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.
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Unit 4 – Public HealthInfectious 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 HealthInfectious 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