Your guide to understanding parasitic diseases in dogs

Parasites survive by feeding on animals and people. Some insects, worms, and other parasites can make pets and people sick. Know what to look for and how to treat.

Lyme disease



Heartworm disease




How does my dog
get infected?

Deer tick or black-legged tick (Ixodes spp.) carries bacteria and bites dogs, spreading infection.

Lone star tick (Amblyomma americanum) or brown dog tick (Rhipicephalus sanguineus) carries bacteria and bites dog, spreading infection.

Mosquito transfers worm larvae from infected dog to your dog; larvae develop into worms that live in the heart and its vessels.

Ingestion of parasite eggs or rodents or direct contact with parasite larvae in contaminated environment. Also spread through mother’s milk and placenta.

Ingestion of parasite eggs from a contaminated environment (soil, kennels, dog parks, etc.)

Most common signs of infection

May not show any signs, or:

  • Lameness

  • Fever

  • Swollen joints

  • Kidney failure

  • “Not himself”

  • Loss of appetite

May not show any signs, or:

  • Lack of energy

  • High fever

  • Swollen, very painful joints

  • Loss of appetite

From mild to severe:

  • Loss of appetite

  • Depression

  • Fever

  • Painful joints

  • Bloody nose

  • Pale gums

No signs at first, then:

  • Mild, persistent cough

  • Reluctance to move or exercise

  • Tiredness after moderate exercise

  • Reduced appetite

  • Weight loss

May not show any signs, or:

  • Diarrhea

  • Pale gums

  • Poor health

  • Poor hair quality

May not show any signs, or:

  • Diarrhea

  • Pot-bellied appearance

  • Poor hair quality

  • Cough

  • Vomiting

May not show any signs, or:

  • Intermittent diarrhea

  • Loose poop

  • Blood in poop

Disease progression if left untreated

Damaged joints, fatal kidney disease (rare), neurological signs (rare)

Very low numbers of platelets and white blood cells, chronic joint pain, neurological signs (rare)

Permanent blindness, autoimmune diseases, bleeding complications, death

Heart failure, lung disease, sudden death

Intestinal inflammation, failure to grow/thrive, weight loss, severe anemia

Intestinal inflammation, failure to grow/thrive, weight loss

Chronic bloody diarrhea, dehydration, weight loss and anemia


Coinfection with Lyme disease and anaplasmosis is possible. In addition, it’s possible for your dog to become infected with any combination of parasitic diseases—including those not listed here.

Roundworm, whipworm

Hookworm, whipworm

Hookworm, roundworm


Simple blood test: IDEXX SNAP® 4Dx® Plus Test

(can detect six infections in one blood sample in less than 10 minutes)

Other tests: Complete blood count, chemistry profile, urinalysis, other special tests (depending on initial findings and clinical signs)

Test poop sample for presence of parasites (eggs, larvae, antigen)


Antibiotics: doxycycline, tetracycline

Antibiotics: doxycycline, tetracycline

Antibiotics: doxycycline, tetracycline

Adulticides (kills adult heartworms), monthly products licensed to treat microfilaria

Source: Companion Animal Parasite Council

Deworming medication


If caught and treated early, the outcome is usually very good for a full recovery from symptoms. Some of these infections cannot be cured completely, but early intervention usually provides the best prognosis.




Vaccine available?








Other prevention

Daily tick inspection and removal, and the use of oral or topical preventives. Ask your vet for more information.

Oral and topical preventives

Monthly parasite control products (available from your veterinarian), often included in your monthly heartworm preventives. Also remember to pick up your dog’s waste regularly.

No prevention is 100% effective. Test your dog every year.

Ask your veterinarian about testing and prevention for parasites.

Learn more about dogs, ticks and tick-borne parasites

Reviewed on: 
Monday, June 17, 2019