Parasitism and Anemia

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Abstract
The main parasites causing blood loss in man and leading to direct iron-deficiency anemia are the common worm infections. These include hookworm infection (Necator americanus and Ancylostoma duodenale); whipworm infection (Trichuris trichiura); and schistosomiasis (Schistosoma mansoni, S. haematobium, and S. japonicum). Radioisotope studies with chromium 51-tagged red blood cells have shown that patients with heavy hookworm infection can lose up to 250 ml, or a quarter of a liter of blood, daily, and up to 29 mg of iron in the gastrointestinal tract, thus leading to direct iron-deficiency anemia. Workers from South America and East Africa have shown that each Necator americanus worm can cause a daily blood loss of 0.03 ml, which means that patients infected with approximately 1,000 worms can lose up to 30 ml of blood daily. More recent work from London and Egypt has shown that the Old World hookworm, Ancylostoma duodenale, can cause a daily blood loss of 0.2 ml, approximately 10 times more than the American hookworm, Necator americanus. Layrisse and his colleagues (24–27), using 51Cr-tagged red cells, measured the blood loss caused by T. trichiura in heavily infected children and showed that the daily blood loss can reach up to 8.6 ml. These workers concluded that infection of over 800 parasites can lead to anemia. Using 51Cr-isotopes, Farid (10–15) and his colleagues measured the blood loss in patients with chronic Schistosoma mansoni polyp formation of the colon and showed that these patients can lose up to 12.5 ml of blood daily. Using 59Fe-isotopes, these workers also measured the blood loss in the urine in patients infected with Schistosoma haematobium and demonstrated that these patients can lose up to 120 ml of blood daily. Blood loss in schistosomiasis, however, is intermittent and not constant and though it may be severe for a few days it usually ceases for prolonged periods. It has been shown by 51Cr and body surface counting of radioactivity that the large spleen in chronic schistosomiasis, leishmaniasis, and malaria, can destroy the red blood cells and lead to anemia secondary to hypersplenism. Recent work has also shown that a malabsorption syndrome leading to poor absorption of essential nutrients may occur in patients heavily infected with hookworms, Strongyloides stecoralis and Giardia lamblia. Destruction of red blood cells leading to a hemolytic anemia has been shown to occur in malaria, and vitamin B12 megaloblastic anemia has been demonstrated to occur in patients infected with the intestinal fish worm, Diphyllobothrium latum.