What is Strongyloidosis?
Strongyloidiasis is a chronic nematodoz that does not have a tendency to self-healing, characterized by an extraordinary variety of organ pathology of the gastrointestinal tract and the hepatobiliary system.
Strongyloidosis called “Kokhinkha diarrhea” was first described by the French doctor Normand in 1876, finding the pathogen in the feces of soldiers returning from Cochinchina (Vietnam), who suffered from persistent diarrhea.
Fundamentals of the pathogen biology, its life cycle was decoded by R. Leucart in 1882
In recent years, interest in this invasion by the medical community has increased due to its possible attribution to AIDS-related parasitosis.
Causes of Strongyloidiasis
Strongyloidosis pathogen – Strongyloides stercoralis (synonyms: intestinal eel, Anguillula stercoralis belongs to the type Nemathelminthes, class Nematoda, order Rhabditida, family Strongydoidae, genus Strongyloides.
The name of the helminth comes from the Greek strongylos – round, eidos – form, stereos – feces. These dioecious, filiform, colorless, semi-transparent nematodes are small. Parasitic female reaches 2.2 mm in length and 0.03 – 0.04 mm in width. Free-living female of smaller sizes (1 x 0.06 mm). The oral opening has subtle lips. Esophagus rhabditnogo structure. The female sexual apparatus is paired. The uterus contains 5-9 eggs, 50 – 58 x 30 – 34 microns in size, resembling ankylostomid eggs. From the eggs laid by the female into the lumen of the Liberkyun glands of eggs, rhabditiform larvae are released with a length of 0.2–0.3 mm and a width of 0.01 mm. The front end of the body of the female is blunt, the rear end is conically pointed. The esophagus has a characteristic rhabditiform structure – two extensions, bulges and constriction between them. It takes 1/3 of the body length. Rabbit-like larvae are non-invasive; in the process of development, they turn into invasive larvae, filariform. Filar-like larva has a length of 0.5 – 0.6 mm and a thickness of 0.01 mm. The esophagus is long, cylindrical, without swelling, occupying almost half the body length.
Males of the parasitic and free-living generations of a spindle-shaped form have dimensions of 0.7 x 0.04 – 0.06 mm. The posterior end of the male body is pointed and bent ventrally. The sexual bursa is absent, but there is a rulec and two curved spicules.
Strongyloides stercoralis has a complex development cycle, which is characterized by a change of free and parasitic generations.
Human infection with filarial larvae of S. stercoralis occurs in two ways – percutaneous or oral.
The larvae are able to penetrate the intact human skin, piercing the epidermis, or through the sweat glands and hair bags. Having penetrated into the tissues, they migrate into the bloodstream, with a current of blood are brought into the right atrium and ventricle, lungs, from there they advance into the throat and are swallowed. Through the esophagus and the stomach into the duodenum and small intestine. During migration, sexual differentiation occurs, sexually mature females and males are formed. Fertilization of females is carried out mainly in the lungs and trachea, ends in the intestine.
Mature females linger in the intestine and penetrate the mucous membrane. Males who are not capable of introduction die and are thrown into the external environment with faeces.
When orally infected, filarial larvae penetrate the oral mucosa, pharynx, enter the bloodstream and also migrate.
Adult individuals, represented predominantly by parthenogenetic females, parasitize in the liberkuenov glands of the duodenum, with intensive invasion in the mucosa of the small intestines, the pyloric part of the stomach, and even the cecum and colon.
The females that have settled in the mucosa, lay eggs at the bottom of the liberkuen glands – up to 50 pieces per day, from which the rabbitous larvae emerge. With feces, rhabditiform larvae stand out, where their further development takes place.
The development of S. stercoralis by KI Scriabin and GF Wagner (1924) can occur in three ways: direct, indirect, and intraintestinal.
With a direct path of development, rhabditiform larvae in feces or in soil turn into filariform, capable of infecting.
