Nematodes, or roundworms themselves (Nematoda), are a type of protostomes, protozoans, bilaterally symmetrical morphotypes.
Hearsay. Nematodes are one of the most widespread types of animals that have been able to colonize a variety of habitats - from interstitium (the space between sand grains) and moss communities to arctic ice (such asTheristis Melnikovi and Cryonema crissum, located in the thickness of multi-year ice in the central part of the Arctic Ocean).Parasitic nematodes are of particular interest to researchers, not least because of the wide variety of their hosts.
Building plan. Slender fusiform body, tapering towards the ends, round in cross-section.The mouth is at the front end and the anus (anus) is at the back.The outside of the body is covered with a multi-layered elastic epidermis - a non-cellular formation secreted by the hypodermis.The hypodermis, or epidermis, lies beneath the epidermis.Muscles are represented by a layer of longitudinal oblique striated muscle fibers.The main body cavity (schizocoel), without its own epithelial lining, is filled with fluid.
Digestive system. The oral opening at the anterior end of the body is surrounded by protrusions - lips (usually three) and leads to a muscular ectodermal pharynx with a triangular lumen.The pharynx leads to the endodermal midgut from a single layer of columnar epithelial cells.Then follows a short ectodermal hindgut, which opens into the anus.
Excretory system. The excretory organs are unicellular glands that replaced the protonephric.There is usually a jugular gland at the front of the body, from which a short excretory duct arises.There are also "storage kidneys" - phagocytic organs that accumulate insoluble metabolic products that are not removed from the body.
Circulatory and respiratory system. These systems are missing.Respiration takes place through the skin.Anaerobic metabolism is also possible (anaerobic breakdown of glycogen into butyric and valeric acids in parasites).
Nervous system. The nervous system is scaly.It is represented by a nerve ring and six longitudinal trunks.The two nerve trunks that run along the ventral and dorsal lines are stronger and are connected by semicircular nerve bridges (commissures).
Sense organs. There are papillae and papillae - tactile organs located around the mouth.Some marine representatives have primitive eyes - pigment spots.The chemosensory organs of amphibians are usually pocket, coil or slit shaped.They are located on the sides of the tip of the head and are particularly well developed in males, as they help in finding females.
Reproduction and growth. Nematodes are dioecious animals.The internal genitalia are paired and have a tubular structure.Reproduction is only sexual.Sexual dimorphism is pronounced: females are larger, in males the posterior end of the body is convex.Fertilization is internal and zoogenesis occurs.During development, nematodes go through four larval stages, separated by molting, which are accompanied by shedding of the epidermis.The third stage in some species (including the famous Caenorhabditis elegans) under unfavorable conditions, changes to the so-called dauer stage - a resting larva.
Parasitism. Currently, of the more than 24,000 described species of nematodes, about half are parasitic.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.
The following are descriptions of the most important representatives of roundworms from the point of view of medical parasitology.
Human roundworm(Ascaris lumbricoides)
Appearance.The body, pointed at the ends, is pinkish-white.Dimensions: males - 15-25 cm, females - 20-40 cm.The body is covered with a ten-layer flexible epidermis that protects against mechanical stress and the digestive enzymes of the host.
Hearsay. The species is cosmopolitan - distributed everywhere, but different countries have different rates of infected people.In Japan, for example, more than 90% of the population is infected with roundworms due to the use of human feces as fertilizer.In areas with a hot, dry climate, the roundworm is less common.
Life cycle.The development continues without a change of owners.Adult worms parasitize the small intestine, causing ascariasis.A person is usually affected by several dozen roundworms (the record is 900 pieces).The life span in the intestines is about one year.Roundworms are dioecious, as are other nematodes.A sexually mature female lays about 200 thousand oval eggs per day, which are released into the external environment with feces.Roundworms are classified as geohelminths - they require a larval stage to develop in the soil.When exposed to favorable conditions (moist soil at a temperature of about 25 °C and with sufficient access to oxygen), a larva develops in the egg.The growth period varies from 16 days to several months and depends on the air temperature.Such eggs containing larvae can be considered invasive.
Infection occurs when eggs are ingested in food or water.transmission does not occur directly from person to person.In the intestine, the larvae traverse the intestinal wall, enter the blood vessels and liver, and then migrate through the inferior vena cava to the right atrium and right ventricle.From the latter, the larvae move through the pulmonary circulation to the lungs, where they move from the blood to the alveoli, bronchi, trachea and oral cavity.Secondary infection occurs in the oral cavity: the larvae are swallowed, enter the intestines and mature sexually after three months.The process of "growing up" in nematodes is associated with molting (usually four of them).
