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.
 

There are three species of roundworms that infect dogs and cats, Toxocara canis in dogs, Toxocara cati in cats, and Toxascaris leonina in both.
 

TOXOCARA SPECIES
 

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.

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.
 

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.

WHY ARE ROUNDWORMS BAD FOR YOUR PET?

 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.
 

HOW DO WE DIAGNOSE ROUNDWORMS?

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.
 

HOW DO WE TREAT ROUNDWORMS?

 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.