Conquest of Infectious Diseases

Conquest of Infectious Diseases

• Bubonic Plague (black death) wiped out 75% of the population of Europe and Asia in the 4th century
• The causative agent is Yersinia pestis, formerly Pasteurella pestis aka Plague Bacillus
• Bubonic plague comes from the bite of an infected flea and involves high fever and inflammatory swelling of the axilla and groin (buboes)
• Pulmonary plague is acquired by close contact with other victims, and occurs secondary to the bubonic plague
• Tuberculosis, caused by Mycobacterium tuberculosis (an acid-fast bacilli), was the #1 killer in England in the mid-19th century
• Smallpox (Variola Virus- Orthopoxvirus genus) and Cholera (Vibrio cholerae) swept through cities, killing many
• Typhoid, caused by Salmonella typhi, was a problem in the mid-19th century
• These diseases were largely conquered through public health measures like water purification, sewage disposal, milk pasteurization, immunization, nutrition, and personal hygiene

Infectious Agents: Bacteria, Viruses, and Parasites

• Bacteria definition, single-celled organisms that can grow/reproduce outside the body

Bacteria

• Bacteria that are rod-shaped are called Bacilli
• Tetanus causative agent is Clostridium tetani
• Clostridium tetani is also known as "Tack head bacillus"
• Clostridium tetani lives in soil and the environment
  • Endospores are found in hospitals, soil, dust, and animal feces
  • Tetanospasmin is a virulence factor (neurotoxin)
    • It causes tension/cramping with twisting in skeletal muscles surrounding the wound and tightness of the jaw muscles.
  • Tetanus is associated with trismus (lockjaw) and risus sardonicus (distorted grin)
    • This happens when the organism (spore) enters an open wound and mediates generalized muscle spasms
    • Symptoms include muscular rigidity (jaws, neck, lumbar region), difficulty swallowing, and rigidity of the abdomen, chest, back, and limbs
    • Incubation period is 3–21 days, depending on the injury location relative to the CNS
    • Tetanus neonatorum is caused by contaminated instruments used for newborns
• Diphtheria causative agent is Corynebacterium diphtheriae
  • Diphtheria is a contagious disease characterized by systemic toxin production and a false membrane lining (pseudomembranous formation) in the throat, causing respiratory obstruction
  • The only effective control measure is immunization (DPT), and diphtheria antitoxin helps neutralize any unabsorbed exotoxin
  • Corynebacterium diphtheriae, also known as Diphtheria bacillus/Kleb Loeffler’s bacillus
    • It lives in the human nasopharynx, but only as a carrier state, not part of the normal respiratory flora
    • It spreads through contaminated respiratory droplets or direct contact with infected cutaneous lesions (hand-to-mouth)
    • Humans are the only hosts
    • It can be readily killed with heat and disinfectants
    • It is very resistant to drying and remains viable for weeks in the environment
    • Diphtheria toxin is a virulence factor that causes tissue necrosis and exudate formation on the tonsils, spreading down into the larynx and pharynx
• Dysentery/Bacillary dysentery causative agent is Shigella dysenteriae
  • Marked by penetration of intestinal epithelial cells by the organism, following attachment of the organisms to mucosal cells
  • Symptoms include acute inflammatory colitis and bloody diarrhea (blood, mucus, and WBCs in the stool), indicating improper sanitary conditions/poor hygiene
  • Transmission can occur person to person via the fecal-oral route, flies, fingers, and food/water contaminated by infected persons.
• Spherical/round-shaped bacteria are called Cocci
  • Cocci can cause skin disease, septic shock, pneumonia, and meningitis (meningitidis)
• Staphylococci are normal inhabitants of the skin, mucous membrane, and intestine
  • Human infections associated with species colonizing skin/mucosal surfaces
  • Spherical cells appear in clusters
  • Staphylococcus aureus is the most virulent Staphylococci species, causing infection that enters normally sterile sites due to trauma or abrasion
    • Chiefly responsible for skin, wound, and deep tissue infections
• Streptococci definition, commonly found as part of normal human flora
  • Streptococci that gain access to normally sterile sites can cause life-threatening infection
  • Streptococcus pyogenes is the causative agent for strep throat, scarlet fever, and septic shock
    • Streptococcus pyogenes is a fever-producing/flesh-eating bacteria that involves the deeper issues and organs
    • Pharyngitis/Tonsilitis aka Strep Throat
      • Spreads through droplets/close contact
      • Diagnosis relies on specimen (throat swab) culture or direct antigen detection
    • Scarlet Fever
      • Communicable and spread through infectious respiratory droplets
      • Cardinal signs include a diffused red rash that spreads throughout the body and a strawberry-colored tongue.
    • Septic Shock/Streptococcal TSS (Toxic Shock Syndrome)
      • An organism shuts down the organ system, leading to death
• Pneumonia causative agent is Streptococcus pneumoniae
  • Streptococcus pneumoniae aka Diplococcus/Pneumococcus
    • Considered part of the normal flora (25-50%) of the Upper Respiratory Tract of preschool children
    • It is commonly isolated as both a pathogen and member of the normal respiratory tract
    • It is the causative agent of lobar pneumonia and is the most common cause in the elderly, and in patients with underlying disease
    • Most common cause of bacterial meningitis in adults
    • Gram-positive cocci in pairs, oval or lancet shape
• Neisseria meningitidis (Meningococci) definition, a gram-negative diplococci
  • It is the leading cause of fatal bacterial meningitis
  • It is also the causative agent of epidemic meningococcal meningitis/meningococcemia/cerebrospinal fever.
  • May be found as a commensal inhabitant of the upper respiratory tract of carriers as it colonizes the mucous membranes of nasopharynx and oropharynx
• Spirochetes definition, corkscrew-shaped bacteria
  • Syphilis causative agent is Treponema pallidum
    • Treponema pallidum subspecies pallidum is the specific causative agent
    • Crosses intact mucous membranes/the placenta and spreads throughout the body
    • Remarkable tropism to arterioles.
    • Inhibited rapidly by heat and dryness, and is susceptible to disinfectants.
    • Microscopy: appears white against a dark background.
• Leptospirosis causative agent is Leptospira interrogans