Clinical picture of ascariasis. In the migratory stage of ascariasis, coughing (helps the larvae to enter the throat), chest pain, allergic reactions and fever are observed.
In the intestinal stage, there is damage to the intestinal mucosa and poisoning of the body with toxic metabolic products.Symptoms: nausea, vomiting, stool disorders, loss of appetite.
Long-term effects of contamination: general decrease in performance, sleep disturbances.When the worms crawl into the bile ducts and respiratory tract, the result is fatal.Also, roundworm larvae can enter the brain (for example, from the inferior vena cava to the superior vena cava, then along the brachiocephalic vein), causing meningoencephalitis, accompanied by migraines.
Prevention. Washing hands before eating and preparing food.Washing vegetables and fruits.Eggs are also carried by flies, so fighting these diptera using, for example, Velcro also helps prevent ascariasis.
Interesting fact. There are studies showing the positive effects of roundworm infection in alleviating the symptoms of autoimmune diseases and increasing fertility in women.Scientists attribute this to the parasite's effect on the immune system by affecting the level of T cells in the body, but at the moment the mechanism is too poorly understood to draw reliable conclusions.
pinworm(Enterobius vermicularis)
Appearance. Grey-white filamentous, males 2-5 mm long, females 8-14 mm long.The tip of the tail is pointed (hence the name).At the anterior end of the body, a characteristic swelling of the esophagus is noticeable.
Life cycle.The worms parasitize the lower part of the small intestine and large intestine, causing enterobiasis.Shelf life is 1-2 months.The anterior end of the worm attaches to the intestinal wall.A sexually mature female crawls out of the large intestine through the anus and lays from 5 to 15 thousand eggs on the skin near the anus, after which she dies.
The crawling of females is accompanied by itching.When scratching the skin, the eggs are transferred to the hands and not only.Flies also participate in the transfer of eggs.Infection occurs through ingestion.Larvae hatch from eggs that enter the intestines.
Epidemiology and clinical picture of enterobiasis. Enterobiasis is widespread, especially common in children due to non-compliance with the rules of personal hygiene and "overcrowding" in kindergartens and schools.It is transmitted from person to person without an intermediate host.It reduces the effect of vaccinations.
Symptoms: abdominal pain, loss of appetite, headaches, allergic manifestations, perianal itching (leads to sleep disturbances, increases irritability).
Trichinella(Trichinella spiralis)
Description.Small filament 2-4 mm long.It parasitizes the mucous membrane of the small intestine.Distributed in Eurasia and North America.
Life cycle. A change of hosts is necessary for the growth of Trichinella.Usually these are wild animals (foxes, wolves, bears, wild boars), as well as people and animals.Females anchor from the anterior end of the body to the intestinal epithelium and give birth to 1-2 thousand larvae.Spawning is characteristic: hatching of larvae from eggs occurs in the female genital tract.The larvae are carried throughout the body via the blood and lymphatic vessels and settle in the striated muscles.At this stage, they have a stylet, which they use to destroy the muscle tissue, causing the host to form a capsule in which, coiled, they reside in the future.After a few months, the capsule is soaked in lime.Such muscle trichina can exist for several years and survive even after the death of the owner and the decomposition of his corpse.
Once in the stomach of the new host (after it has eaten the corpse of the previous one), the larvae are released from the capsule, penetrate the mucous membrane and within a few days, after undergoing four falls, turn into adult worms.
Clinical picture of trichinosis. Increased temperature, swelling of the face, muscle pain, allergic reactions.
Prevention. Trichinosis is transmitted through food through contaminated meat.Therefore, to prevent the disease, the meat must undergo a veterinary examination and be properly prepared - boiled for 2-3 hours.Cooking methods such as smoking and salting do not destroy Trichinella.
Whip(Trichocephalus trichurus)
Appearance.The worm is whitish in color, about 4 cm long.The front end is thin, resembling hair (hence the name).
hearsay.They prefer countries with a humid and warm climate.
Life cycle.The worm parasitizes in the initial part of the large intestine, only in humans.It causes hair loss.The lifespan of an individual is several years.The thin end penetrates the thickness of the mucous membrane of the intestinal wall.It feeds on tissue fluid and blood.
