation) and the nervous system (dizziness, epileptiform seizures in children).

Traumatization of the intestinal wall contributes to the attachment of a secondary infection, as a complication, appendicitis can develop.

Laboratory diagnostics. Detection of eggs in faeces.

Ankylostomides

Under this name, representatives of two types of nematodes are united

crooked head duodenum(Ancylostoma duodenale)
Necator (Necator americanus)

Localization. Small intestine, duodenum.

Geographic distribution. Hookworms are common in countries with a tropical and subtropical climate, where about 50% of the population is infested, which is approximately V "of humanity. There are underground foci of ankylostomidosis (mines, mine workings), which do not depend on ground temperature conditions. In the USSR, they are registered in Transcaucasia and Central Asia.

Morphophysiological characteristics. The duodenal crookhead has dimensions: female - 10-13 mm in length, male - 8-10 mm. The anterior end of the body is slightly bent to the ventral side (hence the name). A characteristic feature of the structure is a wide-open oral capsule, in which four ventral and two dorsal cutting teeth are located. At their base are two glands that secrete enzymes that prevent blood clotting. With the help of teeth, the hookworm is attached to the intestinal mucosa. Hookworms feed on blood. At the place of fixation, ulcers up to 2 cm in diameter are formed, bleeding for a long time. In the male, the posterior end of the body has a characteristic structure. Capulative bag, resembling a bell in shape, consists of two large lateral lobes and a small middle one. The eggs are oval, with bluntly rounded poles. Their shell is thin and colorless. The necator differs in the structure of the oral capsule (instead of teeth it has two semilunar cutting plates) and the copulatory bag.

Life cycle. Geohelminths. Humans are the only source of infection. Eggs that come out with feces develop in the soil. Under optimal conditions (28-30 °C), a non-invasive rhabditoid larva emerges from the egg. Distinctive feature structures - the presence of two bulbs in the esophagus. After molting, it turns into a filariform larva with a cylindrical esophagus. After the second molt, the filariform larva becomes infective. The larva can actively move in the soil vertically and horizontally.

On contact skin in humans with soil, the filariform larva is attracted by body heat and is actively embedded in the skin. Most often, infection occurs when a person walks without shoes or lies on the ground. Penetrating into the body, the larvae enter the blood vessels and begin to migrate throughout the body. First they go to the right heart, then to pulmonary artery, capillaries of pulmonary alveoli. Through the rupture of the walls of the capillaries enter the alveoli, and then through the respiratory tract penetrate into the pharynx. Together with saliva, the larvae are swallowed and enter the intestines, where they turn into sexually mature forms. They live in the intestines for 5-6 years.

If the larva enters the human body through the mouth with contaminated food or water, then migration, as a rule, does not occur, and the adult form immediately develops. However, this method of penetration of the larvae - passive hit - is much less common. The main route of infection is active penetration through the skin.

Especially often people of a certain profession (miners, miners, diggers, workers in rice and tea plantations) suffer from ankylostomidosis.

Pathogenic action. Progressive anemia (anemia). The hemoglobin content can drop to 8-10 units, erythrocytes - up to 1,000,000 in 1 µl. The causes of anemia are considered blood loss and intoxication. Possible disorders of the digestive system. In children, physical and mental underdevelopment is observed, in adults - disability. The intensity of invasion can be very high (hundreds and thousands of copies).

Laboratory diagnostics. Detection of eggs in faeces.

Prevention: personal - in the foci of ankylostomiasis, it is mandatory to wear shoes and it is forbidden to lie on the ground; to prevent infection through the mouth - compliance with the rules of personal hygiene. Public - improving the sanitary culture of the population; identification and deworming of patients; arrangement of latrines of a special type with a receiver impervious to larvae; disinfection of soil and mines with sodium chloride and soil predatory fungi; in mines - checking incoming workers for the presence of helminths, annual examination of miners. In the USSR, by 1960, underground foci of ankylostomiasis were completely eliminated.

strongiles [show]

Localization. Small intestine.