With the indirect path of development, the parasitic generation of helminths is transformed into a free-living (heterogony). In this case, rhabditiform larvae released from faeces with favorable temperatures and humidity turn in the external environment into a free-living generation of females and males. Here fertilized females produce rhabditiform larvae, which give rise to the next generation of free-living individuals. This may last for a long time, but the rhabditiform larvae of the free-living generation can turn into filar-like, capable of infecting on any generation. The third pathway of development, the intraintestinal, is characterized by the transformation of rhabditiform larvae into filarlike directly in the intestine without access to the external environment. This path of development of S. stercoralis, described by KI Scriabin and G. F. Wagner (1924), has been confirmed experimentally. Nishigori (1927) found that autoinvasion is performed under the condition that rhabditiform larvae remain in the human intestine for more than 24 hours. Autoinvasion contributes to constipation, the presence of intestinal diverticulum, ulcerative lesions of the mucous membrane, facilitating the penetration of filariform larvae into the intestinal wall. V.P. Podyapolskaya and V.F. Kapustin (1958) believe that the long, long-term course of strongyloidosis is due to the possibility of developing S. stercoralis in all three ways – which is evidence of the presence of a mixed (fourth) path of development.
Regardless of the pathways of penetration, filarial larvae perform compulsory migration along the large small circulation. The duration of the migration is 17-27 days.
Pathogenesis during Strongyloidiasis
Strongyloidosis – geohelminthiasis, anthroponosis. It is distributed in all countries of the tropical and subtropical zone with a humid climate, as well as in areas of temperate climate. The affection of the population in the tropical zones of Southeast America reaches 24% or more.
Strongyloidosis is registered in North America, in many European countries, including Georgia, Azerbaijan, Moldova, the North Caucasus, and Ukraine. The level of infestation of the population, as a rule, does not reflect the true situation, since mass special examinations for strongyloidosis were carried out to a limited extent, the available indicators of invasion are based mainly on the data of examinations of people according to clinical indications. According to some generalized data of E. A. Shablovskaya, the prevalence of the population in different regions of Ukraine ranges from 0.1-10% (1978).
The established uneven distribution of strongyloidosis in countries with a temperate climate is determined both by microclimatic features characteristic of the locality (for example, the height of groundwater) and by the influence of social factors (for example, nature of management, development of vegetable growing, sanitary improvement, etc.). The micro-focal distribution of strongyloidosis with a single case in the estate, as well as the formation of family micro-foci in rural areas has been established.
Intense foci of strongyloidiasis with a prevalence of 6-7 to 100% are registered in psychiatric hospitals, orphanages for mentally retarded children and the elderly, where, due to violation of hygienic rules of behavior, invasion is transmitted in a team not only in the warm season, but also in the winter .
The main source of invasion is a person with strongyloidiasis.
Among human invasions caused by nematodes, only strongyloidosis has a long course due to the fact that parthenogenetic females that have penetrated the mucous membrane of the upper small intestine can produce new generations of invasive larvae. At the same time, the duration of invasion can reach 20-30 years.
Under the experimental conditions, the possibility of adapting a human strongyloidosis pathogen to various types of animals, mainly carnivorous (dogs, cats), and also omnivores (pigs) was established. However, the role of these animals in the distribution of strongyloidosis among people has not yet been proven with complete certainty. At the same time, isolated reports have been published about the experimental self-infection of humans with porcine strongyloidosis and infection as a result of contact with secretions of an invasive dog.
With the feces invaded into the external environment, non-invasive rhabditiform larvae stand out, which turn into invasive filar-like with sufficient temperature and humidity. The optimum conditions for the development and preservation of viability in the external environment are air temperatures of 28-34 ° C, neutral or slightly alkaline soil reaction, the presence of organic nutrients, and sufficient humidity.
