Fleas, Pets — Parasites: The Pet Owner s Parasite Resource


Fleas are the most common external parasite found on cats (and dogs). (Parasites are «freeloaders» that live in or on another creature.) Although fleas are more likely to be a problem during warm-weather months, they can also cause problems during cooler seasons due to their ability to continue their life cycle indoors.

How will fleas affect my cat?

You will probably first notice the effects of fleas when your cat repeatedly nibbles at and licks its haircoat and skin. On occasion you may actually see tiny brown fleas moving quickly through your cat’s haircoat. Cats are very skilled groomers, however, and may remove fleas so well that you do not see them. Your cat’s constant nibbling and licking may lead to noticeable patches of hair loss, tiny crusts (called miliary dermatitis by your veterinarian), and reddened, irritated skin. Fleas may also cause skin allergies and can transmit other parasites, such as tapeworms, to your cat.How do I check my cat for fleas?
Adult fleas are usually more difficult to find on cats than on dogs. One of the best methods for checking your cat for fleas is to look for flea dirt (actually flea feces) in your cat’s haircoat.

To check for flea dirt, briskly comb or rub a section of the hair on your cat’s back while your cat is sitting or lying on a white piece of paper. If your cat has fleas, black flecks that look like dirt (as a result, we use the term «flea dirt») will fall onto the paper. If you transfer these black flecks to a damp piece of paper, in a short time they will appear red or rust-colored. The red color results because blood sucked from your cat is passed in the flea’s waste matter. If the dirt specks do not turn red, then they are probably «regular» dirt.

How do I prevent my cat from getting fleas?


To control fleas, you must stop them from reproducing. Carpets, pet bedding, furniture, wood floors, and other indoor areas where your cat spends much time will contain the highest number of developing fleas (see the video above). Frequent vacuuming of these areas (throw the vacuum cleaner bag away afterwards) and frequent washing of pet bedding can greatly reduce the number of developing fleas inside your home.


Fleas also develop in shady, protected outdoor areas, although the outdoor areas are usually of less concern to pet owners who only have cats and do not have dogs. Most flea problems can be managed by treating and preventing fleas right on your cat. Remember that dogs and cats can share fleas, so be sure that dogs in your house are treated, too. It is important to remember that flea problems may be different from pet to pet or between households, and each problem may require a special method of control.

Steps to Take

See your veterinarian for advice on your specific situation. Your veterinarian can recommend safe and effective products for controlling and killing fleas and can determine exactly what you need. Your veterinarian can also determine whether you should consult with a pest control specialist about treating your home and yard or recommending products that will break the flea life cycle in the environment.

For veterinary professionals, more detailed information on fleas can be found at https://www.capcvet.org/guidelines/fleas/.

Did you know?

  • You may see fleas in your home or on your cat, or simply see your cat nibbling at and licking itself.
  • If not treated, you cat may suffer patches of hair loss or reddened, irritated skin. Fleas can also carry other parasites.
  • Frequent vacuuming and/or washing of pet bedding, carpets and furniture can help control fleas.
  • Cats and dogs can share fleas.
  • Flea treatments for your cat can protect it and break the flea life cycle.

Learn More about Specific Parasites

Ask Your Veterinarian

While fleas are primarily an annoyance, they can carry other illnesses. Dealing with fleas requires both controlling flea populations in your pet’s environment and killing fleas on your pet. Your veterinarian has treatments that are not available over the counter.


5 Strategies for Preventing Parasites in Dogs

Parasites in dogs include fleas, worms, ticks and heartworms. While parasitic infestation is common, you can reduce the incidence of infestation by taking steps to protect your dog. Here are some ways that you can reduce and prevent parasites in dogs.

1. Practice Flea Control

Flea control is difficult. You not only have to keep fleas off your dog, but also out of your house and lawn. Start by controlling the fleas on your dog.

The best way to control fleas on your dog is to use a monthly topical flea preventative like Frontline or Advantage. Not only are these flea repellents the most effective, they’re also easiest to use. They repel ticks, too.

Flea collars also provide some level of effectiveness, but they won’t kill all the fleas on your dog; dips provide good residual flea control, but they may irritate the skin of some dogs. Shampoos, powders and sprays kill adult fleas on your dog, but they don’t kill flea eggs or larvae and the effects don’t last very long.