Parasites/Protozoa

• Parasites and protozoa are single-celled organisms
• Hookworm is an intestinal parasite, Necator americanus, that feeds of blood
• The roundworm, Ascaris lumbricoides, causes infection in the small intestine
• The pinworm, Enterobius vermicularis, is a parasite causing itching around the anus
• Tapeworm is caused by the consumption of infected fecal matter and not well-cooked pork (Taenia solium) or beef (Taenia saginata)
• Malaria causative agent is Plasmodium species with a vector of mosquitos
  • Plasmodium falciparum and Plasmodium vivax/ovale/malariae are causes
    • Plasmodium falciparum is the main cause of severe clinical malaria/death.
  • These parasites infect red blood cells when mature
    • Causes malaria symptoms
  • Transmitted from mother to unborn child, through blood transfusions, or by sharing needles used to inject drugs
• Cryptosporidiosis (Milwaukee diarrhea) causative agent is Cryptosporidium parvum
• Giardiasis is a diarrheal condition with the causative agent Giardia lamblia
  • Giardia lamblia aka Giardia duodenalis/intestinalis definition, protozoan parasite/pathogen causing gastrointestinal diseases in humans
    • It can be found in streams, lakes, and rivers
• Amoebic Dysentery is a severe form of amoebiasis, with causative agent of Entamoeba histolytica

Viruses

• Viruses are not complete cells, they can survive extreme conditions, and they can reproduce themselves
• Examples include Poliovirus, Hepatitis, Measles, AIDS, and Rabies
• Viruses can survive alcohol, drying in a vacuum, and can become active when introduced into a living cell
• Polio, also known as, poliomyelitis, is caused by the poliovirus in the picornaviridae family
  • Infects only human beings and has the potential to be eradicated
    • In 1988, 350,000 children were paralyzed by polio each year
    • The WHO goal was set to eradicate polio by 2000
    • In 1999 polio was eliminated in the WESTERN HEMISPHERE, EUROPE, WESTERN PACIFIC, and cases were reduced by 99%
    • National Immunization Days distribute oral polio vaccine to children
    • It attracts the nervous system, causing permanent paralysis and mostly occurs in children less than 5 years old
  • 2 types of Polio
    • Non-paralytic Polio shows symptoms in 10 days, including flu-like symptoms, fever, sore throat, vomiting, and fatigue
    • Paralytic Polio shows paralysis in the spinal cord (spinal polio), brainstem (bulbar polio, or both (bulbospinal polio)
• Post-Polio Syndrome occurs 15–40 years after recovering
  • Symptoms include continuing muscle and joint weakness, muscle pain that gets worse, and becoming easily exhausted or fatigued
  • Transmission, fecal-oral route (from infected feces)
    • More difficult to eradicate than smallpox
    • Vaccine must be administered multiple times to work, mainly in poverty-stricken areas where children with other intestinal infections tend not to develop immunity after vaccines
• Hepatitis causative agent is Hepatovirus, family Picornaviridae
• Measles causative agent is Rubeola virus, family Paramyxoviridae
  • Causes 400-500 deaths each year
  • 750,000 children in the year 2000
  • Vaccine was available in 1963
    • Two problems interfered with vaccinations as outbreaks of measles occurred among vaccinated students
      • The outbreaks mean booster is necessary in adults
      • Not enough children were vaccinated unless required for school
• Yellow fever is caused by Flavivirus, family Flaviviridae that's transmitted through mosquito bites and can fever and jaundice
  • Found in Africa and South America, it is incurable but preventable with the vaccine
• West Nile Encephalitis is caused by the West Nile virus, family Flaviviridae, and is vector-borne
• Aids/HIV: check lesson 2 notes
• Rabies is caused by the RNA Virus and is in the Rhabdovirus family
  • The rabies virus leads to a fatal nervous system disease caused by the virus via the brain and travels to the salivary glands to be secreted in the saliva
  • An animal capable of secreting the virus in its saliva will already exhibit brain involvement with symptoms and is dead within a few days
  • Mandatory immunization of dogs against rabies is the first line of defense, immunizations are given to anyone who is bitten by a wild animal that cannot be tested
  • 55,000 deaths per year attributable to rabies
  • Bats are the most dangerous rabies threat to humans

