Chapter 21 - Diseases of Skin and Eye

What are vesicles?

• small, fluid-filled lesions

• fluid can be clear, yellow, or filled with blood 

What are bullae?

• like vesicles but larger

What are macules?

flattened red lesions (red splotches)

What are pustules?

when something contains pus

What are papules?

raised lesions 

What are exanthens?

• skin rash that arises from diseased conditions

• could be viral

• caused by chicken pox, rubella, measles, etc.

What are enanthens?

• skin rash localized to the mucous membranes 

• caused by toxins, drugs, or microorganisms

• usually found in children 

What is folliculitis?

• an infection of hair follicles (pimple)

What is a boil?

• more serious hair follicle infection (type of abscess)

• localized region of pus surrounded by inflamed tissue

What is a carbuncle?

• a hard, round deep inflammation of tissue under the skin

• abscess 

• typically from a staphylococcus bacteria 

What is a sty?

• infected eyelash follicle

What are staphylococcal skin infections, and how are they classified?

• Gram + spherical bacteria 

• Divided into positive and negative 

• Coagulase enzyme causes fibrin to clot in the blood 

What is Staph. epi. and when does it become pathogenic?

• coagulase-negative bacterium

• very common on the skin

• becomes pathogenic when the skin barrier is broken (cuts, etc.)

What is Staphylococcus aureus?

• Gram + ; coagulase positive bacteria 

• lives in the nose of about 20%

• causes strong inflammation 

• makes toxins and proteins that stop white blood cells

• can cause skin infections like boils and impetigo 

• high toxin production = genome is bigger 

What is impetigo and how does it spread?

• Caused mostly by Staphylococcus aureus or Streptococcus pyogenes

• Very contagious skin infection

• Spreads by touch (direct contact)

• Can spread to other parts of the body called autoinoculation

• Looks like red sores that crust over, often near the mouth or nose

What causes Ballous impetigo and what are it’s toxins?

• Caused by Staphylococcus aureus

• Due to staphylococcal toxins called exfoliative toxins

  • Toxin A: stays local and causes bullous impetigo (blister-like sores)

  • Toxin B: spreads through the blood, leading to scalded skin syndrome

• Skin looks like it has been burned or peeled

What are Streptococcal skin infections and what do they cause?

• Gram-positive cocci (round bacteria) in staph arrangement 

• Can cause:

  • Sore throat (strep throat)

  • Ear infections (otitis media)

  • Meningitis

  • Pneumonia

• They release toxins and enzymes that make infections worse

What do Streptococcal hemolysins do, and what are the 3 types?

• Hemolysins destroy (lyse) red blood cells

• 3 types of hemolysis:

  • Beta (A): complete hemolysis — clear zone

  • Alpha (B): partial hemolysis — greenish zone

  • Gamma (C): no hemolysis

What is Group A Streptococcal (GAS) infection and what causes it?

• Caused by Streptococcus pyogenes

• Beta-hemolytic → completely destroys red blood cells

• Makes exotoxins that come from M-proteins (help bacteria avoid the immune system)

• Causes many human diseases (like strep throat, impetigo, and scarlet fever)

What is the M protein and how does it help Group A Streptococcus (GAS)? 

• Found outside the cell wall

• Looks like a fuzzy layer on the surface

• Prevents complement activation (so the immune system can’t attack)

• Prevents phagocytosis (being eaten by white blood cells)

• Helps bacteria stick to surfaces and colonize (start infections)

What is the hyaluronic acid capsule in GAS and what does it do?

• Makes bacteria look slimy (mucoid) on blood agar

• Hides from immune system because it looks like human tissue

• Helps bacteria avoid detection and survive longer

What enzymes help GAS spread infection?

• Streptokinase → dissolves blood clots

• Hyaluronidase → breaks down connective tissue

• DNase → breaks down DNA in damaged tissue

What is Erysipelas, and what bacteria causes it?

• Caused by Streptococcus pyogenes

• Infection of the dermal layer (deeper skin)

• Causes red, raised patches on the skin

• Can damage tissue if untreated

• Usually starts on the face

• Treated with cephalosporins (antibiotics)

What is Necrotizing Fasciitis, and what causes it?

