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.


image image

Figure 6-1 A, Canine skin and underlying subcutaneous tissue. Notice that epidermis of canine skin includes folds from which compound hairs arise. B, Normal canine skin. C, Normal feline skin. Note the thin epidermis and compound hair follicle arrangement of both species.


(A, From Colville T, Bassert JM: Clinical anatomy and physiology for veterinary technicians, St Louis, 2002, Mosby, by permission; B and C, From Scott DW, Miller WH Jr, Griffin CE: Muller and Kirk’s small animal dermatology, ed 6, Philadelphia, 2001, WB Saunders, by permission.)


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


• Enclosing barrier: Protects the internal environment of the body from water and electrolyte loss.

• Environmental protection: Protects the internal environment from the external environment.

• Temperature regulation: Maintains the animal’s coat and regulates the blood supply to the cutaneous tissues, which regulate heat dissipation and retention.

• Sensory perception: Contains sense organs for touch, temperature, and pain.

• Motion and shape: Allows for motion and provides a definition to the body.

• Antimicrobial: Contains antimicrobial and antifungal properties.

• Blood pressure control: The peripheral vascular beds within the skin help to control blood pressure.

• Secretion: Contains both apocrine and sebaceous glands.

• Adnexa: Produces hair, nails, hooves, and horny layers of the epidermis.

• Storage: Stores electrolytes, water, vitamins, fat, proteins, carbohydrates, and other substances.

• Pigmentation: Processes within the skin (e.g., melanin formation) help to determine coat and skin color and provide solar protection.

• Excretion: The animal’s skin has a limited excretory function.

• Vitamin D production: The skin is essential for solar energy activation of vitamin D, which is necessary for normal calcium absorption.



TECH ALERT


The skin is an important indicator of internal disease.


Any physical condition that disrupts the normal functions of this barrier can result in disease. Increased moisture, chemical exposure, increased temperature, hormonal change, and physical damage can produce a breach in the barrier, allowing the invasion of disease-producing microorganisms.


Problems relating to the skin are the most frequent complaints presented in smallanimal medicine. Technicians deal with these complaints daily as clients ask questions and seek help for the treatment and prevention of skin diseases afflicting their pets. This chapter focuses on the most commonly seen skin problems of companion animals.



ECTOPARASITES


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:


• Ear mites (Otodectes cynotis)

• Fleas (Ctenocephalides spp.)

• Ticks (Ixodes spp., and others)

• Mange (Demodex canis, Sarcoptes scabiei, Notoedres cati)

• Warbles (Cutebrae spp.)

• Myiasis (fly maggots)

• Lice (Linognathus setosus)

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).


image

Figure 6-2 Adult male ear mite, Otodectes cynotis.


(From Hendrix CM, Robinson E: Diagnostic parasitology for veterinary technicians, ed 3, St Louis, 2006, Mosby, by permission.)



CLINICAL SIGNS



• Ear canals may be filled with a brown-black, crusty exudate.

• Mites are extremely irritating, so animals will scratch their ears.

• Scrapes (wounds) may be visible on the side of the face or head.


DIAGNOSIS



• Under an otoscope, the large, white, adult mites can be seen crawling on the surface of the crusty exudate.

• Adult mites and eggs can be seen on microscopic examination of smears taken of the exudate.


TREATMENT


Many otic products contain ingredients that will kill mites. The technician should first carefully clean the exudate from the ear canal, then apply a miticide into the canal. Recommended miticides include the following:


Thiabendazole/neomycin/dexamethasone (Tresaderm): 5 to 15 drops twice a day topically to ear canals


Piperonyl butoxide, pyrethrins (Otomite): 4 to 15 drops daily in ear canals


Ivermectin (off-label uses): 300 μg/kg subcutaneously (SQ) or orally (PO) (repeat in 14 days)




TECH ALERT


Owners must be informed that ivermectin is not licensed for subcutaneous use in companion animal species.



INFORMATION FOR CLIENTS



• The life cycle of the parasite is 3 weeks. Eggs hatch every 10 days, so treatment must be continued for no less than 30 days.

