Conquest of Infectious Diseases

• BUBONIC PLAGUE (black death), wiped out 75% of the population of Europe and Asia in the 4th century
• Causative agent of Bubonic plague

  Yersinia pestis (formerly Pasteurella pestis) aka Plague Bacillus
• Bubonic plague


  • Associated with high fever and painful inflammatory swelling of axilla and groin (buboes); it results from the bite of an infected flea
• Pulmonary plague


  • Acquired by close contact with other victims; it occurs secondary to the bubonic plague
• TUBERCULOSIS- #1 killer in England in the mid-19th century (Mycobacterium tuberculosis: an acid-fast bacilli)
• SMALLPOX (Variola Virus- Orthopoxvirus genus) and CHOLERA (Vibrio cholerae)- swept through the city few years, killing many people in each wave
• TYPHOID (Salmonella typhi)- mid-19th century
• Public health measures that conquered infectious diseases

  • Purification of water
  • Proper disposal of sewage
  • Pasteurization of milk
  • Immunization
  • Improved nutrition
  • Personal hygiene
• INFECTIOUS AGENTS: BACTERIA, VIRUSES, AND PARASITES
• Bacteria


  • Single-celled organisms
  • Can grow and reproduce outside the body
  • Dependent on cell production
• Bacilli


  Rod-shaped bacteria
• Tetanus


  Causative agent is Clostridium tetani
• Clostridium tetani


  • Soil and environmental inhabitants
  • Endospores found in hospital environments, in soil and dust, and in the feces of many farm animals
  • Virulence factor: tetanospasmin (neurotoxin) causes tension or cramping and twisting in skeletal muscles surrounding the wound and tightness of the jaw muscles
• Tetanus


  • Characterized by "trismus" (lockjaw) and "risus sardonicus" (distorted grin)
  • Occurs when the organism (spore) enters an open wound and elaborates the potent toxin that mediates generalized muscle spasms
  • Symptoms: muscular rigidity (jaws, neck, and lumbar region), difficulty in swallowing, rigidity of the abdomen, chest, back, and limbs
  • Incubation Period: 3 to 21 days (the long incubation period is related to the distance from the injury to the CNS)
  • Tetanus neonatorum: caused by contaminated instruments used for newborns
• Diphtheria


  • Causative agent is Corynebacterium diphtheriae
  • Acute, contagious disease characterized by the production of a systemic toxin and a false membrane lining (pseudomembranous formation) of the mucous membrane of the throat leading to respiratory obstruction
  • The only effective control is through immunization (DPT) – diphtheria antitoxin is administered to neutralize any unabsorbed exotoxin in the patient's tissues
• Corynebacterium diphtheriae


  • Inhabits human nasopharynx but only in carrier state; not part of the normal flora of respiratory tract
  • Acquired through contaminated respiratory droplets or direct contact with infected cutaneous lesions (hand-to-mouth) – humans are the only host
  • Readily killed by heat and most of the usual disinfectants
  • Very resistant to drying and remains viable in the environment for weeks
  • Virulence factor: diphtheria toxin causes tissue necrosis and exudates formation (pseudo membrane) on the tonsils spread downward into the larynx and pharynx
• Dysentery/Bacillary dysentery

  • Causative agent: Shigella dysenteriae
  • Marked by penetration of intestinal epithelial cells by the organism, following attachment of the organisms to mucosal cells
  • Characterized by acute inflammatory colitis and bloody diarrhea (blood, mucus, and WBCs in the stool) and its presence usually indicates improper sanitary conditions and poor personal hygiene
  • Transmission: person to person, fecal-oral route, flies, fingers and food or water contaminated by infected persons
• Cocci


  Spherical/round-shaped bacteria
• Staphylococci


  • Normal inhabitant of the skin, mucus membrane, and intestine
  • Associated with human infections are colonizers of various skin and mucosal surfaces
  • Microscopy: spherical cells that appear in clusters, some singly
  • Staphylococcus aureus: the most virulent Staphylococci specie
• Staphylococcus aureus


  • Causes infection when it enters a normally sterile site due to trauma or abrasion to the skin or mucosal surfaces
  • Chiefly responsible for the various skin, wound, and deep tissue infections
• Streptococci


  Commonly found as part of normal human flora, however, when these organism gain access to normally sterile sites, they can cause life threatening infection
• Streptococcus pyogenes


