Effects of the dose of Ehrlichia phagocytophila on the severity of experimental infections in lambs

Twenty-one lambs were used to investigate whether their response to an infe ction with Ehrlichia phagocytophila was dose-dependent. Four groups of four lambs were infected intravenously with a dilution in physiological saline of E phagocytophila-infected sheep blood containing either 1-3 x 10(5) infe cted cells, or approximately 43 infected cells, 4-3 infected cells, or 1-3 infected cells (mean values) and four lambs were left uninfected. The incub ation period was significantly shorter in the lambs infected with the highe st dose of E phagocytophila. However, the clinical and haematological chang es observed, and the weekly weight gains of the lambs were independent of t he dose of E phagocytophila. As little as one E phagocytophila infected cel l may be enough to transmit the infection.