The female lays 1-3 thousand eggs, which are released into the external environment with the feces.Like the roundworm, the whipworm is also related to geohelminths: for the eggs to become invasive, they must remain in the soil at a certain humidity and temperature (25-30 ° C) for a month.After that, infection occurs when the eggs are ingested.The larvae emerge from them into the host's intestines, penetrate the intestinal villi and develop in them for about a week.Then, having destroyed the villi, they go out into the lumen of the intestine, reach the large intestine, settle there and mature within a month.
Clinical picture of trichocephaly. The worm destroys the mucous membrane of the large intestine and causes poisoning of the host with waste products.Whipworm is a blood eater, so it can lead to anemia.Trichocephaly is accompanied by abdominal pain, headaches and dizziness.Because the flagella adheres to the intestinal wall, it is more difficult to remove from the host than other parasites.
Rishta(Dracunculus medinensis)
Appearance.A thin whitish filament, females 30-120 cm long, males no more than 4 cm.There is a small spine on the tail.
Distribution: tropical countries of Asia and Africa.
Life cycle.Contamination occurs when drinking unboiled water containing copepods.Crustaceans in the stomach die under the influence of hydrochloric acid, but the larvae of the Indian worm survive and spread throughout the body through the lymphatic system.They then penetrate the body cavity, where they melt and reach sexual maturity.After mating, the male dies and the female moves to the subcutaneous tissue, where a purulent abscess forms, accompanied by burning and pain.Cool water is best for pain relief.
The development of the eggs causes the female to begin to move the "head" forward towards the surface of the skin, leaving an inflammatory process in its course, turning into a purulent abscess, which then bursts.When the female's uterus enters the water, it ruptures and the larvae hatch from the eggs.To ensure that development is not interrupted, the larvae must infect the cyclops crustacean, which is an intermediate host.Any larvae that remain in the water die.After ingestion of the crustaceans by the definitive host, under the influence of stomach acid, the crustaceans dissolve and the larvae easily enter the intestine, pass through its walls and end up in the lymph nodes, where the growth cycle continues.The disease caused by the Indian worm is called dracunculiasis.
Dracunculiasis.The incubation period lasts up to nine months and ends when the female reaches sexual maturity.And in a person who has already fallen ill with dracunculiasis, purulent abscesses begin to form at this time.The only escape from pain is a pond.Relief is immediate, but on contact with water the bubbles burst and the Indian worm throws the larvae into the water.Crustaceans consume them and the cycle of life begins again.
In the treatment of dracunculiasis, an incision is often made at the site of the blister and the worm is gradually pulled out by wrapping it around a stick.This takes days, sometimes weeks (you have to pull the worm slowly and carefully so it doesn't break).It has been suggested that the appearance of an Indian worm wrapped around a stick became a kind of prototype for the symbol of medicine - the staff of Asclepius entwined with a snake.
Bancroft's thread (filaria), or Bancroft's string(Wuchereria bancrofti)
Appearance.Filamentous white thread, females 10 cm long, males 4 cm long.
Distribution. Tropical, subtropical Asia, Africa, Central and South America.
Life cycle. Adults usually appear in the lymph nodes and vessels, blocking the drainage of lymph and causing persistent swelling.Females produce larvae - nocturnal microfilariae, which appear in the peripheral blood at night and during the day go deep into the body (in the pulmonary vessels and kidneys).This is because the intermediate host is mosquitoes, which usually suck blood in the evening and at night.The larvae enter the mosquito's stomach, then the body cavity, where they develop, after which they accumulate near the proboscis, from which they are transmitted to humans by sucking blood.Bancroft's yarns cause elephantiasis, or elephantiasis, or elephantiasis.It is worth noting that this disease can also be caused by other nematodes.
Clinical picture and treatment of elephantiasis. Enlargement of any part of the body is due to hyperplasia (painful growth) of the skin and subcutaneous tissue, which is caused by inflammatory thickening of the walls of the lymphatic vessels and stagnation of lymph, which occurs due to blockage of the lymphatic vessels by filamentous individual Bancroft adults.The skin on the diseased part of the body is covered with ulcers.
Treatment of elephantiasis is aimed at improving the outflow of fluids.The use of anthelmintic drugs is effective.In later stages, surgery may be required.
