Acute schistosomiasis (Katayama fever): steroids before praziquantel
Acute schistosomiasis (Katayama fever) is an immune over-reaction to a parasitic worm infection, starting weeks after freshwater exposure in an endemic area, as the worms begin laying eggs.
Remember
Severe symptoms of acute schistosomiasis come from the immune system, so a short steroid course comes first, and praziquantel, the drug that kills adult worms, follows once symptoms have settled.
Acute schistosomiasis, also called Katayama fever, is an immune reaction to a parasitic worm infection after exposure to freshwater in an endemic area, such as sub-Saharan Africa. Adult worms do not cause it. The immune system over-reacts to the parasite, in a hypersensitivity reaction that begins 14 to 84 days after heavy exposure, as the worms begin laying eggs.
The picture is flu-like. It includes fever, chills, cough, nausea and abdominal pain, along with myalgia (muscle pain), an urticarial rash (itchy raised weals) and a raised eosinophil count. The illness resembles serum sickness, an immune reaction to foreign proteins. It is commoner in visitors than in local residents, and more severe.
Chronic disease is different. It causes damage over months to years where the eggs lodge, for example bleeding from the bladder wall, anaemia or neurological problems. Blood in the urine, anaemia and seizures are chronic complications, but not the acute illness.
The symptoms come from inflammation, so for severe symptoms a short course of oral glucocorticoids (steroids, which damp down inflammation) is used, such as prednisone. Praziquantel, the drug that kills adult worms, does not act on developing worms (schistosomula) or on eggs, and both are present early in infection. It is therefore given once symptoms have subsided and repeated 4 to 6 weeks later, after the parasites have reached adulthood. Treatment is based on limited data.
Key facts
- Cause
- an immune over-reaction to the parasite, not damage by adult worms.
- Timing
- illness starts 14 to 84 days after heavy freshwater exposure in an endemic area, as egg laying begins.
- Features
- fever, chills, cough, nausea, abdominal pain, myalgia (muscle pain), an urticarial rash (itchy raised weals) and a raised eosinophil count.
- First treatment
- a short course of oral glucocorticoids (steroids) for severe symptoms, and low-dose prednisone for 5 days is usually effective in adults.
- Praziquantel
- it kills adult worms but not developing worms or eggs, so it is given once symptoms have subsided and repeated 4 to 6 weeks later.
Exam traps
- Giving praziquantel straight away in acute schistosomiasis does not settle the reaction, because it kills adult worms but not the developing worms and eggs present early in infection.
- Antibiotics do not treat the fever and rash of acute schistosomiasis, because these come from the parasite and the immune reaction to it, not from bacteria.
- Oral antihistamines would calm an itchy rash, but they do not control the hypersensitivity reaction of acute schistosomiasis, which is treated with a short course of steroids when symptoms are severe.
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