Under favorable conditions, rhabditiform larvae can turn into sexually mature individuals of a free-living generation. These free-living individuals lead a saprophytic lifestyle, can breed, giving rhabditiform larvae. When adverse conditions occur, these rhabditiform larvae turn into filar-like, capable of infecting.
At a temperature of 24-27 ° C ripening is completed in 24-48 hours. The life span of invasive larvae in the external environment under favorable conditions is 2-3 weeks. When the soil and faeces dry, as well as at temperatures below 0 ° C and above 50 ° C, the larvae quickly die. An important condition for the habitat of intestinal eel larvae is the type of soil into which they fall (its composition, acidity, humus content).
The larvae of S. stercoralis do not possess an active migratory ability, either vertically or horizontally. Disperse larvae in the external environment, contact with garden, berry and melon crops contributes to indiscriminate faecal contamination of the soil, erasing them with rain, irrigation water. Human infection occurs through percutaneous penetration of invasive larvae through the skin, when it comes into contact with soil contaminated with feces, which is the main factor of transmission. Infection occurs when walking barefoot, lying on the ground without litter, performing agricultural earthen garden and garden work.
Oral infection is possible when eating vegetables, berries, fruits with a damaged surface polluted by soil containing larvae. With such an infection, the filarial larvae also migrate, penetrating through the oral mucosa and the esophagus. In cracks and dents of vegetables, the larvae survive up to 4 days.
There are single reports of intrauterine infection with strongyloidosis of the fetus, does not exclude the possibility of transmammary transmission of invasion.
The pathogenesis of strongyloidosis is associated with the sensitizing, mechanical, and toxic effects of helminths, which are distinguished by significant features of biology. These features are related:
- with the possibility of two ways of infection – percutaneous and oral;
- with the obligatory migration of larvae in any route of infection, which determines the presence of two phases of the disease – migration and intestinal;
- with the possibility of intraintestinal autosupinasia;
- with the possibility of extraintestinal self-infection through the skin of the perianal area.
The leading role in the pathogenesis is sensitization of the organism by products of the parasite’s metabolism. This mechanism is particularly pronounced not only during the migration of larvae in the early phase, but also in the intestinal and is expressed in the appearance on the skin of itchy rashes, urticaria, typical in character and localization. At the same time, in most cases eosinophilia is detected, sometimes reaching very high rates.
Mechanical damage to the intestinal mucosa is associated with the possibility of parasitizing the female helminths in the depths of the Liberian glands and thereby facilitating the penetration of the microbial flora. As a result, an inflammatory reaction develops in the intestine with infiltration of cellular elements, the formation of granulomas, edema, hyperemia of the mucous membrane. There are erosions, ulcers, hemorrhages in all layers of the intestinal wall, an increase and inflammation of the mesenteric lymph nodes are observed, and cellular infiltration is also expressed around the larvae penetrating into them. Helminth larvae can migrate to various organs and tissues, where granulomas and dystrophic changes also occur – in the liver, lungs and other organs. Repeated migrations of larvae are accompanied by increased allergenicity. Reducing the body’s resistance to HIV infection, cancer, as well as immunosuppression due to prolonged use of steroid hormones or cytotoxic drugs create conditions for autosupervination from the intestine. Intensive reproduction leads to the generalization of the migration of larvae into the brain, liver, myocardium, lymph nodes and, as a result, the development of meningoencephalitis, myocarditis, etc., which can be fatal.
Symptoms of Strongyloidiasis
The presence of two phases of invasion, the possibility of extra- and intra-intestinal reinvasions, a variety of syndromes of lesions of various organs and systems, caused both by the direct effect of the helminth and by severe sensitization of the body, makes the clinic of strongyloidosis a polysymptomatic.
The incubation period, its duration is difficult to establish. In the experiment, he was 17 days. Usually invasion lasts a long time – for years and even dozens of years with periods of remission and exacerbations.
In the early, migratory phase, the symptom complex of allergic reactions prevails – the wrong type of fever, itchy skin rash, urticaria, myalgia, arthralgia, hypereosinophilia, leukocytosis, increased ESR.
