Page 874 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Gastrointestinal system: 4.2 The lower gastrointestinal tr act 849

VetBooks.ir Diagnosis Aetiology/pathophysiology
Strongyloides are unique in that they are capable of
A history of imminent or recent parturition or pre-
vious management changes is typical of horses with
Only female worms are involved in the parasitic
large-colon volvulus. Severe colic associated with both a parasitic and a free-living reproductive cycle.
abdominal distension that is non-responsive to anal- cycle, living in the small intestine and producing
gesics is characteristic of strangulated large-colon eggs via parthenogenesis. After hatching, larvae
volvulus. On rectal palpation, large-colon distension usually mature into free-living adult worms. Under
with tight teniae can be identified. In horses with certain conditions the L3 can be infective and infect
strangulated volvulus, oedema of the large-colon horses via skin penetration or ingestion, followed by
wall, reflecting compromised venous blood return, development of adult worms in the small intestine.
is occasionally palpable. Foals may also be infected from larvae present in the
tissues of mares. These larvae mobilise from arrested
Management states in tissues of the abdominal wall and are subse-
Rarely, non-strangulated volvulus responds to con- quently excreted in milk. This route of infection is
servative medical treatment; however, most horses believed to account for the uncommon cases of clini-
require surgical treatment. Strangulated volvulus is a cal S. westeri infection in young foals. Infections tend
surgical emergency. Correction of equine large-colon to peak within 4–6 weeks of age and are eliminated
volvulus is performed through a midline coeliotomy. naturally by 20–25 weeks.
The large colon is identified and exteriorised. A pel-
vic flexure enterotomy is performed to evacuate the Clinical presentation
accumulated gas and digesta. The volvulus is then Infection is usually inapparent. Disease is character-
corrected. Large-colon resection is indicated if the ised by acute diarrhoea in foals in the first few weeks
strangulated tissues appear devitalised. of life.
Large-colon volvulus recurrence is only about 5%
in non-breeding mares and males, but broodmares Differential diagnosis
are at a higher risk. After one episode, a broodmare Other causes of neonatal diarrhoea including foal
has a 15% chance of developing a second large-colon heat diarrhoea, clostridial diarrhoea, salmonellosis
volvulus. After two episodes, the risk is increased to and rotavirus should be considered.
80%. Colopexy or large-colon resection is indicated
to prevent recurrence in broodmares after two epi- Diagnosis
sodes of large-colon volvulus. Eggs may be evident on faecal flotation. Fresh fae-
ces should be used to avoid confusion with larvated
Prognosis strongyle-type eggs. Identification of eggs in faeces
The prognosis for non-strangulated large-colon is not diagnostic by itself because high faecal egg
volvulus is guarded to good, whereas strangulated counts can be present in healthy foals.
volvulus is associated with fatality rates of approxi-
mately 70%. The time from development of volvulus Management
to surgical intervention is critical, with strangulating Specific treatment is rarely indicated because S. westeri
lesions corrected within 4 hours of onset of signs hav- is rarely a cause of disease. Transmission of S. westeri
ing a better prognosis than longer standing lesions. from mares to foals can be markedly reduced by treat-
ment of mares with ivermectin (0.2 mg/kg p/o) within
STRONGYLOIDES WESTERI INFECTION 24 hours of parturition. Treatment of foals with iver-
mectin at 1–2 weeks of age can hasten the elimination
Definition/overview of S. westeri.
Strongyloides westeri, also known as ‘threadworm’, is a
common parasite in foals, but is usually of minimal Prognosis
clinical significance. Excellent.