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

   Gram-positive cocci in clusters

   Found in the nostrils of virtually everyone at some point



Staphylococcus aureus: 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 digests blood clots

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



Staphylococcus aureus: Diseases

   Folliculitis inflammation of a hair follicle

   Hidradenitis inflammation of a gland

   Furuncles (boils) infection extends from the follicle/gland 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 - occurs when aggressive strains inhabit wounds

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

  flesh-eating disease

  can cause shock and death from toxic products in the bloodstream        

   early treatment with antibiotics may avoid amputation




Streptococcus pyogenes

   Gram-positive cocci in chains

   Beta-hemolytic colonies and group A carbohydrates



Streptococcus pyogenes: Virulence Factors

   Streptokinase cleaves plasminogen to degrade tissues

   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

  gram positive, spore-forming, anaerobic rods found in soil and GI tract

   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

   Can 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

  virus invades nasal mucosa, multiplies in lymph nodes, and travels to dermis

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

  Pustules are usually indented in the middle

   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 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

   Diseases caused by fungi are called mycoses

   Dermatophytes - the most common cause of fungal skin infections

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

   Dermatophytes digest keratin; 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 manuum hand

  Tinea cruris groin (jock itch)

  Tinea pedis feet (athletes foot)

  Tinea unguinum nails

  Tinea versicolor - patchy scaling