Facioliasis: is the anemia caused by hematophagia?

In fascioliasis, anemia is a well-recognized symptom but its etiology is controversial. There is disagreement on whether hematophagia occurs, and if it does, whether it is sufficient to produce the anemic symptoms observed. Another opinion is that a toxic substance emanating from the fluke causes the anemia. In the present study the anemia was investigated in rats. Hematological parameters measured over the course of infection showed significant decreases in erythrocyte counts and hemoglobin after the flukes entered the bile duct. Significant increases were observed in reticulocyte counts and mean corpuscular volume upon entry of flukes into the bile duct. Urobilinogen levels increased in early stages of infection but returned to near normal levels after the worms reached the bile duct. To determine whether Fasciola hepatica could produce an anemia in rats when hematophagia was prevented, uninfected rats were peritoneally implanted with worms in fine-mesh sacks which prevented worms from feeding on blood. Hematological parameters indicated that the anemia produced in rats with implanted worms was very similar to that produced by mature, per os infections. This study indicates that the anemia is caused by a substance released by the worms and supports previous work suggesting that proline released from the worms may be inducing the anemia.