Keep fleas out of your house by vacuuming high traffic areas, and the area around your dog’s bedding, daily. Keep linens, upholstery and curtains clean. If you have a lot of fleas in your house, and especially if you’re not using a topical flea preventative, you might want to consider using an indoor insecticide to kill fleas in your home.

Kill fleas in your yard by keeping your property neat, clean and free of leaves, brush piles and other debris where fleas might live. Mow your lawn regularly; fleas, flea eggs and flea larvae like moist, shady soil, so if the sunlight reaches your soil fleas won’t be able to thrive there.

See also:  Symptoms and treatment of otodectosis in dogs

2. Prevent Tapeworms by Controlling Fleas

Tapeworms use the adult flea as an intermediary host. The flea ingests the tapeworm egg, and then, when the dog bites or scratches a flea bite, he ingests the egg-carrying flea and becomes infested with tapeworms. Keeping fleas off your dog prevents tapeworm.

3. Don’t Let Your Dog Eat Feces

Your dog can catch whipworms and roundworms from the feces of other dogs who might be infected with these parasites. When walking your dog, avoid feces and don’t let your dog eat any of it. Clean up after your dog; he might be infested with these parasites without your knowledge, and cleaning up after him helps prevent the spread of parasites.

4. Use a Heartworm Preventative

Heartworm infestation is spread by mosquito bites and, if left untreated, can be fatal. Often, symptoms of heartworm infestation don’t appear until the condition has become serious. Use a monthly heartworm preventative medicine to protect your dog against heartworm.

5. Get Your Dog Checked for Parasites Every Six Months

No matter what you do to prevent parasitic infestation, your dog may still become infested with parasites. Some parasites, like hookworm, infest your dog by burrowing through the skin, and can live in the soil for a long time. Get your dog checked for parasites regularly, that way, if he does become infested, you can treat the problem before it becomes serious.


Parasite Control in Dogs

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Fleas, ticks, heartworms and intestinal worms – for their small size, these parasites pack a lot of misery for you and your pet. Besides driving your faithful companion crazy, they pose a hazard to pets and people.

Fortunately, you’re not without the means to fight back. What follows are guidelines and recommendations to keep your household safe and happy.

Know the Enemy

The first thing is to know what you’re up against:

Intestinal Parasites.

Dogs are victims of several internal parasites including roundworms, coccidia, giardia, hookworms and whipworms and can cause nausea, vomiting, diarrhea and anemia. The most common are roundworms (ascarids) that infest nearly every puppy at some time in his life. Usually they are born with them; they are passed from mother to young.

Tapeworms can be a big problem when flea infestation is high. Adult dogs typically acquire worms when they lick up microscopic eggs that are ever-present in contaminated soil or grass, or they swallow a flea. Mature dogs usually develop a resistance to most intestinal parasites, but the whipworm (Trichuris vulpis) can still cause problems, leading to colitis (inflammation of the colon) and weight loss.

Evidence of roundworms and tapeworms can be seen without the aid of a microscope, but other worms are not so easily diagnosed. Early diagnosis is important because all worms do not respond to the same treatment.

For information on illness caused by these internal creatures, see the articles “Intestinal Parasites” and “Protozoan Parasites.”


Watching a flea-bitten pet scratch herself desperately is a heart-rending sight. Fleas are a common problem for dogs, cats and people, who can also be bitten. As if the bite wasn’t bad enough, many dogs are allergic to fleas.

When a flea bites your dog, it injects a small amount of saliva into the skin to prevent blood coagulation. Some animals may have fleas without showing discomfort, but an unfortunate number of dogs become sensitized to this saliva. In highly allergic animals, the bite of a single flea can cause severe itching and scratching. Fleas cause the most common skin disease of dogs, which is called Flea Allergy Dermatitis. Other concerns regarding fleas can be found in the article The Dangers of Fleas in Dogs.


These creatures present another set of problems. When ticks are in need of a blood meal, they seek out prey by heat sensors. When a warm object passes by them, they attach themselves by clinging to clothing or fur or falling from trees onto the object and insert pincher-like mouthparts into the skin and begin feeding. These mouthparts are locked in place and will only dislodge when the tick has completed the meal. Once the meal is complete, the adult female falls from the prey and seeks shelter. Eggs are born and the adult female dies.