Smallpox, Measles, and Polio: Universal Immunization

• Smallpox spread by AEROSOL or by TOUCH
  • Edward Jenner (1796) after observing that milkmaids appeared to be immune, proved that inoculation with cowpox matter to prevent smallpox/Cowpox
  • It used to kill 2 million per year and routine immunization in the US was in 1958
  • 1967-1977 total eradication of smallpox due to medical teams traveling the world
  • One of Public Health’s GREATEST Achievement in 1977
  • Now, smallpox remains in CDC and a Russian laboratory in Siberia
• Major epidemic diseases are caused by BACTERIA, VIRUSES or PARASITES
  • It was established in the 1880s and 1890s that each of these diseases is caused a specific microbe
    • Robert Koch developed techniques to classify bacteria by their shape

Koch's Postulates

• The organism must be present in every case of the disease
• The organism must be isolated and grown in the laboratory
• When injected with the laboratory-grown culture, test animals must develop the disease
• The organism must be isolated from the newly infected animals and the process repeated

Means of Transmission

• Direct Transmission is transmittal person to person
• Indirect Transmission is via water, food, or insects/animals

Examples for Means of Transmission

• Bacteria and viruses can be transmitted via respiratory infections
  • Examples are colds, influenza, and tuberculosis
    • This can occur through transmission on air via aerosols as well as water droplets. Transmittal can also occur via infected objects like door knobs, towels and utensils
• Intestinal infections are another mode of transmittal
  • Examples like cholera, Cryptosporidiosis and diphtheria are fecally transmitted
• Vector borne diseases are spread through insect
  • Example are malaria, yellow fever and West Nile encephalitis

Chain of Infection (IREMEs)

• Control of infectious diseases by interrupting the chain of infection

Chain of Infection

• Pathogen (Infectious Agents) is a virus, bacterium, or parasite that causes disease in humans
• Reservoir is a place where the pathogen lives/multiplies
• Method of Transmission is how the pathogen travels from one host into another
  • Contaminated food (food-borne) and cholera (water-borne) are examples
• Susceptible Host determines if potential host may not be susceptible because the host has immunity via previous exposure or naturally lacks
• Portal of Exit is when pathogen finds another susceptible host
• Public health measures control the spread of disease by interrupting the chain of infection, here's how
  • Pathogens can be killed using antibiotics to destroy disease-causing bacteria
  • Reservoirs can be eliminated by controlling rat populations via garbage, adequate water and sewage treatment, and following proper food-handling methods -Quarantine infected individuals, preventing transmission from one host to another (boiling water) -Increasing people's resistance via immunization by stimulating immunity

Epidemiologic Surveillance

• Public Health Response: locate people who have contact with the infected individual, immunize, or provide medical treatment
• Quarantine examples include Severe Acute Respiratory Syndrome (SARS) and tuberculosis
• Contact Tracing can track people exposed to the patient and help control sexually transmitted diseases like syphilis (Treponema pallidum) and gonorrhea (Neisseria gonorrhoeae)

Fear of Vaccines

• Nigeria had resistance to Polio vaccination with the rumor of infertility and measles immunization causes autism
• Vaccines to consider include
  • Measles-Mumps-Rubella MMR and Autism
  • Dengvaxia scare
  • COVID-19 scare