Geographic distribution. It is mainly found in countries of the tropical and subtropical belt, but is also found in areas with a temperate climate. In the USSR it is registered in Transcaucasia, in Ukraine, in Central Asia. Isolated cases are also known in middle lane RSFSR.

Morphophysiological characteristics. Has a filamentous body small sizes- up to 2 mm. The anterior margin of the body is rounded, the posterior margin is conical. The larvae hatch from the eggs in the intestines of the host.

Life cycle. Very complex, has much in common with the development cycle of hookworm. Geohelminth. Sexually mature males and females live in the human intestine. From the laid eggs, rhabditoid larvae develop, which, together with feces, are carried out into the external environment. Further development of rhabditoid larvae can go in two directions:

if a rhabditoid (non-invasive) larva, having entered the soil, encounters unfavorable conditions (temperature, humidity), it molts and quickly turns into an invasive - filariform larva, which actively penetrates the human skin and migrates throughout the body. In this case, the larva sequentially penetrates into the veins, right heart, pulmonary arteries, pulmonary alveoli, bronchi, trachea, pharynx, and then is swallowed and enters the intestines. During migration, the larvae turn into sexually mature individuals. Fertilization can occur in the lungs and in the intestines;
if rhabditoid larvae find favorable conditions in the external environment, they turn into males and females of a free-living generation that live in the soil, feeding on organic residues. When saving favorable conditions from eggs laid by free-living females, rhabditoid larvae emerge, which again turn into a free-living generation.

Laboratory diagnostics. Detection of larvae in faeces.

Prevention: the same as in ankylostomiasis.

trichina [show]

Trichinella (Trichinella spiralis)

Causes the disease trichinosis, belonging to the group of natural focal.

Localization. Mature forms live in small intestine host, larval - in certain muscle groups.

Geographic distribution. On all continents of the globe, except Australia, but it has not a universal, but a focal distribution. In the USSR, regions greatest defeat observed in Belarus, Ukraine, North Caucasus, Primorye.

Morphophysiological characteristics. It has microscopic dimensions: females 3-4 x 0.6 mm, males - 1.5-2 x 0.04 mm. Characteristic features serve as an unpaired genital tube in females and the ability to live birth.

For the transformation of the larvae into a sexually mature form, they must enter the intestines of another host. This happens if the meat of an animal infected with trichinosis is eaten by an animal of the same or a different species. For example, the meat of a trichinosis rat can be eaten by another rat or pig. In the intestines of the second host, the capsules dissolve, the larvae are released and within 2-3 days turn into sexually mature forms (males or females). After fertilization, the females give birth to a new generation of larvae. Thus, each organism infected with Trichinella first becomes the final host - sexually mature individuals are formed in it, and then intermediate - for larvae hatched by fertile females.

For the full development of one generation of helminths, a change of hosts is necessary. The main form of existence is the larval or muscular form, which lives up to 25 years.

Trichinosis refers to natural focal diseases. natural reservoir are wild carnivores, omnivores and insectivores. An important role in the spread of trichinosis in nature is played by insects that feed on corpses. Dead-eater beetles serve as permanent constituent element diet of various animals (bear, marten, fox). By eating insects, various animals become infected with trichinosis, including those whose diet is dominated by plant foods.

Pathogenic action. Symptoms of the disease appear a few days after infection. The initial period is associated with the introduction of hatched larvae and toxic effect their metabolic products. Swelling of the face, especially the eyelids, a sharp rise in temperature to 40 ° C, and gastrointestinal disorders are characteristic. Later, there are pains in the muscles, convulsive contraction chewing muscles(rheumatoid period). With intense infection, death is possible. In mild cases, recovery occurs in 3-4 weeks. Possible Complications: damage to the heart muscle, pneumonia, meningoencephalitis.

The severity of the disease depends on the number of larvae that have entered the body. The lethal dose for humans is 5 larvae per 1 kg of the patient's body weight. The amount of meat containing lethal dose may be negligible - 10-15 g.

Laboratory diagnostics. The most reliable method is the detection of larvae in the muscles (biopsy) and immunological reactions. The most common skin-allergic test. Great importance has a survey of the patient, since group infection usually occurs.

