Bacterial Diseases of the Skin

what are superficial infections of the skin?

bacteria are confined to the epidermis (they have not penetrated through the basement membrane into the dermis); many do not require treatment

what is a pyoderma?

deep bacterial infection of the skin, defined by the presence of bacteria within the dermis, likely to result in clinical signs such as fever, lymphadenopathy and scarring

what is superficial pustular dermatits

aka ‘impetigo’ and ‘puppy pyoderma’ (but it is NOT a pyoderma as the infection is superficial)

how does superficial pustular dermatitis develop?

transient loss of skin defenses around the time of puberty, which allows overgrowth of commensal bacterial resulting in pustules (little red spots that may have a white center) developing on the skin

where does superficial pustular dermatitis develop most often?

almost always in the glabrous skin on the ventrum, extending into the inguinal regions

what treatment is needed for superficial pustular dermatits?

can just be left and will spontaneously resolve when immune function is fully restored. alternatively, bacterial numbers can be reduced using antibacterial shampoos or washes

what is canine pyotraumatic dermatitis?

aka hotspot dermatitis; skin defenses are impaired due to self-trauma (scratching), resulting in loss of keratin and leakage of serum that gets trapped in dense hair coats

why does canine pyotraumatic dermatitis look like?

a sudden onset of painful, rapidly expanding skin lesions where the animal was scratching

usually secondary to an allergic disease so hot spots can develop around the tail base in animals with flea allergy dermatitis or around the face in dogs with atopy

what is the treatment plan for canine pyotraumatic dermatitis?

heavy sedation is often required as the lesions are so painful;

treatment involves clipping the hair to allow the lesion to dry → without moisture, the overgrowth of bacteria cannot continue and hot spots will spontaneously resolve

what is dermatophilosis?

disease of horses, sheep, and cattle (aka mud fever, rain scald, lumpy wool), caused by Dermatophilus congolensis

chronic moisture impairs skin defenses and allows disease development

where are dematophilosis lesions typically found?

around the feet in animals that have been standing in too much mud and over the dorsum in animals that have been standing in the rain too much

presence of bacteria results in development of a thick crust over the skin (which can protrude and may be mistaken as a wart)

how do you treat dermatophilosis?

simply get the animals out of the mud or rain to allow the skin to dry up and the skin defenses to be restored → if moisture can be avoided, then no treatment is required

although antibiotics will kill the bacteria resulting in resolution of the lesions, they will rapidly return of the animal remains in damp conditions

what is exudative epidermatitis (Greasy pig disease)?

loss of skin defenses caused by piglets fighting and poor hygiene in the piggery allowing overgrowth by Staphyllocus hyicus, which produces a toxin that damages the epidermis and allowing serum to leak out

what does exudative epidermatitis look like?

skin is reddened and is covered by dried exudate (that apparently makes them look greasy)

what is fleece rot

long fleece of some sheep can trap moisture that degrades the skin defenses and allows proliferation of bacteria

what is equine pastern dermatitis?

horses that stand in mud for too long lose normal skin defenses, allowing overgrowth of a variety of different bacterial species

what is interdigital dermatitis (scald) and footrot?

common disease of sheep, cattle and goats caused by chronic dampness allowing infection of the hoof by Fusobacterium necrophorum, Arcanobacter pyogenes and benign strains of Dichelobacter nodosus which produce toxins that allow penetration into the hood and can result in necrosis and separation of the hoof wall

what is folliculitis?

bacterial infection within the hair follicle

what is furunculosis?

if folliculitis continues, the epithelium lining the follicle can become damaged and rupture, spilling bacteria, cell debris and inflammation into the dermis

what causes folliculitis?

loss of skin defenses when the normal maturation and shedding of the keratin lining the follicle and the hair shaft are altered → can be due to functional or physical changes

what’s an example of folliculitis and furunculosis?

feline acne

what is feline acne?

the hair follicles on the chin and around the lips become blocked, resulting in development of folliculitis

in some cats it may progress to furunculosis and the chin becomes swollen, painful and reddened due to subsequent furunculosis and pyoderma

what is an example of a pyoderma due to a penetrating wound?

a cat bite abscess! → penetration of the skin by another cat’s tooth results in deposition of bacteria in the dermis or subcutaneous tissues

what is feline leprosy?

deposition of Mycobacterial species in the skin of cats by mouse bites, resulting in deep skin infections

what are some features consistent with superficial bacterial skin infections?

caused by excessive moisture; pyotraumatic dermatitis; dermatophilosis; bacteria on the outside of the layer of basal cells; quick to resolve, but recurs unless skin defenses are restored

what are some features consisted with deep bacterial skin infections?

systemic illness; lymphadenopathy; bacteria in the dermis; furunculosis; mycobacterial dermatitis

Describe the 3 components that make up the defenses of the skin

physical barrier - surface keratin, but also hair and keratin within the hair follicle

chemical barrier - secretions from adnexal glands and immunoglobulins

microbial barrier - normal bacteria on the surface of the skin which are in balance and do not overgrow and stop colonization by more pathogenic bacteria

what can alter normal skin defenses (generally)?

moisture or friction will impair the keratin layer; anything that alters the adnexal secretions or is immunosuppressive and stop normal immunoglobulin production