Abstract
The primary aim of this study was to investigate the prevalence and pathogenic
characteristics of enterotoxigenic E. coli (ETEC) in diarrhoeic calves in Britain.
Developing from the results obtained were studies on a combined vaccine for passive
protection of neonatal calves against ETEC and rotavirus infections, Cryptosporidium
sp infections in laboratory mice, calves and lambs, and the effects of mixed enteric
infections in calves and lambs using ETEC, Cryptosporidium sp and rotavirus.
Eighty-eight of 1529 E. coli isolates (5.75%) from diarrhoeic and clinically normal
calves in Scotland and Northern England were found to possess the K99 antigen (K99 ).
There was complete correlation between possession of K99, heat stable enterotoxin (STa)
production and activity in the calf ligatedintestinal loop test. All K99+ ETEC were
isolated from 23 of 306 (7.5%) diarrhoeic calves (1 to 3 days of age) and from 8 of 70
(11.4%) diarrhoea outbreaks. A survey of bovine sera for K99 antibodies by ELISA found
2.96?o and 3.9% of sera from calves and cows respectively to be sero-positive.
An ELISA specific for the detection of K99 antigen was used to evaluate the sero¬
logical response of laboratory animals and cows vaccinated with a K99/rotavirus vaccine.
Cows vaccinated with an oil adjuvant vaccine comprising a K99 antigen extract from
ETEC strain B41 (0101:K-:K99) and inactivated calf rotavirus, induced high K99 antibody
responses in sera and colostrum, with prolonged antibody secretion in milk for 7 to 14
days post parturition. Calves from vaccinated dams were protected against experimentally
induced enterotoxigenic colibacillosis by challenge with ETEC strain B44 (09:K30:K99).
The vaccine also significantly reduced faecal excretion of the challenge ETEC in calves
from vaccinated dams.
Calf faeces containing Cryptosporidium sp were used to subclinically infect 8 strains of
laboratory mice at 1 to 4 days of age; transient infections only could be established in
21-day-old mice. Laboratory storage conditions for Cryptosporidium sp were investigated,
freezing inactivatedCryptosporidium sp, but storage was possible at 4 C in PBS or 2.5%
potassium dichromate for 4 to 6 months. The parasite could be repeatedly passaged in
mice without loss of pathogenicity for gnotobiotic lambs and a system using suckling mice
was used to quantify the infectivity of experimental inocula.
Clinical and subclinical infections were established using Cryptosporidium sp in 5 to 10-
day-old SPF and conventional calves. Pathological changes associated with infection by
the organism were found predominantly in the distal small intestine.
Mixed enteric infections were studied in gnotobiotic lambs and conventional calves.
Clinical infections were established by inoculation of gnotobiotic lambs with either
ETEC, Cryptosporidium sp or lamb rotavirus at less than 2 days of age. At 4 days of
age or older only subclinical infections could be established using either ETEC, rota¬
virus or ETEC and rotavirus. Clinical infections were induced with Cryptosporidium sp
either on its own or in conjunction with ETEC or rotavirus in gnotobiotic lambs 6 days
of age or older. There was no evidence from these experiments to suggest that Crypto¬
sporidium sp or lamb rotavirus enhanced the pathogenic effect of ETEC in 4 to 7-day-old
gnotobiotic lambs
Only subclinical infections were induced in 9-day-old conventional calves inoculated
with ETEC; Cryptosporidium sp at this age produced variable clinical responses. Dual
infection using ETEC and Cryptosporidium sp could not be analysed because of the
inadequacy of data.
