The first stage, schistosomal dermatitis, may develop acutely within a day of cercarial penetration of the skin. Because this entity develops early after exposure, it usually will have subsided in patients before they are seen by physicians in the continental United States. Swimmer's itch, a similar reaction caused by exposure to animal schistosomes in fresh water and salt water, is seen in the United States. The schistosomes penetrate human skin and then die, causing no further infection. The second stage of disease, acute schistosomiasis, or Katayama fever, develops four to eight weeks after heavy, presumably primary, infection.
Patients have fever, cough, hepatosplenomegaly, malaise, myalgias, urticaria, and eosinophilia.
Chronic schistosomiasis, the third stage, is caused by the heavy deposition of eggs in the intestine or bladder and in the liver. In S. haematobium infection, the principal symptoms are terminal hematuria, dysuria, and frequent urination. Hydronephrosis and pyelonephritis may develop as a result of fibrosis and infection. In S. mansoni, S. mekongi, or S. japonicum infection, manifestations may include fever, malaise, abdominal pain, diarrhea, and hepatosplenomegaly. Presinusoidal hepatic trapping of S. mansoni, S. mekongi, or S. japonicum eggs and the consequent granulomatous reaction induce portal hypertension and collateral esophageal varices.