• This parasite is highly contagious. All animals that have had contact with the infested animal should be treated.

• Humans do not become infested with this parasite in most cases.

• The mites may spend time elsewhere on the animal’s body, especially on a cat’s tail. If infestations recur, treat the entire animal with dip or shampoo.


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.


image

Figure 6-3 Adult male and female Ctenocephalides felis, cat fleas, the most common flea found on dogs and cats.


(From Hendrix CM, Robinson E: Diagnostic parasitology for veterinary technicians, ed 3, St Louis, 2006, Mosby, by permission.)



CLINICAL SIGNS



• Animals infested with fleas will continually scratch or bite at their skin.

• Areas commonly affected include the tail-head area and the inner thigh region of the animal. These areas may be red, inflamed, and scabbed. In cats, small scabs may cover the entire dorsum (miliary dermatitis).

• Small, pepper-like granules may be found on the skin and hair coat. When placed on white paper wet with alcohol or water, the granules give off a red color. These granules are dried flea excrement, which contain blood products.


DIAGNOSIS



• Finding fleas on the animal

• Finding flea dirt on the animal

• Finding lesions consistent with flea infestation


TREATMENT



• Several flea products currently are available on the market. They can be broken down into those that are applied topically (sprays, dips, powders, and shampoos) and those that are applied systemically (spot-ons, oral, or injectable). All these products act at some point in the flea’s life cycle to interrupt development of the adult flea or to repel the adult flea from the animal.


Sprays and powders



• Many products that contain a combination of ingredients are on the market. Most act to repel or kill the adult flea. Each product has specific species and age specifications; therefore, you must read the label carefully before use. Become familiar with the products sold in your clinic.


Shampoos



• Shampoos provide no residual effect. The product will kill fleas that come into contact with the shampoo, but it will not remain on the skin after rinsing. Read the label carefully for species specifications.


Dips



• Dips provide residual effect on the animal. These products are more toxic than other topical preparations. Read the label carefully for species specifications and proper dilution techniques.


Systemics


Systemics are one of the newest treatments for fleas. These products are absorbed and distributed within the skin to kill the flea when it feeds, or it renders reproduction impossible.


Advantage: A once monthly spot-on helps to kill adult fleas and prevent reproduction; it is dosed according to weight and species.


Program: Lufenuron, the active ingredient, is absorbed by the fatty tissue and slowly distributed to the bloodstream. This ingredient interferes with the synthesis of chitin, a necessary element in flea development. It is given by tablet once monthly or every 6 months by injection to cats. It takes 30 to 60 days to reach full effectiveness. Adult fleas may continue to be seen on the animal.


Frontline: Apply monthly to skin.


Sentinel: Contains lufenuron; also contains milbemycin for heartworm prevention. It is dosed by weight in dogs.


Revolution (selamectin; Pfizer, Cambridge, Mass.): Kills fleas for 1 month by preventing the eggs from hatching. It is also used to treat heartworms, ear mites, intestinal parasites, and sarcoptic mange in dogs and cats older than 6 weeks. It is dosed by body weight.



INFORMATION FOR CLIENTS



• Control of ectoparasites such as fleas can be a frustrating task. Environmental factors, geographic location, and species sensitivity affect the development of disease.

• Treatment of the environment is essential in preventing flea infestation. Fleas spend most of their life cycle off the host.

• If one animal in the house has fleas, they all have fleas!

• Flea infestation results in damage to the skin, allowing other skin problems to develop.

• Fleas will bite and feed on humans if animals are not available.

• Some fleas can remain dormant in the environment for months if conditions are suitable. You must clean the environment by vacuuming and treating with sprays or foggers.


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.


image

Figure 6-4 Rhipicephalus sanguineus (brown dog tick) invades both kennel and household environments.


(From Hendrix CM, Robinson E: Diagnostic parasitology for veterinary technicians, ed 3, St Louis, 2006, Mosby, by permission.)


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.