• Caused by Group A Streptococcus

• Happens from small skin breaks (cuts or wounds)

• Early signs are hard to notice, which delays treatment

• Quickly destroys skin and deeper tissues

• Treated with broad-spectrum antibiotics

What are Pseudomonas infections, and where are they found?

• Caused by Pseudomonas bacteria

• Gram-negative rods that need oxygen (aerobic)

• Found in soil, water, and moist areas (like sinks or wounds)

• Can survive in hospitals, pools, and burn wounds

• Hard to treat — resistant to many antibiotics and disinfectants

What is Pseudomonas dermatitis, and where does it come from?

• Caused by Pseudomonas bacteria

• Found in pools, saunas, and hot tubs

• Happens when chlorine stops working well (too many people = pH rises)

• Can cause rashes or “swimmer’s ear” (otitis externa)

• Swimmer’s ear = infection of the outer ear canal leading to the eardrum

What makes Pseudomonas aeruginosa dangerous, and where is it found?

• Makes endotoxins and exotoxins that damage tissue

• Common cause of hospital infections (tubes, catheters, etc.)

• Opportunistic — affects burn patients and weak immune systems

• Can produce blue-green pus

• Grows in water, flower vases, and cleaning supplies

• Treated with quinolones (antibiotic)

What causes warts, and how are they treated?

• Caused by a virus that makes benign (non-cancerous) skin growths

• Spread by direct contact (touching skin or objects)

• Takes weeks before the wart appears

• Treatment options:

  • Freeze with liquid nitrogen

  • Dry with electric current

  • Burn with acid

What is smallpox, and how was it stopped?

• Caused by the Variola virus

• Spread through the air (respiratory route)

• Virus travels through the bloodstream to the skin

• In the Middle Ages, 80% of Europe was infected

• Brought to the Americas by colonists, infecting Native Americans

• Eradicated (wiped out) thanks to Edward Jenner vaccination

What are the symptoms and transmission of chickenpox (Varicella)?

• Usually a mild childhood illness

• Can cause serious issues like encephalitis (brain swelling) or pneumonia in rare cases

• Causes blister-like spots filled with pus that burst and scab

• Spread through the air (respiratory route)

• Virus then moves to skin cells

What causes shingles, and how is it related to chickenpox?

• After a person gets chickenpox, the virus stays “sleeping” in the nerve cells

• Later in life, the virus can wake up and cause shingles

• The virus moves down the nerves to the skin, causing painful red blisters

• Often appears on one side of the body or face

• Caused by the same virus as chickenpox: Varicella-zoster virus (VZV)

What causes cold sores, and how does Herpes Simplex (HSV-1) spread?

• Caused by Herpes Simplex Virus type 1 (HSV-1)

• Spread by oral, respiratory, or skin contact (like kissing or sharing utensils)

• About 90% of people are infected

• Causes cold sores (blisters around the mouth)

• Can infect fingers of healthcare workers — called herpetic whitlow

• Virus stays hidden in nerve cells and can come back later (latent infection)

What is HSV-2, and how is it transmitted?

• Caused by Herpes Simplex Virus type 2 (HSV-2)

• Spread mainly by sexual contact

• Causes genital herpes (painful blisters around genital area)

• Virus hides in nerves near the base of the spine (sacral nerve ganglia)

• Very rarely, it can reach the brain and cause herpes encephalitis

What causes measles (rubeola) and how is it prevented?

• Caused by the measles virus

• Spread through the air (respiratory route) — like coughing or sneezing

• Causes fever, cough, and a red rash

• Koplik’s spots appear inside the mouth (tiny white dots)

• Complications: ear infections or pneumonia

• Vaccine gives strong, long-term protection

What is Rubella (German Measles) and who is most at risk?

• Caused by the rubella virus

• Spread through the air (respiratory route)

• Causes red rash and mild fever

• Dangerous in pregnancy — can cause Congenital Rubella Syndrome in babies if the mother gets infected in the first trimester

• Prevented by vaccine (MMR – with measles and mumps)

What are the symptoms and risks of Fifth Disease?

• Caused by a virus (Parvovirus B19)

• “Slapped-cheek” rash on the face

• Feels like a mild flu (fever, tiredness)

• In adults, can cause joint pain or even miscarriage if pregnant

How does Hand-Foot-and-Mouth Disease spread and what are the symptoms?

