SchistosomiasisFabian Dupont is a freelance writer for NetDoktor's medical editorial team. The human physician is already for scientific work among other things Belgium, Spain, Rwanda, the USA, Great Britain, South Africa, New Zealand and Switzerland. His doctoral thesis focused on tropical neurology, but he is particularly interested in international health science (public health) and the comprehensible communication of medical ies.
The Schistosomiasis is a tropical disease caused by a worm – the couple fluke. After malaria, it is one of the most widespread parasitic infectious diseases worldwide. Especially in developing countries, schistosomiasis is a major problem, for example in Africa, Latin America and Southeast Asia. Read all the important information about the cause, symptoms, treatment and prognosis of schistosomiasis here!
The causative agent of schistosomiasis is the couple fluke (Schistosoma). Its name comes from the fact that it always requires a male and a female to reproduce in order to complete the cycle of infection. The worms live in the blood vessels in the trunk. Excrete their eggs through the infected person's feces or urine. There are different types of the couple fluke, which can cause a different clinical picture (intestinal bilharzia or bladder bilharzia).
According to estimates by the World Health Organization (WHO), approximately 250 to 300 million people worldwide are infected with schistosomes. About 200 die each year.000 people died as a result of schistosomiasis, most of them in Africa. In Germany, about 200 cases of schistosomiasis occur annually (among immigrants or vacationers arriving from infected areas).
Schistosomiasis: life cycle of the parasite
The eggs of the mating flukes develop in fresh water. Larvae hatch from them (Mirazidia), which nest in a certain type of freshwater snails. In the snails, thousands of Cercariae – another stage of development of the pathogen. The cercariae get back into the water, from where they can infect humans. If someone bathes in or wades through infected water, they can become infected. In the process, the head of the cercariae penetrates the human skin while shedding its tail.
It takes about two days for the invader to adapt to the human organism and travel to the lungs via the venous system. After a few more stages of development, the now adult schistosomiasis pathogens reach the blood vessels of the liver. The males and females mate there. Most schistosomiasis pathogens use the intestine for egg laying, some also use the bladder. For this, they migrate into the vascular plexus of the affected organ.
At least one week passes between the infestation of the skin and the appearance of the adult couch flukes. Egg production begins after about six to eight weeks. And this production is huge: schistosomes can produce several hundred to a thousand eggs per day.
So that the eggs enter the intestine (intestinal bilharziasis) resp. enter the bladder (bladder schistosomiasis), they slowly fester through the intestinal/bladder wall. This process is often accompanied by a strong immune reaction.
What does the World Health Organization (WHO) do about schistosomiasis??
The WHO is trying to prevent the spread of schistosomiasis through targeted treatment of risk groups. If a certain number of people in a village or region are infected, all people in the village or community are treated as a precautionary measure. Thus, in 2017, at least 220.8 million people received precautionary schistosomiasis therapy, and more than 102.3 million infected people were treated.
In schistosomiasis, acute symptoms occur within hours to days. If schistosomiasis is not recognized and treated, chronic schistosomiasis develops.
Symptoms of acute schistosomiasis
The first symptoms of schistosomiasis appear only a few hours after contact with the contaminated water. After the larvae of the couch flukes have penetrated the skin, there is a skin reaction at the entry sites, which is reminiscent of a allergic skin rash Remembers (cercariae dermatitis).
Acute schistosomiasis can also be accompanied by fever. Temperature increase occurs a few days to weeks after infection. Fever caused by schistosomiasis is called Katayama fever. Typically accompanied by cough, chills and headache. These symptoms are often mistaken for a flu-like infection, so that in most cases the schistosomiasis infection remains untreated.
After several weeks the worms are sexually mature and lay their eggs (mostly) in the intestinal wall (intestinal bilharzia) – there are thin stool with small blood admixtures. The worm type S. haematobium causes a blood admixture in the urine, as it lays its eggs in the bladder wall (bladder bilharzia). The schistosomes can survive for years in the vessels in the abdomen. Then cause great damage, especially with their eggs. Because even though cercariae and worms cause some immune response, it is mainly the eggs that massively trigger the immune system. The organs involved take on a large size. Mostly irreparable damage. Generally, two different types of schistosomiasis are distinguished: bladder and intestinal schistosomiasis.
Bilharzia of the bladder (urogenital bilharzia)
Couple flukes of the type Schistosoma haematobium lay their eggs in the bladder wall. Due to the resulting immune reaction, bleeding and scarring occurs in the bladder wall. Patients then often report pain when urinating and blood in the urine.
In 60 percent of the people with this form of schistosomiasis, the genital tract is also affected. In women, the fallopian tubes become blocked, which often leads to infertility. In addition, there is an increased risk that a fertilized egg will implant in the abdominal cavity instead of the uterus (abdominal pregnancy). This complication can lead to life-threatening bleeding and is therefore an emergency!
Due to the damage to the bladder and ureter, bladder schistosomiasis more frequently triggers urinary tract infections. Bacteria can colonize the damaged bladder wall more easily. In addition, the constant struggle between the immune system and the. Schistosoma eggs can cause malignant degeneration of the bladder tie (bladder cancer).
bilharzia of the intestine
Other types of couple flukes are responsible for schistosomiasis of the intestine. They lay their eggs in the intestinal wall. These then slowly penetrate the wall, thus reaching the inside of the intestine and are finally excreted in the stool. This is often accompanied by abdominal pain. recurrent diarrhea with blood admixtures.
