Page 875 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

850 CHAPTER 4

VetBooks.ir LARGE-STRONGYLE INFESTATION then moult in the pancreas and return to the large
intestine. Strongyle migration has also been sug-
Definition/overview
Large strongyles are of significant importance in gested to be the cause of haemomelasma ilei, a typi-
cally benign condition (Fig. 4.169).
areas where routine deworming is not performed.
Prior to the widespread availability of ivermectin, Clinical presentation
large strongyles were a common cause of severe colic. Few clinical signs are produced by the presence of
adult worms in the GI tract. Mild diarrhoea, ill-
Aetiology/pathophysiology thrift and anaemia are possible with chronic, severe
Strongylus vulgaris, S. edentatus and S. equinus may be burdens. Migration of S. edentatus and S. equinus lar-
involved; however, S. vulgaris is of the greatest clinical vae can produce haemorrhagic tracts in the liver and
importance. Adult strongyles live in the large intestine nodule formation in the gut wall or peritoneum, but
and caecum. They are reddish, thick and up to 4 cm clinical signs are rare. Pancreatitis has been reported
in length. Eggs are passed in the faeces and infective but is rare or rarely identified.
L3 develop in the environment. Following inges- Intestinal infarction is more serious. Clinical pre-
tion, S. vulgaris L3 penetrate the intestinal mucosa sentation varies, depending on the degree of intesti-
and moult to L4 in the submucosa. They then invade nal ischaemia, duration of disease and location of the
small arteries and arterioles and migrate to the cranial lesion. Pain may be mild to severe. Heart rate will be
mesenteric artery and its main branches. After several elevated and can exceed 100 bpm. Respiratory rate
months, they moult and L5 migrate to the intestinal may also be elevated. Horses may sweat profusely
wall. Nodules form around them and subsequently and appear anxious. Mucous membranes may be
rupture into the intestinal lumen, releasing young congested and hyperaemic, with a prolonged CRT if
adults. Inflammation of the cranial mesenteric arter- significant intestinal ischaemia or septic peritonitis
ies can develop in response to the larvae. Thrombosis is present. Borborygmi are decreased to absent.
can cause ischaemia in areas of the intestinal tract.
Thromboemboli may also develop and cause isch- Differential diagnosis
aemic necrosis of other areas of the intestinal tract. Strangulating intestinal infarction, severe enteroco-
Intestinal aneurysms are less common. litis and peritonitis are the main differential diag-
After ingestion, S. edentatus penetrates the intes- noses. Other clinical syndromes are uncommon and
tinal mucosa and reaches the liver via the portal cir- vague.
culation. Further migration in the liver occurs, then
larvae travel under the peritoneum and eventually Diagnosis
reach the intestinal lumen. Eggs are usually readily identifiable on a faecal flo-
The migratory route of S. equinus is less well tation test. Large-strongyle eggs cannot be differ-
understood. L4 larvae form in the intestinal wall, entiated from small-strongyle eggs, therefore they
enter the peritoneal cavity, migrate into the liver are generally classified as ‘strongyle-type’ eggs.
Absence of identifiable eggs does not rule out infec-
tion. It is virtually impossible definitively to identify
4.169 a non-strangulating infarction without surgery or
necropsy. Diagnostic findings may be suggestive of
infarcted colon; however, differentiation between a
strangulating and non-strangulating aetiology is not
possible. Definitive diagnosis is made at surgery.

Management
Fig. 4.169 Characteristic appearance of Large strongyles are generally susceptible to iver-
haemomelasma ilei, a benign condition. mectin (0.2 mg/kg p/o), moxidectin (0.4 mg/kg p/o)