Bacterial Skin Diseases of Large Animals and Horses

Dr. Kedar Karki

1. Dermatophiliosis
   1. Be able to recognize or list factors that contribute to infection of the skin with Dermatophilus.

i. The etiologic agent is the gram +, filamentous actinomycete, Dermatophilus congolensis. The infective stage is a motile zoospore that is liberated from crusts (on or off carrier animals) after wetting.

ii. More common in fall and winter and following periods of overcast and rainy weather

iii. Intact skin is resistant to infection. Abrasion, overzealous grooming, chronic moisture, chronic wetness, insect bites are all predisposing injuries.

iv. Host factors play a role with debilitation and immunosuppression and also individual susceptibility having been demonstrated to allow infection to be established more readily in some exposed animals.

v. In show barns or training barns, the disease may be spread by contaminated clippers (trauma and source).

vi. Dermatophilosis may be associated with chorioptes and/or tick infestations and may be spread among animals by biting flies.

vii. Therefore, the 3 factors that are necessary for establishment of the disease are: EXPOSURE, MOISTURE, and SKIN INJURY.

2. Be able to recognize the clinical syndromes or presentations for which dermatophilosis is part of the differential diagnosis.

i. Horses:

1. Usually dorsal surfaces of the animal and occasionally the extremities and the muzzle

2. white skinned areas may be more severly affected

3. Lesions: small (1-20 mm), thick, circular crusts that can often be felt before they are seen. Looks like hair is raised in tufts by the crust and the hair usually comes off with the crust.

4. Under the crusts, is a superficial erosion with exudate and acute lesions are painful. But, chronic lesions are scaly and have no exudate.

5. Occasionally, an acutely affected horse will exhibit limb edema and local heat.

6. Young foals kept in bad conditions may be badly affected with acute moist eczematous dermatitis involving the entire body and muzzle lesions that are prominent. Adult horses that are immunosupressed may also develop very severe disease. These are protein losing dermatopathies.

ii. Cattle:

1. Scaly crusts as in horses:

2. 6 forms:

a. face and ears of calves (milk scald) and bulls

b. rump and top line (rain scald)

c. brisket, axillae, groin

d. udder, teats, genitalia

e. distal limbs

f. perineum and tail

iii. Sheep:

1. Endemic in most sheep flocks though the importance is varied

2. Fine-wooled breeds more susceptible to severe dz, esp. in warm climates

3. Lambs: scabs on face, ears, and nose; may be concurrent with and hard to tell from orf

4. “lumpy wool”- mild form with moist scabs drying to form pyramidal crusts on top line; in severe cases, lesions extend over the flanks and lead to wool loss

5. “Strawberry Foot Rot”-crusts from coronets to tarsi and carpi with underlying bleeding granulation tissue; considered a complication of viral dermatitis

iv. Goats:

1. Inner surface of pinnae; also nose, muzzle, feet, and tails of kids; muzzle, dorsal midline, scrotum of adults; may get strawberry foot rot; rain scald; damage to hides important

v. In Llamas and other Camelids:

1. Very important

2. May be pruritic

3. “Rain scald” and leg disease

3. Given a case description of a typical case of dermatophilosis in horses or cattle, be able to choose an appropriate list of differentials.

i. Dermatophiosis DDX: pemphigus, Zinc dermatopathies, Staph folliculitis

ii. Pastern disease in horses (scratches) DDX: allergic or contact dermatitis, photosensitization, dermatophyte, pastern follicultis, acute pyotraumatic dermatitis

4. Be able to choose from a list the appropriate diagnostic specimens to be collected to establish a diagnosis of dermatophilosis.

i. Histo exam of skin biopsy or just the crusts is very important to the diagnosis; crusts should always be submitted with biopsies

ii. Cytology: mince a crust in sterile water or saline on a glass stain, allow to air dry or heat fix, wright-geimsa stain. See branching “railroad tracks” of filamentous bundles of diplococci. Smears of pus from under an acute crust may occasionally yield organisms.

iii. Culture: minced crusts placed on selective media (blood agar with polymixin b 1000 IU/mL). It takes 72 hours to grow.

