Schistosomiasis

Fabian Dupont is a freelance writer in the medical department. The human medicine specialist is already doing scientific work in Belgium, Spain, Rwanda, the USA, Great Britain, South Africa, New Zealand and Switzerland, among others. The focus of his doctoral thesis was tropical neurology, but his special interest is international public health and the comprehensible communication of medical facts.

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Schistosomiasis is a tropical disease that is triggered by a worm - the pair of leeches. After malaria, schistosomiasis is one of the most common parasitic infectious diseases worldwide. It is a major problem, especially in developing countries, such as Africa, Latin America and Southeast Asia. You can read everything you need to know about schistosomiasis here.

ICD codes for this disease: ICD codes are internationally recognized codes for medical diagnoses. They can be found, for example, in doctor's letters or on certificates of incapacity for work. K77B65

Schistosomiasis: description

The causative agent of schistosomiasis (schistosomiasis) is the pair of leeches (schistosoma). This is its name because it always takes a male and a female to reproduce in order to close the infection cycle. The worms live in the blood vessels of the human abdomen and excrete their eggs in the faeces or urine of the infected person.

There are different types of pair leeches, which can cause different clinical pictures. The most common schistosomiasis pathogens are:

Schistosoma haematobium: Trigger of bladder bilharzia; Occurrence in Africa, the Orient and India
Schistosoma mansoni: Trigger of intestinal bilharzia; Occurrence in Africa, the Orient, South and Central America
Schistosoma mekongi: Trigger of intestinal bilharzia; Occurrence in Southeast Asia
Schistosoma japonicum: Trigger of intestinal bilharzia; Occurrence in East Asia
Schistosoma intercalatum: Trigger of intestinal bilharzia; Occurrence in Central Africa

According to estimates by the World Health Organization, approximately 250 to 300 million people worldwide are infected with schistosomes. Every year around 200,000 people die as a result of schistosomiasis, most of them in Africa. In Germany around 200 cases of schistosomiasis occur annually (in immigrants or holidaymakers who come from areas of infection).

Schistosomiasis: life cycle of the parasite

The eggs of the pair of leeches develop in fresh water. Larvae (miracidia) hatch from them and nest in a certain type of freshwater snail. Thousands of cercariae develop in the snails - a further development stage of the pathogen. The cercaria get back into the water, from where they can attack humans. For example, if someone bathes in the infected water or wades through such water, he can become infected. The head of the cercaria penetrates the skin (shedding the tail).

It takes about two days for the intruder to adapt to the human organism and travel to the lungs via the venous system. After a few further stages of development, the now adult schistosomiasis pathogens reach the blood vessels of the liver. There it comes to mating. Most schistosomiasis pathogens use the intestines to lay eggs, and some also use the bladder. To do this, they migrate into the vascular network of the organ in question.

At least one week elapses between the attack on the skin and the appearance of the adult pair of leeches. Egg production begins approximately after six to eight weeks. And this production is enormous: Schistosomes can produce several hundred to a thousand eggs a day. In order for the eggs to get into the intestines or the bladder, they slowly fester through the intestinal / bladder wall. This process is often accompanied by a strong immune reaction. In many cases, this is when the patient first begins to feel symptoms of schistosomiasis.

What is the World Health Organization (WHO) doing against schistosomiasis?

The WHO tries to prevent the spread of schistosomiasis through targeted treatment of risk groups. If a certain number of people in a place or region are infected, all people in the village or community are treated as a precaution. In 2017, at least 220.8 million people received preventive schistosomiasis therapy, and over 102.3 million infected people were treated.

Schistosomiasis: symptoms

In schistosomiasis, acute symptoms appear within hours and days. If the schistosomiasis is not recognized and no treatment is given, chronic schistosomiasis develops.

Symptoms of acute schistosomiasis

The first symptoms of schistosomiasis appear a few hours after contact with the contaminated water. After the larvae of the pair of leeches have penetrated the skin, a skin reaction occurs at the entry points that is reminiscent of an allergic rash (cervical dermatitis).

Acute schistosomiasis can also be accompanied by fever. The increase in temperature occurs a few days to weeks after infection. Fever caused by schistosomiasis is called katayama fever. Typically, the fever is accompanied by a cough, chills, and headache. These complaints are often misunderstood as a flu-like infection, so that the schistosomiasis infection remains untreated in most cases.

After several weeks, the worms are sexually mature and lay their eggs (mostly) in the intestinal wall. There is thin stool with small amounts of blood. The worm species S. haematobium causes blood in the urine as it lays eggs in the bladder wall.

Symptoms of chronic schistosomiasis

The schistosomes can survive for years in the vessels in the abdomen and then cause great damage, especially with their eggs. Because even if cercaries and worms provoke a certain immune response, it is mainly the eggs that trigger an enormous immune response. The organs involved suffer great and mostly irreparable damage. A general distinction is made between two different types of schistosomiasis: bladder and intestinal schistosomiasis.

Schistosomiasis of the bladder (urogenital bilharzia)

at S. haematobium the eggs are deposited in the bladder wall. The immune reaction causes bleeding and scarring in the bladder wall. Patients then often report pain when urinating and blood in the urine.

In 60 percent of those affected by this form of schistosomiasis, the genital tract is also affected. In women, the fallopian tubes stick together, which often leads to infertility. This also increases the risk that a fertilized egg will implant itself in the abdominal cavity instead of in the uterus (extrauterine pregnancy). This complication can lead to life-threatening bleeding and is therefore an emergency!

