Schistosomiasis: what it is and how it is contracted

Schistosomiasis is a parasitic disease caused by the Schistosoma. It is also known as'bilharziasis' Within the biological classification, the parasite in question is a trematode, a kind of worm.

The global data on the distribution of the disease are striking. Mainly, it is located in Africa, Brazil and Asia. The countries that have certified transmission within their territory are seventy-eight. Two hundred million people are infected and eight hundred million with the possibility of contagion.

The last relatively reliable fact of the calculation of deaths that the pathology generates is from the year 2000. For that time, The World Health Organization estimated at two hundred thousand deaths per year. It is assumed that this number has decreased due to the more massive use of antiparasitic drugs.

Schistosomiasis: parasitic disease

The parasite in question is the only one of its biological family able to penetrate the skin. That is your resource to infect. Schistosomiasis, as a parasitic disease that is, requires hosts. And the guests who lodge it are two: the human being and the freshwater snail.

The freshwater snail functions, in the cycle of contagion, as an intermediate host. Inside the animal, the Schistosoma It fulfills part of its growth to then swim and stay in the human.

To know more: Gastrointestinal parasites

If we had to summarize the Lifecycle In a brief manner, we could describe the following stages:

  • Within a previously infected human being, Parasite eggs leave in the stool or in the urine and they reach water courses.
  • In the water, the eggs release the parasite in a stage called 'miracidium'.
  • Miracidia penetrate the skin of the freshwater snail.
  • The parasite, inside the snail, grows and arrives at a stadium called 'cercaria'.
  • The cercarias leave the body of the snail and swim in fresh water courses until they run into a human being. At that moment penetrate the skin of it.
  • Within the human being, the Schistosoma reaches the blood vessels and migrates to the liver. In the liver it matures to become an adult parasite.
  • The adults, within the human bloodstream, they are distributed and reproduced by laying eggs. They can restart the cycle when the human eliminates the eggs by feces or urine, or they can lodge in different organs producing clinical pictures.

The symptoms of schistosomiasis

The first sign of schistosomiasis, as a parasitic disease, is the injury that occurs at the site where the Schistosoma. In this area of ​​the skin usually appears a rash with change in coloration. The rash, in some cases, may appear up to a week after penetration.

What follows is known as Katayama syndrome; it's about the body's reaction to the eggs of parasitic adults that have been reproduced within the human being. Appears:

From here, the infection can become chronic, moving to the persistent forms of parasitosis. The most common chronic forms of the disease are:

  • Gastrointestinal: the eggs are installed in the wall of the intestine. There is alternate diarrhea with constipation and blood in the stool. In severe forms can block intestinal transit.
  • Hepatic: the eggs remain in the liver, causing inflammation and enlargement. They can cause obstruction of the hepatic blood vessels leading to portal hypertension.
  • Genitourinary: eggs are deposited in the urinary tract and blood appears in the urine. If it progresses, it is possible that it will reach a nephrotic syndrome, where the kidney removes proteins. The most lethal form is renal failure, when the organ can no longer fulfill its function.

It may interest you: Ascaridiasis: intestinal parasite

Treatment for schistosomiasis

Once the parasitic disease is diagnosed, the medication of choice for schistosomiasis it is an antiparasitic. The diagnosis is reached through a microscopic examination of the stool or urine.

In the microscope you can easily detect the eggs of the Schistosoma, which have a characteristic shape. In some cases, eggs are not visible until at least two months after skin penetration by the parasite.

The antiparasitic praziquantel is the medication of choice, scientific studies support its use. The World Health Organization distributes it free of charge.

Alternatives were proposed, with ivermectin for example, but so far no scientific trial has shown greater efficacy.

As the infection is associated with activities linked to freshwater courses, especially when the stay in them is greater than thirty minutes, preventive recommendations point there.

In areas where the disease is endemic, such as in Africa or parts of Brazil, collections should be made in watercourses, where people swim, bathe, practice fishing or wash clothes. It is also important to control the freshwater used for agriculture.