Irradiated vaccines for helminth control in livestock.

For nearly 40 years, irradiated larval vaccines have been available for the control of parasitic bronchitis in cattle and sheep caused by Dictyocaulus spp. Despite research on a number of other host/parasite systems, no other vaccines have been commercially successful. Vaccination could provide a useful addition to other control methods in an integrated parasite management system where the criteria for vaccine success may not be complete control and sterile immunity, but a sufficient reduction in worm burden to decrease overall reinfection levels at the flock/herd level and, hence, prevent clinical disease and subclinical effects including production loss. Indeed, vaccination against Dictyocaulus spp. relies on continued natural infection to maintain levels of immunity. However, the difficulties of producing live larval vaccines are often cited as a reason why this line of research should not be pursued. This paper discusses some of the difficulties in vaccine production and offers some solutions and recommendations for those wishing to develop and register irradiated larval vaccines for other helminth diseases.