Influence of digestive microflora on parasite development and the pathogenic effect of Eimeria ovinoidalis in the axenic, gnotoxenic and conventional lamb.

The interaction between the digestive microflora and the development and pathogenic effect of Eimeria ovinoidalis was studied in lambs. All animals were reared and fed in the same conditions and were infected on the second day after birth with 150,000 sterilised oocysts. Two conventional lambs that had absorbed colostrum had haemorrhagic diarrhoea for several days and excreted 10(5) to 10(6) oocysts g-1 faeces. One lamb died. Similar results were recorded in two gnotoxenic lambs inoculated with 63 pure bacterial strains representative of the dominant digestive microflora and free of all pathogenic organisms. By contrast, no clinical signs and, in particular, no diarrhoea were observed in nine axenic lambs. OOcyst excretion in these only started on the 16th day, and the number of oocysts was between 10(2) and 10(3) g-1. The presence of digestive microflora is thus essential to the development of the parasite's pathogenic expression.