What is Manson Intestinal Schistosomiasis?
Manson intestinal schistosomiasis (schistosomosis enterica Mansoni) is a helminthiasis affecting mainly the intestines, which is long-lasting, with periodic exacerbations, complicated by anemia, cirrhosis of the liver and cachexia.
Intestinal schistosomiasis is common in South America, in several Caribbean countries, in Africa and in the Middle East.
Causes of Intestinal Manson Schistosomiasis
The causative agent of intestinal schistosomiasis is Schistosoma mansoni (Sambon). The male is 10 mm long, 1.2 mm wide, the female is 15 mm long and 0.17 mm wide. Oval-shaped eggs with a spike located on the side. During puberty, it parasitizes the human body, rarely the possum, some rodent species, and also domestic pigs. The females of schistosomes lay their eggs in small blood vessels of the intestine, from where they enter the intestinal lumen, and then into the external environment with feces (in rare cases with urine). Helminth can live in the body for 25 years. Snails of the genus Biomphalaria serve as intermediate hosts.
The final owner of schistosomes is a human (sometimes rodents and other animals), with the faeces of which the helminth eggs are released into the external environment, enter the freshwater basin, where a mobile larva is released from the eggs — a miracid supplied with cilia. Helminths further develop in the organism of an intermediate host, freshwater mollusks, in which, after 4–5 weeks, invasive stages — cercaria — form. Cercariae penetrate the skin or mucous membranes of a person in the water, then immature or young helminths migrate through lymphatic and blood vessels, get into the right heart and lungs (4-7th day after infection), then reach the liver. After maturation (the 26th day of invasion), schistosomes from the liver rush into the mesenteric venules, where they are fixed, and after 30–40 days the females lay eggs (100–300 eggs per day). In the feces of an infected person, schistosome eggs can be detected 40–55 days after infection. Life expectancy of mature schistosomes in the human body is 5-25 years.
Pathogenesis during Intestinal Schistosomiasis Manson
Infection occurs during their contact with parasite-contaminated water when the parasite larvae, released by freshwater gastropod mollusks, penetrate the skin.
The basis of the pathogenesis of schistosomiasis are toxic-allergic reactions caused by secretions of the glands during the introduction of parasites and waste products and the breakdown of helminths. In the epidermis around the sites of introduction of cercaria edema develops with lysis of epidermal cells. In the course of the migration of larvae in the skin, there are infiltrates of leukocytes and lymphocytes.
Parasite eggs make their development cycle in the body of freshwater mollusks to the stage of cercariae, which are introduced through the skin into the human body. The cercariae very quickly mature and turn into schistosomils, which penetrate into the peripheral veins, where mature individuals are formed. From here, fertilized females are sent to their favorite habitat: pelvic veins, mesenteric and hemorrhoidal veins, as well as into the wall of the large intestine. Here the females lay their eggs, which causes tissue damage. Some eggs are excreted in the urine and feces into the external environment, being the source of the spread of helminthiasis.
Period infectious source. Infected people and animals secrete schistosomid 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 there are known cases of sexually mature worms in the human body up to 30 years. In infected mollusks, cercariae develop in water over a period of 4-5 weeks.
The natural susceptibility of people is high. The disease does not provide resistance to reinfection.
In intestinal schistosomiasis, the same inflammatory changes (schistosomotic colitis) develop in the colon, resulting in sclerosis of the intestinal wall. There are cases of schistosomotic appendicitis.
The hematogenous spread of the process is possible: parasites are introduced into the liver, lungs, brain, and inflammatory infiltrates appear on the site of their introduction, granulation tissue (granulomas) is formed, and sclerosis develops.
Symptoms of Intestinal Schistosomiasis Manson
Despite the high prevalence of intestinal schistosomiasis, which reaches 100% in endemic foci, clinical manifestations are relatively rare. Their occurrence is determined by the duration of the disease and the intensity of invasion. In residents of endemic foci, the disease is chronic and often lasts for decades. In the indigenous population immediately after infection, the disease is usually asymptomatic. During the first 10 years of life, the intensity of invasion (which is estimated by the number of parasite eggs in the feces) increases, and the prevalence of the disease in this age group often approaches 100%.
The peculiarities of clinical manifestations are determined by the cycle of development of schistosomes in the human body and therefore are quite variable. There are periods of egg laying and tissue proliferation. In some cases, intestinal schistosomiasis may be asymptomatic. The earliest clinical manifestations are primary dermatitis, itchy urticaria, fever, and eosinophilic infiltrates in the lungs. The period of laying and excretion of eggs is accompanied by a feeling of weakness, headaches, increased body temperature, pain in muscles and joints, the appearance of tenesmus during defecation, rapid stool, mucus and blood in the stool. When eggs are introduced into the central nervous system, paresis, paralysis, epileptiform seizures may occur, and appendicitis symptoms may appear if the appendix is damaged. When eggs get into the vessels of the pulmonary circulation, the walls of the vessels are affected, which leads to the development of a pulmonary heart. Sometimes eggs penetrate the urinary system.
The period of tissue proliferation is characterized by the development of fibrosis in the lesions of the intestinal mucosa, which can lead to the formation of polyposis and fistulas. Distinguish between mild, moderate, severe and very severe forms of the disease.
Mild form occurs with intermittent abdominal pain and enterocolitis diarrhea nature. The performance of the patient is not disturbed.
