The veterinarian confirms the diagnoses of most worm infections by identifying the
characteristic eggs of the different species in cattle faeces. Several exceptions
exist to this general rule. The filarial worms shed tiny, worm-like microfilariae
larvae into surrounding tissues. Microfilariae of Stephanofilaria are found
in skin lesions with adult worms, while those of Onchocerca and Parafilaria
are found in tissue fluid under the skin. Larval eyeworms (Thelazia) are
present in tears. Lungworm (Dictyocaulus) eggs usually hatch in the intestine,
so that larvae are shed with the faeces. Lungworm (Dictyocaulus) eggs resemble
those of Strongyloides, as described below, but are twice as large.
The major types of eggs which are present in cattle faeces include:
The egg of this roundworm is roughly spherical, with a thick, pitted, outer layer
"Strongyle-type" eggs are laid by many important bovine nematodes, including the
stomach worms (Haemonchus, Mecistocirrus, Ostertagia, Trichostronglyus) and
intestinal worms (Bunostomum, Cooperia, Nematodirus, and Oesophagostomum).
These eggs are elliptical or oval, with smooth, thin shells. When laid, the eggs
have already begun to develop and are called "segmented" because the inner mass
has split into a group of cells (fig 2). Nematodirus eggs are the largest
strongyle-type eggs; however, eggs of other species in this group cannot usually
be identified precisely. Species determination can be made by identifying adult
worms at autopsy or by culturing the eggs in faeces until the distinctive larvae
The eggs of threadworms each contain a larva when laid. The eggshell is thin and
smooth, and the egg is oval in shape with blunted ends. The gullet worm (Gongylonema),
of much less clinical importance, lays eggs that resemble those of Strongyloides
Whipworm eggs are brown and barrel-shaped, with a clear plug at each end (fig 4).
Cattle tapeworms shed segments full of eggs to be passed in the faeces. The segments
are rectangular and up to 3 cm. wide. Eggs are also found in the faeces because
some segments break apart. The eggs are square or triangular with thick, smooth
coats. Each egg contains a larva with 6 hooks known as a "hexacanth". The hooks
are on a characteristic pear-shaped structure known as the "pyriform body" (fig
Similar eggs are passed by cattle infected with Cotylophoron, Dicrocoelium, Eurytrema,
Fasciola, Fascioloides, or Paramphistomum. The eggs of Dicrocoelium
each contain a developed miracidium larva when passed in the faeces. At one end
of fluke eggs is a cap, the "operculum", through which the larva hatches. (fig 6).
Schistosome eggs are usually spindle-shaped, and may be present in the urine as
well as in the faeces of infected cattle.