Diseases of the Integumentary System

Chapter 6 Diseases of the Integumentary System

The skin makes up the largest organ system in the body. It comprises approximately 24% of the total body weight of a newborn puppy and about 12% of the body weight of an adult animal. It consists of three distinct layers: the epidermis, the dermis, and the hypodermis, or subcuticular layer (Fig. 6-1) (refer to an anatomy and physiology textbook for the exact function of each layer). The skin serves as a barrier between the animal’s body and the environment. It not only protects the animal from physical, chemical, and microbiological injury, but the sensory organs found in the skin allow the animal to feel pain, heat, cold, touch, and pressure. The skin is also a storage depot for electrolytes, water, proteins, fats, and carbohydrates, and it assists in the activation of vitamin D by solar energy.

The hypodermis stores fat for insulation and energy reserves. The animal’s skin has many functions:


External parasites are responsible for many skin problems seen in small-animal medicine (see a parasitology text for detailed information on the life cycles of the individual parasites discussed in this chapter). The most commonly diagnosed ectoparasites are as follows:

Some of these parasites live on the skin; some live within or under the skin; and some pierce the skin, sucking blood meals that produce severe cutaneous reactions. These reactions include inflammation, edema, and itching. In many cases, the animal itself is responsible for increased damage to the skin through licking, chewing, and scratching.

Ear Mites (Otodectes cynotis)

Ear mites live on the surface of the skin in the external ear canal, feeding on epidermal debris (Fig. 6-2).

Fleas (Ctenocephalides spp.)

Fleas are blood-sucking ectoparasites that feed sporadically on mammals and birds (Fig. 6-3). Fleas produce severe skin irritation as a result of their frequent bites. Flea saliva is highly antigenic in some animals and will produce an allergic dermatitis. Fleas can act as vectors for diseases and as intermediary hosts for the dog tapeworm (Dipylidium canium). Pets, as well as their environment, can become infested with massive numbers of fleas.


Ticks (Ixodes spp. and Argasid spp.)

Ticks are seen commonly on outdoor dogs and cats, especially during the summer months. These blood-sucking, arthropod parasites are not host specific and will infest all warm-blooded animals in the area (including humans). Heavy infestation may produce anemia in the host. Ticks also can transmit many bacterial, viral, rickettsial, and protozoan diseases. Lyme disease is one high-profile example of tick-borne disease. Ticks are divided into two main families: Ixodidae (hard ticks) and Argasidae (soft ticks). Most of the commonly found ticks belong to the Ixodidae family. Some of the best known members of this family include Rhipicephalus sanguineus (the brown dog tick (Fig. 6-4), Dermacentor variabilis (the American dog tick), and Amblyomma spp. All but Rhipicephalus spp. gain access to the host outdoors. Rhipicephalus spp. typically inhabit buildings and kennels. One soft tick, the spinose ear tick (Otobius megnini) can be found in the ear canals of dogs and cats in the southwestern United States.

Ticks injure animals by several means: irritation of the actual bite, as vectors of disease, and through a neurotoxin found in the saliva of 12 different Ixodes species. This neurotoxin causes tick paralysis, an ascending, flaccid paralysis of dogs.


Demodectic Mange

Demodex canis, a cigar-shaped mite, lives within the hair follicles of most dogs and some cats (Fig. 6-5). These mites spend their entire life cycle on the host. In most dogs, the immune system holds the number of mites in check; however, in dogs with compromised immune systems (such as puppies with poor nutrition or other parasites, or dogs with chronic disease), the number of mites becomes excessive, causing disease. There appears to be a hereditary predisposition to demodectic mange, and certain breeds seem to be at greater risk.

Demodectic mange occurs in two forms: localized, the more commonly seen form, and generalized, the more severe but less common form.

Sarcoptic Mange (Scabies)

Scabies is an intensely pruritic, contagious disease of animals. The mite, Sarcoptes scabiei var. canis, has a rounded body with four pairs of legs (Fig. 6-6). The female mite burrows into the epidermis and lays eggs. This burrowing produces intense itching and inflammation within the skin. Scabies can occur in dogs of any age, sex, or breed. Humans may experience development of visible lesions after exposure to infected animals; however, the mites do not survive off the animal host for longer than a few days. If the owner experiences development of small, red papules on his or her skin, a medical doctor should be consulted.

Aug 31, 2016 | Posted by in GENERAL | Comments Off on Diseases of the Integumentary System
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