Schistosomiasis symptoms diagnosis and treatment of tropical disease

Hardly known and yet so dangerous: As early as 5.000 years, the inhabitants of Egypt have suffered from schistosomiasis. In 1852, the tropical disease was first described there by the German pathologist Theodor Bilharz. Today, the World Health Organization (WHO) estimates that 200 million people are affected by this parasitic infectious disease. Learn all about the risks and transmission as well as symptoms and treatment of schistosomiasis here.

What exactly is schistosomiasis?

Schistosomiasis, also known as bilharzia, is a worm disease that can be transmitted both from person to person and from animals to humans. It occurs in about 70 predominantly tropical countries. According to the WHO, an estimated 50 deaths occur each year.000 to 300.000 people from this tropical disease. In Germany, the disease is rare. Primarily affects immigrants or rice returnees. Around 90 percent of those affected in Germany were infected in Africa. Of note are the cases of infection in 2013/14 in Corsica – where tourists were affected. As the infection remains undetected for a long time, but can lead to severe organ damage and even bladder cancer in the long term, a screening examination is recommended after trips to the tropics with contact with freshwater.

Incidence of schistosomiasis

The pathogen is particularly widespread in the sub-Saharan parts of Africa. But the disease also occurs in certain regions of South America (especially Brazil, Suriname and some regions of Venezuela). The pathogens "Schistosoma japonicum" and "Schistosoma mekongi" occur in Southwest and Southeast Asia, but travelers are infected with them much less frequently than with the African species. The majority of German travelers have been infected in West Africa as well as in Lake Malawi and Lake Victoria.

Note: Data collected in 1987 but still the most important source on the incidence of schistosomiasis worldwide. If a region is not listed, this does not automatically mean pathogen-free.

schistosomiasis symptoms diagnosis and treatment of the tropical disease

The schistosomiasis pathogen

Cause of schistosomiasis resp. Schistosomiasis is a sucking worm (trematode) that feeds on human blood and protein. It is called a couple fluke because the female worm lies in the abdominal fold of the male one. Five species can cause schistosomiasis in humans:

– Schistosoma mansoni – Schistosoma haematobium – Schistosoma intercalatum – Schistosoma mekongi and – Schistosoma japonicum

The life cycle begins with the egg laid by the female, which is excreted by an infected human or animal and enters the water with the stool or urine. In fresh water, a so-called ciliated larva (mirazidium) hatches after a few minutes. This infects certain freshwater snails that serve as intermediate hosts. Therefore, schistosomiasis only occurs where the appropriate snails (Bulinus, Biomphalaria, Oncomelania, Tricula) live. In them, the ciliated larvae mature into so-called cercariae, which have a forked tail and are therefore known as "fork-tailed larvae.

One ciliated larva gives rise to several thousand cercariae, which are released from the snail back into the water. When bathing in fresh water – especially in stagnant or stagnant water. slow-moving waters or weakly concentrated brackish water, z.B. in river estuaries – the risk of infection with schistosomiasis is particularly high in overgrown shore zones, as this is where the snails live. A few fleeting splashes of water containing cercariae are sufficient for infection.

Typical symptoms of schistosomiasis

Stage 1: Cercarial dermatitis

If the cercariae enter the human body through the skin during bathing, it can lead to itchy skin inflammation with redness and wheal formation, cercarial dermatitis. This also occurs in Germany – through water fowl infected with the bilharzia pathogen ("duck bilharzia"). It occurs mainly in summer after bathing in lakes or ponds and can cause excruciating itching. It is harmless in itself, because these cercariae do not develop in us and die off.

Phase 2: Katayama fever

The second phase of schistosomiasis – after infection – begins after three to ten weeks. It is called Katayama fever and in some cases manifests itself with fever, chills, headache, pain in the limbs, and hives. Likewise, the spleen and liver may be enlarged or bronchitis may occur. In addition, cardiac arrhythmias or life-threatening neurological complications are possible. In the blood, the eosinophilic white blood cells multiply – a typical sign of a parasite infection. This phase of the disease can lead to acute death or severe organ damage.

