Mechanism of Anaemia in Experimental Bacterial Endocarditis

Rabbits with Streptococcus viridans aortic valve endocarditis develop anaemia and reticulocytosis which increase with the duration of infection. Mean red cell counts decreased from 6.05 ± 0.29 × 106 per μl before infection to 4.10 ± 0.18 × 106 per μl after 11 to 20 days of endocarditis and reticulocytes increased from 1.16 ± 0.14 × 105 per μl to 4.91 ± 0.83 × 105 per μl after more than 20 days of endocarditis. The anaemia could not be explained by intravascular haemolysis. Anti-erythrocyte antibodies were not detected. Splenomegaly was a consistent finding and also increased with the duration of infection. Red cell half life (T½) was shortened to 4.7 ± 0.3 days in rabbits with endocarditis compared with normal T½ of 11.1 ± 0.5 days. The T½ of red cells from infected animals was prolonged when measured in noninfected rabbits and splenectomized animals had a mean red cell T½ of 9.25 days after three weeks of infection. These studies suggest that splenic enlargement associated with infection results in red cell sequestration, a mechanism not well recognized as contributing to the anaemia of endocarditis.