Nematodes, or nematodes themselves (Nematoda), are a type of protozoa, protozoa, and bilaterally symmetrical molting animals.
Widespread. Nematodes are among the most widespread animals capable of colonizing a wide variety of habitats - from interstices (spaces between sand grains) and moss communities to Arctic ice (e.g.Theristis Melnikovi and Cryonema Crissum, found in thick multi-year ice in the central part of the Arctic Ocean).Parasitic nematodes are of particular interest to researchers, including because of the diversity of their hosts.
Construction plan. The body is thin, diamond-shaped, tapering towards the end, round in cross-section.The mouth is located in front and the corpus (anus) is in the back.The outside of the body is covered by a multilayer elastic epidermis - an acellular form secreted by the subcutaneous layer.The subcutaneous layer, or epidermis, lies below the epidermis.Muscles are represented by a layer of oblique longitudinally striated muscle fibers.The primary (schizophrenic) body cavity, which does not have its own epithelial layer, is filled with fluid.
Digestive system. The oral opening at the anterior end of the body is surrounded by protrusions - the lips (usually three) and leads into the muscular ectodermal pharynx with a triangular lumen.The pharynx enters the endodermal midgut from a layer of columnar epithelial cells.Next is a short ectodermal hindgut, opening into the anus.
Excretory system. Excretory organs are unicellular glands that replace protonephridia.There is usually a cervical gland in 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 eliminated from the body.
Circulatory and respiratory system. These systems are lacking.Breathing occurs through the skin.Anaerobic metabolism (anaerobic breakdown of glycogen to butyric and valeric acids in parasites) can also occur.
Nervous system. The nervous system is of the scalariform type.Represented by a nerve ring and six longitudinal trunks.The two nerve trunks run more strongly along the ventral and dorsal lines and are connected by a semicircular nerve bridge (commissure).
Sensory organs. There are papillae and setae - sense organs located around the mouth.Some marine representatives have primitive eyes - pigment spots.Amphibians' chemical sense organs are often saccular, spiral or slit shaped.They are located on both sides of the head and are especially well developed in males because they help find females.
Reproduction and development. Nematodes are hermaphrodites.The internal sex organs are paired and have a tubular structure.Reproduction is only sexual.Sexual dimorphism is clearly manifested: females are larger, in males the posterior part of the body is curved.Fertilization takes place internally and parturition occurs.During development, nematodes go through four larval stages, separated by molting, accompanied by the shedding of the cuticle.The third stage in some species (including the famous Caenorhabditis elegans) under unfavorable conditions, it enters the so-called dauer stage - the resting larva.
Parasites. Currently, of the more than 24,000 described nematode species, about half are parasitic.They can affect almost all tissues and organs: connective tissue, muscles, blood and lymphatic vessels, gonads, sensory organs, as well as body cavities, etc.Among them are both ectoparasites and endoparasites of plants, vertebrates and invertebrates, including other nematodes and even protozoa.
The following is a description of the most important representatives of roundworms from the point of view of medical parasitology.
Human roundworm(Ascaris lumbricoides)
Appearance.The body is pointed at both ends and has a pinkish white color.Size: males - 15-25 cm, females - 20-40 cm.The body is covered by a ten-layer flexible cuticle that provides protection from mechanical stress and the host's digestive enzymes.
Widespread. The species is cosmopolitan - distributed everywhere, but different countries have different rates of infection.For example, in Japan, more than 90% of the population is infected with roundworms due to the use of human feces as fertilizer.In hot, dry climates, roundworms are less common.
Life cycle.The development took place without a change of ownership.Adult worms parasitize in the small intestine causing ascariasis.A person is usually affected by several dozen roundworms (the record is 900).Lifespan in the intestine is about one year.Roundworms are very virulent like other nematodes.A sexually mature female lays about 200 thousand oval eggs per day, which are released into the external environment along with feces.Nematodes are classified as earthworms - they require development of the larval stage in the soil.When conditions are favorable (moist soil at a temperature of about 25 °C and enough oxygen), larvae will develop in eggs.Development time varies from 16 days to several months and depends on air temperature.Eggs containing such 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 burrow through the intestinal wall, enter the blood vessels and liver, and then migrate through the inferior vena cava into the right atrium and right ventricle.From the latter, the larvae migrate through the pulmonary circulation to the lungs, where they move from the blood into the alveoli, bronchi, trachea, and oral cavity.Secondary infection occurs in the oral cavity: the larvae are swallowed, enter the intestines and become sexually mature after three months.The process of "growing up" in nematodes is associated with molting (usually four).