Prevention. Public prevention is of primary importance:

organization of sanitary and veterinary control at slaughterhouses and markets, examination of pig, bear, and boar carcasses for trichinosis, for which 2 samples from the legs of the diaphragm are taken from each carcass for microscopic examination; in case of detection of trichinella, the meat is subject to mandatory destruction or processing into technical products; heat treatment meat is not effective, as the capsules ensure the survival of the larvae;
zoohygienic keeping of pigs (prevention of eating rats);
fight against rats (deratization).

Personal prevention consists in not eating meat that has not passed veterinary control.

roundworm

Ascaris human (Ascaris lumbricoides)

Causes ascariasis.

Morphophysiological characteristics. Large worm, whitish-pink. The female reaches 20-40 cm in length, the male - 15-20 cm, the rear end of the male's body is bent to the ventral side. The body is fusiform. The epithelium (hypoderm) of the roundworm forms a multilayer flexible cuticle on the outside, which functions as a kind of external skeleton, and also protects the animal from mechanical damage, toxic substances and digestion by the host's digestive enzymes. Beneath the hypodermis are the longitudinal muscles. Roundworms do not have attachment organs, they are held in the intestines, moving towards food. The mouth openings are surrounded by three cuticular lips - dorsal and two ventral. In the body cavity there are phagocytic cells (insoluble metabolic products accumulate in them), the genitals and the tubular intestine, in which the foregut is distinguished, consisting of the oral cavity and esophagus; middle (endodermal) intestine and short ectodermal hindgut.

The reproductive organs look like thin thread-like winding tubules. The female has two ovaries, the male has one testis. A fertilized female has an annular depression on the border of the anterior and middle thirds of the body - a constriction. Every day, one female of human roundworm is capable of producing 200-240 thousand eggs. The eggs are large, oval or round in shape, covered with three shells that protect them from the effects of adverse factors (drying, etc.). The outer shell has a bumpy surface, when in the intestine it is stained with fecal pigments in a brown color, the middle one is glossy, the inner one is fibrous. Cleavage of the egg and development of the larva lasts about a month and can only occur in a humid environment with a sufficient amount of oxygen.

Of the sense organs, only tactile tubercles are developed around the mouth, and in males also at the posterior end of the body (near the genital opening).

Localization. Small intestine.

Geographic distribution. In terms of prevalence, ascariasis is second only to enterobiasis. It is found throughout the globe, with the exception of the Arctic and arid regions (deserts and semi-deserts).

Human infection occurs when eggs with larvae are ingested with contaminated water or food. Eggs can be found on poorly washed berries (especially strawberries) or vegetables from areas where human excrement is used to fertilize. Some synanthropic insects (for example, flies, cockroaches) can also transfer roundworm eggs to food. The swallowed egg passes into the intestine, where the shell of the egg dissolves and the larva emerges from it. It pierces the intestinal wall, enters the blood vessels and migrates throughout the body. Together with the blood flow, the larva enters the liver, then into the right heart, pulmonary artery and capillaries of the pulmonary alveoli. Starting from this moment, the larva passes to active movement. It perforates the wall of the capillaries, penetrates into the cavity of the alveoli, into the bronchioles, bronchi, trachea and, finally, into the pharynx. From here, together with sputum and saliva, the larvae enter the intestine for the second time, where they turn into sexually mature forms. The entire development cycle of ascaris occurs in one host.

In total, the migration lasts about two weeks. Transformation into adult form occurs within 70-75 days. The life span of adults is 10-12 months. The lower temperature threshold at which the development of ascaris eggs is possible is about 12-13 ° C, the upper one is about 36 ° C. At temperatures below the minimum, roundworm eggs, without developing, can remain viable and, gaining the so-called "sum of heat" in warm seasons, reach the invasive stage. A number of researchers believe that a person can become infected with the eggs of the pig roundworm, which is morphologically indistinguishable from the human one, while the migration of larval stages is possible, but sexually mature forms are not formed.