Phase 3: Settlement in the human body

After that the infection often goes unnoticed. The cercariae grow into worms via an intermediate stage. They reach a size of one to two centimeters. Eventually live permanently in the blood vessels for many years. Females lay 100 to 3.000 eggs per day. The body reacts to the schistosome eggs by forming a connective tie barrier called a granuloma from defense cells. Later, scarring changes grow out of them. These interfere with blood circulation. Cause organ damage. Some species (S. mansoni, S. japonicum, S. mekongi u.a.) settle preferentially in the blood vessels of the intestine and cause intestinal bilharzia with inflammation of the intestinal mucosa and later damage to the liver: Blood stasis in the portal vein, the most important blood vessel of the liver, leads to the formation of bypass circulation (portal hypertension). In addition, varicose veins form in the esophagus, which can lead to severe bleeding. As a result of liver dysfunction, fluid may collect in the abdominal cavity (ascites).

Schistosoma haematobium prefers veins of the urinary tract and genital area, causing urogenital bilharziasis with formation of bladder polyps or bladder cancer. However, the pathogen can also infect the intestine. In the tropics, chronic inflammation of the genital tract can lead to infertility in women. Increase the susceptibility to HIV infection.

In principle, however, the eggs can be washed out into all organs of the human body. The higher the "worm burden" and the more eggs laid in the body, the greater the extent of organic damage.

Make a correct diagnosis of schistosomiasis

After freshwater contact in regions where schistosomiasis is present, screening should be done after six weeks at the earliest – regardless of whether symptoms are present or not, and even if water contact is not explicitly recalled. The examination is carried out by determining the antibodies against schistosomiasis. In case of small amounts of red blood cells in the urine or vague symptoms (such as fatigue), the doctor should be consulted and informed about the stay abroad. If treated early, schistosomiasis can be well managed. Schistosome eggs can be detected in stool and urine about eight to twelve weeks after infection. Alternatively, tie samples from the intestine or bladder can be examined; it is not uncommon for the eggs to be found only after multiple searches. The worm eggs have characteristic spines that are specific to each schistosome species and facilitate diagnosis.

The schistosomiasis treatment

For the treatment of schistosomiasis the so-called "praziquantel" is the drug of choice. It damages the surface of the worms so that the body's defense system can eliminate the pathogens. Thus, ideally, no more eggs are produced. Praziquantel is taken in tablet form. Is very well tolerated. Side effects of treatment may include headache, dizziness, nausea or vomiting, although these are rare. Pregnant women should not start schistosomiasis treatment until after delivery to avoid possible harm to the unborn child from medication.

After the therapy, six to twelve months later, the stool or urine is examined again for worm eggs and the antibodies in the blood are measured. A further control can take place after 24 months. It is not uncommon for patients to need multiple treatments – especially when infected with S. japonicum. In some cases, a bladder or rectal endoscopy is also useful.

How to protect yourself?

If you are in a known risk area for schistosomiasis, you should not bathe in natural or artificial freshwater – even if the water is claimed to be free of the pathogen. It is not sufficient to avoid the shore zone when bathing. Even when doing water sports in the middle of the water or wading in the water, one can get infected. Properly maintained pools, however, are safe.

When crossing a body of water, wearing protective clothing is advisable. Although schistosomiasis is not transmitted through drinking water, it should be boiled, chlorinated or filtered to sterilize it. This also reduces the risk of other infections. After longer stays in the tropics, a timely control by means of an antibody test should be carried out. The appearance of schistosomiasis in a river in Corsica that is popular with tourists has shown that it is quite possible for the disease to spread to southern Europe.

Tip: You are planning a long-distance trip and want to learn more about travel diseases in high-risk countries? Then take a look at our free travel guide, where Dr. Hinrich Sudeck educates about traveling to countries with special health risks.

About the author

Dr. med. Hinrich Sudeck, born in 1956, is an internist and tropical medicine specialist who was a resident and senior physician at the Bernhard Nocht Institute for Tropical Medicine in Hamburg from 1990 to 2007. He was head of the German Armed Forces' Department of Tropical Medicine in Hamburg from 2010 to 2015 and completed missions as a soldier in Afghanistan, Mali and in Liberia as part of the fight against Ebola, having already served as a WHO expert in dealing with highly contagious viral diseases since 2003. In addition to many trips to tropical countries, he lived and worked for four years in Ghana and Nigeria.

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