Dogs are a common target for ticks. If you live in an area populated with ticks you should keep a sharp eye on these parasites. They can transmit serious diseases (such as rickettsial diseases like Rocky Mountain spotted fever and ehrlichiosis) to dogs and even to humans. Find out more by reading The Dangers of Ticks in Dogs.


Heartworms have the potential to cause serious illness. All it takes is one bite from a mosquito carrying a heartworm larva. In time, the larva develops into a full-fledged adult worm, finding a home in the arteries of the lungs. Without treatment, dogs with heartworm disease will become lethargic, lose their appetite and begin to have difficulty breathing. Heart failure can also occur. For more information, read Canine Heartworm Disease.

The Battle Plan

Preventing Intestinal Parasites.

Puppies are regularly dewormed for roundworms and hookworms at the time of their “puppy shots.” If your puppy hasn’t been dewormed, talk to your veterinarian about getting this important step taken care of. A stool sample should be collected prior to each puppy vaccination visit, and a follow up sample examined at the appropriate interval after the last deworming medication has been given.

Worms can affect mature dogs as well. A yearly fecal exam is recommended for most adult dogs unless the dog is taking a heartworm preventative that also controls intestinal parasites. With primarily outdoor dogs, it may be beneficial to evaluate stool samples two or three times a year if the risk of infection is high. Or you may decide to administer a heartworm preventative that also controls intestinal parasites. Some of the newer heartworm combinations fight all three threats: heartworms, intestinal parasites and fleas.

Fighting Fleas and Ticks.

Even minor flea bites can cause severe reactions in some pets. Though the itching component to flea-allergy can be treated with antihistamines or even corticosteriods (prescribed by your veterinarian), the best approach is to kill the flea and prevent its return. There are many products available to treat flea infestations. Some of the over-the-counter powders, sprays and collars (such as those from Hartz® or Sergeants®) contain permethrin, which is moderately effective.

However, the best flea products are prescription – see your veterinarian for these. Products such as Program® (lufenuron) and Sentinel® (which also prevents heartworm disease) prevent development of fleas that attack your dog. If your dog already has fleas, then you need to kill them first with a product like Capstar® brand of nitenpyram, Frontline® brand of fipronil or Advantage® brand of imidacloprid. Some of these have residual effects that can also control ticks. A new product, Revolution®, is a topical treatment to prevent external parasites, heartworm and intestinal parasites. In addition to these prescription products, a collar tag called Preventic® is also effective in controlling ticks on some dogs. Other ideas can be found in Flea Control and Prevention.

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In tough cases, you may have to wage all-out war to conquer fleas. This means a comprehensive flea control program, requiring treatment of the pet, the pet’s bed, the yard and the house. A variety of sprays, dips, powders, foams and oral products may be recommended.

Ticks are very difficult to control, but a program of tick prevention and meticulously combing and grooming your dog can keep them at bay. See the related article “How To Remove and Prevent Ticks.”

Preventing Heartworm Disease.

Preventing heartworm disease is easier and much preferred to treating an active heartworm infection. Treatment is easy – just one tablet once a month. Please see “Heartworm Prevention Guidelines for Dogs.”

Not all parasitic diseases can be prevented but many can be treated. Mites are parasites that can cause serious illness in your dog. For more information, see Ear Mites in Dogs, Sarcoptic Mange, Demodicosis and Cheyletiellosis.

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Feline Health Topics

Gastrointestinal Parasites of Cats Brochure

Gastrointestinal parasitism is a common problem in cats, with prevalence rates as high as 45 percent. The parasites can be wormlike (e.g., stomach worms, roundworms, hookworms, tapeworms) or one-celled (e.g., Isospora, Giardia, Toxoplasma) organisms. The signs associated with parasite infections are fairly nonspecific, such as a dull haircoat, coughing, vomiting, diarrhea, mucoid or bloody feces, loss of appetite, pale mucous membranes, or a pot-bellied appearance. The vomiting, diarrhea, anemia, and dehydration caused by intestinal parasites will weaken a cat, making it more susceptible to viral and bacterial infections and diseases; thus robbing your cat of good health. Furthermore, some parasites have the potential of infecting humans.

Wormlike Parasites

Roundworms (Toxascaris leonina and Toxocara cati) are the most common intestinal parasite of cats, with an estimated prevalence of 25% to 75%, and often higher in kittens. The adult roundworms are 3 to 5 inches long, cream-colored, and live in the cat’s intestine. The adult female worm produces fertile eggs that are passed in the infected cat’s feces. The eggs require several days to several weeks to develop into the infective larva stage.

