Page 869 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

844 CHAPTER 4

VetBooks.ir Younger horses are more likely to be infected with Clinical presentation
Infection with adult small strongyles may produce
large numbers of small strongyles and may be more
likely to develop clinical disease with lower numbers
thrift, and may predispose to the development of
compared with adults. High stock density, inappro- mild and vague signs, such as weight loss or ill-
priate deworming programmes, poor manure man- colic. This may be seasonal, recurrent or sporadic.
agement and overgrazing of pastures are risk factors Chronic weight loss and chronic diarrhoea have also
for small-strongyle infection. been reported and the clinical presentation often
Larval cyathostominosis is typically a seasonal mirrors low-grade, undifferentiated IBD.
problem and is more common during the late win- The main concern is larval cyathostominosis.
ter and spring in most temperate areas, but in some Affected horses may present with severe diarrhoea,
areas, cases are more common in late autumn and weight loss, depression and peripheral oedema.
winter. Horses 1–3 years of age are most commonly Diarrhoea is not present in all cases, and weight loss,
affected. Recent anthelmintic treatment is also a risk depression and severe hypoproteinaemia may be the
factor. Anthelmintic treatment may trigger disease only clinical abnormalities.
by removing the negative feedback of adult worms in
the intestinal lumen, thereby resulting in excysting Differential diagnosis
of larvae. Protein-losing enteropathy, acute infectious coli-
Small-strongyle eggs are shed in faeces and tis of a variety of aetiologies and right dorsal colitis
develop into infective L3 on pasture. After inges- should be considered. Various differential diagnoses
tion, the L3 enter the mucosa of the large colon exist for the mild, general disease that may be caused
and caecum, where they encyst. Encysted larvae by adult small strongyles.
may remain hypobiotic for up to 2 years. At any
point, L3 can develop into L4, excyst and migrate Diagnosis
back to the intestinal lumen, where they mature Diagnosis of larval cyathostominosis is difficult.
into adults. The pre-patent period varies with Faecal egg counts are often low when clinical dis-
different strongyle species, and ranges from 5 to ease is present, largely because disease is associated
18 weeks. with encysted larvae, not egg-producing adults.
Encysted larvae may incite a granulomatous Furthermore, disease may be triggered by recent
reaction; however, the main problem occurs dur- anthelmintic therapy, therefore eggs and adult worms
ing emergence of hypobiotic larvae. A marked would be less commonly present. Haematology is
inflammatory response can ensue, characterised by non-specific and peripheral eosinophilia is uncom-
oedema, ulceration and protein exudation. Nutrient mon, even in severe cases. Hypoalbuminaemia is
and fluid absorption and intestinal motility can be common and may be severe. The degree of hypoalbu-
affected. This syndrome is termed ‘larval cyathos- minaemia is often more severe than would be expected
tominosis’. Encysted larvae are more common in the from the severity and duration of the diarrhoea.
caecum and ventral colon and represent the majority Elevations in alpha-2 and beta-1 globulins have been
of small-strongyle burden, although this may vary reported. Late L4 larvae are occasionally evident on
with geographic region and time of year. The ventral faecal smears or on rectal gloves following palpation.
colon is the main site for adult worms, followed by Thickening of the large colon wall may be evident
the dorsal colon and caecum. ultrasonographically; however, all these findings are
Adult worms in the intestinal lumen may cause non- specific for larval cyathostominosis. Diagnosis
disease, but this is of lesser importance. Pinpoint involves identification of large numbers of encysted
mucosal ulceration may be produced and vague signs and/or emerging larvae in the large colon. Encysted
such as ill-thrift may be present. An increased risk cyathostomes can sometimes be detected on rectal
of colic may also be present. An association with the mucosal biopsy. Exploratory laparatomy can be diag-
development of caecocaecal and caecocolic intussus- nostic, but affected animals are often poor surgical
ceptions has been reported. candidates, particularly if severely hypoproteinaemic.