Ascaridosis

Ascariasis (Latin: ascaridosis) is a helminthiasis from the group of intestinal nematodoses caused by roundworms (usually Ascaris lumbricoides), characterized in the early stage by allergic phenomena, and in the late stage by dyspeptic phenomena and complications when helminths penetrate into other organs, as well as as a result of intestinal obstruction or spasm.

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Epidemiology of ascariasis

Ascariasis is a geohelminthiasis. The source of environmental contamination is only a person with ascariasis. He becomes infected by swallowing invasive eggs. Contaminated vegetables, berries, other food products, water, and hands serve as transmission factors. In the temperate climate zone, the infection season lasts up to 7 months - from April to October, in warm, humid climates - all year round.

The female ascaris lays up to 240,000 eggs per day. The maximum number of eggs is released at 5-6 months of the female's life. By the 7th month, ovulation ends and the female stops releasing eggs.

For eggs to become invasive, the following conditions are necessary: oxygen, humidity of at least 8%, temperature of 12-37 °C and a certain amount of time. Under optimal conditions (temperature of 24-30 °C and humidity of 90-100%), an invasive larva is formed in the egg 2-3 weeks after the first molt, which can infect humans. Egg development takes longer in moderate and cool climates than in warm ones. Under favorable conditions, eggs can remain viable for up to 10 years.

In a moderate climate, the development of eggs in the soil begins in April-May. In winter, no egg development occurs. In May-July, invasive larvae will form in the egg. Human infection with invasive ascaris eggs can occur throughout the year, since they are resistant to external influences and remain viable for a long time. The greatest number of invasive eggs accumulate in the soil in the summer-autumn period, when mass infection of the population with ascariasis occurs. The longest infection season is observed in the south, and the shortest - in the northern regions. The highest degree of invasion of the population by adult ascarids occurs in winter, and the lowest - at the beginning of summer.

Ascariasis transmission factors are soil contaminated with ascarid eggs, vegetables, berries, fruits, and water. Wastewater from sewers or fecal matter from nearby toilets may enter water bodies. Flies and cockroaches may be mechanical carriers of eggs.

Humans become infected through direct contact with soil containing invasive eggs. If personal hygiene rules are not observed, eggs from the soil can enter a person's mouth with unwashed hands. Infection can occur through various household items and food products contaminated with ascaris eggs. Eggs can enter living quarters with dust or be brought in on shoe soles.

Ascariasis foci vary in the intensity of transmission of the invasion, depending on the degree of contamination of the external environment with invasive ascaris eggs, sanitary conditions, hygienic skills of the population and climatic factors. Ascariasis foci usually form in rural areas or in those areas of cities where there are sources of infection, insufficient sanitary improvement, there are features of life and economic activity that contribute to the penetration of invasive eggs from the external environment to humans. In cities, people most often get ascariasis after returning from rural areas, from garden plots and summer cottages, where undisinfected human feces are sometimes used as fertilizer, as well as when eating unwashed vegetables and fruits, berries brought from ascariasis foci, and when failing to observe personal hygiene rules.

Susceptibility to ascariasis is high. In highly epidemic areas, up to 90% of children are sick with ascariasis. This is explained by the fact that ascariasis does not leave any pronounced immunity.

Ascariasis is the most common helminthiasis in the world. According to WHO, more than 1.2 billion people are infected with ascariasis in the world. Of these, approximately 100,000 die from this invasion every year. Ascariasis is common in 153 of the 218 countries in the world, located in temperate, subtropical and tropical climate zones.

More than 50% of the population examined is infected with ascariasis in Nigeria, Congo, Brazil, Ecuador, Iraq, Malaysia, Afghanistan, Indonesia. Ascariasis is very rare in desert, semi-desert and permafrost zones.

In endemic foci, people develop immunity to superinvasion and reinvasion. The immune response is more pronounced during the period of parasitism of the larval stages of the helminth, which are in the process of migration. Immune reactions against the helminth larvae protect the host from an uncontrolled increase in the intensity of invasion during repeated infection. For residents of endemic foci, subject to frequent repeated infections, the development of a certain immunity is characteristic and, accordingly, low-intensity intestinal invasion.

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Causes of ascariasis

Ascariasis is caused by Ascaris lumbricoides, which belongs to the Nematheiminthes type, Nematoda class, Rhabditida order, Oxyuridae family. The following stages are distinguished in the development cycle of A. lumbricoides: sexually mature form, egg, invasive egg, larva.

Due to significant morphological and metabolic changes at different stages of development in roundworm, as in other types of helminths, exogenous and endogenous antigens and their immunogenic properties change significantly.