Cats become infected with Toxocara cati by ingesting eggs or by eating rodents (transport hosts) that have larvae in their tissues. Kittens can become infected by larvae that are passed through an infected queen’s milk. In those cases, it is possible for kittens to become infected soon after birth. Cats become infected with Toxascaris leonina in a manner similar to Toxocara cati, but unlike Toxocara, the parasite is not transmitted through the milk.

Roundworm infections can potentially become life-threatening if the numbers are so great that intestinal blockage occurs. Usually, roundworm infections are relatively benign when compared to other intestinal parasites. However, infected kittens are in serious danger if left untreated. Diagnosis is confirmed by finding parasite eggs in the stool during microscopic examination. Many medications are effective, but reducing exposure to the feces of an infected cats and prohibiting hunting are the best means of prevention. Treatment of queens prior to breeding reduces the likelihood that the parasite will infect kittens.

Visceral larval migrans and ocular larval migrans are diseases caused by the migration of Toxocara larvae through the tissue of people, particularly children. Although these diseases are rare, they can be quite serious, especially when they occur in young children. They can be easily avoided by preventing ingestion of Toxocara eggs in contaminated soil or on the hands.

Hookworms (Ancylostoma and Uncinaria) are less than 1/2 inch long, slender, thread-like worms that as adults live in the cat’s intestine. Because of their small size, they usually are not visible in the feces of infected cats. Hookworms are long-lived and are capable of living as long as the cat. Less common than roundworm infections, the prevalence of hookworm infections in North America is estimated to be between 10% and 60%.

Adult cats usually become infected by larvae that penetrate their skin or that are ingested. Once the larvae gain entrance into the host, they migrate to the lungs and then to the intestines to develop into adult worms. It is uncertain whether cats can become infected by eating rodents containing larvae in their tissues, or ingesting queen’s milk that contain larvae.

Severe parasitism can cause anemia due to blood loss from the intestines where the worms attach themselves. The cat’s feces will appear black and tarry due to blood in the feces. If too much blood is lost, the cat can become anemic and may die if left untreated. Fortunately, like roundworms, these worms are easily diagnosed and treated. Good sanitation and daily cleaning of the litter box are keys to controlling hookworm infections.

Hookworm larvae can penetrate human skin. As they migrate under the skin, they cause a dermatitis called cutaneous larval migrans.

Tapeworms (cestodes) have long flattened bodies that resemble a tape or ribbon. The body is comprised of a small head connected to a series of segments that are filled with eggs. The adult tapeworm lives in the small intestine with its head embedded in the mucosa. As the segments farthest from the head become fully mature, they break off and are passed in the feces. These segments can be observed near the cat’s tail and rectum, or in the feces. The segments are about one-quarter inch long, flat, and resemble grains of rice when fresh or sesame seeds when dry. When still alive they will usually move by increasing and decreasing in length. Microscopic examination of fecal samples may not always reveal the presence of tapeworms, because eggs are not passed singly, but as a group in the segments. Although the discovery of tapeworm segments can be quite alarming to cat owners, tapeworm infections only rarely cause significant disease in cats.

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Cats usually become infected with tapeworms by ingesting infected fleas while grooming or by eating infected rodents. Fleas and rodents become infected by eating the tapeworm eggs that are in the environment. Modern medications are highly successful in treating tapeworm infections, but reinfection is common. Controlling the flea and rodent populations will reduce the risk of tapeworm infection in cats.

Some tapeworm species that infect cats can cause disease in humans if the eggs are accidentally ingested; but good hygiene virtually eliminates any risk of human infection.

Whipworms are an uncommon parasite of cats in the United States. Adult whipworms reside in the large intestine of infected cats but do not cause serious disease.

Stomach Worms
Ollanulus tricuspis and Physaloptera species are worms that can inhabit the feline stomach. Ollanulus infections occur only sporadically in the United States and are more common in free-roaming cats and those housed in multiple-cat facilities. Cats become infected by ingesting the parasite-laden vomitus of another cat. Chronic vomiting and loss of appetite, along with weight loss and malnutrition may be seen, although some infected cats show no signs of disease. Diagnosis of Ollanulus infection can be difficult, and depends upon detecting parasite larvae in the vomitus. The most effective treatment is not known; avoiding exposure to another cat’s vomitus is the most effective means of controlling infection.

