What is Schistosomiasis (Bilharziosis)?
Schistosomiasis (bilharziosis) is a chronic helminthiasis caused by trematodes of the genus Schistosoma, with a primary lesion of the genitourinary system and intestines.
More than 207 million people are infected worldwide, and an estimated 700 million people in 74 endemic countries are at risk of infection.
Schistosomiasis has a significant impact on the economy and health. In children, schistosomiasis can lead to anemia, stunted growth and reduced learning abilities, despite the fact that, as a rule, the effects of the disease are reversible during treatment. Chronic schistosomiasis can affect people’s ability to work, and in some cases lead to death. In sub-Saharan Africa, more than 200,000 people die each year from schistosomiasis.
Causes of Schistosomiasis (Bilharziosis)
The causative agent of schistosomiasis in humans is Schistosoma haematobium (urogenital schistosomiasis), Schistosoma mansoni (intestinal schistosomiasis) and Schistosoma japonicum (Japanese schistosomiasis with allergies, development of colitis, hepatitis, cirrhosis). Schistosomiasis of the genitourinary system, which was first discovered by the Bilharz, was called bilharziosis.
Schistosomiasis affects mainly people involved in agriculture and fishing. Women who use parasite-contaminated water in their homework, such as laundry, are also at risk. Children are especially vulnerable to infection due to their hygiene and play habits.
In northeastern Brazil and Africa, refugee movements and urban migration contribute to the spread of the disease to new areas. An increase in population and, consequently, energy and water needs often leads to development patterns and environmental changes that also contribute to the transmission of infection.
As ecotourism develops and trips to “unbroken places” more and more tourists become infected with schistosomiasis, sometimes in the form of a severe acute infection and with the development of unusual symptoms, including paralysis.
Pathogenesis during Schistosomiasis (Bilharziosis)
Infection of people occurs during their contact with water infected with parasites with the penetration of parasite larvae secreted by freshwater gastropods through the skin.
The pathogenesis of schistosomiasis is based on toxic-allergic reactions caused by the secrets of the glands during the introduction of parasites and the waste products and the breakdown of helminths. In the epidermis, edema with lysis of epidermal cells develops around the sites of cercaria introduction. During the migration of larvae, infiltrates from leukocytes and lymphocytes appear in the skin.
Parasite eggs undergo their developmental cycle in the body of freshwater mollusks to the stage of cercariae, which are introduced through the skin into the human body. Cercariae very quickly mature and turn into schistosomules, penetrating into the peripheral veins, where mature individuals form. From here, the fertilized females are sent to the place of their favorite habitat: pelvic veins, mesenteric and hemorrhoidal veins, as well as into the wall of the colon. Here, females lay their eggs, which causes tissue damage. Part of the eggs is excreted in the urine and feces into the external environment, being a source of the spread of helminthiasis. The foci of urinary schistosomiasis are mainly in Africa; intestinal – in South and Central America, Africa, Japanese – in Japan and Southeast Asia.
Source contagious period. Infected people and animals secrete schistosomide eggs 40-60 days after infection or 1-2 weeks after the onset of clinical signs of the disease and then up to 1-2 years, although cases of the occurrence of mature worms in the human body up to 30 years are known. In infected mollusks, cercariae develop within 4-5 weeks before they enter the water.
The natural susceptibility of people is high. Past disease does not provide resistance to reinfection.
Pathological anatomy. The most common is urinary schistosomiasis, in which the bladder is affected. In the early period of the disease, inflammation, hemorrhages, desquamation of the epithelial cover develop in the surface layers of the mucous membrane of the bladder. Then the changes extend to deeper layers of the wall. In the submucous layer around the eggs of schistosomes, leukocyte infiltrates appear, they cover the entire thickness of the mucous membrane in which ulcers form. Over time, the exudative tissue reaction changes into a productive one, granulation tissue with a large number of epithelioid cells forms around the eggs, and schistosomal granuloma forms. The process acquires a chronic course, the outcome of which is sclerosis and deformation of the wall of the bladder. Dead eggs calcify. The spread of the parasite into the veins of the pelvis leads to the occurrence of foci of damage in the prostate gland, epididymis.
With slow healing of bladder ulcers, cancer may develop in it. With intestinal schistosomiasis in the colon, the same inflammatory changes develop (schistosomal colitis), resulting in sclerosis of the intestinal wall. There are cases of schistosomal appendicitis.
The hematogenous spread of the process is possible: parasites are introduced into the liver, lungs, and brain, and inflammatory infiltrates occur at the site of their introduction, granulation tissue (granulomas) forms, and sclerosis develops.
Symptoms of Schistosomiasis (Bilharzioza)
The cause of schistosomiasis symptoms is the body’s reaction to the eggs of the worms, and not to the worms themselves.
At an early stage of the disease, itching, local erythema, papular rashes may appear. During the migration of schistosomules in the body, especially when they pass through the lungs, a cough with thick sputum may develop, the liver, spleen, and lymph nodes increase. The period of puberty of helminths and the onset of oviposition is characterized by a combination of chronic inflammatory phenomena. In the late stage of the disease, chronic colitis, embolism of the veins of the liver and lungs, pseudo-elephantiasis of the genital organs, obliterating endoarteritis, myocarditis, etc. are possible.
