Fleas, Ticks, Lice, Mites, and Flies

By Lynn P. Schmeitzel and Peter J. Ihrke.

Fleas are wingless, brown, bloodsucking insects that may infest dogs and cats, and other warmblooded animals.

Fleas transmit several diseases (for example, plague) and parasites such as tapeworms. Young animals heavily infested with fleas may die from severe blood loss. Fleas prefer certain species of animals but will attack any source of blood if the preferred animal is not available.

The cat flea (Ctenocephalides felis) and the dog flea (Ctenocephalides Canis) both infest dogs and cats. C. fells is the most common flea found on dogs and cats. Cat and dog fleas move rapidly on the skin and are most easily found on the rump and in the groin area.

Sticktight fleas (Echidnophaga gallinacea) are found on birds (especially chickens) and may attack dogs and cats exposed to infested birds. This flea attaches to the face of the animal and moves slowly.

The human flea (Pulex irritans) may attack dogs and cats.

Flea eggs laid on the host are smooth and quickly fall off into the animal's environment. The eggs are oval, white, and glistening.

Small larvae hatch from the eggs and feed on the feces from adult fleas. After several molts, the last larval stage forms a pupal case. While in the case, the larva develops into an adult flea. The adult flea emerges from the pupal case and searches for an animal.

Time required for the flea to develop from egg to adult may be as short as 16 days during periods of warm temperatures and high humidity.

A small amount of flea saliva is deposited in the skin each time the adult flea bites an animal. This saliva is very irritating and an allergic reaction can cause severe itching, resulting in the skin disease termed flea allergy dermatitis.

Biting and scratching around the rump and groin areas is the most common sign of flea allergy. Hair loss, a red rash, and thickening of the skin are commonly seen. Fleas may be difficult to find in allergic animals since very few flea bites are needed to cause an allergic reaction. In areas of the United States where fleas are common, flea allergy dermatitis is the most common itchy disease of the skin.

Flea feces (flea dirt) in the haircoat confirms the presence of fleas. Flea dirt consists of dehydrated blood from the dog or cat and is reddish-black and comma-shaped.

Successful treatment of flea allergy dermatitis requires the absolute elimination of fleas from contact with the affected dog or cat. If one dog or cat in a household has fleas, it may be assumed that all animals in the household have fleas. Therefore, all animals in the household must be treated. All animals, the house, and premises should be treated with appropriate insecticides at frequent intervals to prevent reinfestation.

Contrary to recent folklore, brewers yeast (a thiamine or B, source), garlic, or sulfur are not effective in either repelling or killing fleas.

Ticks, Hard and Soft

Ticks are bloodsucking arthropod parasites of the skin. They transmit many diseases such as Rocky Mountain Spotted Fever to people and animals. Severe blood loss may result from heavy infestation. Tick paralysis is a rare disease caused by a toxic substance in the saliva of some ticks. Recovery is rapid if the ticks are removed.

Ticks have a four-staged life cycle including an egg, a six-legged larva (seed tick), an eight-legged nymph, and an eight-legged adult. Ticks are identified as one-host, two-host, and three-host ticks depending on the number of hosts required to complete their life cycle.

Hard ticks (Ixodidae) and soft ticks (Argasidae) are the two main families of parasitic ticks.

Hard ticks have a hard shield on their backs distinguishing them from soft ticks which do not. Most hard ticks require three different hosts to complete their life cycle and each stage only feeds once.

Thirteen species of economically important ticks are in the hard tick (Ixodidae) family. Most of these ticks are acquired outside except for the Brown Dog Tick (Rhipicephalus sanguineus) which can infest buildings.

The Brown Dog Tick is widely distributed in North America. Since this tick survives indoors, it can infest kennels and households. The Brown Dog Tick is a three-host tick but all three stages can parasitize the dog. This tick also parasitizes cats, horses, rabbits, and humans. The Brown Dog Tick has no white markings on the shield on its back.

The American Dog Tick (Dermacentor variabilis) is widely distributed in North America but is most common on the Atlantic coast. These ticks, unlike the Brown Dog Tick, live only in grasses and shrubs.

The larval and nymphal stages of the American Dog Tick parasitize field mice. The adult tick usually infests the dog but also can parasitize humans, wild animals, cattle, and horses. Adult American Dog Ticks have white markings on the shield on their backs. Outdoor areas such as fields are the major sources of American Dog Ticks.

