Common Pet Parasites


External Parasitism

Cheyletiella Dermatitis

Cheyletiella dermatitis is caused by the mite Cheyletiella. The mite affects dogs, cats, rabbits and people. Signs include flakes (“walking dandruff”) and pruritus. Diagnosis is afforded via microscopic exam of the exudate. Treatment includes antiseborrheic shampoo, insecticidal shampoo, ivermectin and treatment of the affected premises. Isolate the pet during treatment (approximately 2-3 weeks) since the mite may survive up to 10 days off the host.

Cuterebra Larval Infestation

Cuterebra flies lay eggs on the fur of rabbits, dogs and cats that hatch larvae which burrow into the animal’s skin. A cyst forms around the larva with a opening at the surface from which the larva breaths. After approximately one month, the mature larva emerges and drops to the ground to continue its life cycle. Larva should not be crushed while embedded in the skin, since this may produce a shock-like reaction in the pet. Treatment requires removal of the larva and medical management of the resultant skin lesion.

Demodectic Mange

Demodicosis is a skin disease caused by the skin mite Demodex. The mites are normally found in small numbers within hair follicles of dogs, cats and even people. Individuals are believed to acquire the mites from their mothers. In pets with demodicosis, these mites proliferate and inhabit greater areas of the skin and hair follicles. Demodicosis may involve one or two small areas (localized) or large areas of the body (generalized). The disease may affect young pets (under 1 year of age) or may affect adults. Demodicosis is believed associated with immune suppression. Signs include areas of redness, hair loss, scales, crusts and secondary skin infections. Diagnosis is afforded via physical exam and skin scrapings. Localized demodicosis or disease affecting young pets is usually self limiting and mild. Treatment is directed at secondary skin disorders such as bacterial infections. Generalized demodicosis or disease affecting older pets is serious and often difficult to treat. Treatment is directed at the underlying immune suppressive disorder(s) as well as secondary skin infection, etc. Direct treatment may include miticides such as topical amitraz and oral milbemycin oxime.


Fleas are blood sucking insects that infest the haircoats of animals and occasionally feed on people. These insects cause irritation and distress to infested pets while severe infestations may lead to anemia via blood loss. Very young or debilitated pets can die from flea bite anemia. Fleas spread dog and cat tapeworm as well as various viral and bacterial diseases. Flea bites may also cause skin allergies, rashes and sores on both pets and their owners. Flea infestation is determined by either direct visualization of the fleas (especially at the rear end of the pet) and/or the finding of flea dirt (ie. tiny, black granules that resemble black pepper). This material is flea feces and consists of digested blood from the pet. To distinguish this material from dirt, place it on white paper and add a drop of water to it. If the material disperses (ie. dissolved flea feces), your pet has fleas even if none are found. Fleas multiply rapidly. A single breeding pair of fleas may produce tens of thousands of offspring within months. Feeding females can produce hundreds of eggs which drop off the pet into cracks, crevices and carpeting. Eggs hatch after 2-12 days into larvae that feed in the environment; larvae molt 2 times within 2-200 days; and larvae spin a cocoon in which they can remain for 1 week to 1 year! An adult flea emerges from the cocoon when stimulated by a passing pet. As you can surmise, flea control requires treatment of both the pet and the pet’s environment. Treatment of the pet is best accomplished with safe (eg. pyrethrin) shampoos to minimize the pet’s current flea load followed by one of the once a month veterinarian prescription products. Consult your veterinarian. The environment can be treated via thorough vacuuming with flea collars or moth balls within your vacuum bag to kill any fleas which are picked up. Once a month veterinarian prescription products which render flea eggs non-viable can also be used. Do not treat the yard nor utilize flea collars on your pet, since neither practice effectively diminishes flea problems and also subject pets and people to unnecessary toxins!


Lice are small, wingless insects that are “species specific”. This means lice of one species only infect that species and do not infect other species (eg. dog lice only infect dogs; cat lice only infect cats; human lice only infect humans) Lice are either biting lice or sucking lice. Cats are only affected by biting lice. Biting lice do not penetrate the skin but feed on dead skin, body secretions and hair and are very irritating to dogs and cats. Sucking lice penetrate the skin and feed continually on the animal’s blood, also causing great discomfort. Heavy infestations may result in blood loss anemia. The entire louse cycle occurs on the infested animal. The female louse lays eggs which attach to your pet’s hair. These are called nits. In approximately one week, the eggs hatch, and a nymph emerges. In about 3 weeks, the nymph matures to an adult and begins to lay eggs. Full cycle requires about 1 month. Diagnosis is afforded via microscopic exam of the pet hair. Treatment includes topical insecticides and environmental cleanup.

Notoedric Mange

Notoedric mange is a skin disease caused by the highly contagious mite, Notoedres cati. The mite can infest cats, dogs, rabbits and may cause temporary skin irritations in people. Cats are the main host (feline scabies). Female mites burrow into the skin and deposit eggs that hatch larvae in 3-10 days. The larvae return to the skin surface to feed, molt into nymphs and finally adults. The entire life cycle is approximately 3 weeks. The mite can survive off the host for only a few days. Signs include intense itching, thinning of the hair, adhering/yellow-gray crusts and scales (especially about the ears, neck and face). As the disease progresses, the skin becomes thickened with secondary bacterial infections. Diagnosis is afforded via skin scrapes and physical exam. Treatment includes topical miticides, injectable ivermectin and environmental cleanup.

Pelodera Dermatitis

Pelodera strongyloides is a small worm-like organism found in the soil. Signs include skin rash and loss of hair. Skin areas that contact damp, soil infested bedding (usually the abdomen and legs) are most commonly affected. Dogs scratch and bite the irritated areas, thereby aggravating the dermatitis. Diagnosis is afforded by clinical signs and skin biopsy. Treatment is directed both at the parasite as well as secondary skin disorders.