Pathogenic action. Larval and sexually mature forms have different pathogenic effects. Larval stages cause sensitization ( allergic reactions) of the body with protein products of metabolism and damage to the liver tissue and, above all, the lungs. In the lung tissue with migratory ascariasis, multiple foci of hemorrhages and inflammation (pneumonia) are observed. With intensive invasion, the process can capture entire lobes of the lungs. It has been experimentally established that infection of animals with a large dose of eggs leads to death from pneumonia on the 6-10th day. The duration of the disease and the severity of symptoms varies depending on the degree of invasion. With a slight degree of infection, the inflammatory process in the lungs stops without complications. In addition, migratory roundworm larvae, when penetrating into the alveoli, violate the integrity of the latter, thereby opening the "gate" to bacteria and viruses.

Depending on the location and degree of invasion, the symptoms of ascariasis can vary from minor manifestations to death.

Laboratory diagnostics. Detection of eggs in faeces.

Ascaris eggs are characterized by high resistance to factors external environment. They can overwinter and remain in polluted soil for 5-6 years. IN cesspools they last up to 8 months. In compost heaps, where the temperature reaches 45 ° C, the eggs die in 1-2 months.

According to the shape of the body, worms are divided into three types: Flat, Round and Ringed. All worms are three-layer animals. Their tissues and organs develop from three germ layers - ectoderm, endoderm and mesoderm.

Type Flatworms their characteristics

Type Flatworms unites about 12,500 species. In their organization, they are higher than the coelenterates, but among the three-layered animals they are the most primitive. These animals can crawl slowly. Most feature flatworms - a flattened (flattened) body, in the form of a long ribbon.

The figure below shows the structure flatworm on the example of Planaria.

Structure	The body is flattened in the dorsal-abdominal direction, the space between the organs is filled with a special tissue - the parenchyma (there is no body cavity)
body integuments	Skin-muscular sac (skin fused with muscle fibers)
Nervous system	Two nerve trunks connected by nerves ("ladders")
sense organs	Ocelli in front of body, tactile cells scattered throughout body
	The digestive system is blindly closed; have mouth --> pharynx --> branched intestine
	Whole surface of the body
Selection	A system of tubules that open outward on the sides of the body
reproduction	Hermaphrodites; spermatozoa ripen in the testicles, eggs - in the ovaries; the female lays eggs that hatch into young worms

Variety of Flatworms, their main classes

Type Roundworms and their characteristics

Type Roundworms- a large group of animals with a long, round body in cross section, which is pointed at the front and rear ends. Roundworms are characterized by the presence free space inside the body primary cavity. It contains internal organs surrounded by cavity fluid. Washing the cells of the body, it is involved in gas exchange and the transfer of substances. The body of roundworms is covered with a strong shell - cuticle. This group has about 20 thousand species.

The figure below shows the structure Roundworm on the example of Ascaris.

Structure	elongated cylindrical body, pointed at both ends, round in cross section, there is a body cavity
	Skin-muscular sac
Nervous system	Abdominal nerve cord
	Mouth (3 hard lips) --> pharynx --> intestinal tube --> anus
	Whole surface of the body
Selection	Through the surface of the body
reproduction	Most are dioecious; the female lays eggs that hatch into young worms
Representatives

Type annelids their characteristics

Type Annelids- a group of animals whose representatives have a body divided into segments resembling rings folded one after another. There are about 9 thousand species annelids. Between the skin-muscle sac and internal organs they have in general - secondary cavity body filled with fluid.

Structure	The body consists of segments, there is a body cavity
	Leather; muscles - longitudinal and circular
Nervous system	Supraesophageal and subesophageal ganglions and the abdominal nerve chain, from which the nerves depart in each segment
	Mouth --> pharynx --> esophagus --> crop --> stomach --> intestine --> anus
	the entire surface of the body; marine have special outgrowths of the body - gills
Selection	In each segment - a pair of tubules that open outwards with excretory pores
reproduction	Hermaphrodite; the female lays eggs in a cocoon, from which young worms emerge
Manifold	1. Class Small-haired - live mainly in soil and fresh water, have small bristles on each segment (representative - earthworm) 2. Class Multi-haired - live in the seas; have paired outgrowths with bristles on the sides of the body (representative - nereid, sandworm)