In moderate form, non-permanent abdominal pain is joined by anemia and weight loss of the patient. Such a patient is not able to do hard work.
Severe form with severe weakness, severe anemia; diarrhea and urge to stool become debilitating and very frequent. They lead to dehydration and exhaustion. Such patients are not able to perform physical work.
In very severe form, symptoms of advanced cirrhosis of the liver with portal hypertension, ascites, splenomegaly and severe cachexia join. Liver cirrhosis is a leading pathogenetic and clinical sign.
Diagnosis of Intestinal Schistosomiasis Manson
It is necessary to differentiate from amebiasis, bacterial dysentery, balantidiasis. Often, schistosomiasis is associated with these diseases. Epidemic data are of diagnostic importance. The diagnosis is based on the detection of eggs in feces. There are many eggs in the feces only with intensive invasion. About 80% of the eggs laid by helminths are delayed and die in the host’s tissues. Therefore, smears on glass slides should be made large and viewed under a binocular microscope, or “thick” smears should be prepared according to the Kato method, as well as deposition methods should be used and repeated studies should be carried out. The eggs of schistosomes are larger in the first portion of feces, since they are separated from the mucous membrane of the large intestine mainly in its lower parts. For negative results, koproskopii examine rectal mucus, which can be taken with a finger in a rubber glove immediately after the act of defecation.
They also use the method of detection of larvae of schistosomes in feces, based on their phototropism. To do this, use a flask with a capacity of 500 ml with a glass tube which is soldered to the side at the bottom and directed upwards. 20 g of faeces are placed in a flask and washed with a stream of tap water. 250 ml of water is left in the flask, covered with a cap of opaque black paper or placed in a dark box so that the side tube remains lit. After 2 h at a temperature of 25 ° C, miracidia hatch from the eggs of schistosomes, which, due to positive phototropism, accumulate in the side tube. Here they can be observed with a magnifying glass or even with the naked eye.
To identify inactive schistosomiasis, sometimes with rectoscopy, a biopsy of a piece of pathologically modified tissue from the intestinal mucosa is performed at a distance of about 10 cm from the anus. The pieces of biopsy tissue are crushed between two glass slides in a few drops of a 50% glycerol solution and microscopically. In positive cases, characteristic schistosome eggs are found in the mucosa.
Also, when sigmoidoscopy revealed hyperemia of the mucous membrane of the distal segment of the colon, erosive and ulcerative changes, schistosomous tubercles, intestinal polyposis (in later stages of the disease). In recent years, immunological methods for recognition of schistosomiasis have become widely used – an intradermal allergy test with an antigen prepared from miracidia, the liver of infected mollusks, cercariae and matured schistosome, complement fixation, precipitation and flocculation reactions.
Treatment of Intestinal Schistosomiasis Manson
The prognosis and effectiveness of treatment depend on the stage of the disease. In some patients with periportal fibrosis who have taken anthelmintic drugs, ultrasound reveals a partial regression of the pathological process, but far gone liver fibrosis cannot be reversed. Glomerulonephritis and pulmonary heart are observed exclusively in patients with periportal fibrosis. CNS damage is possible at any stage of the disease and does not depend on the severity of the invasion.
Since the anthelmintic drugs used to treat schistosomiasis are quite effective and safe, they are prescribed to all patients who release viable parasite eggs into the environment. Signs of egg viability — the presence of cells with a ciliated flame — the end portions of the protonephridia (an experienced parasitologist can easily distinguish them under a microscope), as well as the release of miracidia when eggs get into the water. In the past, anthelmintic drugs were more toxic, and treatment was carried out only with severe invasion with a high risk of complications. However, the risk of complications, in particular due to the atypical localization of the parasite’s eggs (for example, in the spinal cord), is even with mild invasion.
The number of eggs released may be small, which makes diagnosis difficult. Then come to the aid serological tests. Since with light invasion, praziquantel does not cause severe adverse reactions, the drug is prescribed even in cases where the release of viable eggs with feces is very likely or cannot be excluded. After treatment, the results of some serological tests become negative (it should be borne in mind that the production of these samples is technically difficult and is not available everywhere). After successful treatment, after 2-3 months, the excretion of eggs with feces stops, and in some patients the size of the spleen decreases and the severity of periportal fibrosis decreases. Most of them are young people with unheard of disease.
For the treatment of intestinal schistosomiasis, there is a large arsenal of drugs, but the drugs of choice are praziquantel and oxamnichin. Both drugs are equally safe and effective in intestinal schistosomiasis in the Caribbean and South America. In Africa, pathogens that are moderately resistant to oxamniquin are common, therefore praziquantel is preferable there. Both drugs can be used for periportal fibrosis. Side effects are frequent, but weak and transient.
Many of the side effects of praziquantel are associated with the immune system’s reaction to damaged worms and their eggs. Because parasites are mostly localized in the intestines, side effects most often boil down to abdominal pain, diarrhea, drowsiness, and fever. In contrast, in the treatment of cysticercosis with praziquantel (when helminths are often localized in the CNS), neurological symptoms often occur.
Side effects of oxamnicin include dizziness, fatigue, nausea, vomiting, neurological and mental disorders, and (rarely) seizures.
Prevention of Intestinal Schistosomiasis Manson
The prevention and control of schistosomiasis is based on preventive treatment, the treatment of gastropod mollusks, improved sanitation and health education.