Nematodes are helminthiasis caused by roundworms of the Nematoda class. They occur when infected with parasites by fecal-oral or transmissible means. The most common representatives of this group of diseases include enterobiosis, ascariasis, strongyloidosis. Symptoms of nematodoses include toxic-allergic syndrome, dyspeptic disorders, organ lesions, taking into account the parasitizing sites of mature individuals. To diagnose helminthic invasion, fecal microscopy, serological reactions, instrumental visualization of the thoracic and abdominal organs are used. Treatment is carried out with etiotropic anthelmintic agents.
More than 24,000 species of nematodes have been described in microbiology, among which more than half are capable of causing parasitic diseases. Roundworms affect almost all parts of the body: internal organs, blood and lymph vessels, muscles and other connective tissues. In developed countries, the proportion of helminthiasis in infectology is about 4%. Enterobiosis and ascariasis – typical representatives of nematodes – occupy the 1st and 4th places in the structure of parasitic diseases in USA. The number of cases detected annually is 222.7 thousand and 18.6 thousand, respectively.
Representatives of the Nematode class have an elongated fusiform body with a round cross-section. Their sizes range from a few millimeters to 6-8 m. The largest individuals are found in parasitic worms that infect humans and vertebrates. Parasites are covered with a skin-muscle sac, have a primary body cavity (schizocele). The digestive system is represented by a tube, the circulatory and respiratory systems are absent.
Such nematodes are recognized as the most common in humans:
- ascariasis (Ascaris lumbricoides);
- Enterobiosis (Enterobius vermicularis);
- strongyloidosis (Strongyloides stercoralis);
- various filariatoses (Filariata).
More rare representatives of this group of helminthiasis include trichinosis (Trichinella), dracunculiasis (Dracunculus medinensis), trichocephalosis (Trichocephalus trichiurus), toxocarosis (Toxocara canis).
Children of preschool and primary school age are considered to be the most vulnerable risk group for the development of nematodes. The high frequency of worm infestations in this period is due to the underdevelopment of hygiene skills, games in sandboxes and on the ground, the habit of licking fingers and biting nails. Also, risk groups include people who visit exotic countries, live in conditions of crowding and unsanitary conditions.
Infection with most types of nematodes occurs by the fecal-oral mechanism. The transmission factors are contaminated water, contaminated food, unwashed hands. The invasive stage for roundworms are eggs or larvae, which after ingestion enter the gastrointestinal tract, where they begin to parasitize and / or penetrate through the intestinal wall into blood vessels, spread with the blood flow to other organs.
A large group of filariatoses has a special life cycle. These are transmissible parasitoses that are transmitted to humans from midges, mosquitoes, horseflies and other blood-sucking insects. Through the system of blood vessels, they reach the lymph nodes, subcutaneous tissue and body cavities, where they parasitize for many years. The life span of some filaria species reaches 20 years.
In the pathogenesis of nematodes, immune reactions of the body are isolated in response to the penetration of roundworms and local pathomorphological changes in the place of their parasitization. With prolonged invasion, a violation of metabolic processes is added, since helminths consume the host’s nutrients. The situation is aggravated against the background of the neuro-reflex effect of nematodes – irritation of nerve endings, stimulating autonomic disorders.
Most types of helminthiasis have an early and late clinical phase. At the initial stage, the symptoms are caused by the general allergic and toxic effect of roundworms on the body. The late stages are characterized by syndromes of damage to the gastrointestinal tract, hepatobiliary system, central nervous system and other organs. The duration of these phases depends on the type of parasitic helminth and is consistent with its life cycle.
For the early phase of ascariasis, strongyloidosis, filariasis and toxocarosis, skin rashes like urticaria, fever, muscle and joint pain are characteristic. Bronchopulmonary syndrome often develops, which is manifested by dry cough, shortness of breath, chest pain. With nematodoses, headaches, sleep disorders, increased irritability and decreased performance occur. Such symptoms last for several weeks.
During the transition of the disease to the second phase, all nematodes with fecal-oral transmission are manifested by gastrointestinal disorders. Patients complain of cramping pains in the abdomen, frequent and loose stools, rumbling in the intestines. Nausea, vomiting, decreased appetite are characteristic. Due to maldigestion and malabsorption, vitamin deficiency, protein-energy deficiency develop. With enterobiosis, symptoms are accompanied by painful anal itching.
The clinical picture of the late stages of filariasis is different, since these helminths have a different typical localization of the lesion. With brugiosis and vuhereriosis, the lymphatic system is involved in the process: edema of the upper and lower extremities occurs up to the development of elephantiasis, the volume of the abdomen increases due to chyletic ascites. For loiasis, parasitism in the tissues of the eyeball is typical, which is manifested by conjunctivitis or blepharitis.
