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Question: What is schistosomiasis? How is it connected to pulmonary hypertension?
Schistosomiasis is caused by infection with the parasite schistosoma, which is a flatworm or fluke. Schistosomiasis is the third most common parasitic disease in the world after malaria and amoebiasis. It is endemic in more than 70 countries, affecting about 200 million people worldwide, of whom 80 percent are in sub-Saharan Africa. There are also pockets of infection in northeastern Brazil, near the Yangtze River in China, and in south East Asia and the Middle East.
After infection, the schistosoma worm usually resides in humans and animals in targeted organs: the liver and the gastrointestinal tract for schistosoma mansoni or schistosoma japonicum, and the urinary tract for schistosoma haematobium. The worms may reside there for 30 years or more, and both male and female worms excrete eggs. The adult worms do not cause disease, but the eggs they release are highly antigenic (toxic) and the cause of disease. The eggs will produce pathological changes, mainly complex inflammatory lesions called granuloma which lead to scarring.
Some of the eggs may escape from where the adult worms are and migrate to other tissues, particularly to the lung. The inflammation caused by the eggs causes changes in the blood vessels that leads to pulmonary arterial hypertension (PAH). Patients with schistosomiasis-associated PAH may have no symptoms. Others with more extensive changes have symptoms that are the same as other forms of PAH.
The diagnosis of schistosomiasisassociated PAH is similar to other types of PAH. Studies are done to rule out other causes of the disease, and for persons from areas where infection is common, specific tests for schistosomiasis are needed.
It is important to treat active schistosomiasis infection if present. This may help to decrease the inflammation and possibly prevent further worsening of the PH. For schistosomiasis-associated PAH, treatment is similar to other forms of PAH. However, there are no clinical trials to confirm the effectiveness of treatment in these patients. Our current evidence is mainly observational from various centers all over the world. Reported treatment has included PDE5 inhibitors, endothelial receptor antagonists, or a combination of both therapies with improvement in six-minute walk distance.
The prognosis of schistosomiasisassociated PAH is not well understood and is likely very similar to that of idiopathic PAH.
Answer provided by Ghazwan Butrous, MB, ChB, PhD, FESC, FRSA, Professor of Cardiopulmonary Sciences, University of Kent, Caterbury, UK; Hon. Professor of Medicine, Imperial College, London; Managing Director, Pulmonary Vascular Research Institute
This article was first published in Pathlight Spring 2014.
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