TRYPANOSOMA-CONGOLENSE - HIGH ERYTHROPOIETIC POTENTIAL IN INFECTED YEARLING CATTLE DURING THE ACUTE-PHASE OF THE ANEMIA

N'Dama (Bos taurus) cattle are known to tolerate trypanosome infection s, developing less severe anemia and lower parasitemia, compared to Bo ran (Bos indicus) cattle. Young calves were also reported to be more r esistant to trypanosomiasis than adult cattle. To explore the basis fu r this resistance, the erythropoietic response was evaluated in four n aive yearling N'Dama calves and four age-matched Boran calves which de veloped anemia over a 140-day primary infection with Trypanosoma congo lense clone IL 13E3. Similar levels of parasites were detected in the two breeds until 42 day, postinfection (dpi). During the same period, a rapid and greater colony-forming units-erythroid response in the bon e marrow of yearling Boran calves, compared with N'Dama calves, may ex plain the unusual absence of breed differences in mean packed cell vol umes (PCV). However, this early erythropoietic response was transient and did not result in any rise in PCV in the Boran calves. Moreover, d espite the persistent severe anemia, the erythroid response subsided f rom 70 dpi onward. In contrast, in the N'Dama calves, following the er ythroid response, the mean PCV was gradually compensated from 56 dpi o nward and reached 30% by 126 dpi. This period of PCV recovery coincide d with low and intermittent parasitemia and a return of the erythroid progenitor levels to near preinfection values. Elevated levels of eryt hroid progenitors in the N'Dama calves, occurring 1 week after trypano cidal treatment, returned the PCV to preinfection values. These result s suggest that the aye of the Bos indicus cattle has an important impa ct on the early bone marrow response in primary T. congolense infectio n and confirmed previous suggestions of a high erythropoietic potentia l in trypanosome-infected young calves. (C) 1996 Academic Press, Inc.