Chapter 18 & 19 micropara

• How viruses cause disease


  Viruses multiply within host cells. It is during their escape from those cells either by cell lysis or budding – that the host cells are destroyed. This cell destruction leads to most of the symptoms of a viral infection, which vary depending upon the location of the infection.
• Viral infections of the skin

  • Chickenpox and Shingles (Varicella-zoster virus)
  • German Measles (Rubella virus)
  • Measles (Measles (rubeola) virus)
  • Monkeypox (Monkeypox virus)
  • Smallpox (Variola virus)
  • Warts (Human papillomaviruses)
• Viral infections of the eyes

  • Adenoviral conjunctivitis and keratoconjunctivitis (Adenoviruses, Herpes simplex virus, Varicella-zoster virus)
  • Hemorrhagic conjunctivitis (Adenoviruses, Enteroviruses)
• Viral infections of the upper respiratory tract

  • The Common Cold (Rhinoviruses, Coronaviruses, Parainfluenza viruses, Respiratory syncytial virus, Influenzaviruses, Adenoviruses, Enteroviruses)
• Viral infections of the lower respiratory tract

  • Acute, Febrile, Viral Respiratory Disease (Parainfluenza viruses, Respiratory syncytial virus, Adenovirus, Rhinoviruses, Coronaviruses, Coxsackieviruses, Echoviruses)
  • Avian Influenza (Avian influenza virus)
  • Hantavirus Pulmonary Syndrome (Hantaviruses)
  • Influenza (Influenza viruses)
  • Severe Acute Respiratory Syndrome (SARS-associated coronavirus)
• Viral infections of the oral region

  • Cold Sores (Herpes simplex virus type 1, Herpes simplex virus type 2)
• Viral infections of the GI tract


  • Viral Gastroenteritis (Enteric adenoviruses, Astroviruses, Caliciviruses, Rotaviruses, Norovirus-like viruses)
• Types of viral hepatitis

  • Type A Hepatitis (Hepatitis A virus)
  • Type B Hepatitis (Hepatitis B virus)
  • Type C Hepatitis (Hepatitis C virus)
  • Type D Hepatitis (Hepatitis D virus)
  • Type E Hepatitis (Hepatitis E virus)
  • Type G Hepatitis (Hepatitis G virus)
• Viral STDs


  • Anogenital Herpes Viral Infections (Herpes simplex virus type 2, Herpes simplex virus type 1)
  • Genital Warts (Human papillomaviruses)
• Viral infections of the circulatory system

  • Human Immunodeficiency Virus (HIV) Infection, Acquired Immunodeficiency Syndrome (AIDS) (Human immunodeficiency virus)
  • Infectious Mononucleosis (Epstein-Barr virus)
  • Mumps (Mumps virus)
  • Viral Hemorrhagic Diseases (Dengue virus, Yellow fever virus, Crimean-Congo hemorrhagic fever virus, Lassa virus, Ebola virus, Marburg virus)
• Viral infections of the CNS

  • Lymphocytic Choriomeningitis (Lymphocytic choriomeningitis virus)
  • Poliomyelitis (Polioviruses)
  • Rabies (Rabies virus)
  • Viral Meningitis (Various viruses)
• Most of the bacterial diseases described are caused by a single bacterial species, many other diseases are thought to be the result of communities of bacteria consisting of more than one species.
• How bacteria cause disease

  • Adherence and colonization factors
  • Factors that prevent activation of complement
  • Factors that enable escape from phagocytosis by white blood cells (WBCs)
  • Factors that prevent destruction within phagocytes
  • Factors that suppress the host immune system
  • Endotoxin (a component of the cell walls of Gram-negative bacteria)
  • Production of exotoxins (e.g., cytotoxins, enterotoxins, neurotoxins)
  • Production of necrotic and other types of destructive enzymes
• Bacterial infections of the skin