Due to continuous blood loss, patients may even develop anemia (anemia). This is indicated, for example, by pallor of the skin and excessive tiredness.
The migrating parasite eggs leave numerous small injuries in the intestinal wall. Possible consequences are scarring. Some loss of mucosal function. In addition, the open areas provide a portal of entry into the body for other organisms such as Salmonella, making patients more susceptible to further infections.
If there is a heavy infestation of schistosomes, so many eggs are deposited in the vascular plexuses of the bladder or intestine that some eggs also reach the liver, spleen, brain or lungs. If this happens, the immune system tries to eliminate the parasite eggs in these organs as well. The organs are severely damaged. The symptoms that may result from a severe infestation of schistosomiasis depend on the organ system affected.
If, for example, schistosomiasis patients increasingly suffer from shortness of breath or shortness of breath, this may indicate progressive scarring of lung tie (pulmonary fibrosis) as a result of the parasite infestation. A slow yellowing of the skin (jaundice) is often restricted Liver function causes. It can even lead to liver failure.
Since schistosomiasis not only damages the organs themselves, but also disturbs their blood flow, it can lead to a change in the prere conditions in the vascular system: If a large number of pairs of worms live in the vessels of the abdominal cavity, the blood can no longer flow back to the heart via the liver as usual. It then backs up in front of the liver, which is called a portal hypertension is called.
The congested blood finds a detour via other vessels that are not actually designed to transport large amounts of blood, for example in the area of the esophagus, stomach and anus. The overstressed vessels dilate (formation of varicose veins), can burst and bleed profusely – for example, there is vomiting of blood, tarry stools (black blood admixtures in the stool) and/or bleeding hemorrhoids. Such bleeding, if severe, can be life-threatening!
Schistosomiasis: Causes and risk factors
There are several types of couch flukes that can be considered to cause schistosomiasis. The most common are:
Schistosoma haematobium: causative agent of bladder schistosomiasis; occurs in Africa, Orient and India Schistosoma mansoni: causative agent of intestinal schistosomiasis; occurs in Africa, Orient, South and Central America Schistosoma mekongi: Inducer of intestinal schistosomiasis; occurs in Southeast Asia Schistosoma japonicum: Inducer of intestinal schistosomiasis; occurs in East Asia Schistosoma intercalatum: Inducer of intestinal schistosomiasis; occurs in Central Africa
You can become infected with these schistosomiasis pathogens in stagnant fresh water in tropical countries. Children and young adults are especially at risk, as they come into more contact with rivers and lakes.
Before each trip to the tropics, you should discuss the country-specific risks (such as the risk of schistosomiasis) with a tropical physician.
Bilharzia: examinations and diagnosis
If you suspect you have schistosomiasis, a tropical medicine doctor or gastroenterologist is the right person to contact. The first thing the doctor will do is talk to you and take your medical history. He might ask the following questions:
– Have you been to the tropics recently? – Have you bathed there in inland waters? – Have you had a skin rash recently? – Do you have a fever? – Do you suffer from diarrhea and/or abdominal pain? – If blood is visible in your urine? – Have pain when urinating?
This is followed by physical examination. If the doctor palpates the abdomen, he often finds an enlarged liver, enlarged spleen, and swollen lymph nodes in schistosomiasis cases. However, such changes can also have other causes. Therefore, further examinations are necessary to make a diagnosis.
This includes Blood testsIncreased levels of certain white blood cells (eosinophilic granulocytes) can be measured in the blood during the first weeks of a schistosomiasis infection. In addition, specific antibodies against the parasites are searched for in the blood.
stool and urine examinations are also informative: a few weeks after infection, eggs of the schistosomiasis pathogens can be detected directly in the stool or urine of patients.
A Ultrasound examination and a endoscopic intestinal or. Bladder examination (Colonoscopy resp. cystoscopy) can show what organ damage schistosomiasis has already caused.
If you have been infected with schistosomiasis for many years, the immune response in the various ties can lead to calcifications and scarring (fibrosis) come. These changes may be so pronounced that they can even be seen on a X-ray recognizes. This then speaks for an already very advanced schistosomiasis.
Treatment for schistosomiasis is relatively simple and is also used by the WHO in whole populations to limit the spread of the parasite. The one-time administration of the anti-worm drug Praziquantel is sufficient in most cases. For infected travelers, on the other hand, the German Society for Tropical Medicine recommends taking the medication for three days. In these cases, the slightly longer treatment seems to be more effective than a one-day therapy. The dosage depends on the exact pathogen type.
Praziquantel paralyzes the muscles of the couch fluke so that it dies off. This stops further egg production, and the patient no longer excretes any more eggs – the infection cycle of schistosomiasis is interrupted. Stop immune reaction. Not to endanger the patient. This is sometimes the case in the initial phase of infection (z.B. in the case of severe Katayama fever) or if, for example, nerve disorders, paralysis or seizures occur (neuroschistosomiasis, neurobilharzia). Caution is also advised when other parasites are suspected to have attacked the nervous system (e.g.B. neurocysticercosis caused by pork tapeworm).
In such cases (acute and severe schistosomiasis and infestation of the nervous system), doctors usually do not use praziquantel (or delay its use): This is because the active ingredient may worsen the condition of the affected person. Moreover, it has an insufficient effect on the still-young worms.
For such episodes, treatment is best done in a tropical medicine center. Doctors there then concentrate on alleviating the symptoms (symptomatic therapy). Praziquantel is not used until about three months after the suspected infection, when the pathogen is fully grown.