Ectoparasites in cats and dogs
Ectoparasites are parasites that live on the skin of their host. They include parasitic insects like fleas and lice and parasitic arachnids like ticks and mites. Most ectoparasites feed on the blood of their hosts and can cause health problems including dermatitis and anaemia.
fleas and lice
Fleas and lice are parasitic insects belonging to the same class of arthropod animals as wasps, bees, flies and mosquitoes.
- Fleas have a four-stage life cycle; the egg, larva, pupa and adult. The eggs are laid usually on the host, then they fall off and are deposited along with faeces on the ground. When the larvae hatch, they feed on the faeces and grow by moulting three times then spin a cocoon to become a pupa. This stage can lie dormant for some time both indoors and outdoors until vibration, warmth or carbon dioxide indicates that a suitable host is nearby, like the family cat or dog, the adult then emerges and uses its long hind legs to jump onto the host, bites it with specially adapted mouthparts and sucks the blood. Flea bites can cause severe irritation and itching that can lead to flea allergy dermatitis, which is a reaction to flea saliva. If the infestation is severe particularly in puppies or kittens, they can cause anaemia. Fleas are also carriers of disease like tapeworm, plague and typhus.
- Lice are transmitted by direct contact with another infested pet. There are two types; sucking lice that feed on blood and biting lice that feed on skin cells. Lice can spend their entire life-cycle on the host animal. They lay their eggs on the hair follicles in the skin, where they hatch and transform through three nymph stages into adults. Symptoms of lice include scruffy dry hair, itching and hair loss due to scratching.
ticks and mites
Ticks and mites are parasitic arachnids belonging to the same class of arthropod animals as spiders and scorpions.
- Ticks attach to the skin of its host with special adapted mouthparts and feed from their blood. They have a life-cycle of four stages, the egg, larva, nymph and adult. Adult ticks lay eggs on the ground which hatch into larvae that attach to the first host, which is usually a small animal like a rodent or bird. Each stage feed on blood and then falls off he host and transforms into the next stage by moulting. Dogs and cats pick up ticks either at the nymph or adult stage by physical contact from the outdoors, such as a wooded area, long grass or amongst short shrubs. Ticks are carriers of several diseases including tick paralysis, caused by a toxin produced by the tick resulting in symptoms like difficulty walking, swallowing and breathing and can lead to death; also Lyme disease, caused by transmission of a bacteria by the tick resulting in symptoms like fever, lameness, swelling of joints and lymph nodes and loss of appetite.
- Mites are transmitted by direct contact with another infested pet and can live on any part of the animal’s body and feed on skin cells and keratin in the outer layer of skin. The ear mite is one of the most common forms and these live in the ear canal feeding on wax and skin scales. Eggs are laid in the ear or on the skin and hatch into larvae, transforming into the nymph stage and finally maturing into adults. Symptoms of ear mite infestation includes a black discharge from the ear resembling coffee grounds with severe irritation causing the animal to scratch and shake its head and can result in ear damage and loss of hearing if left untreated.
Insecticide is a general term used for treatment of insect ectoparasites but may also be effective against other parasites including arachnid parasites. Some also have anthelmintic properties and are effective against internal parasites, like some worms.
- Fipronil is a broad spectrum topical insecticide that kills fleas at adult and larval stages, particularly newly emerged adult fleas before they lay eggs and usually before they bite, which helps prevent flea allergy dermatitis. It also kills biting lice, and is effective against all stages of ticks, which are parasitic arachnids, and this helps prevent tick-borne disease transmission. Fipronil is applied to the skin, spreads by mixing with body oils and collects in the hair follicles of the skin, where it is slowly released to provide long-lasting protection. Fipronil works by blocking nerve transmission and disrupting the insect central nervous system, causing paralysis and death within 24-48 hours of application.
- Methoprene is an analogue of the growth hormone of insects, which mimics the action of the natural juvenile hormone and works as an insect growth regulator. Insect juvenile hormone is needed for the larval stages to develop but it prevents the formation of the insect pupa and its development into the adult. Methoprene disrupts the life cycle of insects like fleas that pupate, thereby attacking all stages of the flea while on the host animal reducing risk of further infestation.
- Selamectin is an antiparasitic drug that acts as an Insecticide and is effective against parasitic insects like fleas, also parasitic arachnids like ticks and ear mites. Selamectin is applied to the skin, spreads by mixing with body oils and collects in the hair follicles of the skin, where it is slowly released to provide long-lasting protection. It is also absorbed through the skin into the blood stream and acts as an effective anthelmintic in cats against parasitic worms like roundworm and hookwork that feed on the host blood. Selamectin works by blocking nerve transmission and disrupting the central nervous system, causing paralysis and death and is effective for up to 30 days.