Patients with immunosuppression are susceptible to severe forms of nematodoses. This pattern is especially typical for strongyloidosis, hyperinvasive and generalized forms of which occur mainly in people with HIV/AIDS. The probability of a severe form of helminthiasis increases with combined infection, for example, with simultaneous parasitization of the whipworm and ascaris in the intestine. Bacterial intestinal infections that have joined can aggravate the situation.
With untreated nematodes with massive helminthic invasion, there is a risk of intestinal obstruction, mechanical jaundice, acute pancreatitis and peritonitis. With ascariasis, respiratory failure and asphyxia are possible in the pulmonary phase of migration of the pathogen. With the long-term existence of the disease, there are lesions of the nervous system, insomnia, meningism and epileptiform seizures.
The basis for the diagnosis is clinical and anamnestic data. At the initial reception of the infectious disease specialist, the time of the appearance of symptoms and possible risk factors are specified, information about the patient’s recent travels is collected, and a standard physical examination is performed. To confirm the parasitism of a particular type of helminth, the following diagnostic methods are prescribed:
- Microscopy of feces. Fecal examination is recognized as the most reliable way to verify nematodosis. The most informative analysis will be 3 months or more after infection, especially with ascariasis, the causative agent of which goes through a difficult migration path. If infection with pinworms is suspected, the study of feces is supplemented with scraping for enterobiosis.
- Serological tests. The comprehensive diagnosis includes a blood test for specific antibodies to roundworms, in particular, the determination of IgM – a sign of an acute form of invasion. Such analyses are informative in the early phase of the disease, when helminths are almost impossible to detect in the feces.
- Standard blood tests. Typical signs of helminthic invasion in the hemogram are eosinophilia, increased ESR. Biochemical blood examination shows hypoproteinemia, increased liver tests, electrolyte imbalance and other pathological changes taking into account the type of helminthiasis.
- Instrumental methods. In dyspeptic disorders, abdominal ultrasound, overview and contrast radiography of the intestine are shown. With respiratory symptoms, lung radiography is prescribed, revealing “volatile infiltrates”. With filariatoses, sonography of lymph nodes, biomicroscopy of the eye is required.
The early phase of nematodoses should be differentiated with allergic bronchitis, pneumonia, exacerbation of pulmonary tuberculosis. Acute bacterial infections, neoplasms of the lungs and mediastinum are also excluded. In the late phase, differential diagnosis is performed with other types of parasitosis: amoebiasis, balantidiasis, teniosis and teniarinchosis. It is necessary to exclude NYAK and Crohn’s disease, chronic hepatitis, neurocirculatory dysfunction.
Uncomplicated forms of helminthic invasion are treated on an outpatient basis, other patients require hospitalization in an infectious hospital. Non-drug measures include a gentle regime, a diet according to the degree of digestive disorders, maintaining water balance. The basis of therapy for nematodoses are medications of the following groups:
- Etiotropic agents. To destroy and remove parasites from the body, anthelmintic drugs are used that disrupt neuromuscular transmission in roundworms or negatively affect their energy processes. The specific medicine and the scheme of its administration are selected individually.
- Pathogenetic drugs. Taking into account the clinical features of nematodosis, detoxification solutions, antihistamines, glucocorticosteroids are used. Enterosorbents, antispasmodics, probiotics and enzyme preparations are used to eliminate gastrointestinal dysfunction in the late phase. With repeated vomiting, prokinetics are used.
Complex conservative therapy is indicated for lymphedema caused by filariasis. From medicines, patients are prescribed diuretics, lymphokinetics and venotonics, drug sympathectomy with procaine solution. Elastic bandaging of the limb, medical lymphatic drainage massage, special physical therapy complexes are performed. To prevent tissue fibrosis, injections of fibrolytic enzymes are performed.
The help of surgeons is required for patients with complications against the background of large accumulations of adult helminths in the intestine or other organs. Mechanical intestinal obstruction, intestinal perforation, appendicitis and other urgent conditions require urgent laparotomy to remove worms and repair tissue defects. For the treatment of elephantiasis with filariasis, dermatofasciolipectomy, operations to create lymphovenous anastomoses are performed.
Prognosis and prevention
With timely and adequate treatment, deworming is achieved in most patients, after which the impaired functions of the body are restored. For recovered patients, dispensary supervision is established for up to 3 years. To prevent nematodoses, it is necessary to follow standard measures: monitor personal hygiene, avoid drinking water from unknown sources, thoroughly wash and, if possible, thermally process products.