Nematodes, or actually roundworms (Nematoda), are a type of bilateral symmetrical molting animal in the protostom primary cavity.
Spread.Nematodes are one of the most widespread species of animals that have been able to inhabit a variety of habitats, from interstitials (gaps between sand grains) and algae communities to Arctic ice (eg).Theristis melnikoviandCryonema crissumIn the central part of the Arctic Ocean, perennials have been found in the thickness of the ice). Parasitic nematodes are of particular interest to researchers due to the diversity of their hosts.
Construction plan.Thin fusiform trunk, transverse to the ends. There is a mouth at the front and anus at the back. Externally, the body is covered with a multi-layered elastic cuticle - a cellless formation secreted by the hypodermis. The hypodermis, or epidermis, is under the cuticle. The muscle is represented by a layer of longitudinal oblique striped muscle fibers. The primary body cavity (schizocell), which is deprived of its own epithelial lining, is filled with fluid.
Digestive system.The oral cavity at the anterior end of the body is surrounded by protrusions - the muscle with the lips (usually three) and a triangular lumen leads to the ectodermal pharynx. The pharynx carries a layer of columnar epithelial cells to the endodermal midgut. After that, a short ectodermal hindgut that opens with the anus.
Excretory system.Excretory organs are single-celled glands that replace protonephridia. There is usually a cervical gland in the front of the body through which a short secretory duct emerges. There are also "assembled kidneys" - phagocytic organs that store insoluble metabolic products that are not eliminated from the body.
Circulatory and respiratory system.These systems are lacking. Breathing occurs through the skin. Anaerobic metabolism is also possible (anaerobic breakdown of glycogen in parasites to butyric and valeric acids).
Nervous system.The nervous system is a type of root ladder. It is represented by a nerve ring and six longitudinal trunks. The two nerve trunks running along the ventral and dorsal lines are stronger and are connected by semicircular nerve bridges (commissars).
Sense organs.There are papillae and hairs - tactile organs located around the mouth. Some marine representatives have primitive eyes - pigment spots. Amphids, which are chemical sensory organs, are usually in the form of pockets, spirals or slits. They are located next to the tip of the head and are especially well developed in men because they help find women.
Reproduction and development.Nematodes are dual animals. The internal genitals are paired and have a tubular structure. Reproduction is purely sexual. Sexual dimorphism manifests itself: women are larger, in men the back of the body is bent. Fertilization occurs internally, vitality. In development, nematodes go through four larval stages, separated by molts, accompanied by cuticle shedding. The third stage is in some species (including popular)Caenorhabditis elegans) in unfavorable conditions turns into the so-called dauer stage - resting larva.
Parasitism.About half of the more than 24, 000 nematode species currently described are parasites. They can affect almost all tissues and organs: connective tissues, muscles, blood and lymphatic vessels, gonads, sensory organs, as well as the body cavity, etc. including other nematodes and the simplest.
The following are descriptions of the most important representatives of roundworms in terms of medical parasitology.
Man built a round(Ascaris lumbricoides)
Appearance.The body with the pointed ends is pinkish-white. Dimensions: men - 15-25 cm, women - 20-40 cm. The body is covered with a ten-layer elastic cuticle that protects it from mechanical impacts and the host's digestive enzymes.
Spread. The species is cosmopolitan - widespread, but different countries have different rates of infection. In Japan, for example, more than 90% of the population is infected with roundworms due to the use of human feces as fertilizer. Roundworms are less common in hot and dry climates.
Life cycle.Development owners continue unchanged. Adult worms parasitize the small intestine and cause ascariasis. A person is generally affected by several flatworms (note - 900). The life of the intestine is about a year. Roundworms, like other nematodes, are double. A sexually mature woman lays about 200, 000 oval-shaped eggs a day that enter the environment through feces. Roundworms belong to geohelminths - the development of the larval stage in the soil is mandatory for them. When exposed to favorable conditions (at a temperature of about 25 ° C and moist soil with sufficient oxygen access), a larva develops in the egg. The development period varies from 16 days to several months and depends on the temperature. This type of egg with larvae can be considered invasive.
