Susceptibility to periportal (Symmers) fibrosis in human schistosoma mansoni infections: evidence that intensity and duration of infection, gender, and inherited factors are critical in disease progression.

Lethal disease in Schistosoma mansoni infections is mostly due to portal hypertension caused by hepatic periportal fibrosis. To evaluate the factors that may determine severe disease, livers and spleens were examined by ultrasound in a Sudanese population living in a village where S. mansoni is endemic. Early (FI), moderate (FII), or advanced (FIII) fibrosis was observed in 58%, 9%, and 3% of the population, respectively. Although FI affected 50%-70% of the children and adolescents, FII prevalence was low in subjects </=20 years old but increased sharply (45%-58%) in men 21-30 years old and was associated with the highest infections. Portal and splenic vein diameters were increased in one-third of persons with FII and in almost all with FIII disease. Severe disease, FII or FIII with portal hypertension, affected 6% of the population, was associated with splenomegaly, occurred mostly in adult men, and was clustered in a few pedigrees. These observations suggest that infection intensity and duration, gender-related factors, and inherited factors are important in fibrosis development.