CLINICAL SIGNS



• Owners report a tick or “a lump” attached to the animal

• Weakness or pale mucous membranes when infested with large numbers of ticks

• Ascending, flaccid paralysis

• Arthritis-like symptoms of lameness, joint and muscle pain, fever (Lyme disease)


DIAGNOSIS



• Finding a tick on the animal is the definitive diagnosis.

• A history of exposure to wooded, grassy areas known to have tick infestations suggests the diagnosis.


TREATMENT



• Manual removal of all ticks. Soak the tick in alcohol; firmly grasp the head parts using a curved mosquito hemostat and pull to remove the tick. Destroy the tick by crushing or soaking in alcohol. One should never use bare hands to remove a tick or crush a tick, because the blood contained within the tick may contain infectious microorganisms. Never use a lighted cigarette, gasoline, or kerosene to remove a tick, because their use will result in serious damage to the animal’s skin.

• Topical treatments (dips, sprays, and powders): The following list is only a sample of some of the more commonly used products:

Paramite Dip (Vet-Kem)


Pyrethrin Dip (VetMate)


Durakyl Pet Dip (DVM Pharmaceuticals, Miami, Fla.)


Adams Flea and Tick Dust


VIP Flea and Tick Powder (Veterinary Products Laboratories, Phoenix, Ariz.)


Adams Flea and Tick 14-day Mist


• Collars: Preventic collar (Virbac, Inc., Fort Worth, Tex.) is the only collar that is effective against ticks (even though others claim to be effective). These collars are effective for about 3 months if they do not get wet.

• Topical systemic treatments: Frontline is a spot-on product that is effective against fleas.

• Advantix

• Revolution

• Environmental treatments include the following:

Adams Home and Kennel Spray


Vet-Fog Fogger


Siphotrol Plus Fogger


Permectrin Pet, Yard, and Kennel Spray (Bio-Ceutic, St Joseph, Mo.)


Some yard sprays and garden sprays will also kill ticks


• The tick population in the environment can be decreased by removing brush, limiting rodent populations, and keeping grassy areas cut.


Information for Clients



• Routinely check all animals for ticks, especially after they spend time outside during the spring and summer. Check around the ears and between the toes, as these are areas where ticks are commonly found.

• Do not use gasoline, kerosene, or lighted cigarettes to remove ticks from the animal.

• Do not use your bare hands to remove or crush ticks.

• You will need to treat the environment to prevent reinfestation of your pets.

• If infestation is severe, you may need to call a professional exterminator.

• Ticks are not species specific; they will feed on humans whenever they get the chance. They can carry disease.

• Destroy outdoor habitat by cutting brush, trimming trees, and eliminating rodents. Repellant collars and sprays may help keep ticks off pets while outdoors.


Mange


Three primary diseases called “mange” are seen in the dog and cat: demodectic mange, sarcoptic mange, and notoedric mange. These diseases are the result of tiny mites living on or in the skin, where they produce irritation and inflammation. The symptoms for each of the diseases are distinct, and diagnosis must include identification of the mite through skin scrapings or biopsy.



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.


image

Figure 6-5 Adult Demodex canis. These mites resemble eight-legged alligators.


(From Hendrix CM, Robinson E: Diagnostic parasitology for veterinary technicians, ed 3, St Louis, 2006, Mosby, by permission.)


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



CLINICAL SIGNS (LOCALIZED DEMODEX)



• Animal is almost always a young dog (3 months to 1 year). When found in the localized form in adults, the animals have a history of the disease earlier in life.

• Alopecia (hair loss) appears especially on the face, around the eyes, mouth, and ears. The next most frequently involved areas are the forelegs and, occasionally, the trunk.

• Erythema (redness) is common; the patches are red and sometimes crusty. This type of mange has been called red mange.



TECH ALERT


The animals are nonpruritic (not itching). This is an important distinguishing characteristic to help differentiate demodectic mange from other types of mange.



CLINICAL SIGNS (GENERALIZED DEMODEX)



• Animals usually will be febrile.

• The entire body surface will be involved.

• Secondary bacterial skin infections with pustules will be seen.


DIAGNOSIS



• Diagnosis is by mite identification, usually through skin scrapings. Place a drop of mineral oil on the lesion and firmly scrape while squeezing the skin. Transfer the material to a clean glass slide and examine under a microscope. This mite is found easily.

