Zoonosis and People

By Dr. Vanessa Vandersande

Did you just eat your sandwich after playing with your puppy? Did you remember to wash your hands before eating? If so, you might have just gotten a little more fun then you bargained for! Zoonosis is any disease or infection that is naturally transmissible from animals to humans. One commonly seen zoonosis are roundworms which are often associated with young animals.

Roundworms are a common infestation of young animals such as puppies and kittens, though any dog or cat can be a carrier with little to no clinical signs. It is thought that 30% to 50% of dogs and cats carry gastrointestinal (GI) parasites and that 1 to 3 million people in the U.S. have infections from the same parasites carried by pets. Roundworms are a big reason that veterinarians, as well as the CDC, recommend monthly parasite control for pets.

Infection in the dog and cat can occur in several ways:

  • During embryonic development when an infected mother dog is pregnant (most puppies and kittens are infected this way during gestation).
  • Consuming infective worm eggs from soil in the environment. This happens when the pet has laid on soil with old stool in it and then grooms themselves.
  • Nursing from an infected mother dog.
  • Consuming a prey animal (usually a rodent) that is carrying developing worms.

Animals with roundworms are one thing but the science gets really interesting when a human accidentally ingests an infective egg. Remember the handwashing you missed? Well the puppy had some infective dirt on it which ended up on your hand. The egg passed onto your sandwich and you ingested a roundworm egg on that last bite. Yuck!

Now the egg will start moving through your system, possibly ending up in the lung, brain or eye- a process known as visceral larval migrans. While treatable, damage from the migration can be permanent. I knew of one young child who was affected and lost vision in one eye. That is why every one of my clients always gets the zoonosis talk and a good discussion about monthly preventive at their annual exam. The choice is always in the hands of the pet owner but when children are concerned, my motto is “Not on my watch!”