Malignant Catarrhal Fever in East Africa: III. Neutralizing Antibody in Free-Living Wildebeest

Abstract

Serum samples from 181 East African wildebeest were inactivated at 56°C. for 30 min. and examined for neutralizing activity against the virus of malignant catarrhal fever (MCF or snotsiekte). All animals over the age of 7 months were serologically positive and the mean SN50 titre for those aged 3 years or more was 10-1·70. Half of 12 calves in the birth to 4 weeks age group possessed high-titre antibody, presumably acquired from the colostrum of their dam. The other 6 had no antibody, although their mother’s serum contained the usual quantities; the normal transmission of rinderpest antibodies, from dam to offspring, also did not occur in these instances. No explanation was found for the failure, which was probably limited to animals in this age group. The mean antibody titre fell continuously during the second to fourth months of life, but then increased steadily from a minimum of 10-1·19 to a peak of 10-2·29, in animals 13 to 18 months old. In the great majority of calves there was no period when passively-acquired antibody had reached very low levels and active “immunization” had yet to take place. Viraemia was detected in 12 of 43 animals aged from one to 20 weeks and 11 of them had circulating antibody at the time of sampling; yearlings and adults which were viraemic also had antibody in their serum. It was concluded that colostral antibody did not interfere significantly with active infection and the establishment of a permanent “immune” state. Although some wildebeest are probably infected congenitally with MCF virus, immunological tolerance does not develop to this agent.