Common Parasites and How to Prevent Them

From heartworm prevention to worms, learn about the common pet parasites and what you can do to prevent them.

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Mar 27, 2023

As a pet owner, you’re probably familiar with fleas, ticks, and worms—pesky parasites that can cause discomfort to your pet and family and potentially even transmit deadly diseases. It’s our goal at Parker & Ace that your pet never has to experience the irritation and unpleasant sensations that parasites cause, which is why we’ve put together this quick cheatsheet on parasites and how to prevent them.

As always, remember that a member of the Parker & Ace veterinary team is available to customize a prevention plan for your pet based upon their lifestyle and the other pets in your household. Get in touch with us to discuss parasite prevention (or anything else on your mind). 


Parasites are tiny organisms that live on or inside your pet. They can be separated into two groups: external parasites (such as fleas, ticks, and mites) and internal parasites (such as hookworms, roundworms, and tapeworms).

How common are parasites?

Whether your pet spends their time mostly indoors or outdoors, parasites are a common threat for both dogs and cats. 

What are common symptoms?

External parasites tend to lead to skin irritation and disease transmission; internal parasites can affect various systems including the gastrointestinal tract, blood vessels, heart, lungs, and brain. 

How are they spread?

Some parasites are transmitted through contact with infected feces (poop) or urine; others attach themselves directly onto our pets' bodies where they bite into the flesh under the surface layer.

Why is prevention important?

Other than being annoying to both the pet and their parent (anyone who has experience fleas in the house can attest to this) they can also cause a variety of health problems, including anemia, diarrhea, skin irritation, and even death if left untreated.

Some parasites can infect humans, making parasites a health issue for pets and humans alike. Because of this public health risk, we recommend screening feces for intestinal parasites at least once a year (or even more frequently in our patients that visit areas with higher dog densities, such as dog parks and daycares) and using year-round parasite prevention products.

How can you prevent the most common parasites?

We generally recommend using Simparica Trio—a monthly tablet that protects against heartworm, fleas, ticks, and gastrointestinal parasites. Please keep in mind that while this is our general recommendation, it’s always best to speak to your Parker & Ace vet team for a personalized recommendation specific to your pet and their needs.



  • What it is: An external parasite that is the most common among dogs and cats.
  • Time of year most active: Warmer months, usually from early spring to fall
  • Common symptoms & how to spot them: Fleas can cause severe itching and other problems such as skin infections and hair loss and they thrive particularly well in the well-regulated temperatures in the home. They particularly like to congregate around the rump of your pet—be on the lookout for any dry, dark debris in the fur or jumping fleas! Pet parents may also notice itchy flea bites and scars on their ankles and legs.
  • Why you should care: Fleas can carry and transmit a bacterium called Bartonella that can cause health issues in cats, dogs, and people. They can also carry the tapeworm Dipylidium caninum that can suck nutrients from the pet’s intestine and cause anal itching. Additionally, fleas can reproduce quickly, leading to a full-blown infestation if not addressed promptly. 
  • How to prevent it: We generally recommend using Simparica Trio—a monthly tablet that protects against heartworm, fleas, ticks, and gastrointestinal parasites.
  • Recommendation for fighting an infection:  If a flea infestation is suspected, it's important to thoroughly clean and treat the home (including washing all bedding with warm soapy water and vacuuming daily), as well as consult with your Parker & Ace vet team for proper treatment of affected pets.


  • What it is: Internal parasite that is spread more commonly to dogs via bites from infected mosquitoes. Usually it takes 6-7 months from the time an infected mosquito bites your pet for the larvae to develop into adult heartworms.
  • Time of year most active: Warmer months when mosquitos are most active or year-round in warm and humid climates. 
  • Common symptoms & how to spot them: Heartworm disease can cause inflammation within the lungs and the most common symptom is a mild yet persistent cough.
  • Why you should care: Heartworm disease is a serious and progressive disease that can be fatal if untreated.
  • How to prevent it: It is recommended that pet parents administer Simparica Trio to their dog at monthly intervals year‑round—even though the risk of contracting heartworm and tick borne diseases steeply declines during the winter months, continuing treatment is still recommended, as it is difficult to predict abrupt changes in weather patterns, and your pet could still be at risk during warm spells. Developing the monthly habit can keep your pup happy and healthy and also give you the peace of mind that they are protected. 
  • Recommendation for fighting an infection: Call your Parker & Ace vet team so we can assess the situation and work to kill the heartworms already in the bloodstream. We will determine the specific injection schedule according to your dog's condition.


  • What it is: Internal parasite that is contracted by ingesting eggs (most commonly by licking or sniffing infected feces or contaminated plants), passed from the mother during pregnancy, or eating a flea or a rodent that has ingested roundworm eggs
  • Time of year most active:  While pets at any age can get roundworms and hookworms, they are most vulnerable when they are very young, as these worms are often passed from a mother to her puppies before the puppies are born.
  • Common symptoms & how to spot them:  Puppies infected with roundworms may have stunted growth, a pot-belly, and recurrent diarrhea. Adult roundworms can sometimes be spotted in your dog’s vomit or feces.
  • Why you should care:  Roundworms are common intestinal parasites among dogs especially, and can cause illness or even death with a heavy burden. They can also be transmitted to people.
  • How to prevent it: Many medications that protect against heartworm also protect your pet against roundworms and other gastrointestinal parasites. 
  • Recommendation for fighting an infection: The infection can be diagnosed through a fecal examination and treatment involves repeated doses of a medication to eliminate the parasites.


  • What it is: External parasite that is usually picked up in the woods, bushes, tall grasses, or other outdoor places
  • Time of year most active:  Year-round
  • Common symptoms:  Incessant itching and scratching at the site in which the tick has embedded itself (usually on the head or neck area, and in or around the ears). More severe symptoms might arise within a few weeks after the tick bite, including fever, low appetite, labored breathing or rapid breathing, a change in bark, and in severe cases, a loss of coordination
  • Why you should care:  Depending on the tick species, your pet can experience irritation at the bite site, paralysis, or be transmitted harmful or fatal diseases from the tick.
  • How to prevent it: We generally recommend using Simparica Trio—a monthly tablet that protects against heartworm, fleas, ticks, and gastrointestinal parasites. Also, make sure to actively check for ticks after spending prolonged periods outdoors.
  • What to do if a tick is found: Call your Parker & Ace vet team so we can assess the situation and remove any tick(s) from your pet.

At Parker & Ace, we don’t just look for parasite eggs in the feces, we screen pets with an advanced PCR test for over 20 common parasites—ensuring that no parasites are missed because they are not shedding eggs at the time of collection. The P&A Veterinary Team can prescribe a preventive program to help your pet remain parasite free, and implement a treatment program to fight off any existing infestation.