Assuming the pressure difference between the two sides of the barrier is much smaller than 
  
    
      
        
          P
          
            
              a
              v
              g
            
          
        
      
    
    {\displaystyle P_{\rm {avg}}}
  , the average absolute pressure in the system (i.e.
Host immune defenses are capable of producing superoxide, but these are counterattacked by antioxidant proteins produced by the parasite. Schistosomes have four superoxide dismutases, and levels of these proteins increase as the schistosome grows. Antioxidant pathways were first recognised as a chokepoints for schistosomes, and later extended to other trematodes and cestodes. Targeting of this pathway with different inhibitors of the central antioxidant enzyme thioredoxin glutathione reductase (TGR) results in reduced viability of worms. Decay accelerating factor (DAF) protein is present on the parasite tegument and protects host cells by blocking formation of MAC. In addition, schistosomes have six homologues of human CD59 which are strong inhibitors of MAC. Diagnosis
The presence of S. mansoni is detected by microscopic examination of parasite eggs in stool. A staining method called Kato-Katz technique is used for stool examination. It involves methylene blue-stained cellophane soaked in glycerine or glass slides. A bit costlier technique called formalin-ether concentration technique (FECT) is often used in combination with the direct faecal smear for higher accuracy. Serological and immunological tests are also available. Antibodies and antigens can be detected in the blood using ELISA to identify infection. Adult worm antigens can be detected by indirect haemagglutination assays (IHAs). Polymerase chain reaction (PCR) is also used for detecting the parasite DNA. Circulating cathodic antigen (CCA) in urine can be tested with lateral flow immune-chromatographic reagent strip and point-of-care (POC) tests.Egg detection and immunologic tests are not that sensitive. Polymerase chain reaction (PCR) based testing is accurate and rapid.