Patho-physiology of ovine schistosomiasis: II. Some observations on the sequential changes in blood volume and water and electrolyte metabolism following a single experimental infection of Schistosoma mattheei

Abstract

Using sheep albumin trace-labelled with 125I and simultaneously erythrocytes labelled with 51Cr, measurements were made of the total blood volume, plasma volume and circulating red cell mass of 12 worm-free sheep. Four days later 8 of these animals were each exposed to 10 000 cercariae of Schistosoma mattheei and the measurements repeated at intervals of 28 days over a period of 16 weeks. Although mild anaemia as demonstrated by a reduced PCV and circulating red cell mass was recorded for some infected sheep as early as 4 weeks after infection, by far the most dramatic alterations in each of the parameters measured occurred over the following 8 weeks. In all cases these took the form of a pronounced expansion in plasma and blood volumes and a lowering of the circulating red cell volume of infected relative to control animals. Concurrent observations on water and sodium metabolism suggested that increased retention of these substances was to some extent responsible for the initial rise in plasma volume. Marked terminal dehydration manifest by a negative water balance was also shown to be a feature of the disease in 3 of the parasitized animals. The significance of these findings in relation to some clinical features of the disease is discussed.