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Unit 4 – Public Health
Infectious Diseases
Chapter 9 – The “Conquest” of Infectious Diseases
Infectious Diseases – Major Killers
in Past
 Bubonic plague – “Black Death”
 Tuberculosis
 Smallpox
 Cholera
 Typhoid
 Typhus
 Yellow Fever
 Diphtheria
 Measles
 Influenza
Infectious Diseases Were
“Conquered” by 1960s
 Immunization
 Antibiotics
Infectious Agents
 Bacteria – tuberculosis, cholera, typhoid, tetanus,
diphtheria, dysentery, syphilis, streptococci,
staphylococci
 Viruses – smallpox, poliomyelitis, hepatitis, measles,
rabies, AIDS, yellow fever
 Parasites – malaria, cryptosporidiosis, giardiasis,
roundworms, tapeworms, hookworms, pinworms
Chain of Infection
 Pathogen (infectious agent)
 Reservoir
 Means of transmission
 Susceptible host
 Interrupt chain of infection at any link
Means of Transmission
 Aerosol
 Touching contaminated object and putting hands to
mouth, nose, or eyes
 Contaminated water or food: fecal-oral route
 Vectors
 Sexual contact
Interrupting Chain of Infection
 Kill pathogen with antibiotics
 Eliminate reservoir
 Prevent transmission
 Wash hands
 Quarantine
 Condom
 Increase resistance of host by immunization
Public Health Measures
 Epidemiologic surveillance
 Contact tracing
 Immunization and treatment of identified patients to
prevent further spread
 Quarantine if necessary
Examples
 SARS – controlled by classic public health measures
 Rabies
 Surveillance of wildlife
 Immunization of dogs
 Post-exposure prophylaxis
Eradication
 Possible if no non-human reservoir and a vaccine
exists
 Smallpox eradicated in 1977
 Polio eradicated from Western Hemisphere
 Now only in a few countries
 Religious opposition in some countries
 Measles is next target
 Now no longer endemic in U.S.
Fear of Vaccines
 Rumors of vaccines causing autism, SIDS
 Side effects do exist for some vaccines
 Some parents refuse to accept risks
 Herd immunity -- lost if many people do not get
vaccinated
 Pharmaceutical companies reluctant to develop
vaccines
 Low profits
 Risk of lawsuits
Unit 4 – Public Health
Infectious Diseases
Chapter 10 – The Resurgence of Infectious Diseases
HIV/AIDS
 First recognized in U.S. in 1981. Now a world-wide
killer
 Caused by a retrovirus
 Attacks the immune system
 Screening test recognizes antibodies
 Can measure viruses in the blood
 Now many drugs are available, but no cure
HIV/AIDS Transmission
 Sexual contact
 Homosexual – most common in U.S.
 Heterosexual – most common around the world
 Sharing needles
 Intravenous drug use
 Medical use of unsterile needles
 Mother to infant
 Prenatal or during birth
 Breast feeding
 Blood transfusions
 No longer in U.S.
Where Did HIV Come From?
 Probably originated in Africa
 Cross-species transmission from monkeys or apes
 Spread in human populations due to disruption of
traditional lifestyles
 Spread to Western countries due to changing patterns
of sexual behavior and international travel
Other Emerging Viruses
 Ebola
 Monkey pox
 Hantavirus
 Other hemorrhagic fevers
 West Nile virus
 SARS
Factors that Lead to Emergence of
New Infectious
 Human activities that cause ecological damage and
close contact with wildlife
 Modern agricultural practices
 International travel
 International distribution of food and exotic animals
 Breakdown of social restraints on sexual behavior and
intravenous drug use
Influenza
 Virus is constantly mutating
 Vaccine must be changed frequently
 New, lethal strains appear periodically
 Epidemic of 1918-1919 killed 20 million to 40 million
worldwide
 Concern about bird flu in Asia
New Bacterial Threats
 Legionnaire’s Disease
 Lyme Disease
 Streptococcus A
 E. coli O157:H7 in food
 Antibiotic resistance
 From improper medical use
 Use in agriculture
Tuberculosis
 Leading cause of infectious–disease death worldwide;
one third of world population is infected
 There was a resurgence in the U.S. in early 1990s
 Much higher risk for people with HIV
 Transmitted by aerosol
 50% fatality rate for untreated TB
Tuberculosis, ctd
 Antibiotics are effective, but must be taken for several
months
 Improper use of antibiotics leads to resistance,
including multidrug resistance, when mortality rate
can be 50%
 Directly observed therapy works – best approach to
preventing antibiotic resistance
Prions
 Creutzfeld-Jacob disease (CJD) – sporadic, in older
people
 Bovine spongiform encephalopathy (BSE) or “mad
cow disease” in Britain
 New variant CJD in Britain in younger people,
thought to be caused by eating infected beef
 Regulations have been tightened on animal feed
Public Health Response to
Emerging Infections
 Global surveillance
 Improve public health capacity
 Veterinary surveillance
 Reduce inappropriate use of antibiotics
 Need for new vaccines
 Need for new antimicrobial drugs
 Control of vector-borne and animal-borne diseases
Threat of Bioterrorism
 Approach to bioterrorism is the same as that for
natural disease outbreaks
 Will probably first be recognized by surveillance
 Best defended against by same methods as natural
outbreaks