Ascaridosis

Ascaridosis (Latin ascaridosis) is a helminthiosis from the group of intestinal nematodes caused by ascarids (usually Ascaris lumbricoides), characterized in an early stage by allergy phenomena, and in the late stage - by dyspeptic phenomena and complications during the penetration of helminths into other organs, as well as by blockage or spasm intestines.

[1], [2], [3]

Epidemiology of ascariasis

Ascariasis refers to geogelmintosis. The source of environmental contamination is only a person suffering from ascariasis. It becomes infected by ingestion of invasive eggs. Transfer factors are contaminated vegetables, berries, other food products, water, and hands. In the temperate climate zone, the infection season lasts up to 7 months - from April to October, in conditions of warm wet climate - all year round.

The female askarid lays up to 240,000 eggs a day. The maximum number of eggs is allocated for 5-6 months of life of the female. By the 7th month, ovulation is over, and the female stops allocating eggs.

In order for eggs to become invasive, the following conditions are necessary: the presence of oxygen, a humidity of at least 8%, a temperature of 12-37 ° C, and a certain time. Under optimal conditions (temperature 24-30 ° C and humidity 90-100%), after 2-3 weeks, an invasive larva is formed in the egg after the first molt, capable of infecting a person. The development of eggs lasts longer in a temperate and cool climate than in warm weather. Under favorable conditions, eggs can remain viable for up to 10 years.

In a temperate climate the development of eggs in the soil begins in April-May. In the winter, eggs do not develop. In May-July, invasive larvae form in the egg. The infection of humans with invasive eggs of ascarids can occur throughout the year, as they are resistant to external influences and remain viable for a long time. The greatest number of invasive eggs accumulates in the soil in the summer-autumn period, when mass infection of the population with ascariasis occurs. The longest season of infection is in the south, and the least in the northern regions. The highest degree of invasiveness of the adult adult ascarids occurs in winter, and the lowest in early summer.

Transfer factors of ascaridosis are soil polluted with eggs of ascarids, vegetables, berries, fruits, water. Waste water from the sewage system or fecal matter from nearby latrines may enter the water bodies. Mechanical vectors of eggs can be flies, cockroaches.

Infection of a person occurs by direct contact with soil containing invasive eggs. If the rules of personal hygiene are not observed, eggs from the soil with unwashed hands fall into the person's mouth. Infection can occur through various household items and food contaminated with ascarid eggs. In the living quarters, eggs can fall with dust, be carried on the soles of shoes.

Foci of ascariasis are diverse in the intensity of transmission of infestation, depending on the degree of environmental contamination with invasive ascaris eggs, sanitary conditions, hygienic skills of the population and climatic factors. Foci of ascariasis are usually formed in rural areas or in those areas of cities where there are sources of infection, inadequate sanitation, there are particularities of life and economic activity that facilitate the infiltration of invasive eggs from the environment to humans. Ascariasis in the cities people are sick most often after returning from the countryside, from garden plots and dachas where fertilizers are sometimes used for uninfected human feces, as well as for eating unwashed vegetables and fruits, berries brought from foci of ascariasis and non-compliance rules of personal hygiene.

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

Ascaridosis 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, about 100,000 people die each year from this invasion. Askaridoz is common in 153 out of 218 countries in the temperate, subtropical and tropical climate.

More than 50% of the surveyed population is infected with ascaridosis in Nigeria, Congo, Brazil, Ecuador, Iraq, Malaysia, Afghanistan, Indonesia. In the areas of deserts, semi-deserts and permafrost, ascariasis is very rare.

In endemic foci, immunity to superinvasia and reinfusion is formed in humans. The immune response is more pronounced during the parasitic period of larval helminth stages that are in the process of migration. Immune responses against helminth larvae protect the host from an uncontrolled increase in the intensity of infestation upon repeated infection. For residents of endemic foci, prone to frequent repeated infections, the development of a certain immunity is characteristic. Respectively, intestinal invasion of low intensity.

[4], [5], [6]

Causes of Ascaridosis

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

In connection with significant morphological and metabolic changes in different stages of development, ascarid, as in other helminth species, exogenous and endogenous antigens and their immunogenic properties significantly change.

