Page 176 - The Veterinary Laboratory and Field Manual 3rd Edition

Parasitology 145

may occur as a result of an acute allergic vessel walls with resultant changes to the
response if ingested larvae migrate through blood supply to the intestine. In severe cases
body tissues. Infection may be prevented by colic and death may follow. The cyathastomes
ensuring that meat (especially pork and wild or ‘small red worms’ the larval forms of which
game meat) is very well cooked. The life cycle may also cause significant disease in horses.
is illustrated in Figure 3.13. 4
• ‘Roundworm’ – this term is usually used
to refer to the large roundworms which are Large ‘roundworms’ or ascarids
readily seen at necropsy or in the faeces of
puppies and other animals following dosing The large roundworms are known as ascarids
with anthelmintics. Most of the worms in this (family Ascaridoidea) and occur in most domes-
group belong to the super family Ascaridoidea tic animals. The adult stages in the intestine
(that is, Ascaris sp., Toxocara sp. and so on). cause un-thriftiness in young animals and occa-
and are discussed further in the next section. sional intestinal obstruction. Another important
feature of the group is the harmful effect caused
by the migratory behaviour of the larval stages
Nematodes found in the large intestine
and caecum of some ascarids. Ascarid parasites are distrib-
uted worldwide and occur in ruminants, pigs,
• Large mouthed worm (Chabertia sp.) has a horses, poultry, dogs and humans, all are com-
large mouth and sucks the mucosa of the paratively large with an elongated, cylindrical and
intestinal wall causing severe irritation and un-segmented body. The common name used is
diarrhoea, which is sometimes blood stained. ‘roundworm’ and adult specimens may be easily
It is found in the colon of sheep, goats, cattle seen in the faeces after anthelmintic dosing. The
and other ruminants. canine ‘roundworm’ Toxocara canis is common in
• Nodular worm (Oesophagostomum sp.). This is puppies and the life cycle involves transmission
the same size as the large mouthed worm but of infective larvae from the pregnant bitch via
it is white in colour. The larvae of this para- the placenta to unborn puppies and also via milk
site penetrate the intestinal wall, sometimes and from the environment (Figure 3.24). Larvae
causing small abscesses (called ‘pimply gut’ within the adult dog may become encysted as the
condition). It can also cause diarrhoea. These host’s immunity develops. However, encysted
worms are found in sheep, goats and other larvae in the bitch are often activated during
ruminants. pregnancy due to inhibition of the bitch’s immu-
• ‘Whip worm’ (Trichuris sp.). This worm is nity. Infection of young puppies may occur due
found in the caecum and large intestine of a to continued exposure to contaminated bedding
number of species. The adult worms have a where larvae develop or by suckling from the
long tail like a stock whip. Trichuris ovis occurs bitch. If eggs containing larvae (L2) are ingested
in sheep, T. vulpis occurs in dogs and may by human babies or young children, larvae may
cause mucoid diarrhoea and abdominal pain. migrate to the eye causing defects although pat-
• ‘Equine red worms’ (Strongylus sp.). These ent infections do not occur. T. cati and T. leonina
are large worms found in the large intestine occur in kittens and the life cycle involves trans-
of horses (for example, S. vulgaris, S. equinus, mission from cat to kittens in the milk as well as
S. edentatus). Strongylus vulgaris is particularly direct via environmental contamination (but not
pathogenic as it migrates via the mesenteric via the placenta). The clinical signs include pneu-
arteries and may cause damage to the blood monia, ascites and severe emaciation in severe

Vet Lab.indb 145 26/03/2019 10:25