• Spread by mucus or saliva

• After 3–7 days, symptoms start with fever and sore throat

• Causes rash and blisters on hands, feet, mouth, and inside cheeks

What are the symptoms and cause of Roseola?

• Mild, common illness in young children

• Starts with high fever, then a rash appears for 1–2 days

• Caused by Human Herpesvirus 6 or 7 (HHV-6, HHV-7)

• After recovery, the child has lifelong immunity

What are cutaneous mycoses and how do they spread?

• Caused by dermatophyte fungi

• Infect skin, hair, and nails

• Spread by fomites (like towels, shoes, or brushes)

What are the different types of tinea (ringworm) infections?

• Tinea capitis → scalp

• Tinea cruris → groin (“jock itch”)

• Tinea pedis → feet (“athlete’s foot”)

• Tinea unguium → nails

What is Candidiasis and what causes it?

• Caused by the fungus Candida albicans

• Infects mucous membranes (mouth, vagina, skin folds)

• It’s an opportunistic pathogen → grows when your normal bacteria are reduced (ex: after antibiotics or illness)

Who is at risk for Candidiasis, and what are the symptoms?

• Infants may develop oral thrush (white patches in mouth )

• Common when normal microbiota are suppressed

• Appears as white, creamy, or itchy lesions on mucous membranes

What causes Scabies and how is it spread?

• Caused by mites that burrow and lay eggs under the skin

• Leads to itchy, red, inflamed skin lesions

• Spread by intimate or close contact (skin-to-skin or shared bedding)

What causes Pediculosis (lice) and how is it spread?

• Caused by Pediculus humanus capitis (head louse)

• Spread by head-to-head contact

• Feeds on blood several times a day

• Common in poor sanitation conditions

What are the types of lice and what disease can they spread?

• Head louse → Pediculus humanus capitis

• Body louse → Pediculus humanus corporis

  • Can spread epidemic typhus

What is Conjunctivitis, and what causes it?

• Inflammation of the conjunctiva (the eye membrane)

• Also called “pink eye”

• Caused by:

  • Bacteria: Haemophilus influenzae (most common)

  • Viruses: Adenoviruses

• Symptoms: red, irritated, watery eyes

What is Ophthalmia Neonatorum and what causes it?

• A serious form of conjunctivitis in newborns

• Caused by Neisseria gonorrhoeae (bacteria)

• Passed to baby during birth through infected birth canal

What are the symptoms and treatment for Ophthalmia Neonatorum?

• Causes lots of pus and may lead to cornea damage (ulcers)

• All newborns are treated at birth

  • Old treatment: 1% silver nitrate

  • Now replaced by antibiotic ointment

What causes Inclusion Conjunctivitis and how is it spread?

• Caused by Chlamydia trachomatis

• It’s an obligate intracellular parasite (lives inside cells)

• Can spread through unchlorinated swimming pool water

Treatment = tetracycline

What is Trachoma, and what causes it?

• #1 cause of blindness from infection worldwide

• Caused by Chlamydia trachomatis

• Common in Southwestern U.S. and developing countries

How is Trachoma spread, and what does it cause?

• Spread by hand contact, sharing personal items, or flies

• Repeated infections → chronic inflammation

• Can lead to corneal scratches (abrasions) and scarring

• Late stage: trichiasis (eyelashes turn inward and scratch eye)

What causes Herpetic Keratitis?

• Caused by Herpes simplex virus type 1 (HSV-1)

• The same virus that causes cold sores

What are the symptoms and possible outcomes of Herpetic Keratitis?

• Causes infection of the cornea

• Leads to ulcers on the eye

• May be the most common cause of infectious blindness in the U.S.

What is Acanthamoeba keratitis, and where is the organism found?

• Caused by an ameba (Acanthamoeba)

• Found in freshwater, tap water, hot tubs, and soil

• Linked to contact lens use and poor cleaning practices

What damage can Acanthamoeba keratitis cause, and how is it treated?

• Can lead to severe corneal damage

• May require corneal transplant or even eye removal if untreated

• Treated with chlorhexidine eye drops or topical neomycin