External Parasites of Dogs and Cats

CARROLL N. SMITH AND F. D. ENZIE.

ALMOST everyone who keeps dogs or cats is concerned at some time with their external parasites. Among them are several kinds of mange mites, ticks, fleas, and lice. Fleas are the most annoying. Mange mites and ticks also are common and can quickly reduce an animal to a condition of misery or death. Lice are less common on dogs and cats in the United States.

Mange is an unsightly and painful skin condition caused by the burrowing or feeding of mites, several species of which attack dogs and cats. The mites are related to ticks and spiders. Many are microscopic in size, and the others are barely visible. The condition is contagious and is spread by contact with infested animals.

Sarcoptic mange of dogs is related to the human infection called scabies and is caused by the mite Sarcoptes scabiei cants. The female mite burrows into the upper layers of the skin, where she lays 20 to 40 eggs. The eggs hatch after 3 to 7 days and produce larvae, which are tiny mites with three pairs of legs. The larvae grow to nymphs by molting shedding the skin and the nymphs grow to adults in the same way. The nymphs and adults have four pairs of legs, but the nymphs are sexually immature. The entire life cycle requires 2 to 3 weeks. The larvae, nymphs, and males do not burrow into the skin, but live under crusts or scales on the surface.

Sarcoptic mange may occur on any part of the body, but usually it appears first on the head. It spreads rapidly. Red spots appear and develop into small blisters. The scratching of the animal causes the reddish area to spread.

The burrowing of the female causes the skin to exude serum, which dries in crusts or scabs. The infected part of the skin becomes dry and covered with crusts, the hair may come out, and the skin may thicken and become wrinkled.

Itching is intense. The scratching may give rise to secondary bacterial infections and sores. Bacterial action in the scabs and sores causes an unpleasant odor. If the infection is not checked, digestion and other body functions become impaired, and death may result.

This species of mite can live for a time on people. Unnecessary handling of infected dogs should be avoided.

A related mite, Notoedres cati, causes a severe type of mange in cats, which usually starts about the head, forming crusts, until the skin becomes hard, thickened, and creased.

Demodectic, or red, mange of dogs is caused by a long, wormlike mite, Demodex Canis, which lives principally in the hair follicles of the skin. It has been found also in certain lymph glands and in the liver, spleen, lungs, and other internal organs. The mites are found in typical cases in great numbers in association with bacteria, which cause the most unpleasant symptoms of the infection.

The first evidence of demodectic mange is usually the appearance of bald areas, from which the hair has been lost. Itching becomes pronounced as the spots spread, and the area becomes reddened. After invasion by the bacteria, the infection becomes pustular, the skin becomes thicker, poisons formed by the bacteria affect the general health of the animal, and a disagreeable odor is produced. The 'infection may last for several years. It usually causes death if it is unchecked.

Ear mange of dogs and cats is caused by the mite Otodectes cynotis. The mites do not burrow in the skin but live deep in the ear canal, near the eardrum, and feed through the delicate skin. Irritation results. The ear canal becomes congested. The dog scratches and rubs its ears and shakes its head in an attempt to relieve the itching, or it may run in circles or show other evidence of nervous disturbance.

Mange may be confused with other skin conditions. It can be diagnosed positively only by a microscopic examination of scrapings from the diseased parts.

PREVENTION OF MANGE in dogs and cats is largely a matter of good care and management. A well-balanced, nutritious diet; clean, dry, comfortable quarters; protection from the debilitating effects of internal parasites; and regular, thorough grooming all promote good health and tend to increase resistance to skin diseases of all kinds.

Above all, however, the dog or cat should not be permitted to mingle with mangy animals or to frequent premises occupied by them, since they are the main sources of infection.

Rational treatment is contingent upon a prompt, accurate diagnosis, because the various types of mange differ in their response to remedial measures. Improper treatment is costly and may cause injury to the patient or permit the condition to reach an incurable state.

Ear mange will generally respond promptly to one or two weekly applications of olive oil containing 1 percent of rotenone or 0.25 percent of lindane. The materials may be applied with cotton swabs or put into the ear canal with a medicine dropper. Accumulations of foreign matter should be carefully removed from the ear canal before treatment. That can be done more easily if the accumulations are soaked first with the medicated oil.

Demodectic mange is difficult to treat. The results often are disappointing. The response to specific medication varies among individual animals and seems to be influenced by the patient's general condition. In addition to the use of chemical agents for the destruction of the mites, therefore, every effort should be made to build up the general health of the animal by improving the diet and combating secondary bacterial infections.

