ESSENTIALS OF DIAGNOSIS
History of freshwater exposure in an endemic area.
Acute schistosomiasis: fever, headache, myalgias, cough, urticaria, diarrhea, and eosinophilia.
Intestinal schistosomiasis: abdominal pain, diarrhea, and hepatomegaly, then anorexia, weight loss, and portal hypertension.
Urinary schistosomiasis: hematuria and dysuria, then hydronephrosis and urinary infections.
Diagnosis: characteristic eggs in feces or urine; biopsy of rectal or bladder mucosa; positive serology.
Schistosomiasis, which affects more than 200 million persons worldwide, leads to severe consequences in 20 million persons and about 100,000 deaths annually (although estimates vary widely). The disease is caused by six species of trematode blood flukes. Five species cause intestinal schistosomiasis, with infection of mesenteric venules: Schistosoma mansoni, which is present in Africa, the Arabian Peninsula, South America, and the Caribbean; Schistosoma japonicum, which is endemic in China and Southeast Asia; Schistosoma mekongi, which is endemic near the Mekong River in Southeast Asia; and Schistosoma intercalatum and Schistosoma guineensis, which occur in parts of Africa. Schistosoma haematobium causes urinary schistosomiasis, with infection of venules of the urinary tract, and is endemic in Africa and the Middle East. Transmission of schistosomiasis is focal, with greatest prevalence in poor rural areas. Control efforts have diminished transmission in many areas, but high-level transmission remains common in sub-Saharan Africa and some other areas. Prevalence of infection and illness typically peaks at about 15–20 years of age.
Humans are infected with schistosomes after contact with freshwater containing cercariae released by infected snails (eFigure 37–20). Infection is initiated by penetration of skin or mucous membranes. After penetration, schistosomulae migrate to the portal circulation, where they rapidly mature. After about 6 weeks, adult worms mate and migrate to terminal mesenteric or bladder venules, where females deposit their eggs. Some eggs reach the lumen of the bowel or bladder and are passed with feces or urine, while others are retained in the bowel or bladder wall or transported in the circulation to other tissues, in particular the liver. Disease in endemic areas is primarily due to a host response to eggs, with granuloma formation and inflammation, eventually leading to fibrosis. Chronic infection can result in scarring of mesenteric or vesicular blood vessels, leading to portal hypertension and alterations in the urinary tract. In previously uninfected individuals, such as travelers with freshwater contact in endemic regions, acute schistosomiasis may occur, with a febrile illness 2–8 weeks after infection.
Life cycle of Schistosoma. Eggs are eliminated with feces or urine
. Under optimal conditions the eggs hatch and release miracidia
, which swim and penetrate specific snail intermediate hosts
. The stages in the snail include two generations of sporocysts
and the production of cercariae
. Upon release from the snail, the infective cercariae swim, penetrate the skin of the human host
, and shed their forked tail, becoming schistosomulae
. The schistosomulae migrate ...