Skin manifestations are very typical. Pink-reddish color, elongated, oval-shaped blisters rise above the surface of the skin, change shape, are accompanied by severe itching and “crawl” after the comb, resulting in a linear eruption of the rash, which are most often localized on the abdomen, buttocks, back, lower back, chest thighs The rash lasts from several hours to 2 – 3 days and disappears, leaving no traces. Traces can be only with severe skin damage during scratching.
Rashes, as a rule, recur from several times a month, to several times a year and less often without any cyclical nature.
In some cases, such patients with a diagnosis of “food allergy,” “drug allergy,” and others receive non-professional treatment tips that do not reach the goal, because the urticaria recurs.
In most cases, urticaria is accompanied by high eosinophilia, which makes it necessary to consult a hematologist.
During this period, patients complain of fatigue, weakness, dizziness, headaches, irritability, and often symptoms of bronchitis with an asthmid component, pneumonia, and asthma attacks.
Radiographically detect volatile infiltrates in the lungs, pneumonic foci. 2-3 weeks after the onset of the disease, abdominal pain and dyspeptic symptoms appear – anorexia, nausea, less vomiting, loose stools, sometimes with blood, tenesmus, symptoms resembling gastroenteritis, dysentery. In some cases, there is hepatomegaly with yellowness of the skin and sclera.
However, often the symptoms of the early phase of strongyloidosis are mild, and in some cases the invasion takes place under a different diagnosis.
You should know that the presence of urticaria, eosinophilia with manifestations of gastrointestinal or gallbladder disease is an important diagnostic indicator for a special examination.
Gradually, the severity of clinical manifestations is smoothed, the disease becomes chronic, late phase of the disease, takes a protracted course. The significant polymorphism of the clinical manifestations of strongyloidiasis in this phase is indicated by the presence of many clinical classifications, depending on the prevalence of symptoms of lesions of various organs or systems.
Clinical experience makes it possible to recognize that the most characteristic of strongyloidosis are duodenal-biliary and hepatohepatic, gastrointestinal, neuro-allergic or allergic-toxic and mixed forms of the disease.
For duodeno-gallbladder forms characterized by a slow monotonous flow. Its main manifestation is in varying degrees pronounced pain syndrome with functional and organic lesions of the gallbladder, dyskinetic disorders, established results of cholecystography (deformation of the shadow of the gallbladder, impaired bias and mobility, etc.). Patients complain of bitterness in the mouth, bitter eructations, loss of appetite, pain in the right hypochondrium, recurring nausea and vomiting.
The leading symptoms in patients with gastrointestinal form of strongyloidosis are dyspeptic symptoms and disorders of the stool, expressed in the alternation of diarrhea with constipation with a stool frequency of 3-4 or more times a day. The stool is watery, sometimes mixed with mucus and blood. An objective examination of patients with a tongue is determined, tenderness to palpation of various parts of the abdomen. Often, symptoms of hypoacid gastritis, enteritis, and enterocolitis are recorded. Some patients have symptoms of duodenal ulcer, stomach. Sometimes patients with suspected dysentery are sent to the infectious wards of hospitals.
The main manifestations of the neuro-allergic form is an allergic syndrome – urticaria, accompanied by severe itching of the skin, and eonosophilia. The nature of the rash can be different, but it is typical for strongyloidosis that the elements of the rash rise above the skin surface, often located in places of skin compression with clothes (belt, bodice, belt), localized mainly on the skin of the abdomen, back, buttocks, thighs, as a rule, rise to the scalp and do not fall below the knees. They have a “creeping” character, often take a “linear” character – “linear urticaria”. Rashes last 12 – 48 hours, less often longer and disappear without a trace. At the same time, functional disorders of the nervous system, astheno-neurotic syndrome are observed. Patients are depressed, they complain of general weakness, headaches, dizziness, sleep disturbance, increased irritability, tearfulness, sweating. Miniera syndrome, fainting and other symptoms may occur.