Removal. Hard ticks usually are found securely attached by their head to the skin. Before removal, these ticks should be sprayed with an insecticide safe for use on animals, or soaked with alcohol. The head should be grasped with an instrument such as tweezers and pulled on gently until removed. Cigarettes, lighters, gasoline and kerosene can severely injure the skin and should never be used to remove ticks. If the ticks are Brown Dog Ticks, the kennels and household premises may need repeated treatment with pesticides.

Soft ticks (Argasidae) have a leathery outer covering. The Spinose Ear Tick (Otobius megnini) is the only medically important soft tick. This tick is most common in the southwestern parts of the United States. The young stages (larvae and nymphs) live in the outer ear canal of dogs, cats, cattle, and horses. Adult soft ticks do not feed and do not live on animals.

The Spinose Ear Tick can cause severe irritation to the ear canal and may occasionally cause paralysis and seizures in some animals. The animal should be taken to a veterinarian for removal of these ticks since the eardrum may be damaged by improper removal of the ticks, especially by sharp instruments.

The Louse

Lice are wingless insects that are uncommon parasites of dogs and cats and are common parasites of livestock and birds in the United States. Lice spend their entire life cycle on the host and are not readily transmitted from one animal species to another (they are host specific). In other words cat lice will not usually infest dogs and vice versa. Lice are spread from an animal to another by direct contact.

Female lice attach their eggs (nits) to the hairs or feathers on their hosts. The Young lice undergo several molts before becoming adults. Development from egg to adult takes about 19 to 28 days.

The two main types of lice include sucking lice (Anoplura) and biting lice Mallophaga).

Sucking lice are larger than biting lice, have piercing mouthparts for obtaining a blood meal, and have pincer-like claws for clinging to the hairs of their hosts. These lice are grey to red depending on the amount of blood they have ingested. Sucking lice may cause severe anemia in heavily infested young or debilitated animals.

Sucking lice can infest most domestic animals (except birds and cats). Infested animals are usually itchy and often have rough dry coats. Sucking lice move slowly.

Biting lice usually are yellow with a large rounded head and mouthparts adapted for chewing and biting. Some species have legs for clasping, others have legs for moving rapidly. These lice may cause severe hair loss from scratching and rubbing. Biting lice can infest dogs, cats, cattle, sheep, goats, horses, and birds.

Specific identification of lice is difficult and is less important than being able to determine if the louse is a biting species or the more harmful blood-sucking species.

The dog has one common biting louse (Trichodectes Canis) and one common sucking louse (Linognathus setosus). The cat has only one common species, a biting louse (Felicola subrostratus).

Adult lice and eggs attached to hair and feathers may be seen with the unaided eye. Lice and nits may be found more readily by using a magnifying hand lens with good lighting.

Many pesticides will kill adult lice but the eggs are quite resistant. Consequently, animals should be treated and then retreated two weeks later to kill the lice that have hatched from eggs not affected by the first treatment.

All About Mites

Demodectic mites (Demodex spp.) parasitize many domestic animals. These mites live in hair follicles in the skin. They crawl from the mother to the nursing puppy or kitten during the first few days of life. They do not cause any harm in small numbers and are considered normal inhabitants of the skin. These mites are not contagious from animal to animal, or animal to human. The skin disease caused by an increased number of mites is called demodicosis or demodectic mange.

Demodex spp. are elongated mites with short stubby legs. The life cycle includes an egg, a six-legged larva, an eight-legged nymph, and an eight-legged adult.

These mites can be demonstrated by a veterinarian performing a skin scraping, removing the superficial layer of a small area of skin with a scalpel blade. The debris is placed on a glass slide with mineral oil and examined with a microscope.

Affects Dogs. Demodicosis is a potentially serious disease in the dog. If large numbers of Demodex canis mites are found in several skin scrapings a diagnosis of demodicosis may be made.

There are two forms of demodicosis in the dog localized and generalized. Patchy hair loss on the head, forelegs, and trunk is called localized demodicosis. In generalized demodicosis hair loss, reddening, and crusts may involve the entire body. These animals also may develop severe bacterial infections in the skin.

An inherited defect in the animal's immune system allowing the mites to multiply is believed to be an important factor in development of generalized demodicosis. Since it is believed that the defect of the immune system is inherited, dogs with demodicosis should not be used for breeding. Demodicosis is not a contagious disease. Affected puppies were born with a predisposition to develop demodicosis.