The Haemagglutination-Inhibition (HI) Test and a Study of its use in Experimental Avian Respiratory Mycoplasmosis

Abstract

A haemagglutination-inhibition (HI) test, using live antigen of a known British strain (A514) of Mycoplasma gallisepticum, is described. The advantages of this test over the slide agglutination or serum-plate tests are discussed. The value of the HI test was demonstrated in following the rise in HI antibody in the sera of chickens and turkeys infected with the homologous strain of Mycoplasma, using birds free from 3 important respiratory viruses and M. gallisepticum. The post-infection rise in HI antibody was shown to correlate with the appearance and persistence of clinical signs, although there was considerable individual variation. HI titres were low in the incubation period of the disease, but approximately 3 weeks after infection, titres generally rose to 320 or above (using 4 HA units) and persisted over a long period (19–34 weeks or longer) whether or not clinical signs remained or pathogenic or viable organisms could still be detected. The usefulness of the HI test for flock surveys is discussed and attention is drawn to the present uncertainty on the significance of low titres.