Vaccination against Parasitic Disease: Reactions in Vaccinated and Immune Hosts in Dictyocaulus viviparus Infection

Abstract

A comparison has been made between the course of infections of normal and irradiated larvae of D. viviparus in calves; this was done to investigate the mode of action of, and the host's reaction to, the vaccine against bovine parasitic bronchitis which is now being widely used in the field. Approximately one-quarter of the irradiated larvae were present in the lungs 11 days after infection, but this level fell steeply until only a few stunted sterile worms with a male/female ratio of approximately 1:10 were found. By the time that full patency had been reached in normal infections no worms could be found in those infected with irradiated larvae. The pathological basis of the mild and transient clinical signs sometimes seen after vaccination is described; the stages in the development of peribronchial lympho-reticular nodules are outlined, and the relationship of these to the clinical signs seen after heavy challenge in an immune animal is pointed out. The possible functions of these sites in antibody production and their influence on interpretation of serological tests are discussed. Vaccines have been developed against certain parasitic diseases by attenuating larvae with ionizing radiation so that they retain their immunizing potential but fail to mature to produce disease (Jarrett et al., 1960c; Jarrett et al., 1959a, b). One of these vaccines, against parasitic bronchitis, has been widely and successfully used in the field (Poynter et al., 1960). In an earlier paper (Jarrett et al., 1957b) we described the course of events caused by infection of calves with normal Dictyocaulus viviparus larvae; this information on the pathogenesis of the disease was obtained by killing experimentally infected calves at fairly close intervals. During the development of the vaccine, due to the nature of the experiments, a similar technique could not be applied and the changes produced could only be studied at a fairly late stage; therefore, only tentative hypotheses could be advanced as to the mode of action of, and the tissue reactions to, the vaccine. The experiments reported below were designed to obtain more details of these and of the reaction of the immune host