Most patients have blood eosinophilia up to 50-70-80%.
A pulmonary form of strongyloidosis has been registered, sometimes with an asthmatic component, when the main pathology is associated with a primary lesion of the respiratory system organs. More often it is a consequence of autoinvasion. All of the listed forms are not strictly limited in the majority and are more often registered as combined with each other – a mixed form. However, it should be emphasized that almost always with strongyloidosis there is an allergy, the most frequent indicators of which are blood eosinophilia and chronic urticaria.
As with all other parasitic and infectious diseases, strongyloidosis can occur in mild, moderate and severe forms.
Unfavorable course of the disease with generalization of the process and autosupinevaziey observed in patients with reduced resistance due to concomitant serious diseases (eg, cancer), malnutrition, as well as the treatment of immunosuppressive drugs (hormonal, cytostatics) and HIV-infected. Examination for strongyloidosis of the above groups of patients should be considered mandatory.
Diagnosis of Strongyloidiasis
Among the large variety of clinical manifestations of strongyloidiasis, there are symptoms that have important diagnostic value. As noted earlier, combinations of diarrhea, biliary and intestinal pathologies with blood eosinophilia and urticaria, chronic course of the disease, ineffectiveness of symptomatic treatment is the basis for the presumptive diagnosis. The following clinical signs can be considered as suggestive of a diagnosis. We cannot exclude also the diagnostic value of the epidemiological history, such as work in mines, in the mining industry, in construction, agricultural work, being in hot spots of strongyloidosis, etc., at which the risk of infection through the soil increases.
The final diagnosis is confirmed only by the positive results of the laboratory examination of feces, duodenal contents, less often sputum upon detection of strongyloid larvae.
For detection of larvae in feces using special methods. Conventional coprooscopic methods (Kato smear), native smear are ineffective, enrichment methods with salt solutions (Fulleborn, Kalantaryan), in which the larvae die and shrink, are also unacceptable.
Therefore, in the direction of analysis for laboratory research, the physician should indicate not just a “analysis of feces for helminthic invasion”, but emphasize – “an analysis of feces for strongyloidosis” or call a special method.
The method of choice for the diagnosis of strongyloidosis is the Berman method, which is based on the thermotropic nature of the rhabditiform larvae of the intestinal eel.
To process the faeces according to the Berman method, a glass funnel is used (the “funnel method”), at the end of which a rubber tube with a clip is put on. Water heated to 38 ° C (preferably an isotonic solution of 0.9% NaCl from A.F. Prokhorov) is poured into the funnel, and a metal grid (tea grid, window grille) is placed on the base of the funnel with the faeces under investigation (20 g), which should be in contact with water surface. Strongyloid larvae are thermophilic, they actively go out into warm water and descend down, accumulating in the tube above the clamp, to ensure temperature differences (water – feces) in high air temperature conditions (especially in summer) F. Soprunov recommends inserting a small test tube with ice, cold water, ether, which accelerates the release of larvae in warm water. After 2 hours, the clamp is opened, the precipitate is discharged into centrifuge tubes and centrifuged for 1-2 minutes, after which the resulting precipitate is microscopically examined.
According to V. A. Gefter, the Berman method with a single examination revealed 98% of the invasions, and the “twisting” method – 36%.
For a mass survey, V. S. Borisenko simplified the technique by proposing instead of a funnel to use ointment jars with warm water, in which gauze bags with test feces were dipped. The principle of the technique is the same – the larvae go into the water, settle to the bottom, after which the sediment is microscopically examined.
Domestic and foreign authors have proposed many modifications of the Berman method, but none of them proved to be more effective.
In difficult conditions for laboratory work expeditions for mass screening E.S. Shulman proposed the method of “twisting”.
