Transcript Chapter 9
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