It was proposed that the large amount of egg antigens released by S. japonicum interact with antibodies leading to the formation of high volume of immune complexes, which cause enlargement of the lymph tissues. This sequence of events can lead to clinical manifestation of fever, enlargement of spleen and liver due to fibrosis, portal hypertension, and death.Chronic Infection
The clinical manifestations of chronic infection is mainly caused by immune reaction to the eggs entrapment within tissues resulting in granuloma formation and chronic inflammation. Adult worms live together in pairs (one male and female), sexually reproduce, and lay eggs in the veins around the intestines and bladder depending on the species, and these eggs can rupture the wall of the veins to escape to the surrounding tissues. The eggs make their way through the tissues to the intestinal or bladder lumen with help of proteolytic enzymes, however, a large amount of eggs are unable to finish their journey and remained stuck within the tissues where they can elicit an immune response. The miracidia in these eggs can then release antigens that stimulate an inflammatory immune response. The miracidia within the eggs live for around 6–8 weeks before they die and stop releasing the antigens. The granulomatous response is a cellular immune response mediated by CD4+ T cells, neutrophils, eosinophils, lymphocytes, macrophages, and monocytes, and this chronic inflammatory response elicited by the eggs can cause fibrosis, tissue destruction, and granuloma nodules that disrupt the functions of the organs involved.
The disease is most commonly found in Africa, Asia, and South America. Around 700 million people, in more than 70 countries, live in areas where the disease is common. In tropical countries, schistosomiasis is second only to malaria among parasitic diseases with the greatest economic impact. Schistosomiasis is listed as a neglected tropical disease. Signs and symptoms
Many individuals do not experience symptoms. If symptoms do appear, they usually take 4–6 weeks from the time of infection. The first symptom of the disease may be a general feeling of illness. Within 12 hours of infection, an individual may complain of a tingling sensation or light rash, commonly referred to as "swimmers itch", due to irritation at the point of entrance. The rash that may develop can mimic scabies and other types of rashes. Other symptoms can occur 2–10 weeks later and can include fever, aching, a cough, diarrhea, chills, or gland enlargement. These symptoms can also be related to avian schistosomiasis, which does not cause any further symptoms in humans.The manifestations of schistosomal infection vary over time as the cercariae, and later adult worms and their eggs, migrate through the body. If eggs migrate to the brain or spinal cord, seizures, paralysis, or spinal-cord inflammation are possible. Acute Infection
Manifestation of acute infection from schistosoma include cercarial dermatitis (hours to days) and acute schistosomiasis (2–8 weeks). Cercarial dermatitis
The first potential reaction is an itchy, maculopapular rash that results from cercariae penetrating the skin within the first 12 hours to days of cercarial skin penetration.