5-8 days after infection, an acute form of schistosomiasis develops. At the site of penetration of the parasite, an allergic reaction occurs in the form of urticaria. Patients complain of general malaise, headache, chills, joint pain, muscle pain. Leukocytosis, eosinophilia, increased ESR are noted.
After 6-8 weeks. after infection, the disease goes into a latent stage, which lasts 3-4 weeks, sometimes up to 3 months.
Intestinal schistosomiasis can cause abdominal pain, diarrhea, and the appearance of blood in the feces. In advanced cases, an increase in the liver is observed, which is often associated with fluid accumulation in the abdominal cavity and hypertension of the abdominal blood vessels. In such cases, an enlarged spleen may also be observed.
Various lesions of the genitourinary system are noted after 4-6 months. after infection.
A classic sign of genitourinary schistosomiasis is hematuria (the presence of blood in the urine). In advanced cases, fibrosis of the bladder and ureters often develops and the kidneys are affected.
With the addition of a secondary infection, urination becomes frequent and painful. When strictures of the ureters appear aching pain in the lumbar region, sometimes attacks of renal colic, which is due to blockage of the narrowed section by blood clots, mucopurulent discharge.
A possible complication in the last stages is bladder cancer. In women, urogenital schistosomiasis can lead to genital lesions, vaginal bleeding, pain during intercourse and the formation of nodes on the external genitalia, colpitis, polyps on the vaginal mucosa and cervix. In men, genitourinary schistosomiasis can lead to the development of pathology of the seminal vesicles, prostate and other organs. This disease can have other long lasting irreversible effects, including infertility.
Patients complain of weakness, poor appetite, fatigue, sleep disorder, headaches. Sometimes with a chronic course of urogenital schistosomiasis, patients do not complain; the disease is detected during the clinical examination.
Urogenital schistosomiasis is also considered a risk factor for HIV infection, especially among women.
Diagnosis of Schistosomiasis (Bilharziosis)
Schistosomiasis is diagnosed by detecting parasite eggs in stool or urine samples.
For the diagnosis of genitourinary schistosomiasis, a standard method is filtration using nylon, paper or polycarbonate filters. Children with S. haematobium almost always have blood in their urine, visible through a microscope. It can be detected using chemical strips. In order to identify communities at high risk of infection, and thus identify priority areas for action, children can also be tested for blood in their urine.
To identify eggs of intestinal schistosomiasis in fecal samples, a technique using methylene blue stained cellophane soaked in glycerol or glass slides can be used.
Treatment of Schistosomiasis (Bilharziosis)
The WHO strategy for the fight against schistosomiasis aims to reduce morbidity through periodic, targeted treatment with praziquantel. Such treatment involves regular treatment of all people at risk.
Target groups for treatment are:
- school-age children in endemic areas.
- adults at risk in endemic areas, such as pregnant women and nursing mothers, people who come in contact with parasitic water, such as fishermen, farmers and irrigation workers, and women who come into contact with parasitic water during homework.
- entire communities living in endemic areas.
Schistosomiasis is safely and effectively treated with praziquantel. The medicine is prescribed for children in a dose depending on body weight (50 mg of praziquantel per 1 kg of body weight). To prescribe the right dose, children are either weighed or, more easily, their height measured. Growth and mass are interconnected, so growth can be used instead of mass to calculate the number of praziquantel tablets that a child should prescribe. The easiest way to do this is with the help of a “tablet meter” (‘tablet pole’), which is a rail for measuring the growth of children with the divisions on it, indicating the number of tablets corresponding to the growth of the child. To determine the correct number of tablets for each child, he is simply leaned against the “tablet meter”.
Praziquantel for the treatment of schistosomiasis can be prescribed without risk to health at the same time as albendazole, which is used to treat infections caused by intestinal geohelminths, such as roundworms, whipworms and hookworms.
Re-infection with schistosomes is very likely, so the course of treatment should be repeated after a year if the child is infected again. The course of treatment is carried out by a doctor or health worker, as well as teachers trained to treat children at school.
Who should not be treated?
- If children already feel unwell for any other reason, for example, have a fever, the treatment should be postponed until they feel better.
- If the girls are pregnant, they should not be given a course of treatment during the first three months of pregnancy.
- Children with a chronic illness such as sickle cell anemia.
- Children under the age of one year.
Are there any side effects?
Praziquantel is completely safe, and most people do not feel any side effects from taking it; only a small number of patients report mild and short-term symptoms. These may include headache, fever, stomach pain, diarrhea, and vomiting. The most likely manifestation of side effects in people with severe helminthiasis. If severe and ongoing side effects are observed, children should be referred to the hospital. Children should be given a small portion of the main food before taking the medicine to prevent any side effects.
What is the benefit of treatment?
Schistosomiasis can lead to a very serious condition of the patient, and therefore it is important, in order to avoid some of the consequences of the infection described above, to treat children. After treatment, children feel better overall, they miss school significantly less due to illnesses, their ability to concentrate improves, and they work more actively during school hours.
Prevention of Schistosomiasis (Bilharziosis)
Prevention and control of schistosomiasis are based on preventive treatment, control of gastropods, improvement of sanitation and health education.