Infection occurs when eggs are swallowed with food or water, there is no direct human-to-human transmission. In the gut, larvae pierce the intestinal wall, enter the blood vessels and liver, and then migrate from the inferior vena cava to the right atrium and right ventricle. Second, along the small blood circulation, the larvae move to the lungs, where they pass from the blood to the pulmonary vesicles, bronchi, trachea, and oral cavity. A secondary infection occurs in the oral cavity: the larvae are swallowed, enter the intestine and reach sexual maturity after three months. The process of "maturation" in nematodes is associated with molts (there are generally four of them).
Clinical manifestations of ascariasis.During the migratory phase of ascariasis, there is a cough (which helps the larvae enter the pharynx), chest pain, allergic reactions, and fever.
In the intestinal phase, there is damage to the intestinal mucosa and poisoning of the body with toxic metabolic products. Symptoms: nausea, vomiting, stool, loss of appetite.
Long-term effects of infection: general decrease in performance, sleep disorders. Worms are deadly when they crawl into the bile ducts and respiratory tract. In addition, roundworm larvae can enter the brain (for example, above the inferior vena cava, further along the brachiocephalic), causing meningoencephalitis accompanied by migraine.
Prevention.Wash your hands before eating and preparing food. Washing vegetables and fruits. Eggs are also carried by flies, so fighting diptera with velcro, for example, also helps prevent ascariasis.
An interesting fact.There are studies showing that Ascaris infection has a positive effect on relieving the symptoms of autoimmune diseases and increasing fertility in women. Scientists attribute this to the effect of parasites on the body's immune system by affecting the level of T cells in the body, but the mechanism for drawing reliable results is currently poorly understood.
Appearance.Gray-white nematode, males 2-5 mm long, females 8-14 mm. The tip of the tail is pointed (as the name implies). A characteristic swelling of the esophagus is noticeable at the anterior end of the body.
Life cycle. . . Pinworms cause enterobiosis by parasitizing the small intestine and lower part of the large intestine. Its life is 1-2 months. The anterior end of pinworms attaches to the intestinal wall. A sexually mature woman emerges from the anus through the large intestine and lays 5 to 15, 000 eggs on the skin near the anus, then dies.
Female crawling is accompanied by itching. Eggs are not only passed on to the hands when brushing the skin. Flies are also involved in egg transplantation. Infection occurs when swallowed. Eggs that enter the intestines come out of the larvae.
Epidemiology and clinical picture of enterobiasis.Enterobiasis is widespread, especially in children, due to the lack of personal hygiene, "squeezing" in kindergartens and schools. It is transmitted from person to person without an intermediate host. Reduces the effect of vaccines.
Symptoms: abdominal pain, loss of appetite, headache, allergic reactions, perianal itching (causes sleep disturbances, increased nervousness).
Description.Small nematode 2-4 mm long. Parasitizes in the mucous membrane of the small intestine. Widespread in Eurasia and North America.
Life cycle.Owners need to be changed for Trichinella to develop. In general, these are wild animals (foxes, worms, bears, boars), as well as humans and livestock. The female is formed in the intestinal epithelium with the anterior end of the body and gives birth to 1-2 thousand larvae. Ovoviparity is characteristic: the emergence of larvae from the egg occurs in the female genitals. The larvae pass through the blood and lymphatic vessels on all sides of the body and are located in the skeletal muscles. There is a style at this stage, with the help of which they destroy the muscle tissue and cause the host to form a capsule that they will collect in the future. After a few months, the capsule is soaked in lime. This type of muscle trichina can last for several years and can survive after the death of the owner and the dismemberment of the body.
Once in the stomach of a new host (after eating the body of the previous one), the larvae are released from the capsule, penetrate the mucous membrane, and in four days pass through four moles and become adult worms.
Clinical manifestations of trichinosis.Fever, swelling of the face, muscle pain, allergic reactions.
Prevention.Trichinosis is transmitted through food, contaminated meat. Therefore, to prevent the disease, the meat should undergo a veterinary examination and be cooked properly - boil for 2-3 hours. Eating habits such as smoking and salting do not destroy Trichinella.
Appearance. . . The worm is about 4 cm long, whitish, the front end is thin, resembling hair (the name is so).
Spread. . . They prefer countries with a humid and hot climate.
