Chapter 18


Infectious Diseases Affecting the Skin and Eyes




  Follicle-associated lesions that result when overproduction of sebum and dead cells clog the pores

  Caused by Propionibacterium acnes which is part of normal flora of the skin

  releases enzymes that cause local inflammatory response

  Cystic acne - occurs when deeper layers of the skin are involved

  Treated with topical agents or antibiotics




Staphylococcus aureus

  Found in the nostrils of virtually everyone at some point

  Contains many virulence factors:

  Coagulase impedes progress of leukocytes into infected areas by producing clots

  Can be used to differentiate S. aureus from other Staphylococcal species

  Proteases, lipases, and hyaluronidase - degrade surrounding tissues so the infection can spread

  Beta-lactamase degrades beta-lactam drugs

  Exfoliative toxin causes separation of the epidermis & dermis

  Staphylokinase dissolves blood clots so infection can spread

  Superantigens stimulate a huge array of T cells, regardless of specificity



Staphylococcus aureus: Diseases

  Folliculitis inflammation of a hair follicle

  Furuncles (boils) infection extends from the follicle into surrounding tissues forming an abscess

  results in localized redness, swelling, tenderness, pain

  Carbuncles larger, deeper lesions resulting from the interconnection of multiple furuncles

  results in furuncle symptoms plus several sites of draining pus

  extremely painful and can spread through blood to heart, bones, and brain

  Impetigo - superficial skin infection that causes the skin to flake or peel off

  marked by burning, itching blisters that break and weep forming a highly-contagious yellow crust

  treated with topical or oral antibiotics

  Cellulitis fast-spreading infection in the dermis and subcutaneous tissues

  localized swelling, tenderness, pain, and warmth; may see red lines leading away from area (lymphangitis)

  treated with oral or IV antibiotics

  Scalded Skin Syndrome (SSSS) - systemic infection from phage-encoded exfoliative toxins in the bloodstream

  potentially fatal disease that occurs mainly in infants

  bullous lesions - form blisters and the top layers of epidermis peel off

  patient is prone to secondary infections; must treat immediately with antibiotics

  Necrotizing fasciitis flesh-eating disease that occurs when aggressive strains inhabit wounds

  enzymes and toxins destroy tissue, allowing bacteria to move into deeper tissues such as muscle

  superantigens can cause shock and death

  early treatment with antibiotics may avoid amputation




Streptococcus pyogenes

  Identified by beta-hemolytic colonies and group A carbohydrates

  Virulence factors:

  Streptokinase dissolves clots to increase spread

  Hyaluronidase digests hyaluronic acid

  M protein - inhibits phagocytosis

  Streptolysins SLO and SLS hemolysins




Streptococcus pyogenes: Diseases


  Catalase Test can distinguish between S. aureus and S. pyogenes


  Necrotizing Fasciitis


  invasive skin infection resulting in edema, redness, fever, and chills

  severe cases can be fatal

  most infections respond to treatment with penicillin early




Gas Gangrene

  Caused by Clostridium perfringens

  Alpha toxins and enzymes produced in muscles cause tissue necrosis, bacterial growth, and gas production

  Causes pain, edema, fever, and blackened necrotic tissue filled with bubbles of gas

  Spores infect anaerobic wounds, incisions, or diabetic ulcers

  Toxins released into the bloodstream can cause death

  Treatment: debridement of diseased tissue, surgery, hyperbaric oxygen therapy, or amputation




Vesicular Rash Diseases: Chicken Pox

  Caused by Varicella-Zoster Virus (VZV)

  Fever then rash, which begins as macules, then papules, vesicles, and pustules (pus-filled blisters)

  Lesions crust over and virus enters sensory nerves and travels to ganglia

  Shingles - can occur years after the primary chickenpox infection and is caused by reactivation of latent virus in the CNS

  may be caused by stress, X-rays, immunosuppressive drugs, surgery, or malignancy

  Virus produces tender vesicles and painful nerve inflammation that can last for months

  Spread via respiratory route or contact with skin lesions

  Complications include secondary bacterial infections, pneumonia, or encephalopathy