By the method of twisting 2-3 g of feces emulsify 8-10 mm of water or saline. A suspension of feces is stirred with a glass rod with fast circular movements, then the rod is removed and a drop at its end is transferred onto a glass slide for microscopy.
Abroad to identify the larvae from feces recommended more cumbersome method of cultivation of larvae on coal (Sasa et al., 1958).
Acne larvae can also be found in duodenal contents. From flakes obtained during duodenal sensing of portions with tweezers, the flakes are selected and microscoped in a drop of warm (37 ° C) isotonic sodium chloride solution. The rest of the contents are shaken with an equal volume of ethyl ether, centrifuged for 3-5 minutes at 800-1000 rpm, the precipitate obtained is microscoped under a small magnification of the microscope.
Abroad, for the detection of larvae, it is recommended to investigate biopsy specimens of the duodenal mucosa, as well as a “rope test” – when the subject swallows a hygroscopic nylon thread 140 cm long placed in a capsule. The capsule dissolves; larvae are detected by microscopy on the selected filament. Patients do not tolerate this method.
Diagnosis is facilitated by repeated research.
In intensive pulmonary form of strongyloidosis, the larvae can be found in the sputum. The sputum is examined in a native smear or its daily portion is mixed with an equal volume of 0.5% caustic alkali solution, after five minutes of shaking, it is centrifuged and the sediment is examined under a microscope.
Serological diagnostic methods are poorly developed and, due to lack of specificity and lack of technological equipment, have not been used in clinical practice (RIF, ELISA).
Patients with strongyloidiasis should be treated in a hospital. The most effective drugs is mintezol (thiabendazole) and ivermectin (mektizan). Mintezol is prescribed at the rate of 25-50 mg / kg of body weight per day in 3 divided doses for 2 days in a row. Ivermectin (mektizan) – 200 mg / kg / day for 2 days. Vermoxa, albendazole can be used. Patients are prescribed desensitizing agents, during intoxication they are given infusion therapy. Monitoring the effectiveness of treatment after 2 weeks and then monthly for 3 months.
Prevention of Strongyloidiasis
Preventive measures for strongyloidosis are aimed at identifying and recovering invasions and protecting the environment from contamination by feces.
Patients suffering from diseases of the digestive system, the hepatobiliary system, especially if they have eosinophilia or urticaria, that is, if there are clinical indications characteristic of invasion, are subject to mandatory examination for strongyloidiasis.
Considering the specific features of the epidemiology of strongyloidosis, the presence of occupational groups of increased risk of infection, excavators, miners, wastewater treatment workers, road builders, greenhouse farms, vegetable bases, etc., as well as persons in hospitals, boarding schools, mental colonies are subject to inspection by the Berman method. .
Identified invasions are subject to deworming better in a hospital or semi-hospital, with follow-up dispensary observation for one year: with a special Berman method examination once a month for 6 months and once a quarter for the next six months. From the dispensary registration is removed one year after a three-time survey with an interval of 2-3 days when receiving negative test results.
An important and decisive method for the prevention of strongyloidosis is the protection of the environment from fecal contamination and decontamination of contaminated soil. First of all, these are measures for sanitary improvement of populated areas, organizing planned cleaning of yard toilets, prohibiting fertilizing the soil of vegetable gardens with non-neutralized feces.
The feces of patients with strongyloidosis can be disinfected with boiling water in the ratio of 1: 2, with bleach at the rate of 200 g per serving of feces at an exposure of one hour.
To disinfect the soil in the microhomes (estates) of strongyloidosis, it is recommended to use a 10% solution of potassium, nitrogen, phosphate fertilizers or a 2% solution of the carbation pesticide.
For personal prophylaxis in endemic areas, one should avoid walking barefoot, lying on the ground without bedding. In order to eliminate the food route of infection – thorough washing of vegetables, herbs, berries.
The success of the prevention of strongyloidiasis is possible under the condition of sanitary education of the population with an explanation of the danger of infection and ways of public and personal prevention.