Page 191 - The Veterinary Laboratory and Field Manual 3rd Edition

160 Susan C. Cork and Mani Lejeune

liver tissue. The flukes can survive in the final 7–8 weeks after infection. The development of
hosts for several years. The prepatent period anaemia and emaciation follows. Diagnosis can
is 10 to 12 weeks. In many instances, clinical be difficult but infection can be confirmed at
signs are not present in the final host but anae- necropsy or by examination of faecal smears for
mia, oedema and emaciation may occur in heavy the characterizitc eggs which usually contain a
infections. Diagnosis is made by finding the developing miracidium. The egg shell is so deli-
characteristic small, thick and dark brown eggs cate that the flotation process may distort them.
during faecal examination. Faecal smears prepared in saline rather than
water are preferred.
PrEvEntIon and controL The eggs of some species of Schistosome
Control is difficult because of the wide distribu- are released in the urine causing bladder irri-
tion of intermediate hosts and the longevity of tation and haematuria (S. haematobium). Nasal
D. dentriticum eggs. Regular anthelmintic treat- schistosomiasis occurs in the nasal mucosal
ment of livestock using a flukicide anthelmintic veins of cattle and horses in Asia (S. nasalis).
will reduce pasture contamination. Infected animals may develop polyps on the
nasal mucosa resulting in blockage of the air
passages, this condition is known as ‘snoring
Schistosomosis (Schistosoma sp.)
disease’. Examination of nasal swabs smeared
Schistosomes generally parasitize the blood in saline on a glass slide will help identify the
vessels of the gastrointestinal tract and other characteristic ‘palanquin/boomerang’ shaped
organs. The parasites of this group are not her- eggs of S. nasalis.
maphrodites (that is, the sexes are separate) but
the male and female are permanently combined.
Most domestic animals are capable of acting as 3.4 Protozoa
a final host for some Schistosoma sp. Some spe-
cies infect humans (S. mansoni, S. japonicum). General protozoology
Schistosomosis is more common in tropical and
subtropical zones but has also been reported in Protozoa are single-celled organisms, which are
southern Europe. As with other flukes, an inter- largely free living but there are some important
mediate host is essential for the completion parasitic species such as the coccidia which are
of the life cycle. The male adult schistosome primarily intestinal parasites of animals (for
is about 2 cm long (the female is smaller) and example, Eimeria sp., Cystoisospora sp.). Coccidia
the eggs are 100 µm long with a characteristic are transmitted from one host to another mainly
spindle shape and a terminal spine. Eggs are by the faecal–oral route. There are some species
usually passed out in the faeces of the host and specific coccidia that usually cause disease in
hatch in the water. Miracidia hatch and infect young animals (for example, Eimeria sp. in calves
the intermediate host. Water snails are particu- and lambs) or when the host’s immune system
larly important in the life cycles of species which is compromised. Coccidiosis tends to become a
infect sheep and cattle (S. bovis, S. mattheei). The serious cause of production loss in extensively
final host is infected by the penetration of skin managed poultry especially when husbandry is
or the gut lining by motile cercaria (there is no poor (for example, lack of hygiene, high stock-
metacercarial stage). In sheep, acute disease ing rates and so on). For the diagnosis of disease
results in severe diarrhoea containing blood caused by coccidia and other gastrointestinal
and mucus and the development of dehydration protozoa it is important that fresh faecal samples

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