Clinical picture of ascariasis. In the migratory stage of ringworm, people will notice coughing (which helps the larvae enter the throat), chest pain, allergic reactions, and fever.
At the intestinal stage, damage to the intestinal mucosa occurs and the body is poisoned with toxic metabolic products.Symptoms: nausea, vomiting, stool disorders, loss of appetite.
Long-term effects of infection: general decrease in performance, sleep disturbances.When the worms crawl into the bile ducts and respiratory tract, the results are fatal.In addition, roundworm larvae can penetrate the brain (for example, from the inferior vena cava to the superior vena cava, then along the brachiocephalic vein), causing meningitis, accompanied by migraine.
Prevent. Wash your hands before eating and preparing food.Wash vegetables and fruits.Eggs are also carried by flies, so fighting this dipteran using Velcro, for example, also helps prevent ringworm.
Interesting fact. There are studies showing the positive effects of roundworm infection in reducing symptoms of autoimmune diseases and increasing fertility in women.Scientists believe this is due to the parasite's impact on the immune system by affecting T-cell levels in the body, but currently, this mechanism is not well understood to draw reliable conclusions.
pinworm(Enterobius vermicularis)
Appearance. Nematodes are grayish white, males are 2-5 mm long, females are 8-14 mm long.The tail is pointed (hence the name).At the anterior end of the body, characteristic swelling of the esophagus can be noticed.
Life cycle.Pinworms parasitize the lower small and large intestines, causing intestinal worms.Lifespan is 1-2 months.The anterior end of the pinworm 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 out of the female is accompanied by itching.When scratching the skin, the eggs will transfer to the hands and more.Flies are also involved in egg transfer.Infection occurs through eating or drinking.Larvae hatch from eggs that enter the intestines.
Epidemiology and clinical picture of enterobosis. Enterobosis is common, especially common in children due to non-compliance with personal hygiene rules and "crowding" in kindergartens and schools.Transmitted from person to person without an intermediate host.Reduced effectiveness of vaccination.
Symptoms: abdominal pain, loss of appetite, headache, allergic manifestations, itching around the anus (leading to sleep disorders, increased discomfort).
Trichinella(Trichinella spiral)
Describe.Small nematodes 2-4 mm long.Parasites of the mucous membrane of the small intestine.Distributed in Eurasia and North America.
Life cycle. For Trichinella to grow, a change of host is necessary.Usually these are wild animals (fox, wolf, bear, wild boar), as well as people and livestock.The female is anchored at the anterior end of the body to the intestinal epithelium and gives birth to 1-2 thousand larvae.Ovulation is typical: hatching of larvae from eggs occurs in the female genital tract.The larvae are carried throughout the body through the blood and lymphatic vessels and settle in striated muscles.At this stage, they have an air duct, which they use to destroy muscle tissue, causing the host to form a cyst in which they curl up for future residence.After several months, the capsule is soaked in lime.Such mechanical trichina can last for several years and survive even after the death of the owner and the decomposition of the corpse.
Once in the stomach of the new host (after it has eaten the corpse of the previous host), the larva breaks out of the shell, penetrates the mucous membrane and within a few days, undergoing four molts, turns into an adult worm.
Clinical picture of trichinosis. Increased temperature, facial swelling, muscle pain, allergic reactions.
Prevent. Trichinosis is transmitted through food through contaminated meat.Therefore, to prevent diseases, meat must be veterinary inspected and properly processed - boiled for 2-3 hours.Processing methods such as smoking and salting do not destroy Trichinella.
roundworm(Trichocephalus tricchurus)
Appearance.Worms are white, about 4 cm long.The front part of the head is thin, reminiscent of hair (hence the name).
Spread.They prefer countries with humid and warm climates.
Life cycle.Parasitic worms in the first part of the large intestine, only parasitic on humans.Causes trichurosis.A person's lifespan is several years.The thin tip penetrates into the thickness of the mucous membrane of the intestinal wall.It feeds on tissue fluids and blood.