  • Fever-producing bacteria; flesh eating bacteria (involves deeper tissues and organs)
  • Causative agent of Pharyngitis or Tonsilitis aka "Strep Throat", Scarlet Fever, and Septic Shock/Streptococcal TSS (Toxic Shock Syndrome)
• Streptococcus pyogenes


  • Pharyngitis or Tonsilitis: spread by droplet and close contact, diagnosis relies on culture of specimen (throat swab) or direct antigen detection
  • Scarlet Fever: communicable and spread by inhalation of infectious respiratory droplet, cardinal signs: diffused red rash on the upper chest and spreads to the trunk and extremities, and "strawberry colored-tongue"
  • Septic Shock/Streptococcal TSS: condition which entire organ system shuts down, leading to death
• Streptococcus pneumoniae


  • Causative agent of lobar pneumonia – most common cause of bacterial pneumonia in elderly as well as in patients with underlying disease
  • The most common cause of bacterial meningitis in adults
  • Microscopy: Gram-positive cocci in pairs, oval, or lancet shape
• Neisseria meningitidis (Meningococci)


  • A gram-negative diplococci
  • Leading cause of fatal bacterial meningitis
  • Causative agent of epidemic meningococcal meningitis/meningococcemia/cerebrospinal fever
  • May be found as a commensal inhabitant of the upper respiratory tract of the carriers – it colonizes the mucous membranes of nasopharynx and oropharynx
• Spirochete


  Corkscrew-shaped bacteria
• Syphilis


  • Causative agent is Treponema pallidum subspecies pallidum
  • Has the ability to cross intact mucous membrane and the placenta, spread throughout the body
  • Has a remarkable tropism (attraction) to arterioles
  • Inhibited rapidly by heat and dryness; susceptible to disinfectants
  • Microscopy: appears white against a dark background
• Leptospirosis


  Causative agent is: Leptospira interrogans
• Parasites/Protozoa


  Single-celled organisms
• Intestinal parasites


  • Hookworm (Necator americanus)
  • Roundworm (Ascaris lumbricoides)
  • Pinworm (Enterobius vermicularis)
  • Tapeworm (Taenia solium, Taenia saginata)
• Malaria


  • Causative agent is Plasmodium species
  • Vector: mosquitos
  • Plasmodium falciparum: main cause of severe clinical malaria and death
  • Plasmodium vivax, ovale, and malariae
  • When these parasites mature, they infect the red blood cells. This is when people typically develop malaria symptoms
  • Modes of Transmission: from mother to unborn child, through blood transfusions, by sharing needles used to inject drugs
• Cryptosporidiosis (Milwaukee diarrhea)


  Causative agent is Cryptosporidium parvum
• Giardiasis


  Diarrheal condition that the causative agent is Giardia lamblia
• Giardia lamblia


  • A protozoan parasite/pathogen causing gastrointestinal diseases in humans
  • Can be found in streams, lakes, and rivers
• Amoebic Dysentery


  Severe form of amoebiasis; causative agent is Entamoeba histolytica
• Viruses


  • Not complete cells
  • Can survive extreme condition
  • Can reproduce themselves
  • Examples: Poliovirus, Hepatitis, Measles, AIDS, and Rabies
  • Can survive extreme conditions such as treatment with alcohol, drying in vacuum and become active again when they are injected into a living cells
• Polio


  • Causative agent is Poliovirus, other name: poliomyelitis, family: Picornaviridae
  • Infects human beings only
  • Has the potential to be eradicated
  • 1988 (350, 000 children were paralyzed each year)
  • 2000 (WHO set a goal of eradicating polio)
  • 1999 (eliminated in WESTERN HEMISPHERE, EUROPE, WESTERN PACIFIC and cases reduced by 99%)
  • National Immunization Days: distribute oral polio vaccine to children
  • Attracts the nervous system and can cause permanent paralysis
  • Mostly occurs to children less than 5 years old
  • 2 types: Non-paralytic Polio and Paralytic Polio
  • Post-Polio Syndrome: possible for polio to return even after recovery, can occur after 15 to 40 years
• Polio


  Poliovirus, other name: poliomyelitis, family: Picornaviridae
• Polio


  • Infects human beings only
  • Has the potential to be eradicated
• 350,000 children were paralyzed each year


  1988