These are usually arthropods that live on the host animal by sucking its blood. Include ticks, mites, and fleas.
Physical Symptoms
Itching or irritation. Upon parting of hairs or combing with a flea comb, parasites may be visible. Ear mites may cause excessive or dark-colored wax in the ears. The animal may have very itchy or smelly ears.
Cause/Transmission
External parasites are transmitted from one infected animal to another or through contact with infected bedding, carpet, or vegetation.
Treatment
Consult your veterinarian. Generally, ticks may be removed easily with tweezers. Be sure you get their heads out of the skin, as the remaining pieces may cause infection. Wash the area where the tick was removed with a disinfecting agent. Generally, fleas may be treated with oral prescriptions, dips, drops, or powders. Mites can usually be treated with dips like flea dips; ear mites will generally warrant an ear wash or oral prescription. Sometimes an anti-itching agent like Benadryl may be prescribed. Remember that when treating external parasites, the entire area that your cat has contact with must be treated as well.