Calf paratyphoid II. Artificial immunization

Abstract

1. Immunization experiments performed on mice with various vaccines prepared from S. dublin and other Salmonella species showed that a formalinized aluminium hydroxide precipitated vaccine gave the best protection against virulent cultures of S. dublin. The immunity produced gave only a partial or incomplete protection, yet when this vaccine was used for the routine immunization of calves on badly infected premises in different parts of the country a marked reduction in deaths from paratyphoid was effected. In a few outbreaks where the routine vaccine failed to prevent losses a vaccine made from a local strain of S. dublin invariably gave complete protection against natural exposure. But unless the vaccine was employed regularly and all the calves born on the farm were inoculated soon after birth, losses continued to occur. In a few cases where the use of the vaccine was discontinued fresh outbreaks of paratyphoid usually occurred. In spite of the excellent results obtained with vaccine in the field, it is admitted that the immunity produced is of a low grade and that it cannot be relied upon entirely to prevent symptoms or even death from paratyphoid. When the immunity in calves was challenged with fresh milk-cultures given by the mouth the majority of them reacted and developed symptoms of paratyphoid, although much less severely than the control calves. 2. The immunization of calves with routine S. dublin vaccine resulted in the production of "H" agglutinins almost exclusively. Whereas the "H" agglutinin titre of the serum of the vaccinated animals rose from 1:25 or less to 1:3,200 or more after immunization, there was hardly any perceptible "0" agglutinogenic response in the majority of these animals, and the "0" titre remained extremely low in all of them. When the immunity was boosted by means of a third injection of vaccine 30 days after the second a very marked rise in the "H" agglutinin titre resulted, but there was only a slight "0" agglutinogenic response in some of the animals and hardly any "0" agglutinins could be detected in the others. 3. An easy method of artificially infecting calves with fresh milk cultures of S. dublin is described. By the utilization of this method the pathogenesis and the course of the disease could be observed and treatment instituted. It was found that when calves manifesting typical symptoms of paratyphoid were treated with large doses of phthalylsulphathiazole by the mouth recovery supervened, whereas untreated calves, infected in the same way and left as controls, died. Phthalylsulphathiazole can, therefore, be regarded as an effective therapeutic agent for calf paratyphoid, and its employment can be recommended for the treatment of this disease. It was observed subsequently, however, that fresh milk-cultures of the same strain of S. dublin, grown under apparently identical conditions, might not always be equally pathogenic for calves. Sometimes an acute and fatal disease was set up, whereas, at other times, very much milder symptoms were produced. Although the cause of this variation is not known it is believed that some factor in the media is responsible.