Chapter 23Skin Infections

Medgar Evers College

Biology 261

Prof. Santos

Anatomy and Physiology

• The skin is a large complex organ with many functions. These functions include temperature regulation, vitamin D production, helping the immune system, forming a protective barrier against environmental conditions.

Normal microbiota of the skin

1) Diphtheroids are gram + rods responsible for body odor, acne, fatty acid secretions from their metabolism keep skin acidic.

2) Staphylococci, gram + cocci arranged in clusters normally present on the skin. They help prevent the colonization of pathogens on the skin.

3) Fungi- Malassezia are yeast normally found on the skin. They normally cause no harm but can give rise to a serious skin disease in immuno compromised patients like people infected with HIV.

Bacterial skin infections

• Folliculitis is the name given to a group of skin conditions in which there are inflamed hair follicles. The result is a tender red spot, often with a surface pustule. The agent of infection is S.aureus

• A carbuncle is a skin infection that often involves a group of hair follicles. The infected material forms a lump, called mass, which occurs deep in the skin.

• Most carbuncles are caused by the bacteria staphylococcus aureus. The infection is contagious and may spread to other areas of the body or other people.

• A carbuncle is made up of several skin boils called furuncles. The infected mass is filled with fluid, pus, and dead tissue. Fluid may drain out of the carbuncle, but sometimes the mass is so deep that it cannot drain on its own.

• Carbuncles may develop anywhere, but they are most common on the back and the nape of the neck. Men get carbuncles more often than women.

Bacterial

disease cause symptoms pathogenesis treatment

Staphylococcal scalded skin syndrome

Strain of S. aureus that produces an exfoliatin toxin.

Exfoliatin is a toxin that destroys the material that binds together the layers of the epidermis.

Tender red rash, fever, large blisters

Toxin is produced by pathogen at infection site, carried into bloodstream and then in the epidermis it causes a split.

Penicillinase resistant penicillin and removal of dead tissue

Virulent factors of S.aureus

• Protein A, an Fc receptor• Coagulase, an enzyme that clots plasma

and coats the bacterial cell to prevent phagocytosis.

• Hyaluronidase, an enzyme that helps to break down ECM material and helps the pathogen spread.

• Staphylokinase, an enzyme to break down fibrin and helps the pathogen spread.

bacterial

disease cause symptoms pathogenesis treatment

Impetigo Streptococci pyogenes and Staphylococcus aureus

Blisters that break releasing plasma and pus, golden crusts, enlargement and tenderness of lymph nodes

Pathogen enters skin through a break

Antibiotic and clean the skin area regularly.

bacterial

disease cause symptoms pathogenesis treatment

Rocky mountain spotted fever

Rickettsia rickettsii, an obligate intracellular bacterium

Muscular pain, headache, fever, hemorrhagic rash that starts on the extremities

Tick bite introduces the pathogen, it multiplies, invades bloodstream, then invades endothelial cells and an endotoxin accounts for pathology.

Avoid tick infected areas, tick repellent, doxycycline, chloroamphenicol.

bacterial

disease cause symptoms pathogenesis treatment

Lyme disease

Borrelia burgdorferi

1-Enlarging red rash at site of infection, fever, malaise, headache, enlargement of lymph nodes

2-dizzy spells, fainting, pain when moving eyes

3-localized pain, paralysis, joint pain and swelling

Infected tick deposits pathogen into host, multiplies, travels through bloodstream, the immune system reacts causing tissue damage

Prolonged antibiotic treatment, tick repellent, protective clothing during camping trips or hiking.

Viral

disease cause symptoms pathogenesis treatment

Varicella or chicken pox

Varicella zoster virus

Itchy lumps and blisters, fever, latent infection can be manifested as shingles later in life.

Incubation period is 10-21 days

Upper respiratory viral multiplication followed by dissemination by the bloodstream to the skin. Virus attacks cells causing blisters.

Vaccination, an antiviral medication can be given such as acyclovir.

viral

disease cause symptoms pathogenesis treatment

German measles or rubella

Rubella virus

A mild fever and cold like symptoms, a rash that starts at the forehead and face, enlarged lymph nodes behind the ears

The virus replicates on the upper respiratory tract, then travels via the bloodstream to other parts of the body. Antibody-antigen complexes lodge in the skin causing the rash.

Attenuated Rubella virus vaccine but no specific antiviral medication recommended.

viral

disease cause symptoms pathogenesis treatment

Measles or rubeola

Rubeola virus

Rash, cough, fever, weepy eyes, nasal discharge

Virus replicates on the upper respiratory tract, travels to other parts via bloodstream such as lungs, skin, and brain. T cells attack virus on skin causing the rash.

Attenuated measles vaccine after 1st birthday and 2nd dose before starting school. No antiviral medication recommended.

Other viral diseases

• Include warts caused by the papillomavirus, fifth disease (Slapped cheek rash) caused by the parvovirus B-19, and Roseola. This is a childhood rash with fever caused by the human herpes type 6 virus.

Fungal infections of the skin

• Include diaper rash caused by Candida albicans, Jock itch, body ring worm, and athlete’s foot.

• Cutaneous mycoses are infections of the upper layer of the skin, hair and nails. They do not invade deep tissue.