There are three usual culprits for cat worms - tapeworms, roundworms and hookworms. It can be very hard for you to tell just by symptoms which type of worms your cat has. The best way is to take a stool sample to the vet to be tested. This will give you an exact answer and help with treatment.
You can take a stool sample to the vet in a ziploc bag, or some vets provide stool sample kits to their clients. In either case, it must be as new a sample as your cat decides to give you (if it has cat litter on it, that is normal!).
In a multi-cat household it can be almost impossible to tell whose stool is whose. Separating the cat you think has cat worms in a different room with food, water and a litter box until your cat goes to the bathroom is the easiest way.
The most common type of cat worms are Tapeworms.
Cats can get tapeworms by eating prey (usually rodents) or uncooked meat, or from infected fleas. The adult tapeworm attaches to the cat's intestinal wall and absorbs nutrients. Eggs produced by the tapeworm pass out in the cat's stool.
The most common signs of tapeworm infection are worm segments or eggs that can be seen on the cat's rear end or in the stool. Tapeworm segments are white or pinkish white, flat and rectangularly shaped. They can move in a stretching and shrinking motion. Dried eggs can look like a grain of rice or a sesame seed.
In a more severe infection, worms can be seen in the cat's vomit.
Other symptoms can be more general - weight gain or loss, loss of appetite or voracious appetite, bony appearance or big distended abdomen, dull coat, hair loss, and excessive licking around the anal area.
Treatment is relatively easy - your vet can prescribe you a dewormer, usually in tablet form. Since many tapeworm problems are caused by fleas, a good flea treatment program is also helpful to prevent re-infection.
There are several kinds of roundworms, but the most common kind are called Ascarids. They are white, cylindrical and pointed at both ends. Cats can become infected with ascarids by eating prey (rodents or cockroaches). Ascarids are also very common in kittens because they can be passed through the mother's milk.
The symptoms of roundworms in adult cats are very similar to tapeworms. In kittens vomiting, diarrhea, dull coats, a pot belly on a thin body, and weakness are symptoms of roundworm. It is a good idea to get your kitten checked for roundworm by your vet, as it can cause serious illness in kittens.
Your vet will prescribe a dewormer, and it may have to be repeated several times before the roundworms are gone. Ascarid eggs are very resistant, so during the treatment litter should be scooped daily and litter pans washed with hot water and detergent regularly. Throw out the litter and disinfect the boxes before the end of the treatment.
Hookworms are less common cat worms, but are found in hot humid areas. They also infect the cat through prey, partially rotten meat, or through their mother's milk. Larvae can also penetrate the skin, especially around the toes, and migrate to the small intestine. Migration through the skin can be seen by scratching, redness, scabs and bumps on the skin.
Hookworms can cause severe anemia, diarrhea, weight loss, a rash between the toes, and dark red or black stool. Hookworm is a very serious parasite infection - it must be treated by a veterinarian. Your cat may require a short (day or two) stay at the vet to be treated for hookworms. The used cat litter needs to be thrown out, and all bedding, litter pans, food and water bowls should be washed in hot water.
If you live in a hookworm area, have your cat tested every few months. It is best to keep your cat indoors and wash litter pans thoroughly.
If you suspect cat worms, have the vet analyze a stool sample to see which type of worms you are dealing with. Always use vet-prescribed dewormer -over the counter dewormer is toxic and does not work on all worms.The dosage needs to be correct for your cat's weight and size. The over the counter wormer is at best ineffective and toxic at worst.
If your cat vomits too soon after you give the dewormer, you may need another dose from the vet.
In a multi-cat household you will need to treat all cats (and probably dogs - you know what dogs like to do with kitty litter...) if they share food, water and litter.