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

Evidence of roundworms 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, click on Intestinal Parasites and Protozoan Parasites.

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

When a flea bites your cat, 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 cats 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 cats – Flea Allergy Dermatitis. Other concerns regarding fleas can be found in the article The Dangers of Fleas in Cats.

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 cat 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.

Cats 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 to dogs, cats and even to humans. Find out more by reading The Dangers of Ticks in Cats.

Heartworms are not just a disease for dogs. Cats can also become infected. 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, cats with heartworm disease will become lethargic, lose their appetite and begin to have difficulty breathing. Heart failure can also occur. For more information, read Feline Heartworm Disease.

The Battle Plan

Kittens are regularly dewormed for roundworms and hookworms at the time of "kitten shots." If your kitten 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 kitten vaccination visit, and a follow up sample examined at the appropriate interval after the last deworming medication has been given.

Worms can affect mature cats as well. A yearly fecal sample is recommended for most adult cats if they are allowed out of the house. If yours is a primarily outdoor cat, you may want have stool samples evaluated every 3 to 6 months.

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 pyrethrin, which is moderately effective.

You must be very careful to only use products designed and approved for cats. Several over-the-counter products for use in dogs are toxic, and potentially fatal, to cats.

The best flea products are prescription, such as Program® (lufenuron). If your cat 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. 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. Other ideas can be found in Flea Control and Prevention.

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 cat can keep them at bay. See the article How To Remove and Prevent Ticks for more suggestions.

Preventing heartworm disease is easier and much preferred to treating an active heartworm infection. Treatment is easy – just one tablet once a month. See Heartworm Prevention Guidelines for Cats.

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