HETEROLOGOUS IMMUNITY STUDIES IN CALVES IN IRAN

Abstract

In a series of heterologous immunity studies S. haematobium, S. bovis and O. turkestanicum in calves, a large number of S. haematobium cercariae (21,000 cercariae) were used repeatedly as the immunization agent. At autopsy, 22 weeks after initial exposure, immature S. haematobium was detected. Thirteen weeks after initial exposure a group of calves was challenged with S. bovis and another group with O. turkestanicum cercariae. The resu1t of this investigation showed that the calves had developed limited S. haematobium infections. The number of worms recovered by perfusion varied from 250 to 640 (378±99) and the mean percentage of worms recovered was 1.8%. Most of the worms were found in the portal veins, but in one calf some larger worms were detected in the lower mesenteric veins of the large intestine with some reformatted eggs in the caecum substances. No worms or eggs were found in the vesicle plexus or bladder tissue. The immune response which developed in calves with S. haematobium infection was considerable. The protective effects of immunity were measured by detecting the effects on the expected worm burden and tissue egg counts of the challenge infection compared with the control group. It was found that the mean reduction of worm recovery and tissue egg counts was 42.3% and 62.2% in group S. haematobium versus S. bovis, and 31.4% and 81.0% in group S. haematobium versus O. turkestanicum infection. This suggests that the immune phenomen will occur in endemic areas like Khuzestan, Iran, and that under natural conditions this might reduce the severity of the disease in livestock.