Q4MBIO | LESSON 1

• The skin, which covers and protects the body, is the body’s first line of defense against pathogens.


  STRUCTURE AND FUNCTIONS OF SKIN
• Impossible for pathogens to penetrate the intact skin.
• Microbes can, however, enter through skin breaks that are not readily apparent, and the larval forms of a few parasites can penetrate intact skin.
• The skin is an inhospitable place for most microorganisms because the secretions of the skin are acidic and most of the skin contains little moisture.
• It is the thin outer portion, composed of several layers of epithelial cells. The outermost layer of the epidermis, the stratum corneum, consists of many rows of dead cells that contain a waterproofing protein called Keratin.


  EPIDERMIS
• The inner relatively thick portion of skin, composed mainly of connective tissue. The hair follicles, sweat gland ducts, and oil gland ducts in the dermis provide passageway through which microorganisms can enter the skin and penetrated deeper tissues


  DERMIS
• It provides moisture and some nutrients for microbial growth.

  But it contains salt, which inhibits many microorganisms; the enzyme Lysozyme can break down the cell walls of certain bacteria and antimicrobial peptides 


  PERSPIRATION
• • Secreted by oil glands
  • Mixture of lipids (unsaturated fatty acids), proteins, and salts that prevents skin and hair from drying out


  SEBUM
• MUCOUS MEMBRANES

  • Linings of body cavities, such as those associated with gastrointestinal, respiratory, urinary, and genital tracts, the outer protective barrier differs from the skin.
  • Consists of sheets of tightly packed epithelial cells.
  • Often acidic, which tends to limit their microbial population.
  • Often folded to maximize surface area.
• Normal Microbiota of the Skin

  Although the skin is generally inhospitable to most microorganisms, it supports the growth of certain microbes (part of normal Microbiota)
• A skin rash that arises from disease condition is called an Exanthem.
• On mucous membranes, such as the interior of the mouth, such as a rash is called an enanthem
• (viral diseases) Usually diagnosed by clinical signs and symptoms and may be confirmed by serology or PCR

  MACULAR RASHES
• • PATHOGEN – Measles virus
  • PORTAL OF ENTRY – Respiratory tract
  • SYMPTOMS – Skin rash of reddish macules first appearing on face and spreading to trunk and extremities
  • METHOD OF TRANSMISSION – Aerosol
  • TREATMENT – No treatment; pre exposure vaccine

  Measles (rubeola)
• • PATHOGEN – Rubella virus
  • PORTAL OF ENTRY – Respiratory tract
  • SYMPTOMS – Mild disease with a macular rash resembling measles, but less extensive and disappearing in 3 days or less
  • METHOD OF TRANSMISSION – Aerosol
  • TREATMENT – No treatment; pre exposure vaccine

  Rubella (German measles)
• • PATHOGEN – Human herpesvirus 6, human herpesvirus 7
  • PORTAL OF ENTRY – Respiratory tract
  • SYMPTOMS – High fever followed by macular body rash
  • METHOD OF TRANSMISSION – Aerosol
  • TREATMENT – None

  Roseola
• • PATHOGEN – Candida albicans
  • PORTAL OF ENTRY – Skin; mucous membranes
  • SYMPTOMS – Macular Rash
  • METHOD OF TRANSMISSION – Direct contact; endogenous infection
  • TREATMENT – Miconazole, clotrimazole (topically)

  Candidiasis
• VESICULAR AND PUSTULAR RASHES

  BACTERIAL DISEASE. Usually diagnosed by culturing the bacteria.
• • PATHOGEN – Staphylococcus aureus
  • PORTAL OF ENTRY – Skin
  • SYMPTOMS – Vesicles on skin
  • METHOD OF TRANSMISSION – Direct contact; fomites
  • TREATMENT – Topical antibiotics

  Impetigo
• VIRAL DISEASES. Usually diagnosed by clinical signs and symptoms and may be confirmed by serology or PCR.
• • PATHOGEN – Monkeypox virus
  • PORTAL OF ENTRY – Respiratory tract
  • SYMPTOMS – Pustules, similar to smallpox
  • METHOD OF TRANSMISSION – Direct contact with or aerosols from infected small mammals
  • TREATMENT – None


  Monkeypox
• • PATHOGEN – Varicella-zoster virus
  • PORTAL OF ENTRY – Respiratory tract
  • SYMPTOMS – Vesicles in most cases confined to face, throat, and lower back
  • METHOD OF TRANSMISSION – Aerosol
  • TREATMENT – Acyclovir for immunocompromised patients; pre exposure vaccine

  Chickenpox (varicella)
• • PATHOGEN – Varicella-zoster virus
  • PORTAL OF ENTRY – Endogenous* infection of peripheral nerves (*Endogenous infections are infections caused by microorganisms already part of the host microbiota.)
  • SYMPTOMS – Vesicles typically on one side of waist, face and scalp, or upper chest
  • METHOD OF TRANSMISSION – Recurrence of latent chickenpox infection
  • TREATMENT – Acyclovir; preventive vaccine


