The significance of infection dose,body weight and age of the host on the pathogenic effect of Eimeria acervulina in the fowl

Summary The pathogenic effect of E. acervulina was enhanced by increasing the initial infection doses. However the relation between infection dose and the pathogenic effect was disproportionate; generally it was enhanced less than the infection dose was increased.It appeared that the moderate doses caused the greatest oocyst productions and are therefore of great epidemiological importance. However also the smaller infection doses caused oocyst productions at comparable levels.The oocyst output did not coincide with the increasing pathogenic effect and there was no correlation between individual body weight, weight loss and oocyst output within a group of chickens of the same age infected with the same number of oocysts. It is concluded that the oocyst output is not a reliable guide to the severity of the individual infection.The significance of the moderate doses was also evident from a marked reduction of the intestinal pH and the serum protein concentration compared with only a slightly stronger reduction of these values in birds infected with higher doses.The most important factor in the pathogenic effect appeared to be the age of the host. The reaction was progressively more severe in birds of increasing age infected with an uniform dose.