Sexually mature individuals have a long thin body of whitish pink color. Female measuring 20-40 cm x 3-6 mm, male - 15-25 cm x 2-4 mm. The oral opening, located at the anterior end of the body, is surrounded by three cuticular lips. The tail is short, the male is bent to the ventral side. The internal structure is common for nematodes. Parasitize sexually mature ascarids in the small intestine of the human, feeding on the contents of the intestine. Each female lays up to 240,000 fertilized and unfertilized eggs a day. Fertilized eggs (50-70 x 40-50 microns) almost spherical or elongated, yellow or yellow-brown in color, have three membranes. Under favorable environmental conditions (presence of oxygen, high humidity, temperature 20-25 ° C), development of the larva in the egg takes 2-3 weeks. Mature larvae are able to persist 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.

[7], [8], [9], [10]

The cycle of ascariasis development

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

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 with sputum, the larvae enter the pharynx, are again swallowed and again appear in the small intestine. During migration, larvae molt two times and increase in size from 0.19-0.25 mm to 1.5-2.2 mm. Migration of ascarid larvae lasts about two weeks. In the intestine, the larvae grow, again molt and after 2-2.5 months they become sexually mature. Life expectancy of adult ascarids is about 1 year.

Pathogenesis of ascariasis

The pathogenesis of ascariasis is different during the migration of larvae in the blood and their stay in the respiratory organs and during the parasitizing of adult helminths in the small intestine of a person. From the invasive eggs of ascarids in the human small intestine, rhabdit-shaped larvae emerge, which in 3-4 hours enter the thickness of the mucous membrane.

Further, the larvae migrate through the portal vein system to the liver, then into the lungs, where they 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 moult. In the lungs, tearing the capillary network and walls of the alveoli, they penetrate into the lumen of the bronchi and move along the airway to the oropharynx. With swallowed saliva and food, the larvae re-enter the small intestine, where they turn into sexually mature males and females, having committed two more molts. The migration time of the larvae is about 2 weeks, and the maturation of females before the laying of eggs lasts more than 10 weeks. In an organism of the person the adult individual lives 11-13 months.

In the early migration stage, the pathogenetic changes are caused by the sensitization of the body by the products of metabolism, molting, and the decay of dead larvae. Askerid allergens are the strongest among allergens of parasitic origin. With intensive invasion there is a mechanical damage to the wall of the small intestine, blood vessels, liver tissue, lungs. There are also eosinophilic infiltrates in the lungs, capillary stasis, hemorrhages. Clinical manifestations in the late intestinal stage are associated with the mechanical action of helminths and the products of their metabolism on the intestinal mucosa, which leads to a violation of digestion, motor function, a violation of nitrogen balance, hypovitaminosis. One of the aspirated polypeptides exerts a toxic effect on the central nervous system. Ascarids can migrate beyond the small intestine: into the bile and pancreatic ducts, appendix, respiratory tract. Occasional clumps of ascarids lead to obstruction, intestinal swelling, and intussusception. Intestinal obstruction often occurs with intensive invasion, and intussusception - in the presence of single helminths or several individuals of the same sex. Ascarids significantly suppress the immunological reactivity of the host.

During parasitization of adult ascarids in the intestine, sensitization of the body continues. In the pathogenesis of the intestinal phase, the main role is played by intoxication of the body with toxic products of the life of ascaris, resulting in disorders from the digestive, nervous, sexual and other systems. Helminthes have a mechanical effect on the mucosa of the intestine, leading to its change: disturbed parietal digestion, it is difficult to absorb and assimilate proteins, fats, vitamins, reduce the activity of the enzyme lactase, etc.

Symptoms of Ascaridosis

There are two clinical stages of the disease - early (migratory) and late (intestinal). Symptoms of ascaridosis at an early stage are often absent. In a clinically pronounced form, on the 2nd-3rd day after infection, such symptoms of ascariasis as malaise, weakness, and subfebrile condition appear. There are urtic rashes on the skin, possibly an increase in the spleen and liver. Symptomatic complex of lung lesions with the formation of transient infiltrates, determined by roentgenologic, and eosinophilia in peripheral blood (Löffler syndrome) is more typical. In these cases, dry cough appears, sometimes with sputum streaked with blood, shortness of breath, chest pains, suffocation. In the lungs dry and wet rales are heard.

In the intestinal stage, ascariasis in adults often occurs with mild symptoms or asymptomatic. Observed symptoms of ascaridosis (worsening of appetite, nausea, sometimes vomiting, cramping in the abdomen, diarrhea or unstable stools) are of little specificity. Patient's state of health worsens, working capacity decreases, headache, dizziness.

