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Title: Infectious diarrhoea in young animals
Author: Snodgrass, David Randall
ISNI:       0000 0001 3469 7166
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1989
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The aetiology of infectious diarrhoea in young animals, particularly calves, was investigated, using techniques appropriate to the detection of viral, bacterial and protozoal pathogens. Rotavirus was established as of prime significance, and the classic 'white scour' syndrome in calves was usually caused by rotavirus with, on occasion, the simultaneous involvement of coronavirus or Cryptosporidium. Enterotoxigenic Escherichia coli (ETEC) infections were much less common, with under 6% of E. coli isolates possessing K99 fimbriae. Outbreaks of cryptosporidiosis were described for the first time from the U.K. The technique for the detection of the characteristic migration pattern of rotaviral double-stranded RNA segments in silver-stained polyacrylamide gels has proved of especial value in diagnostic and epidemiological investigations. Infection of gnotobiotic lambs with lamb rotavirus produced dullness, inappetance, and diarrhoea, and provided a most useful model for pathogenesis studies. A rapid and extensive infection and defoliation of small intestinal epithelium leading to partial villus atrophy was followed within 2-3 days by a return to apparent morphologic normality. However, the underlying continuing dysfunction of an increased cell turnover rate was demonstrated by metaphase accumulation. Animals with acute enteritis were tolerant to levels of lactose normally found in milk, but their ability to digest and absorb increased oral doses of lactose was impaired. In calves, a concurrent rotavirus infection facilitated intestinal ETEC colonisation beyond the normal age of resistance. Studies on passive immunisation in young lambs demonstrated that protection against rotavirus infection by antibody in the gut lumen was more effective than that provided by circulating antibody. The potential value of this technique was shown in experiments in lambs using rotavirus and immunoglobulin of human origin. Experimental adjuvanted vaccines of inactivated rotavirus given to ewes and cows in pregnancy significantly increased the titre of antibody of IgGl isotype in colostrum and milk. Neonates ingesting these secretions were protected to various degrees against rotavirus infection and diarrhoea. The incorporation of commercially-produced K99 fimbriae from ETEC allowed the successful experimental testing and subsequent field trialling of a vaccine which substantially reduced rotavirus and ETEC diarrhoea problems in the progeny of vaccinated cows. Sero¬ logical variation in rotavirus strains was of potential significance to successful vaccination: atypical rotaviruses with no serological relationship to 'conventional' rotaviruses were identified and characterised serologically and genomically, but occurred too infrequently in calves to present a major clinical problem. Distinct calf rotavirus serotypes that did not confer passive cross protection were identified. Cows produced a heterotypic immune response to all serotypes to which they had pre-existing antibody after vaccination with a single serotype. Passive immunisation may therefore largely overcome the practical problems posed by the existence of many rotavirus serotypes. In the course of this work on neonatal diarrhoea, studies on diagnosis, epidemiology, pathogenesis and biochemistry of other enteropathogens, particularly astrovirus, Cryptosporidium, E. coli and Campylobacters were made. A method for exploiting the genetic control of susceptibility of piglets to adhesion with K88 fimbriae from ETEC was devised and tested.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (D.Sc.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Rotavirus pathogenesis