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.