Defence Mechanisms in Calves against Respiratory Infections with Mycoplasmas

Abstract

Mycoplasma dispar, M. bovis and Ureaplasma sp are probably the most important mycoplasmas associated with respiratory disease in calves in the UK. Although there seems to be a basic similarity amongst different animal species in the way the lung reacts to mycoplasma infections, each of these three species presents a different problem when methods of immunisation are being considered. The ureaplasmas are serologically heterogeneous and absence of cross protection between serologically distinct strains has been observed in the bovine mammary gland. Calves become infected very early in life with M. dispar, perhaps the most common micro-organism in the calf respiratory tract, and in this situation the problem may be to remove an existing infection. M. bovis seems to occur more sporadically and to infect more transiently than M. dispar and is thus more amenable to investigation.

Experiments with inactivated M. bovis indicate that local administration of antigen is required in order to induce immunity in the Lung. Thus it may be inferred that local mechanisms are of prime importance. It is also worth noting that local immunity to M. dispar has been demonstrated in the bovine mammary gland.

Certain antibody mediated effects which are potential defence mechanisms have been demonstrated and these include prevention of mycoplasma attachment, direct killing or stasis of mycoplasma growth with or without complement and immune phagocytosis.