  Shingles (herpes-zoster)
• PATCHY REDNESS AND PIMPLE-LIKE CONDITIONS

  BACTERIAL DISEASES. Usually diagnosed by culturing the bacteria.
• • PATHOGEN – Staphylococcus aureus
  • PORTAL OF ENTRY – Hair follicle
  • SYMPTOMS –  Infection of hair follicle
  • METHOD OF TRANSMISSION –  Direct contact; fomites; endogenous infection*
  • TREATMENT – Draining of pus; topical antibiotics

  Folliculitis
• • PATHOGEN – Staphylococcus pyogenes
  • PORTAL OF ENTRY – Skin; mucous membranes
  • SYMPTOMS – Reddish patches on skin; often with high fever
  • METHOD OF TRANSMISSION – Endogenous infection*
  • TREATMENT – Cephalosporin

  Erysipelas
• • PATHOGEN – Propionibacterium acnes
  • PORTAL OF ENTRY – Sebum channels
  • SYMPTOMS – Inflammatory lesions originating with accumulations of sebum that rupture a hair follicle
  • METHOD OF TRANSMISSION – Direct contact
  • TREATMENT – Benzoyl peroxide, isotretinoin, azelaic acid

  Acne
• • PATHOGEN – Mycobacterium ulcerans
  • PORTAL OF ENTRY – Skin
  • SYMPTOMS – Localized swelling or hardness progressing to deep ulcer
  • METHOD OF TRANSMISSION – Contaminated water
  • TREATMENT – Antimycobacterial drugs

  Buruli Ulcer
• • PATHOGEN – Papillomavirus
  • PORTAL OF ENTRY – Skin
  • SYMPTOMS – A horny projection of the skin formed by proliferation of cells
  • METHOD OF TRANSMISSION – Direct contact
  • TREATMENT – Removal by liquid nitrogen cryotherapy, electrodesiccation, acids, lasers

  Warts
• FUNGAL DISEASES. Diagnosis is confirmed by microscopic examination.
• • PATHOGEN – Microsporum, Trichophyton, Epidermophyton
  • PORTAL OF ENTRY – Skin
  • SYMPTOMS – Skin lesions of highly varied appearance; on scalp may cause local loss of hair
  • METHOD OF TRANSMISSION – Direct contact; fomites
  • TREATMENT – Griseofulvin (orally); miconazole, clotrimazole (topically)

  Ringworm (tinea)
• PARASITIC INFESTATIONS. Diagnosis is confirmed by microscopic examination of parasite.
• • PATHOGEN – Sarcoptes scabiei (mite)
  • PORTAL OF ENTRY – Skin
  • SYMPTOMS – Papules, itching
  • METHOD OF TRANSMISSION – Direct contact
  • TREATMENT – Gamma benzene hexachloride, permethrin (topically)


  Scabies
• • PATHOGEN – Pediculus humanus capitis
  • PORTAL OF ENTRY – Skin
  • SYMPTOMS – Itching
  • METHOD OF TRANSMISSION – Primarily direct contact; possible fomites such as bedding, combs
  • TREATMENT – Topical insecticide preparations


  Pediculosis (lice)
• The epithelial cells covering the eye can be considered a continuation of the skin or mucosa. Many microbes can infect the eye, largely through the conjunctiva, the mucous membrane that lines the eyelids and covers the outer white surface of the eyeball. It is a transparent layer of living cells replacing the skin.

   MICROBIAL DISEASES OF THE EYES
• • an inflammation of the conjunctiva, often called by the common name red eye, or pinkeye.
  • Haemophilus influenzae is the most common bacterial cause; viral conjunctivitis is usually caused by adenoviruses.
  • a broad group of bacterial and viral pathogens as well as allergies can also cause this condition.

  INFLAMMATION OF THE EYE MEMBRANE: CONJUNCTIVITIS
• PATHOGEN: Haemophilus influenzae

  PORTAL OF ENTRY: Conjunctiva

  METHOD OF TRANSMISSION: Direct contact; fomites

  CAUSE:

  • Virus: Adenovirus
  • Herpes Simplex Virus
  • Varicella-Zoster Virus
  • Wearing contact lenses that aren't cleaned properly or aren't your own.
  • A chemical splash in the eye
  • A foreign object in the eye
  • In newborns, a blocked tear duct

  SYMPTOMS:

  • Redness & Itchiness in one or both eyes.
  • A gritty feeling in one or both eyes
  • Tearing
  • Photophobia

  CURE/TREATMENT:

  • None

  CONJUCTIVITIS
• Also called


  Chlamydial conjunctivitis
• Chlamydia trachomatis


  • Bacterium that grows only as an obligate intracellular parasite
• PATHOGEN


  Chlamydia trachomatis