Mature individuals have a long, thin, whitish-pink body. The female is 20-40 cm x 3-6 mm, the male - 15-25 cm x 2-4 mm. The mouth opening, located at the front end of the body, is surrounded by three cuticular lips. The tail is short, in the male it is bent towards the ventral side. The internal structure is typical for nematodes. Mature roundworms parasitize the small intestine of humans, feeding on the contents of the intestine. Each female lays up to 240,000 fertilized and unfertilized eggs per day. Fertilized eggs (50-70 x 40-50 µm) are almost spherical or elongated, yellow or yellow-brown in color, have three membranes. Under favorable environmental conditions (oxygen, high humidity, temperature 20-25 °C), the development of the larva in the egg takes 2-3 weeks. Mature larvae can survive for 20 days at a temperature of -20...-27 °C. At -30 °C, the larvae quickly die, and a temperature of 47 °C causes their death within 1 hour.

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The development cycle of ascariasis

A person becomes infected with ascariasis by swallowing eggs containing larvae that have reached the invasive stage. In the small intestine of a person, the larvae are released from the egg membranes, penetrate the intestinal wall into the blood vessels and migrate through the bloodstream and tissues of the host. With the blood flow, they enter the portal vein, the vessels of the liver, the inferior vena cava, the right atrium and through the pulmonary artery into the capillaries of the alveoli of the lungs.

Through the walls of the capillaries, the larvae penetrate into the cavity of the alveoli, then the bronchioles and migrate along the airways. From the trachea, when coughing up sputum, the larvae enter the pharynx, are swallowed a second time and again end up in the small intestine. During migration, the larvae molt twice and increase in size from 0.19-0.25 mm to 1.5-2.2 mm. The migration of ascaris larvae lasts about two weeks. In the intestine, the larvae grow, molt again and become sexually mature after 2-2.5 months. The lifespan of adult ascarids is about 1 year.

Pathogenesis of ascariasis

The pathogenesis of ascariasis is different during the period of migration of larvae in the blood and their stay in the respiratory organs and during the period of parasitism of adult helminths in the small intestine of a person. Rhabditiform larvae emerge from the invasive eggs of ascarids in the small intestine of a person, which penetrate into the thickness of the mucous membrane after 3-4 hours.

Next, the larvae migrate through the portal vein system to the liver, then to the lungs, where they continue to develop for 1-2 weeks. In the liver on the 5th-6th day after infection and in the lungs (on the 10th day), the larvae molt. In the lungs, breaking the capillary network and the walls of the alveoli, they penetrate the lumen of the bronchi and move along the airways to the oropharynx. With swallowed saliva and food, the larvae again enter the small intestine, where they turn into sexually mature males and females, having previously molted two more times. The duration of larval migration is about 2 weeks, and the maturation of females before the start of egg laying lasts more than 10 weeks. In the human body, an adult lives 11-13 months.

In the early migration stage, pathological changes are based on the sensitization of the body by the products of metabolism, molting and decay of dead larvae. Ascaris allergens are the strongest among allergens of parasitic origin. With intensive invasion, mechanical damage to the wall of the small intestine, blood vessels, liver tissue, and lungs is observed. Eosinophilic infiltrates in the lungs, capillary stasis, and hemorrhages are also noted. Clinical manifestations in the late intestinal stage are associated with the mechanical effect of helminths and their metabolic products on the intestinal mucosa, which leads to digestive disorders, motor function, nitrogen imbalance, and hypovitaminosis. One of the polypeptides secreted by the ascaris has a toxic effect on the central nervous system. Ascaris can migrate beyond the small intestine: into the bile and pancreatic ducts, appendix, and respiratory tract. Sometimes accumulations of roundworms lead to intestinal obstruction, volvulus, and intussusception. Intestinal obstruction often occurs with intensive invasion, and intussusception occurs with the presence of single helminths or several individuals of the same sex. Roundworms significantly suppress the host's immunological reactivity.

During the parasitism of adult roundworms in the intestine, the sensitization of the organism continues. In the pathogenesis of the intestinal phase, the main role is played by the intoxication of the organism with toxic waste products of roundworms, which results in disorders of the digestive, nervous, reproductive and other systems. Helminths have a mechanical effect on the intestinal mucosa, leading to its change: parietal digestion is disrupted, the absorption and assimilation of proteins, fats, vitamins is difficult, the activity of the lactase enzyme decreases, etc.

Symptoms of ascariasis

There are two clinical stages of the disease - early (migration) and late (intestinal). Symptoms of ascariasis in the early stage are often absent. In the clinically expressed form, on the 2nd-3rd day after infection, symptoms of ascariasis such as malaise, weakness, subfebrile condition appear. Urticarial rashes on the skin are observed, an enlargement of the spleen and liver is possible. A more typical symptom complex of lung damage with the formation of transient infiltrates, determined radiologically, and eosinophilia in the peripheral blood (Löffler syndrome). In these cases, a dry cough appears, sometimes with sputum with blood streaks, shortness of breath, chest pain, suffocation. Dry and wet wheezing is heard in the lungs.

