The Production and Nature of Anemia in Schistosoma Japonicum Infections

View More View Less
  • The University of Chicago, Department of Microbiology, Chicago, Illinois 60637

This report describes the development of anemia in New Zealand white rabbits that were exposed to varying numbers of Schistosoma japonicum cercariae of the Philippine-Leyte strain. Hemoglobin, hematocrit, and serum iron levels were determined periodically in one group of 25 rabbits during an 8-month infection. Significant anemia appeared as early as 6 weeks in some animals exposed to 250 cercariae. By the 8th week seven, and by the 11th week 15, of the 19 infected animals had significantly decreased hemoglobin values, some falling as low as 9.8 g/100 cc (normal, 14 g/100 cc). After the 11th week the animals began to recover and the hemoglobin levels increased until, by the 31st week, the infected animals exhibited the same hemoglobin values as those found in the control animals. An unexpected finding was that red cell morphology remained normal and the mean corpuscular hemoglobin concentration of all the infected anemic rabbits was in the normal range of 35 ± 2 g/100 cc. All animals were negative for occult blood in their stools, and no change in serum iron levels could be detected during the 8-month course of infection. Reticulocyte counts were also studied in control animals and in animals with infections of 8 weeks' duration. There was no significant difference in the number of reticulocytes in normal and infected rabbits. In another group of seven rabbits, the osmotic fragility of erythrocytes was colorimetrically determined prior to infection and at the 8th week post-infection, at which time red cells were altered, becoming fragile and lysing at saline concentrations which had less effect on normal cells or cells of these animals prior to infection (P ⩽ 0.001 at 0.51% NaCl). Immunofluorescence and Coombs' tests failed to detect immunoglobulin or complement on the surface of red cells from anemic animals. These findings are in contrast to the microcytic, hypochromic anemia described by some investigators in schistosome experimental anemia. We believe that the normochromic, normocytic anemia of acute S. japonicum infection in rabbits is properly characterized as an “anemia of chronic disease,” possibly related to a failure of the bone marrow to respond rather than an autoimmune hemolytic process.