Prolongation of survival in experimental avian tuberculosis from repeated injections of iron dextran

Chickens (Gallus domesticus) were injected twice-weekly by the intramuscular route with large amounts of either iron (20-50 mg per bird), as iron dextran, or dextran (200 mg per bird). These injections began when the birds were 18 days old, and continued until they were 95 days old. Iron-treated birds, infected intravenously when they were 25 days old with 10(4.7), 10(6.3) or 10(7.8) colony-forming units (cfu) of Mycobacterium avium (serotype 1), lived significantly longer on average (about 12, 17 and 7 days respectively) than the corresponding infected, dextran-treated birds. The onset of obvious illness after infection depended on the dose of viable bacilli given but the experimental disease was acute with each dose. The disease was also about equally severe pathologically regardless of whether iron dextran or dextran had been given although anaemia in the dextran-treated birds was absent from those treated with iron, except when they were injected with 10(7.8) cfu. In the iron-treated birds infected with 10(4.7 )or 10 (6.3) cfu abnormal haemopoiesis led to haemoglobin concentrations and haematocrit levels markedly higher than those of the uninfected, iron-treated controls. Despite the very high haematological values in the former birds, hypochromia was also present. A cogent explanation of these peculiar haematological responses is not possible for the infection prevented iron-treated birds from making live-weight gains comparable with those of uninfected controls.