Females lay 1-3 thousand eggs, which they release into the outside environment in feces.Like roundworms, whipworms are related to helminths: for the eggs to be invasive, they need to survive in the soil at a certain humidity and temperature (25-30°C) for a month.Infection then occurs when the eggs are swallowed;The larvae emerge from them in the host's intestines, penetrate the intestinal villi and develop in them for about a week.After destroying the villi, they enter the intestinal lumen, reach the large intestine, form there and mature within a month.
Clinical picture of trichocephalus disease. Worms damage the mucous membrane of the colon and poison the host with waste products.Roundworms are hematomas, so they can lead to anemia.Trichocephalus is accompanied by abdominal pain, headache and dizziness.Because whipworms adhere to the intestinal wall, they are more difficult to remove from the host than other parasites.
Rishta(Dracunculus medinensis)
Appearance.Nematodes are thin, pale white, females are 30-120 cm long, males are no more than 4 cm long.There is a small spike in the tail.
Distribution: tropical countries of Asia and Africa.
Life cycle.Infection occurs when drinking unboiled water containing crustaceans.Crustaceans in the stomach die under the effects of hydrochloric acid, but guinea worm larvae survive and spread throughout the body through the lymphatic system.They then enter the body cavity, where they molt and reach sexual maturity.After mating, the male dies, the female migrates into the subcutaneous tissue, forming a purulent abscess, accompanied by a burning sensation and pain.Cool water is the best way to relieve pain.
The development of the eggs forces the female to begin moving her “head” towards the surface of the skin, leaving an inflammatory process along its path, which turns into a purulent abscess, which then bursts.When the female's uterus falls into the water, it bursts and the larvae hatched from the eggs come out.To ensure uninterrupted development, the larvae must infect the crustacean cyclops, which is the intermediate host.Any larvae left in the water will die.After the host finally devours the crustacean, under the influence of stomach acid, the crustacean dissolves and the larvae easily penetrate the intestine, penetrate the intestinal wall and reach the lymph nodes, where the development cycle continues.The disease caused by the guinea worm is called dracunculosis.
Ascariasis.The incubation period lasts up to nine months and ends when the female reaches sexual maturity.And in a person who already has dracunculosis, purulent abscesses begin to form at this time.The only salvation from pain is a pond.Relief is immediate, but on contact with water, the bubbles burst and the guinea worms throw the larvae into the water.Crustaceans consume them and the life cycle begins again.
When treating ringworm, an incision is often made at the site of the blister and the worm is gradually pulled out and wrapped around a stick.This takes days, sometimes weeks (you have to pull the worm out slowly and carefully so it doesn't break).It is suggested that the appearance of a guinea worm wrapped around a staff became a prototype for the symbol of medicine - the staff of Asclepius wrapped around a snake.
Bancroft filament (filaria) or Bancroft filament(Wuchereria bancrofti)
Appearance.White filament nematode, females 10 cm long, males 4 cm long.
Allocation. Tropical and subtropical regions of Asia, Africa, Central and South America.
Life cycle. Adult disease often occurs in lymph glands and blood vessels, obstructing lymphatic drainage and causing persistent swelling.Females produce larvae - nocturnal filariasis, appearing in the peripheral blood at night, and during the day they penetrate deep into the body (into the pulmonary vessels and kidneys).This is because the intermediate host is the mosquito, which usually feeds on blood in the evening and at night.The larvae enter the mosquito's stomach, then into the body cavity, where they develop, then accumulate near the proboscis, from where they are transmitted to humans by sucking blood.Bancroft's fibers cause elephantiasis, elephantiasis, or elephantiasis.It is worth noting that this disease can also be caused by other types of nematodes.
Clinical picture and treatment of elephantiasis. Hypertrophy of any part of the body occurs due to hyperplasia (painful growth) of the skin and subcutaneous tissue, which is caused by inflammatory thickening of the walls of lymphatic vessels and lymphatic stagnation, which occurs due to blockage of lymphatic vessels by mature individuals of Bancroft's fibers.The skin on the affected part of the body is covered with ulcers.
Treatment for elephantiasis is aimed at improving fluid flow.The use of anthelmintic drugs is effective.At later stages, surgery may be required.