Life cycle. . . The worm parasitizes only humans in the first part of the large intestine. Causes trichocephalus. The lifespan of a person is several years. The thin tip penetrates the thickness of the mucous membrane of the intestinal wall. It feeds on tissue fluid and blood.
The female lays 1-3, 000 eggs that enter the environment through feces. Like the earthworm, the whipworm is a geohelminth: the eggs must remain in the soil for a month at a certain humidity and temperature (25-30 ° C) in order to be invasive. After that, when the infection is swallowed by the egg, when the larvae emerge in the host's gut, it penetrates the intestinal mucus and grows inside for about a week. Then, destroying the villi, they enter the intestinal lumen, reach the large intestine, where they are corrected and reach sexual maturity within a month.
Clinical manifestations of trichocephalus.The worm damages the mucous membrane of the large intestine and causes poisoning of the host with garbage. Vlasoglav is a hematophage, so it can cause anemia. Trichocephalosis is accompanied by abdominal pain, headache and dizziness. Because the whipworm attaches to the intestinal wall, it is more difficult to remove from the host than other parasites.
Guinea established(Dracunculus medinensis)
Appearance.Fine whitish nematode, females 30-120 cm long, males no more than 4 cm. It has a small spine in its tail.
Spread:Tropical countries of Asia and Africa.
Life cycle. . . Infection occurs when drinking unboiled water with copepods. Crustaceans in the stomach die under the influence of hydrochloric acid, but the larvae of the beetle survive and spread to all parts of the body through the lymphatic system. It then penetrates the body cavity, where it is shed and reaches adulthood. After mating, the male dies and the female passes into the subcutaneous tissue, where a purulent abscess is formed, accompanied by burning and pain. Cool water is best to reduce pain.
The development of the eggs forces the woman to move to the surface of the advancing "scalp", leaving an inflammatory process that turns into a purulent abscess and then explodes. The female's uterus explodes when it enters the water, and the larvae hatch. In order to prevent development, the larvae must be infected with intermittent cyclops. The larvae left in the water die. After the crustaceans are swallowed by the final host, the crustaceans dissolve under the influence of stomach acid, and the larvae easily enter the intestine, pass through the walls and reach the lymph nodes, where the developmental process continues. The disease caused by the ring is called dracunculiasis.
Drakunkuliaz. . . The incubation period lasts up to nine months and ends when the female reaches adulthood. In a person with dracunuliasis, purulent abscesses begin to form. It is the only reservoir that relieves pain. Relief occurs immediately, but in contact with water, the bubbles explode and throw the larvae into the water. Crustaceans eat them and the life cycle begins again.
When treating dracunculiasis, an incision is often made at the site of the blister and the worm is gradually removed by wrapping it around a stick. It takes days, sometimes weeks (it should be pulled slowly and carefully so as not to break the worm). It has been suggested that seeing a ring wound on a stick has become a kind of prototype for the staff of Asclepius, the symbol of the serpent.
Bancroft string (filaria) or Bancroft string(Wuchereria bancrofti)
Appearance. . . White filamentous nematode, females 10 cm long, males 4 cm.
Spread.Tropics, subtropics of Asia, Africa, Central and South America.
Life cycle.In adults, it usually occurs in the lymph nodes and blood vessels, impeding lymphatic drainage and causing persistent edema. Females produce nocturnal microfillaria, larvae that appear in the peripheral blood at night and enter the body during the day (pulmonary vessels and kidneys). This is because the host is usually a blood-sucking mosquito in the evening and at night. The larvae enter the mosquito's stomach, then the body cavity where they grow, then collect near the proboscis and pass on to humans by sucking blood. Bancroft fibers cause elephantiasis or elephantiasis or elephantiasis. It should be noted that other nematodes can also cause this disease.
Clinical manifestations and treatment of elephantiasis.There is an increase in lymph blockage in any part of the body due to inflammatory thickening of the walls of the lymphatic vessels and blockage of the lymphatic vessels due to hyperplasia (painful overgrowth) of the skin and subcutaneous tissue. Bancroft by adults of filamentous plants. The skin on the diseased part of the body is covered with ulcers.
Treatment of elephantiasis is aimed at improving fluid flow. The use of anthelmintic drugs is effective. In advanced stages, surgery may be required.