17.1

• Categories of human diseases

  • Degenerative diseases
  • Immune disorders
  • Infectious diseases
  • Metabolic disorders
  • Neoplasms (cancers and other types of tumors)
  • Nutritional disorders
  • Psychiatric disorders
• Only infectious diseases are caused by microbes
• Microbial intoxications


  Diseases that follow ingestion of a toxin produced outside the body (in vitro) by a pathogen
• Infectious diseases (or infections)


  Diseases that follow colonization of some body site by a pathogen
• Some infectious diseases affect more than one anatomic site, and some pathogens move from one body site to another during the course of a disease
• Skin


  • Intact skin is a type of nonspecific host defense mechanism, serving as a physical barrier
  • The indigenous microbiota of the skin, a low pH, and the presence of chemical substances, such as lysozyme and sebum, also serve to prevent colonization of the skin by pathogens
• Epidermis


  The superficial portion of the skin
• Dermis


  The inner layer of skin, containing blood and lymphatic vessels, nerves, nerve endings, glands, and hair follicles
• Dermatitis


  Inflammation of the skin
• Folliculitis


  Inflammation of a hair follicle, the sac that contains a hair shaft
• Sty (or stye)


  Inflammation of a sebaceous gland that opens into a follicle of an eyelash
• Furuncle


  A localized pyogenic (pus-producing) infection of the skin, usually resulting from folliculitis; also known as a boil
• Carbuncle


  A deep-seated pyogenic infection of the skin, usually arising from a coalescence of furuncles
• Macule


  A surface lesion that is neither raised nor depressed, such as the lesions of measles
• Papule

  A surface lesion that is firm and raised, such as the lesions of chickenpox
• Vesicle


  A blister or small fluid-filled sac, such as is seen in chickenpox and shingles
• Pustule


  A pus-filled surface lesion
• Ear


  • There are three pathways for pathogens to enter the ear: (a) through the eustachian (auditory) tube, from the throat and nasopharynx; (b) from the external ear; and (c) via the blood or lymph
• Otitis media


  Infection of the middle ear
• Otitis externa


  Infection of the outer ear canal
• Eye


  • Conjunctiva is the thin, tough lining that covers the inner wall of the eyelid and the sclera (the white of the eye)
  • Conjunctivitis is an infection or inflammation of the conjunctiva
  • Keratitis is an infection or inflammation of the cornea-the domed covering over the iris and lens
  • Keratoconjunctivitis is an infection that involves both the cornea and the conjunctiva
  • Retinitis is inflammation that involves the retina, often caused by viral infection
• Parts of the respiratory system

  • Upper respiratory tract (URT)
  • Lower respiratory tract (LRT)
• Respiratory system infections are the most common cause of death from infectious diseases
• Bronchitis


  Inflammation of the mucous membrane lining of the bronchial tubes; most commonly caused by respiratory viruses
• Bronchopneumonia


  Combination of bronchitis and pneumonia
• Epiglottitis


  Inflammation of the epiglottis (the mouth of the windpipe) may cause respiratory obstruction, especially in children; in the absence of vaccination, frequently caused by Haemophilus influenzae type b
• Laryngitis


  Inflammation of the mucous membrane of the larynx (voice box)
• Pharyngitis


  Inflammation of the mucous membrane and underlying tissue of the pharynx; commonly referred to as sore throat. "Strep throat" is pharyngitis caused by Streptococcus pyogenes.
• Pneumonia


  Inflammation of one or both lungs. Alveolar sacs become filled with exudate, inflammatory cells, and fibrin. Most cases of pneumonia are caused by bacteria or viruses, but they can also be caused by fungi and protozoa.
• Pharyngitis


  Inflammation of the mucous membrane and underlying tissue of the pharynx; commonly referred to as sore throat. "Strep throat" is pharyngitis caused by Streptococcus pyogenes. Even though S. pyogenes is the most "publicized" cause of pharyngitis, most cases of pharyngitis are caused by viruses
• Pneumonia


  Inflammation of one or both lungs. Alveolar sacs become filled with exudate, inflammatory cells, and fibrin. Most cases of pneumonia are caused by bacteria or viruses, but they can also be caused by fungi and protozoa
• Sinusitis


  Inflammation of the lining of one or more of the paranasal sinuses. The most common causes are the bacteria, Streptococcus pneumoniae and Haemophilus influenzae. Less common causes are the bacteria, S. pyogenes, Moraxella catarrhalis, and Staphylococcus aureus
• Typical pneumonia


  • Patients experience chest pain, dyspnea (shortness of breath), fever, chills, and a productive cough (one that produces purulent sputum). Less common symptoms include anorexia, headache, nausea, diarrhea, and vomiting. X-ray abnormalities are proportional to the physical symptoms. Common causes are the bacteria, S. pneumoniae, H. influenzae, and S. aureus, and viruses such as influenza virus types A and B, parainfluenza viruses, and respiratory syncytial virus (RSV). Other causes are Legionella pneumophila, Mycoplasma pneumoniae, Chlamydophila pneumoniae, and other Gram-negative bacilli
• Atypical pneumonia


  • Has a more insidious (slower) onset than typical pneumonia. Patients present with headache, fever, cough with little sputum, and myalgia. X-ray abnormalities are usually greater than physical symptoms would predict. Common causes are the bacteria, M. pneumoniae, C. pneumoniae, and L. pneumophila, and viruses such as influenza viruses, RSV, and adenoviruses. Other causes are Chlamydophila psittaci (a bacterium), Pneumocystis jirovecii (a fungus), varicella-zoster virus, and parainfluenza viruses. Note that some pathogens can produce either typical or atypical pneumonia
• Respiratory tract infections are the most common cause of death from infectious diseases
• Even though S. pyogenes is the most widely "publicized" cause of pharyngitis, viruses cause most cases of pharyngitis