Page 198 - The Veterinary Laboratory and Field Manual 3rd Edition

Parasitology 167

become infected but as the life cycle of the organ-
ism cannot be completed in this species their
role is that of a ‘paratenic host’, that is, a host
in which the parasite may grow or multiply but
that is not required for the parasite to complete
its life cycle. If a woman is pregnant at the time
of infection abortion may follow and congeni-
tal defects in newborns are common. Similarly,
toxoplasmosis may result in high neonatal losses
and abortion in sheep. In non-pregnant animals
and humans there may only be a transient fever
or ‘flu like’ signs with no further development Figure 3.33 Aborted foetus which was lost near
although cystic stages may settle in the tissues. to full term. A healthy lamb was born to the same
ewe. Note the white calcified cotyledons on the
placenta of the aborted lamb, this is indicative of
Diagnosis infection with Toxoplasma gondii, Scotland, UK.
1 Identification of oocysts in cat faecal samples.
2 Serology (paired samples). generally no development in the environment as
3 Abortion: typical lesions in placenta (Figure oocysts are sporulated by the time they are shed
3.33). in the faeces. The oocysts wall is so delicate to
4 In neonatal animals there may be congenital hold two developed sporocysts; therefore, indi-
defects such as microphthalmia (abnormally vidual sporocysts containing four sporozoites
small eyes). are appreciated in faecal examination. Infection
of the intermediate herbivore host occurs fol-
lowing ingestion of fully sporulated oocysts or
Prevention and control
the sporocysts in faecal material from omnivores
1 Keep cats away from ruminant grazing areas. and carnivores. The definitive host becomes
2 Hygiene and hand washing for humans. infected by ingestion of bradyzoites in sarco-
Pregnant women should not clear out cat/kit- cysts in muscle tissue of the intermediate hosts
ten litter trays and should wear gloves when (Figure 3.34). Host relationships of some spe-
gardening. cies of sarcocysts are outlined in Table 3.8.
3 Vaccinate young ewes before breeding or mix Sarcocystis rarely causes clinical disease in
non-pregnant animals with aborting adults to the definitive host but schizogony in the tis-
induce immunity and to reduce future lamb sues of the intermediate host may result in an
losses. elevated temperature, muscular pain, enlarged
lymph nodes and other signs. Some species
of Sarcocystis may cause neurological signs
Sarcocystosis (Sarcocystis neurona of horses). For more infor-
mation see the text list at the end of the chapter.
Many species of Sarcocystis have an obligatory
two host life cycle. Asexual reproduction (schi- Diagnosis
zogony) occurs in the intermediate host and
sexual reproduction (gametogony) including Cysts may be found in muscle tissue at necropsy
sporogony occur in the definite host. There is or at meat inspection and can result in carcass

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