Several chemical agents are available for use against the mites, but none appears to be uniformly effective. Alternative treatments therefore should be tried when little or no improvement is noted after a reasonable period of medication. Among the preparations that have proved most satisfactory are 1 percent of rotenone in vegetable oil; a 25- to 33-percent benzyl benzoate emulsion; 0.15-percent aqueous lindane suspension; 2- to 5-percent tetraethylthiuram monosulfide; and a 0.25-percent chlordane emulsion.

Most of these agents are applied once or twice weekly, as necessary.

The finding of demodectic mites in lymph glands, liver tissue, and other internal organs has suggested the possible need for internal medication to supplement the application of remedial agents to the skin.

Sarcoptic mange may be treated effectively with any of the remedies suggested for demodectic mange. The treatment of sarcoptic mange, however, is less tedious; the disease often responds to a single application of the chlorinated insecticides, such as lindane and chlordane.

Similar response may be had with some of these materials in head mange of cats, although extreme caution must be exercised in the treatment of cats because of their marked sensitivity to most drugs. It is, in fact, advisable in all cases of mange to entrust treatment to a veterinarian.

TICKS of several species may infest dogs, but cats are rarely infested. Many of the dog ticks are also known as wood ticks and infest dogs when they run through woods or fields. The brown dog tick is a truly domestic species that feeds almost exclusively on dogs.

The brown dog tick, Rhipicephalus sanguineus, is particularly troublesome because it is adapted to life in the relatively dry environments of kennels, heated houses, and apartments. Dogs pick up ticks in infested premises and in turn infest their own living quarters. Yards as well as houses in the southern States may be infested. The ticks may survive the winter outdoors in the extreme South. The brown dog tick is the principle vector in this country of canine piroplasmosis, a protozoan infection encountered most frequently in Florida and adjacent States.

The adult ticks are about one-eighth inch long when unfed, flat, and reddish brown. Both sexes feed on dogs. Mating takes place on dogs. The males remain about the same size.

The females become engorged with blood, reach a length of about one-half inch, and turn dark gray. After engorging, which takes about 6 days, the females drop from the dog and seek a hiding place. They usually hide in cracks in the woodwork, under rugs, or behind pictures, mirrors, or draperies. They lay 1,000 to 3,000 eggs, which hatch after 3 to 8 weeks into tiny, six-legged larvae, or seed ticks.

The larvae are light brown and about one-fiftieth inch long when unfed. They feed on dogs and become about one-twentieth inch long and slate gray. Feeding requires 3 to 6 days, after which they drop and hide like the females. They molt after 1 to 3 weeks and become eight-legged nymphs, about one-twentieth inch long and flat and brown. The nymphs feed on dogs becoming about one-eighth inch long and slate gray. They drop, hide, and molt to the eight-legged, sexually mature males and females. Engorgement requires 4 to 9 days and molting about 12 to 29 days.

Ticks crawl about the walls, floors, and furniture in heavily infested houses in search of a host. They very rarely bite people. Their mere presence is annoying. Heavy, continuous infestations on dogs cause irritation and loss of condition. Pulling the ticks off leaves open wounds, which may become infected.

The other ticks that infest dogs also infest other animals. They live outdoors and will not live long in dry, unheated buildings. They pass through the same stages egg, larva, nymph, and adult but all stages do not always have the same host.

The American dog tick, Dermacentor variabilis, is the most widely distributed species. It is most abundant along the Atlantic and gulf coasts, in the Mississippi Valley, and along the Pacific coast as far north as Oregon. Scattered infestations occur in most other parts of the country, except in the Rocky Mountain region and in the Pacific Northwest.

A closely related species, the Rocky Mountain spotted fever tick, D. andersoni, occurs in the Rocky Mountain region. Another, the Pacific coast tick, D. occidentalis, occurs in California and southern Oregon.

The gulf coast tick, Amblyomma maculatum, occurs along the gulf and Atlantic coasts as far north as South Carolina. The lone star tick, A. americanum, occurs from New Jersey west to Iowa and south to Florida and Texas.

Adults of all the foregoing species are reddish or dark brown and marked conspicuously with one or more patches of white.

The black-legged tick, Ixodes scapularis, occurs along the Atlantic and gulf coasts from Massachusetts to Texas and in the lower Mississippi Valley. A closely related species, L pacificus, occurs along the entire Pacific coast of the United States. These species possess a smoky-black shield. The body of the females behind the shield is yellow or light brown.