  • Acne (Propionibacterium acnes and other Propionibacterium spp.)
  • Anthrax, Woolsorter's Disease (Bacillus anthracis)
  • Gas Gangrene (Myonecrosis) (Anaerobic bacteria in the genus Clostridium, especially C. perfringens)
  • Leprosy (Hansen Disease) (Mycobacterium leprae)
  • Staphylococcal Skin Infections (Folliculitis, Furuncles, Abscesses, etc.) (Staphylococcus aureus)
  • Streptococcal Skin Infections (Scarlet Fever, Erysipelas, etc.) (Streptococcus pyogenes)
  • Wound Infections (Opportunistic indigenous microflora and environmental bacteria)
• Viral and bacterial ear infections

  • Otitis Externa (Escherichia coli, Pseudomonas aeruginosa, Proteus vulgaris, Staphylococcus aureus, Aspergillus spp.)
• Skin barrier


  Protective skin barrier that can be broken as a result of burns, punctures, surgical procedures, or bites
• Skin barrier breakdown


  • Allows opportunistic indigenous microflora and environmental bacteria to invade and cause local or deep tissue infections
  • Pathogens may spread through blood or lymph, causing serious systemic infections
• Otitis Externa


  Infection of the outer ear canal
• Otitis externa is common during the summer swimming season due to trapped water in the ear canal
• Otitis Externa (Swimmer's ear)

  Often results from swimming in contaminated water with Pseudomonas aeruginosa
• Pathogens causing Otitis Externa

  • Escherichia coli
  • Pseudomonas aeruginosa
  • Proteus vulgaris
  • Staphylococcus aureus
  • Aspergillus spp.
• Reservoirs and mode of transmission for Otitis Externa


  • Contaminated water in reservoirs
  • Indigenous microflora
  • Objects used for cleaning the ear canal
• In cases of infected ear canals, it is essential to send material to the microbiology lab for culture and susceptibility (C&S)
• Most strains of P. aeruginosa are multidrug resistant
• Otitis Media


  Middle ear infection
• Otitis media is often a complication of the common cold
• Pathogens causing Otitis Media


  • Streptococcus pneumoniae
  • Haemophilus influenzae
  • Moraxella catarrhalis
  • Streptococcus pyogenes
  • Staphylococcus aureus
  • Measles virus
  • Parainfluenza virus
  • RSV
• Otitis Media is probably not communicable
• A sample of discharge from the ear should be sent to the microbiology laboratory, if present
• 1. Lactamase testing should be performed on isolates of H. influenzae and S. pneumoniae
• Conjunctivitis (Pinkeye)


  Irritation and reddening of conjunctiva, edema of eyelids, mucopurulent discharge, and sensitivity to light
• Conjunctivitis is a highly contagious disease
• Standard Precautions should be used for hospitalized patients with conjunctivitis
• Pathogens causing Conjunctivitis


  • Haemophilus influenzae subsp. aegyptius
  • Streptococcus pneumoniae
• Reservoirs and mode of transmission for Conjunctivitis

  • Infected individuals act as reservoirs
  • Transmission occurs from person to person through contact with eye and respiratory discharges, fingers, facial tissues, clothing, eye makeup, medications, instruments, and contact lens solutions
• Infections of the eyes should be differentiated from allergic manifestations and irritation by microscopic examination of the exudate (oozing pus), culture of pathogens, and/or immunodiagnostic procedures
• Chlamydial Conjunctivitis (Inclusion Paratrachoma)


  Conjunctivitis caused by certain serotypes of Chlamydia trachomatis, a Gram-negative bacterium and obligate intracellular pathogen
• Standard Precautions should be used for hospitalized patients with chlamydial conjunctivitis
• Reservoirs and mode of transmission for Chlamydial Conjunctivitis

  • Infected humans serve as reservoirs
  • Transmission occurs via contact with genital discharges of infected people, contaminated fingers to eye, infection in newborns via an infected birth canal, or non-chlorinated swimming pools (swimming pool conjunctivitis)
• Diagnosis of chlamydial conjunctivitis is made by cell culture and/or immunodiagnostic procedure