  Congenital varicella syndrome - when mothers contract VZV early in pregnancy

  Attenuated vaccine is available for children and shingles vaccine for adults

  acyclovir for certain patients



Vesicular Rash Diseases: Smallpox

  Naturally occurring infections have been eradicated, but still a bioterrorism threat

  Caused by Variola virus

  Spread via respiratory route or contact with skin lesions

  Fever then rash (similar to chicken pox), which begins in pharynx and face, then spreads to extremities

  Pustules are usually indented in the middle

  Can cause toxemia and shock

  Prevented with vaccinia (cow pox) vaccine

  high rate of side effects




Maculopapular Rash Diseases: Measles

  Caused by the Measles virus

  One of the most contagious diseases; transmitted by respiratory droplets

  Early symptoms include sore throat, dry cough, runny nose, and fever

  Kopliks spots small oral lesions in the back of mouth

  Spotted rash then starts at the head, progresses to the trunk and extremities, then disappears in the same order

  Ear infections and pneumonia are common secondary infections

  virus compromises immune function

  Usually self-limiting, but can cause lung or brain damage in young children

  Subacute sclerosing panencephalitis (SSPE) - slowly progressive brain degeneration 2-10 years after infection

  Prevented with attenuated MMR vaccine




Maculopapular Rash Diseases: Rubella

  Caused by rubella virus          

  Transmitted via respiratory secretions        

  Postnatal acquired after birth

  symptoms include mild fever, sore throat, and malaise sometimes followed by a spreading pink rash or joint pain

  Congenital rubella syndrome virus is obtained in utero

  First trimester exposure almost always results in miscarriage or multiple, permanent defects of the eyes, ears, brain and heart

  Infants who survive excrete the virus for months after birth

  Prevented with attenuated MMR vaccine




Maculopapular Rash Diseases: Fifth Disease

  Caused by parvovirus B19

  Transmitted via respiratory droplets 

  Begins with fever, malaise, and muscle aches for 5-10 days

  Rash resembles a slapped cheek and then spreads to other parts of the body

  most recover in 2 weeks




Maculopapular Rash Diseases: Roseola

  Caused by Human Herpesvirus Type 6 (HHV-6) or HHV-7

  Begins abruptly with high fever (105 F) that may cause seizures

  A rash then appears on the chest and abdomen 

  Most recover within a week




Wartlike Eruptions:  Warts (Papillomas)

  Caused by Human Papillomavirus (HPV)

  Benign, squamous epithelial growths on skin or mucus membranes

  Transmitted through contact with lesions, fomites, or autoinoculation

  Common warts

  painless, elevated, rough growths on fingers or other body parts

  Plantar warts

  deep, painful warts on the soles of the feet

  Flat warts

  smooth, skin-colored lesions on the face, trunk, elbows, and knees

  Treat by freezing, cauterization, or surgical removal




Wartlike Eruptions:  Molluscum Contagiosum

  Caused by a poxvirus

  Lesions are smooth, waxy nodules  containing a milky, virus-filled fluid

  Spread via direct contact, fomites, autoinoculation, or sexual contact (adults)

  Treat by removal or topical chemicals




Large Pustular Skin Lesions : Leishmaniasis

  Zoonotic disease caused by the protozoan Leishmania and transmitted by sand flies

  Protozoa multiply in macrophages and either remain localized or become systemic

  Cutaneous leishmaniasis

  localized skin infection where a small red papule spreads into a large ulcer

  Mucocutaneous leishmaniasis

  skin lesion on head or face progresses to multiple lesions in mouth and nose

  Systemic leishmaniasis




Fungal Skin Diseases (Mycoses)

  Dermatophytes - the most common cause of fungal skin infections

  Invade and digest the outer nonliving surfaces of the body such as hair, nails, and the keratinized portions of the skin

  Products of fungal metabolism result in localized inflammation and allergic reactions

  Causative agents include: Trichophyton, Microsporum, and Epidermophyton

  Transmitted by direct or indirect contact

  Treat with topical anti-fungals for several weeks


  Tinea capitis - scalp

  Tinea corporis body (ringworm)

  Tinea barbae beard (barbers itch)

  Tinea cruris groin (jock itch)

  Tinea pedis feet (athletes foot)

  Tinea unguinum nails

  Tinea versicolor - patchy scaling