Sarcoptic Mange

Sarcoptic mange is a skin disease caused by the highly contagious mite, Sarcoptes scabiei. Sarcoptic mites burrow into the skin, deposit eggs that hatch larvae in 3-10 days. The larvae surface to feed and molt into a nymph stage. Nymphs travel about the skin surface to feed, molt into adults, mate and deposit more eggs in the skin. The entire life cycle is 3 weeks. Sarcoptic mites prefer the ears, elbows, abdomen and hocks. Signs include intense itching, redness, hair loss, crusts and scabs. Secondary bacterial skin infections commonly occur. Diagnosis is afforded via physical exam and skin scrapes. Treatment includes miticides, anti-inflammatories, antibiotics and supportive care. Sarcoptic mites may also infest people (zoonosis) in contact with infected pets. Anyone in contact with your pet who develops skin problems should consult a physician.

Tick Infestation

Hard ticks are blood-sucking parasites that infest both animals and people. Ticks attach to the skin, feed on the animal’s blood and deposit their eggs in the environment. Their complex life cycle involves one or more species of animals as hosts. Tick bites may become infected, and some produce a toxin that can cause paralysis or even death. Ticks also spread several serious diseases of animals and people, including Rocky Mountain spotted fever and Lyme disease. Pets at risk for tick infestation should be protected via topical prescription insecticides. Dogs should also be vaccinated against Lyme disease. Consult your veterinarian. Although best performed by veterinarians and their trained staff, ticks may be removed via gently “rolling” the tick body under one’s fingertip until the tick releases from the skin, intact. Note that ticks should be removed intact from the pet as soon as possible since ticks remaining on the pet for 48 hours can transmit Lyme disease if infected.

Internal Parasitism

Ancylostomiasis (Hookworms)

Hookworms (Ancylostoma) are intestinal parasites of dogs, cats and other animals. Animals become infected with hookworms by ingesting infective eggs or larvae, larval penetration of the skin/footpads or uterine transmission of larvae from the mother to fetus. The time from infection to the appearance of eggs in the stool is 15-26 days. Hookworms are a serious intestinal parasite because they feed on the blood of their host animal and can cause severe anemia. Other signs include tarry stools, diarrhea, weakness, poor coat and in young, weak or malnourished animals, sudden collapse and death. Mature dogs may be asymptomatic. Diagnosis is afforded via physical exam and fecal exam. Treatment is anthelmintics.

Ascariasis (Roundworms)

Roundworms (ascarids) are the most common intestinal parasite of dogs or cats. Pets become infected by ingesting eggs or larvae found in contaminated soil, feces, etc. Puppies and kittens are commonly infected by the mother while still in the uterus or by eggs/larvae ingested while nursing. Larvae travel through the body eventually to the intestine where they develop into mature worms. Adult females deposit eggs, which pass with the stool and develop into infective larvae thereby completing their life cycle. Signs of infestation include vomiting, diarrhea, bloated stomach, poor coat and weight loss. Diagnosis is afforded via physical exam and fecal exam. Treatment is anthelmintics.


Coccidiosis is a disease of the intestinal tract caused by microscopic organisms called coccidia. The disease is contracted via ingestion of infected feces. Signs include diarrhea which is bloody at times, occasionally vomiting, lethargy, weight loss and dehydration. Diagnosis is afforded via fecal exam and cytology of intestinal scrapes. Treatment usually includes a sulfa drug.


Giardiasis is an intestinal disease of people, dogs, cats and other animals caused by a protozoa called Giardia. Pets, wild animals, etc. ingest cysts in contaminated stool, food or water. The organism infects the upper small intestine preventing proper absorption of nutrients. Infective cysts pass in the stool thereby continuing the cycle. Signs include persistent diarrhea with pale, greasy, foul and occasionally blood-tinged stool as well as weight loss. Diagnosis is difficult but is afforded via multiple special fecal exams, enzyme-linked immunosorbent assay (ELISA), immunofluorescent antibody (IFA) techniques and response to treatment. Treatment may include metronidazole, quinicrine, furazolidone and supportive care.


Strongyloides spp. is a small roundworm found in cats, dogs, foxes and occasionally people. The worms are about 2 mm long, live in the intestinal lining and produce eggs which hatch larvae while still in the intestine. Larvae pass in the feces and can reinfect the host animal or others via ingestion or skin penetration. Signs of the disease include diarrhea and debilitation. Diagnosis is afforded by finding the larvae during microscopic examination of the fresh feces, special fecal exam, endoscopic examination and/or biopsy of intestinal nodules in cats. Treatment is anthelmintics.


The tapeworm is a parasite that consists of a head and long flat body made up of segments. It is found in the intestines of dogs and cats but passes segments in the animal’s feces. The head remains attached to the animal’s intestinal lining, where it produces new segments. Tapeworm rarely cause more than a subtle decline in body condition, digestive upsets, poor appetite, poor haircoat and weight loss. Diagnosis is afforded by finding segments in feces, in bedding or clinging to the hair around the anus. Eggs may not be found on microscopic examination of the feces. Tapeworms are not passed directly from pet to pet, but require an intermediate host such as fleas in which to develop. Treatment includes anthelmintics and flea control.


Trichuriasis (Whipworm)

The whipworm is a small, thin parasite that lives in the large intestine and cecum. The whipworm gets its name from its body shape which has a tapered “whip-like” tail. Signs include diarrhea, bloody feces and poor general health. Diagnosis is afforded via physical exam and microscopic fecal exam. Occasionally it takes several fecal exams to detect whipworm since it takes 3-4 months after infection until eggs are passed in an infected pet’s stool. Treatment includes anthelmintics.