Foal diarrhoea
a) Bacterial
Escherichia coli pathogenic strains
Pathogenic E. coli strains previously isolated and typed from diarrhoea of foals at the
WDL include E. coli O118:K- and E. coli O119:K69 serotypes.
The E. coli O118:K- serotype is related to the enteropathogenic E. coli (EPEC) and
enterohaemorrhagic E. coli (EHEC) biotypes. EPEC strains have previously been
isolated from foals with diarrhoea; the outer membrane proteins of EPEC strains are
responsible for the attaching-effacing lesions associated with EPEC infections.
Although there is no direct evidence of EPEC-associated diarrhoea cases in horses,
it is recommended in the literature that EPEC strains should be considered as
potential equine pathogens.
The E. coli O119:K69 belongs to pathotypes that are associated with the
enteropathogenic E. coli (EPEC) and enteroadhesive or enteroaggegrative E. coli
(EAEC) groups; the enteroadhesive or enteroaggregative E. coli strains have been
associated with gastrointestinal disease in horses.
Salmonella spp.
The results obtained by the WDL indicated that Salmonella enterica subsp. enterica
serovars Anatum and Arizona were the most frequently isolated members from this
genus from foal diarrhoea.
Salmonella enterica subsp. enterica serovar Anatum, is associated with salmonella
enteritidis, and has been reported in domestic animals. Although not commonly
isolated from horses with disease, Salmonella enterica subsp. enterica serovar
Arizona (also referred to as Salmonella enterica subsp. arizonae) of the subgenus III
(Arizona bacteria) has been associated with topical, systemic and gastrointestinal
disease in horses. It may cause serious disease in humans and animals, especially
domestic animals and as with all pathogenic Salmonella spp. it is an organism of
concern.
The recommended antibiotics for Salmonella spp. infections include fluoroquinolones
(Enrofloxacin), phenicols (Chloramphenicol), Trimethoprim-sulfamethoxazole or a
broad spectrum cephalosporin. The Salmonella enterica serovars Anatum and
Arizona isolated by the WDL tested sensitive to all these recommended antibiotics.
The lack of success with certain antibiotics may be associated with the unexplained
prolonged salmonella enteritis that responds poorly to certain combinations of
antibiotics.
Clostridium spp.
Although many foal diarrhoea cases submitted to the WDL test positive for
Clostridium spp. in moderate to high numbers, including Clostridium difficile (toxin
and non-toxin producing strains), C. septicum and C. tetani, few of the cases seem
directly related to clostridial gastroenteritis. In cases of severe bloody diarrhoea in
foals that were treated with antibiotics for other gastrointestinal bacterial pathogens
Clostridium spp. have been identified as the likely secondary agent in
gastrointestinal disease due to antibiotic-associated diarrhoea and colitis. Otherwise,
the presence of high numbers of Clostridium spp. in diarrhoea samples generally go
hand-in-hand with the presence of other primary pathogens, such as E. coli strains
Proceedings
of
the
South
African
Equine
Veterinary
Association
Congress
2016
264