In the intestinal stage, ascariasis in adults often occurs with mild symptoms or asymptomatically. The observed symptoms of ascariasis (loss of appetite, nausea, sometimes vomiting, cramping abdominal pain, diarrhea or unstable stool) are not very specific. The patients' health deteriorates, their ability to work decreases, headaches and dizziness appear.

In children, pneumonia may develop in the early stages of ascariasis, and severe intoxication may occur with intensive invasion. Body weight decreases, children become capricious, absent-minded, epileptiform seizures, meningism, and Meniere's syndrome are possible; blood tests show normo- and hypochromic anemia, eosinophilia.

Complications of ascariasis

There are intestinal and extraintestinal complications of ascariasis, which occur in the late stage of invasion and are often caused by increased mobility of adult helminths. The most common complication, especially in children aged 4 to 8 years, is intestinal obstruction. With destructive changes in the intestinal mucosa or after surgical interventions, penetration of roundworms into the abdominal cavity and development of peritonitis are possible. Introduction of helminths into the biliary and pancreatic ducts can lead to mechanical jaundice, reactive pancreatitis, in case of secondary bacterial infection, purulent cholangitis, liver abscesses, and sometimes appendicitis develop. With vomiting, antiperistaltic movements, roundworms can get into the esophagus, from where they penetrate into the pharynx, respiratory tract, causing asphyxia.

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Diagnosis of ascariasis

When recognizing the early (migration) stage of ascariasis, it is necessary to focus on the symptoms of lung damage in combination with blood eosinophilia. It is rarely possible to detect ascaris larvae in sputum. There is serological diagnostics of ascariasis (ELISA, RLA), but it is not widely used in practice. In the intestinal stage, the diagnosis is established by finding eggs or ascarids in feces. The season of examination is taken into account. The maximum detection of infested individuals occurs in December-February. When parasitizing in the intestines of only males of old or immature females, eggs may be absent.

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Differential diagnosis of ascariasis

Differential diagnostics of ascariasis in the migration stage is carried out with toxocariasis, the early phase of other helminthiases characterized by allergic manifestations, acute bronchitis, pneumonia. In the intestinal stage, it is almost impossible to differentiate ascariasis from chronic gastrointestinal diseases based on clinical symptoms. If complications arise, depending on their nature, differential diagnostics of ascariasis is carried out with intestinal obstruction, cholangitis, liver abscess, pancreatitis of other etiology. In these cases, additional instrumental studies (ultrasound of the abdominal organs) and a surgeon's consultation are necessary.

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Treatment of ascariasis

Indications for hospitalization

Treatment of ascariasis is carried out on an outpatient basis or in a day hospital. Patients with surgical complications of ascariasis are subject to hospitalization.

Drug treatment of ascariasis

All patients with ascariasis are subject to treatment with anthelmintic drugs.

• Albendazole is prescribed to adults in a single dose of 400 mg orally after meals, to children over 3 years old - 10 mg/kg in two doses for 1-3 days.
• Mebendazole is indicated for adults and children over 2 years of age orally at 100 mg twice a day for 3 days.
• Carbendacim is recommended to be taken orally 20-30 minutes after meals at a dose of 10 mg/kg in three doses for 3 days.
• Pyrantel is prescribed at 10 mg/kg once orally after meals.

When taking the indicated anthelmintic drugs, no special diet or prescription of laxatives is required.

Pathogenetic and symptomatic treatment of ascariasis is necessary in case of prolonged and intensive invasion: probiotics and enzymatic preparations are used.

Additional treatment for ascariasis

If surgical complications occur, surgical treatment of ascariasis or instrumental intervention is necessary.

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Clinical examination

Outpatient observation of those who have recovered is carried out for 2-3 months. Control studies of feces for the presence of ascaris eggs are carried out 3 weeks after the end of treatment with an interval of 2 weeks. If the treatment is ineffective, the course of treatment should be repeated.

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Prevention

Ascariasis can be prevented by sanitary improvement of populated areas and protection of soil from faecal contamination. In individual prevention, it is important to strictly observe the rules of personal hygiene, thoroughly wash raw vegetables, berries and fruits consumed in food. In ascariasis foci with an infection rate of less than 10% of the population, 20% of residents undergo parasitological examination once every two years; in foci where more than 10% of residents are infected, the entire population is examined annually. For deworming, anthelmintic drugs are used, taking into account the features of their use in different age groups.

Forecast

Ascariasis in an uncomplicated course has a favorable prognosis. In the absence of re-infection, self-healing occurs after 9-12 months due to the natural death of helminths. Complications of ascariasis are relatively rare, but they pose a serious threat to health and can lead to death, especially in children.

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