Parasitology

What 3 major questions should clinicians ask before designing a parasite control program?

• What parasites occur in the local small-animal population?

• Is parasite control justified? (risk of infection, disease potential, zoonotic risk, local zoonotic pressure, clinician’s own risk tolerance)

• What control program should be implemented?

What additional considerations affect the choice of parasite control program?

• Client risk aversion

• Financial constraints

• Downsides or limitations of the program (e.g., side effects, compliance, cost, environmental impact)

What are the key endoparasites of dogs and cats in Ontario?

Dogs: roundworms, hookworms, heartworm (?), whipworm, tapeworms, Giardia, coccidia.

Cats: roundworms, hookworms, tapeworms, Giardia, coccidia.
Species include Toxocara, Ancylostoma, Dipylidium, Taenia, and Echinococcus (dogs)

What are the primary ectoparasites of dogs and cats in Ontario?

• Fleas

• Ticks (Dermacentor variabilis, Ixodes scapularis), animals need to be outside in the grass

• Otodectes (in cats)

What principles guide appropriate use of antiparasitic drugs?

• Use the narrowest spectrum drug possible.

• Use a route that ensures compliance.

• Use as few products as possible.

• Treat only when the animal is at risk.

• Monitor efficacy routinely

Which human groups are at highest risk for parasitic zoonoses, and how should this influence deworming?

YOPIs: young children, older adults, pregnant individuals, immunocompromised patients.
These households should follow more aggressive preventive deworming strategies

Which two parasites are NOT routinely targeted by preventive treatment in dogs/cats?

• Giardia → common but subclinical

  • 466 dogs ≥6 months old

  • Giardia prevalence: 11.8%

  • More common in <1-year-olds

  • >95% had no diarrhea (subclinical)

• Coccidia
  Because subclinical infections are common and typically don’t justify routine treatment

Do Giardia infections in Ontario dogs and cats present significant zoonotic risk?

Mostly no—because genetic assemblages infecting pets are largely host-specific and not the zoonotic A/B assemblages

Which Giardia assemblages affect dogs and cats, and are they zoonotic?

• Dogs: C, D (dog-specific, non-zoonotic)

• Cats: F (cat-specific, non-zoonotic)

• Zoonotic: A & B (infect humans + multiple hosts)
  Thus >98% of dog infections in Ontario are not zoonotic

What are the major takeaways regarding Giardia infections in Ontario dogs/cats?

• 98% of dog infections are dog-specific.

• Most cases are subclinical.

• Do NOT treat subclinical infections unless zoonotic concern and genotyping cannot be done

How should Giardia be treated when clinical disease is present?

• Fenbendazole(use this)

• Metronidazole(approved for dogs, but is broad spectrum and can lead to resistance) 

• Reinfection from environment/coat is common

• Treat all animals, bathe on day 1 and last day, clean environment, reduce stress

Should healthy animals be screened for Giardia and how can infection be prevented?

• Routine monitoring not justified for healthy animals.

• Prevention: keep animal & environment clean and dry; cysts lose infectivity with dryness and freeze-thaw cycles

What animals are most at risk for coccidiosis Cystoiosospora and what factors trigger disease?

• Mostly affects dogs <6 months

• Triggered by stress: weaning, overcrowding, travel, rehoming

• Ideal environment for outbreaks: kennels

• Treatment: sulfas, TMS, amprolium, toltrazuril (all off-label)

What are important environmental control strategies for coccidia?

• Daily feces removal

• Keep floors clean and dry

• Oocysts resistant to disinfectants → use steam/pressure wash, hot water

• Consider sealing floors

How should subclinical coccidia infections be handled?

Typically not treated so immunity can develop naturally

What is the most important intestinal parasite in cats in Ontario?

Roundworms (Toxocara spp.) are the most significant

What are the 5 major preventive areas for small animals?

• Heartworm

• Intestinal parasites

• Fleas

• Ticks

• Wellness plans

What lifecycle stage do heartworm preventives target?

They target L3/L4 larvae acquired during the previous month. Preventives work with 1-month “reach-back” activity

What factors determine whether a dog needs heartworm prevention?

• Local risk (geography).

• Travel history.

• Client risk tolerance

What drug classes are used for oral, topical, and injectable heartworm prevention?

• Oral: ivermectin+pyrantel, milbemycin(+praziquantel)

  

• Topical: selamectin, moxidectin+imidacloprid.

• Injectable: moxidectin (6 or 12-month).
  Spectrum varies widely (fleas, ticks, GI parasites)

What does interceptor used for?

• Milbemycin → Dirofilaria, Toxocara, Toxascaris, Ancylostoma, Trichuris 

• Praziquantel → D. caninum(eating fleas), T. pisiformis, E. multilocularis (eating rodents)

Why might dogs require monthly praziquantel?

To prevent Echinococcus multilocularis egg shedding if they ingest infected rodents—important in high-risk regions/households

What parasites does revolution?

Selamectin 

• Heartworm 

• Toxocara 

What parasites does Proheart 6 cover?

• Heartworm

• Ancylostoma

• Uncinaria

When should heartworm prevention start and end in Canada?

• Start: Within 1 month after transmission season begins

• End:

  • Most products: 1 month after transmission season ends

  • Interceptor Plus / NexGard SPECTRA: 6 months after season.

  • Credelio PLUS: 2 months after season.
    If transmission >6 months → year-round prevention

If a puppy is born in July in a heartworm-risk area, when should it get its first dose?

At ~8 weeks old (typically August–September), within the seasonal prevention window

What is the minimum age to test for heartworm antigen and why?

7 months old, because antigen is not detectable until worms mature (≈6–7 months post-infection)

How often should dogs be tested for heartworm?

• At first visit if >7 months.

• Annually if following label instructions (USA recommendation).

• Less frequent = off-label, must justify based on low risk + informed consent

What steps should be taken if a dog tests heartworm antigen positive?

• Repeat test using fresh sample.

• Perform microfilaria test (Knott’s or Difil).

• Assess travel and compliance history.

• Evaluate for true infection vs. false positive/imported case

What additional diagnostics are recommended for dogs that test positive?

• Evaluate travel/compliance history.

• If clinical signs present:

  • Thoracic radiographs

  • Echocardiography
    To assess cardiopulmonary impact

• Goes to the R heart: immature adults enter the venous bloodstream, which returns blood to the right atrium → right ventricle → pulmonary arteries

What clinical signs occur in heartworm-infected dogs?

• Usual: exercise intolerance, coughing, dyspnea.

• Severe: weight loss, hemoptysis, ascites, hydrothorax.
  Signs depend on worm burden + activity level