Because of the damage to the bladder and ureter, bladder bilharzia is more likely to cause urinary tract infections: bacteria can colonize the previously damaged bladder wall more easily. In addition, the ongoing battle between the immune system and schistosome eggs can lead to malignant degeneration of the bladder tissue (bladder cancer).

Schistosomiasis of the intestine

In schistosomiasis of the intestine, the pair of leeches lay the eggs in the intestinal wall, which they slowly penetrate until they are then excreted in the stool. This is often accompanied by abdominal pain and recurring diarrhea with blood admixture. Patients can even develop anemia as a result of the ongoing loss of blood. This can be indicated, for example, by pale skin and excessive tiredness.

The parasite eggs migrating through leave numerous small injuries in the intestinal wall. Possible consequences are scarring and a certain loss of mucosal function. Unfortunately, the vacancies also serve as a gateway for other organisms such as salmonella to enter the body, making it more susceptible to infection.

Severe schistosomiasis

If there is a strong infection with schistosomes, so many eggs are deposited in the vascular plexus in the bladder or intestine that some eggs also end up in 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 seriously damaged. The symptoms that can arise from the severe infestation of schistosomiasis depend on the affected organ system.

If, for example, schistosomiasis patients increasingly suffer from shortness of breath or shortness of breath, this can indicate progressive scarring of lung tissue (lung fibrosis) as a result of the parasite infestation. Slow yellowing of the skin (jaundice) is often caused by impaired liver function. Liver failure can even occur.

Since schistosomiasis not only damages organs themselves, but also disrupts their blood flow, the pressure conditions in the vascular system can change: If a large number of worm pairs live in the vessels of the abdominal cavity, the blood can no longer pass through the liver as usual Heart flow back. It backs up in front of the liver, which is known as pulmonary high blood pressure (portal hypertension). The congested blood looks for a detour via other vessels that are not actually designed for the transport of large amounts of blood, for example in the esophagus, stomach and anal area. The overexerted vessels expand (formation of varicose veins), can burst and bleed profusely - this may lead to vomiting of blood, tarry stools (black blood in the stool) and / or bleeding hemorrhoids. Heavy bleeding can be life-threatening!

Schistosomiasis: causes and risk factors

Schistosomiasis can be infected in stagnant fresh water in tropical countries. Children and young adults are particularly at risk as they come into more contact with rivers and lakes.

Before every trip to the tropics, you should discuss the country-specific risks (such as the risk of schistosomiasis) with a tropical doctor.

Schistosomiasis: examinations and diagnosis

If you suspect you have schistosomiasis, it is best to see a tropical medicine or gastroenterologist. He or she will first collect the medical history (anamnesis) in conversation with you. He could ask the following questions:

Have you been to the tropics lately?
Did you swim in inland waters there?
Have you recently had a rash?
Do you have fever?
Do you suffer from diarrhea and / or stomach pain?
Can you see blood in your urine?
Do you have pain when urinating?

This is followed by the physical exam. If the doctor feels the stomach, he often comes across an enlarged liver, spleen and swollen lymph nodes in schistosomiasis. Such changes can also have other causes. Therefore, further investigations are necessary in the following.

These include blood tests: even in the first few weeks of a schistosomiasis infection, increased levels of certain white blood cells (eosinophils) can be measured in the blood. In addition, specific antibodies against the parasites are searched for in the blood (nophilia).

Stool and urine examinations are also revealing: a few weeks after infection, eggs of the schistosomiasis pathogen can be detected directly in the stool or urine of the patient.

An ultrasound examination and a colon / bladderoscopy can show how severely organs have already been damaged as a result of schistosomiasis.

A long-standing schistosomiasis infection can lead to calcification and scarring (fibrosis) due to the immune reaction in the various tissues. These changes can be so pronounced that you can even see them on an X-ray. This then speaks for an already very advanced schistosomiasis.

Schistosomiasis: treatment

The treatment of schistosomiasis is relatively simple and is also used by the WHO in entire population groups to limit the spread of the parasite. A single dose of the anti-worming agent praziquantel is sufficient in most cases. It paralyzes the musculature of the couple's leech, so that it dies. This prevents further egg production and the patient no longer excretes any more eggs - the infection cycle of schistosomiasis is interrupted.

However, there is also criticism of the use of praziquantel in schistosomiasis. If the patient also suffers from another parasitic disease, neurocysticercosis, the drug can seriously damage the patient and even lead to death. In general, however, it is very well tolerated and has few side effects.

If the symptoms are severe, steroids such as cortisone may have to be used to stop the immune response and not to endanger the patient. This is sometimes the case in the early stages of the infection, for example in the case of severe katayama fever.

Schistosomiasis: disease course and prognosis

The earlier schistosomiasis is treated, the better. However, many schistosomiasis infections go unnoticed by patients for years and are therefore not treated. This can ultimately lead to severe organ damage up to kidney, liver, lung and heart failure. Since many of these consequences can be fatal, a quick and consistent diagnosis and therapy is essential. Especially travelers who have stayed in tropical regions should consider the possibility of schistosomiasis or other tropical diseases if they have any complaints (even after returning home) and have themselves examined.

There is another health risk with bladder bilharzia: it increases the risk of bladder cancer. It usually occurs 10 to 20 years after the initial infection.

Schistosomiasis can also lead to complications during pregnancy.

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