MT: Chapter 5 - SCHISTOSOMA

• Schistosomiasis is one of the most important parasitic diseases of humans and is a global public health problem in the developing world.
• The disease is caused by trematodes of the genus Schistosoma, which cause periportal fibrosis and liver cirrhosis owing to deposition of eggs in the small portal venules.
• Schistosoma mansoni and Schistosoma japonicum lead to liver disease.
• Schistosomiasis is known as bilharzia or bilharziosis in many countries, after German physician Theodor Bilharz, who first described the cause of urinary schistosomiasis in 1851.
• The first doctor who described the entire disease cycle was Pirajá da Silva in 1908.
• Five major species of Schistosoma affect humans: S. mansoni, S. haematobium, S. japonicum, S. intercalatum, and S. mekongi.
• Other Schistosoma species that occasionally infect humans include S. bovis, S. mattheei, and some avian schistosomes.
• Schistosomiasis occurs mainly in rural agricultural and periurban areas.
• MODE OF TRANSMISSION: The endemicity of schistosomiasis depends on the urban disposal of urine (S. haematobium) and feces (S. mansoni, S. japonicum, S. intercalatum, S. mekongi)
• MODE OF TRANSMISSION: the presence of suitable snail hosts
• MODE OF TRANSMISSION: human exposure to cercariae
• Adult worms release eggs in the venules of the mesentery, and the eggs enter the liver through the portal vein, where they become lodged in the terminal branches of the portal venules
• The lodged eggs cause a granulomatous inflammation, and the lesions are healed by periportal fibrosis
• In S. haematobium infection, the main organ system involved is the urinary tract.
• the habitat of S. mansoni, S. japonicum, S. mekongi, and S. intercalatum worms is the mesenteric blood vessels, the intestines are involved primarily
• Acute disease is not observed in individuals living in endemic areas of schistosomiasis because of the downmodulation of the immune response by antigens or idiotypes transferred from mother to child.
• DIAGNOSIS: Blood routine examination, Liver function test, Liver ultrasonic, CT, Antibodies detection, Examination of feces, Rectum tissue biopsy
• A definitive diagnosis of schistosomiasis can be made only by finding schistosome eggs in feces, urine, or a biopsy specimen, usually from the rectum.
• Chemotherapy is by far the major method for control and cure of schistosomiasis.
• Three compounds are in use metrifonate, oxamniquine, and praziquantel, and all three are included in the World Health Organization’s list of essential drugs.
• The standard recommended treatment consists of a single dose of praziquantel, 40 mg/kg, for S. mansoni, S. haematobium, and S. intercalatum infection.
• In S. japonicum infection, a total dose of 60 mg/kg is recommended, split into two or three doses in a single day.
• S. mekongi may require two treatments at 60 mg/kg body weight. 
• The intermediate hosts is snail.
• Eggs, causing the portal hypertension and liver fibrosis, is very important in pathobiology and diagnosis.
• Laboratory Diagnosis of Schistosomiasis: Parasitological, Serological, Molecular
• Parasitological: detection of the actual parasite (egg) in the specimen stool, tissues samples
• Serological - detection of antibodies against the parasite or antigens derived from the parasite
• Molecular - detection of schistosome DNA/RNA from the parasite
• Kato-katz Technique - gold standard, involves preparing a thin smear of fecal material on a glass slide
• Mino-FLOTAC - is a disk-shaped device made of polycarbonate amorphous thermoplastic. Produces highly reproducible result. Use when there is a large numbers of fecal samples that need to be rapidly examined
• Direct Microscopy - one of the standard diagnosis. The process involves emulsifying a small quantity of fresh stool in one drop of saline on a microscope glass slide. An eosin or iodine preparation is necessary to identify the cysts/oocysts of intestinal protozoa
• Schistosome DNA: cfDNA or Cell-free DNA from nucleus or mitochondria is detectable in bodily fluids and tissues of hosts
• Nucleic Acid Amplification: Conventional PCR, Nested PCR, Multiplex PCR, Real-Time PCR, Reverse Transcription PCR (RT-PCR)
• Droplet Digitial PCR (ddPCR): employ microfluidics and special surfactants to split PCR samples into tiny droplets. Each droplet contains a fraction of the sample and undergoes PCR amplification separately
• Loop Mediated Isothermal Amplification (LAMP) - Amplification efficiency is extremely high due to the use of 6 primers including a pair of loop primers
• Crude Antigen ELISA: Soluble Egg Antigen (SEA) ELISA, Soluble Worm Antigen Precipitate (SWAP) ELISA
• Recombinant antigen - specific proteins of the parasite produced through recombinant DNA technology. High specificity and high sensitivity
• Immunochromatographic Test (ICT) for schistosomiasis - allow the simultaneous detection of both IgG and IgM class anti-Schistosoma antibodies in human sera