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.
Insecticides
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.
Parasitic worms in pets
Parastitic worms are endoparasites as they live inside their host. They are common to both cats and dogs and can cause serious illness. There are many different species and most of them affect the gastrointestinal system and have complex life cycles. The most common parasitic worms that infect cats and dogs include the following:
Heartworm is a parasitic worm transmitted by mosquitoes. It has two larval stages in the mosquito and another two in its next host, which can be cats or dogs. Following a mosquito bite, the heartworm larvae transform into the next larval stage and migrate through the tissues to the heart and lungs, where they mature into adults, grow rapidly, reach sexual maturity and mate. The females produce microfilariae, which enter the blood stream ready to be transmitted back to the mosquito host to continue the life cycle. Heartworm causes tissue damage and can cause serious health problems that can result in heart failure and eventually death. Symptoms in dogs include coughing up blood, breathlessness, fainting and congestive heart failure. Symptoms in cats include vomiting, diarrhoea, weight loss, lethargy and difficulty breathing.
Roundworms belong to the group of ascarids and are very common in cats and dogs, causing health problems including damage to the intestine and digestion problems as they absorb nutrients from the blood of the host. Adult dogs are infected by ingesting eggs from soil, infected food or water and puppies can be infected while still in the womb or when lactating through infected milk. Once swallowed the roundworm eggs hatch and the larvae migrate through the intestine wall into the lungs and internal organs, where they can lie dormant; they can also migrate through the uterus to infect the foetus. They are eventually coughed up from the lungs and swallowed where they mature in the intestines. Mature worms grow to great lengths and produce eggs, which are passed out of the host in the faeces ready to begin the life-cycle again. Symptoms include an extended abdomen, worms in faeces, coughing, lethargy, intestinal obstruction and colic.
Hookworm infestation is more common in dogs than cats and is transmitted by larvae in infected soil, food or water entering by ingestion or by burrowing through the skin. Like roundworm puppies can be infected while still in the womb by larvae that migrate through the uterus to infect the foetus or when lactating through infected milk. When the larvae reach the intestines they mature into adults and attach to the wall of the intestine where they feed from blood. The mature hookworms produce eggs, which are shed in the faeces and hatch in the soil. Symptoms include poor appetite, blood in the stools and anaemia, which if it becomes severe can be fatal.
Whipworm is a common parasitic infestation in dogs and less so in cats. Dogs and cats become infected by ingesting food or water contaminated with eggs. The eggs hatch in the large intestine and the larvae mature into adults in the large intestine or bowel. The adults attach with specialised mouthparts and burrow through the intestine wall, where they feed on the host blood. The adults lay eggs in the intestine, which are passed out with the faeces and remain in the soil until they are ingested again. Symptoms of whipworm infection include inflammation and bleeding of the intestine and anaemia.
Tapeworms are cestodes that live in the small intestines and can grow to great lengths. The lifecycle consists of the eggs, which are produced by each multiple segments of the adult worm in large numbers. These pass out of the main host in the faces and are ingested by the intermediate host, such as cattle, pigs and sheep, where the eggs hatch and the larva or hyatid tapeworm migrates to various organs and remains dormant as a hyatid cyst. The main host (dog or cat) becomes infected by eating infected meat. Once in the main host intestine, the tapeworm matures and attaches to the intestine wall, using specialised suckers and hooks on the head that allows it to attach and feed on the nutrients of its host. There are several species that can infect dogs, including the Taenia species, but tapeworms do not usually cause any major health problems.
Anthelmintic de-worming drugs
Several anthelmintic drugs are available that are effective for use as de-worming medications for dogs and cats and are generally used as a combination of two or more of the following:
Ivermectin is effective against most common intestinal worms except tapeworm in dogs. It acts on the nervous system of the larval stage of the parasitic worm and causes paralysis and death before it reaches major organs.
Pyrantel and oxantel are effective against most common nematodes in dogs, acting as neuromuscular blocking agents that paralyse the roundworm and hookworm while they are feeding in the dogs’s intestine, so that they lose their grip and pass out in the stools.
Praziquantel is effective against intestinal tapeworms (cestodes) in dogs and works by interfering with the tapeworm’s ability to protect itself against its host, causing the tapeworm to lose resistance to digestion by the host digestive enzymes.
Selamectin effective against heartworm, hookworm and roundworm in cats and dogs and acts as a as neuromuscular blocking agents that paralyses the roundworm and hookworm while they are feeding in the intestine, so that they lose their grip and pass out in the stools.
