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Roundworms
are parasites
that have evolved some remarkable strategies for survival. Unfortunately,
their success is at the expense of not only our pets, but ourselves. |
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There are three species of
roundworms that infect dogs and cats, Toxocara canis in dogs,
Toxocara cati in cats, and Toxascaris
leonina
in both. |
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TOXOCARA SPECIES |
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The life cycles of T. canis and T. cati are very complex and well-suited to exploiting the resources of their host animals. It is no wonder that over 90% of puppies and a significant number of kittens are infected. When an infected dog or cat defecates, microscopic eggs of Toxocara are present in the feces. These eggs are NOT infective immediately. They require a period of 3 to 4 weeks at environmental temperatures to develop into infective larvae (L2). By this time there is no evidence of the fecal material, but the larva-containing eggs are in the soil. The eggs can remain infective for years, even through harsh environmental conditions. They are nearly impossible to kill with household disinfectants. |
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Dogs and puppies swallow the infective eggs along with grass or dirt, or
contaminated toys. Rodents that contain developing larvae are another source
of infection to dogs and cats that prey on them.
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Young
children may also become infected by eating dirt or sticking a dirty hand or
toy into their mouths. This can result in Ocular or Visceral Larva Migrans, in
which the worm larvae migrate into the eyes, causing vision loss, or
throughout the body, causing generalized disease. Click here to get more information from the Centers for Disease control. |
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Once an egg enters the intestinal tract of the dog or cat, the larva hatches out, then burrows out of the intestine and migrates through the animal’s body. In very young puppies and kittens, it travels to the lungs, then the trachea, where it is coughed up and swallowed. Back in the intestines, the now-mature worm completes its life cycle by mating and laying eggs, which will be shed in the puppy’s or kitten’s stools. This entire cycle takes about 3 to 4 weeks.
If the dog
or cat is over 5 weeks old, the larva does not go to the lungs, instead
entering the bloodstream where it travels until it reaches other tissues,
especially the liver. There it encloses itself within a cyst and becomes
dormant until reactivated by stress, illness or suppression of the animal’s
immune system, During the last few weeks of pregnancy in dogs, the encysted
larvae are stimulated to head to the uterus, through the placenta, and into
the lungs of the developing puppies. In cats and dogs, larvae end up in the
mammary glands and pass into the newborns as they nurse. Thus many puppies are
born infected, and kittens can become infected at a very early age, even
though the mother’s stools tested negative for worm eggs before her pregnancy. |
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TOXASCARIS LEONINA T. leonina has a simpler life cycle than T. canis and T. cati. Infection is by ingestion of infective eggs in the soil or rodents that contain developing larvae. Once ingested, the larva hatches out and remains in the intestinal tract for its entire life. Toxascaris leonina does not infect humans. |
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HOW DOES YOUR PET GET ROUNDWORMS?
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T. canis can be acquired by:
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T. canis and T. cati can be acquired by:
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WHY ARE ROUNDWORMS BAD FOR YOUR PET?
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Roundworms live in the intestinal tract and consume the food intended for
your pet. They may cause diarrhea, vomiting, weight loss (or lack of weight
gain in puppies and kittens) and abdominal pain. A heavy infestation can even
obstruct the intestinal tract. Large numbers of larvae migrating through the
lungs may cause pneumonia. |
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HOW DO YOU KNOW IF YOUR PET HAS ROUNDWORMS?
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Heavily infested puppies or kittens may pass the 7 to 10 inch-long worms in the feces or vomit. They are cream to tan in color and are frequently compared to spaghetti in appearance. It is safe to assume that almost any puppy or kitten has at least some roundworms. In most cases, the best way to find out is by routine fecal examinations. |
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HOW DO WE DIAGNOSE ROUNDWORMS?
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When you drop off
a specimen of your pet’s feces, our technicians take a small portion (about
1/2 teaspoon) and mix it thoroughly with a concentrated solution of a special
salt. The mixture is then left to sit for 15 minutes in our vented laboratory
hood. The eggs of the roundworms are lighter than the salt solution, so they
float to the top of the small container and stick to a glass cover slip that
is placed across the top of the fluid. The technician then places the cover
slip onto a microscope slide and examines it under the microscope for eggs. |
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HOW DO WE TREAT ROUNDWORMS?
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There
are a number of medications that are effective against adult roundworms in the
intestinal tract, but it is impossible to eliminate the encysted larvae or
immature worms. That is why we request fecal rechecks, so we can “catch” the
worms at a susceptible time to eliminate them.
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PREVENTION AND CONTROL OF ROUNDWORMS |
In puppies:
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In kittens:
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In children:
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