Children in the early stage of ascariasis can develop pneumonia, with intense invasion - severe intoxication. The body weight decreases, children become capricious, scattered, epileptiform seizures, meningism, Ménière syndrome are possible; in the analysis of blood - normo- and hypochromic anemia, eosinophilia.

Complications of ascaridosis

There are intestinal and extra-intestinal complications of ascaridosis, which arise in the late stage of infestation and are often caused by increased mobility of adult helminths. The most common complication, especially in children aged 4 to 8 years, is an intestinal obstruction. With destructive changes in the intestinal mucosa or after surgery, penetration of ascarids into the abdominal cavity and the development of peritonitis are possible. The introduction of helminths into the bile-excreting and pancreatic courses can lead to mechanical jaundice, reactive pancreatitis, in the case of secondary bacterial infection, purulent cholangitis, liver abscesses, and sometimes appendicitis develop. When vomiting, anti-peristaltic movements, ascarids can get into the esophagus, from where they penetrate into the pharynx, respiratory tract, causing asphyxia.

[11], [12], [13], [14], [15], [16]

Diagnosis of ascaridosis

When recognizing the early (migratory) stage of ascariasis, it is necessary to focus on the symptoms of lung damage in combination with eosinophilia of the blood. Seldom it is possible to find out larvae of ascaris in a sputum. There is a serological diagnosis of ascariasis (ELISA, RLA), but it has no wide application in practice. In the intestinal stage, the diagnosis is made by finding eggs or ascaris in feces. Take into account the survey season. Maximum detection of invasive individuals occurs in December and February. When parasitizing in the intestine only the males of old or immature females, eggs may be absent.

[17], [18], [19], [20], [21], [22]

Differential diagnosis of ascaridosis

Differential  diagnosis of  ascaridosis in the migratory stage is carried out with toxocarosis, the early phase of other helminthiases, characterized by allergic manifestations, acute bronchitis, pneumonia. In the intestinal stage, according to clinical symptoms, it is practically impossible to differentiate ascariasis from chronic gastrointestinal diseases. In the event of complications, depending on their nature, differential diagnosis of ascaridosis is performed with intestinal obstruction, cholangitis, liver abscess, pancreatitis of another etiology. In these cases, additional instrumental studies (ultrasound of the abdominal cavity organs) and surgeon's consultation are necessary.

[23], [24], [25],

Treatment of ascariasis

Indications for hospitalization

Treatment of ascaridosis is carried out on an outpatient basis or in a day hospital. Hospitalization is subject to patients with surgical complications of ascaridosis.

Medicamentous treatment of ascaridosis

All patients with ascariasis are treated with anthelmintic agents.

• Albendazole is prescribed to adults once a dose of 400 mg orally after a meal, children older than 3 years - 10 mg / kg in two doses for 1-3 days.
• Mebendazole is shown to adults and children over 2 years old by 100 mg twice daily for 3 days.
• Carbendacum is recommended by mouth within 20-30 minutes after meals at a dose of 10 mg / kg in three doses for 3 days.
• Pirantel appoint 10 mg / kg once inside after eating.

When you take these antihelminthic drugs, you do not need a special diet and laxatives.

Pathogenetic and symptomatic treatment of ascaridosis is necessary for prolonged and intensive infestation: probiotics and enzymatic preparations are used.

Additional treatment of ascaridosis

If surgical complications arise, operative treatment of ascaridosis or instrumental intervention is necessary.

[26], [27], [28], [29], [30]

Clinical examination

Dispensary follow-up for those who have been ill for a period of 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 treatment is ineffective, repeat the treatment.

[31], [32], [33],

Prevention

Askaridosis can be prevented in case of sanitary improvement of populated areas and protection of soil from fecal contamination. In individual prevention, it is important to strictly follow the rules of personal hygiene, thoroughly wash the raw vegetables, berries and fruits that are eaten. In foci of ascariasis with lesions of less than 10% of the population, once every two years, parasitological examination of 20% of residents; In the outbreaks, where more than 10% of the population is affected, the entire population is examined annually. For dehelminthization, anthelmintic drugs are used, taking into account the features of their use in different age groups.

Forecast 

Ascariasis in uncomplicated course has a favorable prognosis. In the absence of repeated infection, after 9-12 months self-healing occurs 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.

[34]