Physaloptera infections are even more rare than Ollanulus infections. Adult female worms attached to the stomach lining pass eggs that are subsequently ingested by an appropriate intermediate host, usually a species of cockroach or cricket. After further development within the intermediate host, the parasite is capable of causing infection when a cat ingests the insect or another animal (a transport host), such as a mouse, that has eaten an infected insect. Cats infected with Physaloptera may experience vomiting and loss of appetite. Diagnosis relies upon microscopic detection of parasite eggs in the stool, or seeing the parasite in the vomitus. Effective treatment exists, and infection can be prevented by limiting exposure to intermediate and transport hosts.

Neither Ollanulus nor Physaloptera are capable of causing disease in humans.

Protozoan Parasites

Isospora sp. (coccidia) are microscopic one-celled organisms causing the disease coccidiosis. Virtually all cats become infected with Isospora felis during their life. Cats become infected with this parasite by eating the cyst (thick-walled, egg-like stage) that has been passed in the feces and has matured in the soil. The cysts can be infective within six hours after being excreted in the feces.

Isospora infections usually cause no problems in adult cats, but evidence suggests that the parasite can cause significant disease in kittens. In infected kittens, the coccidia destroy the lining of the intestine and cause diarrhea with often contains mucous. Serious infections may develop in crowded environments. Good sanitation and hygiene will help control coccidia, but accurate diagnosis and effective treatment can only be achieved with your veterinarian’s assistance. Isospora of cats cannot cause disease in humans.

Giardia are flagellated protozoa (one-celled organism) that parasitize the small intestine of cats. The prevalence of feline giardia infection (giardiasis) is estimated to be less than 5% but can be much higher in some environments. Cats become infected by ingesting giardia cysts present in the feces of another infected animal, usually a littermate or chronic carrier cat. Giardiasis is more common in multiple-cat households and catteries due to its mode of transmission. Also, the infection rate is greater in cats less than one year old.

The cysts are very resistant to freezing. Also chlorination of municipal water does not destroy the cysts. After ingesting of Giardia cysts, it takes 5 to 16 days before the cat will show signs of diarrhea. Acute or chronic, and continuous or intermittent diarrhea is the most common sign of infection, although the majority of Giardia-infected cats are free of disease. They do, however, remain a source of infection to other cats. The cat probably requires several exposures to the organism before infection actually occurs.

Diagnosis of giardiasis depends upon microscopic identification of cysts in the stool. For accurate diagnosis, several fecal samples may need to be evaluated since cysts are not continuously shed in the stool. Several effective medications are available, but resistance is common. Elimination of Giardia infections from households of cats may be difficult and depends on proper treatment and sanitation.

It is uncertain whether species of Giardia that infect cats are contagious to humans or vice versa. Careful hygiene will eliminate the risk of accidental ingestion of cysts.

Cats are the definitive host for the Toxoplasma organism. Infection with this protozoan parasite is fairly common, but actual disease caused by this parasite is relatively rare in cats. Cats can become infected by Toxoplasma by eating any of the three infective stages of the parasites. The most common route of infection is probably by ingestion of tissue cysts in infected prey or in other raw meat. Toxoplasma multiply in the small intestines and in approximately two to three weeks the oocysts are excreted in the infected cat’s feces. (For more detailed information on this parasite, see Toxoplasmosis.)

Treatment may require administering one or more dosages of the medication prescribed by your veterinarian. Whenever using medications, be sure to carefully follow the directions provided by your veterinarian.

Parasite reinfections are very common, but can be prevented. Parasite control begins with good sanitation procedures. This includes daily removal of feces; washing the litter box with a disinfectant (e.g., diluted household bleach) on a regular basis; avoiding overcrowded conditions; avoiding diets with raw meats; and controlling intermediate hosts (fleas, ticks, and rodents). Good parasite control is the key to a healthier cat.

This brochure was prepared by the American Association of Feline Practitioners and the Cornell Feline Health Center, Cornell University, College of Veterinary Medicine, Ithaca, New York 14853-6401. The center is committed to improving the health of cats by developing methods to prevent or cure feline diseases and by providing continuing education to veterinarians and cat owners. Much of that work is made possible by the financial support of friends. ©2002 by Cornell University. All rights reserved. Cornell University is an equal opportunity, affirmative action educator and employer.


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