• Culture and sensitivity of the skin lesions may be necessary if a secondary bacterial infection is present.


TREATMENT



• Treatment of Demodex depends on the age of the patient, the extent of the lesions, and veterinarian preference.


Localized



• Rotenone (Goodwinol ointment): apply to lesions daily

• Rotenone (Canex): apply to lesions daily


Generalized or severe localized



• Mitaban dips (Amitraz): Clip the dog closely to remove hair. Bathe the entire animal in a mild soap and towel dry. Treat the entire animal with the dip at the proper dilution (1 bottle/2 gallons water). Do not rinse or towel dry the animal. Three to six treatments may be required, each treatment given 14 days apart and continued until skin scrapings are negative.

• Ivermectin: Use of this drug in the dog is “off-label”; therefore, client release forms should be signed. Give 0.3 mg/kg SQ or PO. Repeat in 14 days.

• Interceptor: Administer monthly for a minimum of 90 days.

• Oral antibiotics: Choice is based on culture and sensitivity


INFORMATION FOR CLIENTS



• Many animals will outgrow mange as they age.

• Demodex is not contagious to humans and other animals.

• Treatment will never completely remove the mites from the skin. The goal of treatment is to reduce the number of mites on the animal and to improve the general health of the pet.

• Breeders should not use previously infected animals in their breeding programs.

• Treatment may be prolonged in some animals.

• The generalized form may be fatal in some animals.


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.


image

Figure 6-6 Adult Sarcoptes scabiei mite that causes scabies, an intensely pruritic disease.


(From Hendrix CM, Robinson E: Diagnostic parasitology for veterinary technicians, ed 3, St Louis, 2006, Mosby, by permission.)



CLINICAL SIGNS



• Typical red, crusty lesions appear on the ears, elbows, and elsewhere on the trunk of the animal.

• Intensely pruritic! This distinguishes it from Demodex.

• Secondary bacterial skin infections may be present owing to self-trauma.

• The disease will progressively become more severe.


DIAGNOSIS



• Identification of the mite through skin scrapings. These mites are difficult to find in many cases because they are located deep in the epidermis. Scraping should be deep to maximize the chance of finding the mite. Multiple scrapings of the same animal may be necessary to locate the mite. Mites can also be seen on skin biopsies.


TREATMENT



• Remove the mites! Dips are frequently used for this purpose.

• Paramite Dip (Vet-Kem): Dip every 14 days until the clinical signs resolve.

• Ivermectin: SQ or PO; repeat in 14 days. This constitutes “off-label” use of this drug.

• Paramite Dust (Vet-Kem): Administer per package instructions. Rub through entire coat. Do not treat puppies younger than 12 weeks.


INFORMATION FOR CLIENTS



• Scabies is a highly contagious disease among dogs.

• Humans frequently experience development of visible lesions appearing as small, red papules. Owners should contact their physician if this occurs.

• Mites do not remain on the human for longer than a few hours.

• A similar disease is seen in cats, but the mite is not the same. N. cati produces lesions in cats similar to those seen with sarcoptic mange in dogs. The dog mite will rarely infect the cat.

• Species variants of the sarcoptic mite infest almost all species of haired animals.


Cuterebra “Warbles”


The Cuterebra fly lays eggs in the soil. These eggs mature into a larval stage similar to a grub that directly penetrates the host’s skin (Fig. 6-7, see also Color Plate 5). Here, in a subcutaneous pocket, the larva continues to mature, finally leaving the wound to become an adult fly. A fistula or opening in the swelling allows the larva to breathe while maturing; the larva can be seen moving up and down in the opening to the fistula.


image

Figure 6-7 Cuterebra species, “warbles” or “wolves,” found in skin of dogs or cats.


(From Hendrix CM, Robinson E: Diagnostic parasitology for veterinary technicians, ed 3, St Louis, 2006, Mosby, by permission.)

You may also need

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

Full access? Get Clinical Tree
Get Clinical Tree app for offline access