Page 196 - The Veterinary Laboratory and Field Manual 3rd Edition

Parasitology 165

in the intestinal lumen and penetrate epithelial of immunity, which will result in inhibition of
cells to initiate schizogony by developing into a the reproduction of the protozoa. Developing
large, first generation schizonts. They undergo trophozoites compete with the host for ingested
merogony to produce first generation merozo- nutrients and damage to the intestine results in
ites which then invade other cells to develop as a reduced absorptive capacity of the intestinal
second generation schizonts and subsequently lining. Severe diarrhoea in heavy infections can
as second generation merozoites. There may be be rapidly fatal in young animals.
several cycles of this asexual reproduction with
damage to the gut wall resulting each time. The Disease diagnosis
sexual stage is initiated when merozoites from
last cycle of merogony invade new epithelial Identification of oocysts in a faecal sample
cells and develops as gamonts. Some gamonts (see Figure 3.31b) or examination of intestinal
increase in size (macrogamont) and develop as smears and typical lesions at necropsy. Treatment
female gametocyte while others undergo series and prevention will depend on the veterinary
of division to produce hundreds of microgame- products available in the area (for example, in
tocytes (male gametocytes). Microgametocytes feed anti-protozoal drugs, sulphonamides) but
that are released into the lumen will seek cells the most important factor for the prevention of
containing female gametocyte to fuse with and coccidiosis is good husbandry and hygiene.
complete fertilization. Following fertilization,
a zygote develops in the host’s intestinal cell. Prevention
A wall forms around the zygote until it develops
as an oocyst which is then released by rupture 1 Good hygiene.
of the host cell. Sexual multiplication results in 2 Ensure good husbandry.
the production of oocysts which pass out in the 3 Vaccination (oral vaccines containing attenu-
faeces. Within each oocyst sporogony (sporu- ated forms of Eimeria sp. are available).
lation) ensures development of eight infective 4 Coccidiostats in the feed (must be accompa-
sporozoites. These are infective for the next host nied by 1 and 2).
but the process of sporulation may take a day or
two depending on the ambient environmental Treatment
temperature and humidity. Owing to the fact
that sporulation occurs in the environment this 1 Antiprotozoals mainly coccidiostats (for
is the stage at which good hygiene can prevent example, Amprolium, Decoquinate, Lasalocid,
infection by ensuring all potentially infective fae- Monensin, Sulphonamides and so on).
ces are removed and that the stocking rates are 2 Supportive care (for example, fluid therapy
not too high. for dehydration).
The location of the reproductive cycle in
the intestinal tract depends on the species of
Eimeria involved. In poultry, the location of toxoplasmosis
intestinal lesions at necropsy may assist in the
identification of the Eimeria species involved. Toxoplasma gondii is an intestinal parasite of
The severity of the damage depends on (1) the young cats and may cause transient diarrhoea.
number of organisms present, (2) the species of Cats are the definitive hosts in which oocysts are
protozoa and (3) the immunity of the host. As produced. More than 250 mammals and birds
the host gets older there will be some degree are known intermediate hosts in which tissue

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