SCHISTOSOMIASIS

SCHISTOSOMIASIS

What is it?

An infection caused by a parasitic worm of the Trematoda class. It occurs in diverse parts of the world in an uncontrolled fashion (endemic). In these places, the number of people with this parasitosis remains rather steady.

The parasites of this class are five, and vary as causative agent of the infection according to the world region. In our country, schistosomiasis is caused by the Schistossoma mansoni. The chief host and reservoir of this parasite is man, the eggs being disseminated in the environment from man´s feces and urine.

It also has an intermediate host, namely, the snails and slugs, in which the eggs reach the larval stage. This is spread especially in untreated waters, such as lakes, and infects man through the skin, causing skin inflammation. While in man, the parasite develops and settles down in the veins of the intestine and liver, causing their obstruction, this being the cause of most symptoms of the disease, which can be chronic and lead to death.

How is it acquired?

The eggs eliminated by the urine and feces of contaminated individuals evolve to larvae in the water, these lodge and develop in snails. The snail releases the adult larva, which contaminates man on remaining in the water. In the human venous system, the parasites develop until reaching 1 to 2 cm in length, reproduce themselves and shed eggs. The parasite´s development in man takes about 6 weeks (incubation period), that´s when it takes on the adult and reproductive form already in its final habitat – the nervous system. The release of its eggs by man can last many years.

What does one experience?

At the moment of contamination a kind of allergic response may occur in the skin with itching and redness, triggered by the parasite´s penetration. This reaction occurs approximately 24 h after the contamination. After 4 to 8 weeks, there´s the appearance of fever, chills, headache, abdominal pains, lack of appetite, nausea, vomiting and dry cough.

While examining the parasitosis carrier, the doctor may find in this phase an enlarged liver and spleen as well as enlarged lymph nodes or lymphodenomegaly. These signs and symptoms usually disappear in a few weeks. Depending on the amount of worms, an individual can be a parasite carrier without any symptoms, or present over the months symptoms of the chronic form of the disease: fatigue, abdominal pain of the colic type with intermittent diarrhea or dysentery.

Other symptoms derive from the obstruction of veins in the spleen and liver with consequent enlargement of such organs and deviation of the blood flow that may cause from discomfort or pain in the left upper quadrant of the abdomen to vomiting with blood due to varices that are formed in the esophagus.

How is the diagnosis made?

To diagnose schistosomiasis the information about the suspect having been to an area where there are many disease cases (endemic area) is very important, in addition to the symptoms and signs described above (clinical condition). Feces and urine tests with eggs of the parasite or even small tissue samples from some organs (biopsy of the mucosa from the end of the intestine) are the ultimate exams. More lately, there are exams available that detect, in the blood, the presence of antibodies to the parasite that are useful in those cases of mild or symptom-free infection.

How is it treated?

The treatment of choice is with antiparasitic drugs, chemical substances that are toxic to the parasite. Currently there exist three groups of substances that eliminate the parasite, but the medication of choice is Praziquantel, which is taken in the form of pills, almost always during one day. That´s enough to eliminate the parasite, also getting rid of the dissemination of eggs into the environment. In those cases of chronic disease, the complications require specific treatment.

How to prevent it?

As it is a worldwide disease, endemic in several places (Arabic Peninsula, Africa, South America, and Caribbean), health public organizations (WHO – World Health Organization – and the Health Ministry) have specific programs for managing the disease. Basically, the strategies for managing the disease are based on:

	Identification and treatment of carriers.
	Basic sanitation (treated water and sewers), besides fighting the intermediate molluscan host.
	Health education.