Effect of cyclophosphamide on infections produced by Escherichia coli of high and low virulence in chickens.

The effect of cyclophosphamide (Cy) on infections caused by Escherichia coli strains of high (Expt 1) and low (Expt 2) virulence was examined in 4-week-old specified-pathogen-free chickens. In Expt 1 the mortalities of Cy-treated and non-treated chickens given 5 x 10(7) cfu of a strain of E. coli of high virulence were both 100%. In the groups given 5 x 10(5) cfu, the mortality of Cy-treated chickens was 90% and that of non-treated chickens was 10%. In Expt 2 the groups given 1 x 10(9) cfu of an E. coli strain of low virulence showed a mortality of 30% when treated with Cy and 0% when non-treated. The chickens given 5 x 10(7) or 5 x 10(5) cfu showed no mortality, clinical signs or histological lesions. Cy-treated chickens showed severe hypoplasia of granulopoiesis in the bone marrow. Haematological examination of Cy-treated chickens revealed leukopenia, especially lymphopenia, and thrombocytopenia. This study suggests that Cy treatment may enhance infection caused by E. coli strain of high virulence and manifest signs of infection caused by E. coli strain of low virulence in the chickens.