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What Are Parasites?

Reviewed by Dr. Melissa Beall, DVM, PhD on Wednesday, March 11, 2015
Posted February 14, 2014 in Dog Diseases & Conditions A-Z
Dog rolling around in the grass

Virtually all plants and animals have parasites that make life harder than it should be. I have been looking for a clear working definition of what a parasite is. Does it live inside or outside the body? Does it attach itself or is it free to move about? Actually in looking for the best way to define a parasite I realized it’s simpler than I was making it.


According to the CDC, “A parasite is an organism that lives on or in a host and gets its food from or at the expense of its host.” Parasites have been a part of animal and human societies forever. Poor sanitation, unhealthy food, and infected food or water supplies have in the past led to wide spread infestations. For centuries we coexisted, generally to our detriment and their benefit. Crude and barbaric treatments were largely ineffective: dosing with kerosene, diesel fuel, garlic, tobacco, irritating enemas (intended to flush the parasites from the host) all did little to eliminate parasites.


Fleas are simply an abomination and ticks are disgusting. Seeing a puppy throw up a worm or a cat with a tapeworm segment on its fur will send us at the very least to the internet in search of a solution, and solutions do exist.


Until fairly recently the emphasis was on more effective treatment and only in the latter part of the 20th century did the emphasis shift to control and prevention.  Today we have a number of safe and highly effective methods of prevention, as well as methods of control and treatment.

General prevention and control rely on some pretty basic steps:

  1. Hygiene, sanitation, and habitat control
  2. Regular examinations and tests for parasites accompanied by effective treatments
  3. Administration of an effective preventive or control as directed by the manufacturer and under the supervision of a veterinarian.

The Companion Animal Parasite Council, a non-profit educational foundation comprised of representatives from the academic industry and veterinary practice has more specific recommendations. You can view their list here.

Our pets increasingly interact intimately with our families and in an effort to protect pets, people, and the environment the control and elimination of parasites is everyone’s responsibility.
It is important that pets be tested regularly and that effective prevention and control be adhered to year round. Ask your veterinarian for specific recommendations, precautions and control measures. Also, check out dogsandticks.com for more parasite information.

For the best protection of your pets and family be sure your veterinarian is consulted and get their advice and recommendations for specific products.    

If you have any questions or concerns, you should always visit or call your veterinarian -- they are your best resource to ensure the health and well-being of your pets.

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Mike has more than 35 years of experience in companion animal veterinary practice and is a valued member of IDEXX’s Pet Health Network team since 2013.