Schistosomiasis – Life cycle, Symptoms, Treatment, Prevention.

What is schistosomiasis?

Schistosomiasis also termed snail fever or bilharzia is a disease caused by parasitic flatworms called schistosomes. Infection with Schistosoma mansoni, S. haematobium, and S. japonicum causes illness in humans; less commonly, S. mekongi and S. intercalatum can cause disease. In this disease, the urinary tract or the intestines may be infected. Symptoms are abdominal pain, diarrhea, bloody stool, or blood in the urine.

• More than 200 million people are affected by this disease worldwide.
• Those peoples are affected by this parasite for a long time they can experience the following injuries; liver damage, kidney failure, infertility, or bladder cancer.
• In children, it can result in poor growth and learning difficulty.
• Schistosomiasis can transmit when your skin comes in contact with contaminated freshwater which contains snail that carry schistosomes are living.
• This parasite can penetrate the skin of the individual who is wading, swimming, bathing, or washing in contaminated water.
• In contaminated water, the eggs of Schistosoma develop and multiply within the snails. After development, they leave the snail and enters the water where it can last for about 48 hours. 
• After entering the blood vessels it started to mature into adult worms, and then form eggs. These eggs then migrate to the bladder or intestine and are passed within the urine or stool.
• The symptoms are started to develop within the 1-2 months of infection.

Schistosomiasis Epidemiology

• This disease mainly found in tropical countries such as Africa, the Caribbean, eastern South America, Southeast Asia, and the Middle East.
• Schistosoma mansoni found in Africa, South America (Including Brazil, Suriname, and Venezuela), Caribbean (Dominican Republic, Guadeloupe, Martinique, and Saint Lucia).
• S. haematobium, found in Africa, Middle East, and Corsica.
• S. japonicum, found in Indonesia, China and Southeast Asia.
• S. mekongi found in Cambodia and Laos.
• S. intercalatum found in different parts of Central and West Africa.

Schistosomiasis Causal Agents

• In human Schistosomiasis is caused by three species of Schistosoma such as Schistosoma haematobium, S. japonicum, and S. mansoni. 
• Some cattle origin hybrid schistosomes has been reported such as S. haematobium, x S. bovis, x S. curassoni, x S. mattheei.
• Three additional species, more localized geographically, are S. mekongi, S. intercalatum, and S. guineensis.

Morphology of schistosomiasis worm

• An adult Schistosoma contains all the fundamental features of the digenea.
• They contain a basic bilateral symmetry.
• It has an oral and ventral sucker.
• A body covering of a syncytial tegument present.
• It contain a blind-ending digestive system which is made up of mouth, esophagus and bifurcated caeca.
• The space within the tegument and alimentary canal loaded with a loose arrangement of mesoderm cells, and an excretory or osmoregulatory system based on flame cells. 
• An adult worm can be 10–20 mm (0.39–0.79 in) long.
• They utilize the globins from their hosts’ hemoglobin for their circulatory system.

Schistosomiasis symptoms

The symptoms are mainly developed within 1-2 months of infection. Some common symptoms are rash or itchy skin. Fever, chills, cough, and muscle aches.

• Intestinal schistosomiasis: In this type of infection the eggs are stuck in the intestinal wall and results in granulomatous reaction. This cen results in portal hypertension, splenomegaly, the buildup of fluid in the abdomen, and potentially life-threatening dilations or swollen areas in the esophagus or gastrointestinal tract that can tear and bleed profusely (esophageal varices).
• Dermatitis: In this type the cercariae penetrate into the skin and results in itchy, papular rash.
• Acute schistosomiasis or Katayama fever: The symptoms include Dry cough, Fever, Fatigue, Muscle aches, Malaise, Abdominal pain, Enlargement of both the liver and the spleen. This symptoms are developed when the schistosomulae migrates from lungs to the liver.
• Chronic disease: The common symptoms are abdominal pain with intermittent diarrhea and hepatosplenomegaly.
• Genitourinary disease:  Genitourinary disease occurs when S. haematobium worms migrate to the bladder and ureters. This can lead to hydronephrosis, and kidney failure.
• Gastrointestinal disease: Gastrointestinal disease occurs when S. mansoni and S. japonicum worms migrate to the  gastrointestinal tract and liver. This may lead to the blood in the stool, and diarrhea (especially in children).

Schistosomiasis life cycle

• The eggs of the schistosome are discharged into water from the urine or feces of an infected individual.
• In presence of favorable conditions the eggs are hatch and started to release the free-swimming larval stage which is known as miracidia.
• This miracidia started to swim and enter into specific snail intermediate hosts such as Biomphalaria.
• Within the snail, the miracidia undergo different stages of development; 2 generations of sporocysts and the production of cercariae. After formation, the cercariae released into freshwater and started to swim around looking for a human host.
• Once this infective cercariae comes in close contact with a human host they penetrate the skin of the human host, and dropped their forked tail, becoming schistosomulae.
• After the formation of schistosomulae, it enters into the bloodstream and started to migrate to the person’s liver where they mature into adult worms.
• After that, it pairs with the mate of the opposite sex and migrates with blood vessels against the blood stream to the blood vessels near the bowel, rectum or bladder.
• After reaching the blood vessels near the bowel, rectum or bladder they started to lay their eggs. About half of these eggs will be discharged in the human’s urine and faeces but some will stay in the body and circulate back to the liver where they cause inflammation.

Schistosoma mansoni and Schistosoma japonicum generally migrate to the bowel or rectum and release eggs in the faeces. Schistosoma haematobium tends to migrate to the bladder and release eggs in the urine. 

Schistosomiasis diagnosis

There are different tests that can be performed to detect Schistosomiasis;

• By Studying the urine and feces samples of infected people under a microscope to detect the presence of live schistosome eggs.
• The blood test also helps to detect the presence of anemia or if their liver or kidney function has been affected. It may be signs of schistosomiasis.
• Perform X-ray test to detect if the lungs are damaged by fibrosis and inflammation. This may occur if the parasite larvae move to the lungs or eggs getting trapped in lung tissue.
• Perform ultrasound scan to detect the damage to the liver or heart.
• A colonoscopy (looking at the bowel with a camera) or cystoscopy (looking at the bladder with a camera) can be performed to detect if eggs or inflammation are visible in the bladder or bowel.
• Perform Polymerase chain reaction (PCR) based testing.
• By performing FAST-ELISA test.

Schistosomiasis Treatment

• There are two drugs that can be used for the treatment of Schistosomiasis such as praziquantel and oxamniquine. The drug praziquantel is taken annually by mouth.

Schistosomiasis Prevention and Controll

• If you are in a country where is schistosomiasis common then avoid swimming or wading in freshwater. You can swim in the ocean and in a chlorinated pool.
• Drink safe water, if your mouth or lips come in contact with water containing the parasites, you could become infected. 
• Before bath with water boil the water for 1minute to kill any cercariae present within it.
• We can Control Schistosomiasis by Killing the snails that are needed to maintain the parasite’s life cycle.
• Use chemicals to eliminate snails in freshwater.

Reference

• https://www.yourgenome.org/facts/what-is-schistosomiasis
• https://www.cdc.gov/parasites/schistosomiasis/prevent.html
• https://commons.wikimedia.org/wiki/File:Schistosoma_life_cycle.svg
• https://en.wikipedia.org/wiki/Schistosoma
• https://www.who.int/news-room/fact-sheets/detail/schistosomiasis
• https://en.wikipedia.org/wiki/Schistosomiasis