Ascarids are the most common worm parasite in cats, occurring in a large percentage of kittens and in
25 to 75 percent of adults. There are two common species that infest the cat.
Adult ascarids live in the stomach and intestines and can grow to 5 inches (13
cm) long. The eggs are protected by a hard shell. They are extremely hardy and
can live for months or years in the soil. They become infective in three to
four weeks after being passed out in stool.
The cat passes eggs in her stool or larvae in her milk (1). The larvae
infect her nursing kitten. Eggs from the stool (2) develop into larvae (3) and
are eaten by rodents (4). The cat then eats the rodents while hunting. If the
larvae pass through the kitten before maturing, the mother cat can also
reinfest herself while grooming her kittens.
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Cats acquire the disease by ingesting the eggs, perhaps through contact with
soil containing the eggs, by them licking off their feet, or by eating a host
animal, such as a beetle or rodent, which has acquired encysted larvae in its
tissues. The larvae are then released in the cat’s digestive tract.
Larvae of the common feline ascarid Toxocara cati are capable of migrating
in tissues. Eggs, entering orally, hatch in the intestines. Larvae are carried
to the lungs by the bloodstream. There, they become mobile and crawl up the
trachea where they are then swallowed. This may cause bouts of coughing and gagging. They
return to the intestines and develop into adults. This version of migration is
most common in kittens.
In adult cats, only a few larvae return to the intestines. The others encyst
in tissues and remain dormant. During lactation, these dormant larvae are
released, reenter the circulation, and are transmitted to kittens in the
mother’s milk. When the queen is shedding larvae in her milk,
she may not pass any eggs in her stool. Therefore, it makes sense to deworm
both mother and kittens starting about 3 weeks of age, even if a fecal exam is
Deworming the queen before or
during pregnancy does not prevent all
ascarid infestation of kittens after birth, but it will decrease the frequency
and severity. Medications do not eliminate encysted larvae.
The second most common feline ascarid is Toxascaris leonina. This ascarid is
not passed via the milk into nursing kittens but can be acquired by ingesting
the eggs or by eating infected rodents.
Ascarids usually do not produce a heavy infestation in adult cats, but may
do so among cats who do a lot of hunting. In kittens, a heavy infestation can
result in severe illness or even death. Such kittens appear thin and have a
pot-bellied look. They sometimes cough or vomit, have diarrhea, are anemic, and may develop pneumonia as the worms migrate from the blood
vessels to the air sacs of the lungs. Worms may be found in the vomitus or the
stool. Typically, they look like white earthworms or strands of spaghetti that
are alive and moving.