5. Be able to describe the technique for cytologic examination of specimens for diagnosing dermatophilosis.

i. Discussed above

6. Be able to choose appropriate therapy for a given case of dermatophilosis from among a list of proposed treatment options, or be able to describe your therapy in a short essay format.

i. Therapy:

1. Most cases will regress spontaneously once inciting causes have been corrected (dry weather).

2. chronically affected animals should be sheltered.

3. Gentle grooming to remove crusts and shedding hair coat may hasten resolution (but remember grooming implements can act as fomites).

4. Chlorhexidine or Iodine shampoos may help if animal can be dried thoroughly after bathing. Other topicals: 2-5% lime sulfur, 0.5% Zn sulfate, 0.2% Ca sulfate, 1% K Al sulfate (Alum)->favored for sheep

5. In severe cases, systemic Abx therapy may hasten resolution. Injections of Penicillin 22-44,000 IU/kg or long-acting oxytetracycline 20 mg/kg for 7-10 days. (TMP-S is not effective.

7. Be able to list and/or describe the 3 forms of dermatophilosis of sheep.

i. Maybe Strawberry foot rot, lumpy wool, scab form

8. Be able to list various predilection sites for lesions on cattle and horses.

i. Discussed above

2. Be able to recognize the agents associated with bacterial folliculitis/furunculosis in the horse.
   1. 3 bacterial agents:

i. Staphylococci (S. aureus, S. hyicus, S. intermedius);

ii. Actinomyces (Corynebacterium) pyogenes

iii. Corynebacterium pseudotuberculosis

3. Be able to give a DDX for causes of pastern dermatitis/folliculitis in the horse. Be able to choose from a list the most common causes.
   1. Allergic or contact dermatitis
   2. Photosensitization
   3. Dermatophyte
   4. Pastern folliculitis
   5. Acute pyotraumatic dermatitis
4. Be able to list a DDX for scaling, crusting skin disease in the horse.
   1. I think this is what she means!:

i. Dermatophilus

ii. Pemphigus

iii. Zinc dermatopathies

iv. Staph folliculitis

5. Be able to name or recognize the agent of exudative epidermitis of swine and be able to name or recognize the age group affected. Be able to describe the signs seen in the peracute form. Be able to choose an appropriate therapeutic agent from a list.
   1. Agent: Staph. Hyicus toxin
   2. Age group:Piglets 1-7 weeks old
   3. Peracute form signs: See exudate periocularly, then vesiculo-pustular eruption on nose, lips, tongue, gums, coronets. Red-brown macules behind ears, ventral abdomen, then whole body erythema with moist greasy exudate and thick brown crusts. Anorhexia, depression, death in 3-5 days.
   4. Tx: Good husbandry, EARLY tx with penicillin, ampicillin, lincomycin, tylosin, cephalosporins, much Ab resistance-rec sensitivity testing in important outbreaks.
6. Be able to name or recognize the agent of caseous lymphadenitis of sheep or goats, and given a typical case history be able to give a diagnosis or suggest appropriate diagnostic tests to establish a diagnosis.
   1. Agent: Corynebacterium pseudotuberculosis
   2. Typical case history: See cold abscesses associated with lymph nodes (inc. internal nodes), cutaneous nodules an draining tracts; thick cheesy exudate—yellow, greenish, or tan, most lesions on head and neck, or associated with shearing injuries in sheep.
   3. Diagnostic tests: Direct smears (diptheroid gram + intracellular rods) and culture, ELISA test?
7. Be able to give a DDX for nodular or fistulous skin disease of cattle with exudate that contains sulfur grains (see also infectious nodular notes).
   1. DDX: Actinomyces bovis (lumpy jaw), Actinobacillus ligniersi (wooden tongue), Botryomycosis, (all I could find)
8. Be able to give a DDX or recognize a list of causes of cellulitis, skin necrosis, or purpura in swine.
   1. DDx: Erysipelothrix rhusiopathiae, malignant edema clostridial infection (many different Clostridial species including C. septicum), possibly black leg caused by Clostridium chauvoei, Fusiform necrophorus (necrobacillosis), Porcine spirochetosis (Borrelia suilla plus poor hygiene thats complicated by Fusiformis necrophorus)

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