Transcript Chapter 12
CHAPTER 12 INFECTIOUS DISEASES INFECTIOUS DISEASES • Diseases caused by organisms called pathogens • Communicable: meaning they can be passed from person to person • Carrier: person with active pathogen but lack symptoms • Transmission: mechanism of spreading disease • Vector: organisms that acts as carrier of disease INFECTIOUS DISEASES • Epidemic: a widespread occurrence of an infectious disease in a community at a particular time • Pandemic: prevalent over a whole country or the world. • Endemic: regularly found among particular people or in a certain area. CHOLERA • Caused by bacterium Vibrio cholerae • Transmission: waterborne • Occurs where people do not have access to proper food and water treatment • Site of action: small intestine, where they secrete choleragen that disrupts epithelial lining, causing severe diarrhea • Death by dehydration TREATING CHOLERA • IV salt and glucose solution to rehydrate body • Oral rehydration • Glucose solution PREVENTING CHOLERA • Clean water and sewage! • Almost unknown in developed world due to raw sewage treatment and clean water pipes • Cholera outbursts common following natural disasters (Ex: Haiti 2010) STRAINS OF CHOLERA • Until 90’s only strain 01 known. Several 20th century cholera pandemics began in SE Asia (all 01 strain) • total pandemics:7 • Quickly spread throughout world due to sewage dumping and traveling and accumulation in shellfish • New strain V. cholerae 0139 (Oct 1992) more virulent and becoming 8th pandemic MALARIA • Caused by protist Plasmodium (4 species) • Passed through vectors (mosquito bites) and blood transfusions • Can pass through placenta from mother to fetus • Mortality high during first 5 yrs of infection • Death by flu-like symptoms • People continually reinfected are immune to further infections • Endemics occur during mosquito breeding cycles (during rainy season) PREVENTING MALARIA • Reduce number of mosquitoes • Stop transmission cycle by destroying mosquito eggs • Stock areas of water with fish that eat mosquito larvae • Avoid being bitten by mosquitoes • Nets, protective clothes, repellant • Use drugs to prevent the parasite infecting people TREATING MALARIA • Anti-malarial drugs: quinine & chloroquine • Taken before, during, and after visiting an area where malaria is endemic • Inhibit protein synthesis in parasite • Chloroquine resistance is widespread in Africa, South America, New Guinea • Often misdiagnosed in developed countries as influenza by doctors who are unfamiliar with malaria • Common w/settled immigrants who visit family in malaria endemic areas WORLDWIDE CONTROL OF MALARIA • WHO tried eradicating Malaria in 50’s. generally successful, but not 100% because • Plasmodium became resistant to drugs used • Mosquitoes became resistant to DDT and other insecticides used at time • Also, program was expensive and super unpopular (people lost their immunity and when malaria came back they suffered) MALARIA CONCERN WORLDWIDE • • • • • Increase in resistant Plasmodium Increase in species that causes severe Malaria Difficulties in vaccine development Increase in # of epidemics Migration of people from endemic areas due to economics/politics MALARIA CONCERN WORLDWIDE • 40% world population lives in endemic Malaria regions • Improvements in control methods: • Use of modern techniques (gene sequencing, etc.) • Development of new vaccines for different stages in life cycle • Renewed international will to remove Malaria ACQUIRED IMMUNE DEFICIENCY SYNDROME (AIDS) • Caused by HIV (human immunodeficiency virus) • HIV is a retrovirus, meaning its genetic material is RNA not DNA • Uses our cells to convert its RNA into our DNA. • Infects and destroys cells of the immune system, allowing for opportunistic infections of other pathogens (collected called AIDS) AIDS • Spread through direct exchange of body fluid • Ex: sexual intercourse, blood donation, sharing of needles by IV drug users, through placenta and mixing of blood during birth • NOT spit or sweat!!! • Initial epidemic in North America and Europe discovered in early 1980’s amongst male homosexuals • Now very serious pandemic, over 25 million people have died from AIDS (2010) AIDS • HIV is a slow virus and takes several years to develop AIDS symptoms • Death NOT directly from HIV, but from opportunistic infections • Pneumonia, cancer, oral thrush, brain disease TREATING HIV/AIDS • No cure for AIDS/vaccine for HIV • Some people display natural HIV immunity (HIV positive, but never develop AIDS) • Drug therapy (antiretroviral) severely slows down progression of AIDS • Several medications used in combination to increase efficiency • Zidovudine similar to nucleotide thymine and binds to viral enzymes to stop replication of viral genetic material PREVENTING HIV/AIDS • Difficult to control: long latent stage (lots of carriers) • Virus changes it surface proteins quickly, so vaccines are near impossible to develop • public health measures to prevent HIV infection are leading way to stop HIV • Barrier protection during intercourse (estimated to be largely responsible for 25% decrease in HIV infections between 2001 and 2009) • IV user education PREVENTING HIV/AIDS • Contract tracing: tracking transmission of HIV (getting tested and informing partners) • Needle exchange schemes • Blood donations are screened for HIV • HIV testing is not expensive, but governments are reluctant to widespread testing b/c infringement of personal freedom • Highly suggest for people in high-risk groups TUBERCULOSIS (TB) • Caused by two bacteria: Myobacterium tuberculosis and Myobacterium bovis • Pathogens live inside human cells (particularly lungs) • Can develop quickly or remain dormant for years • Inactive carriers cannot spread infection, but bacteria can later become active, especially is weakened by other factors like malnourishment or HIV • Usually first opportunistic infection to strike HIV positive people • TB is leading cause of death for HIV positive people TB • Carried in the air through drops of liquid (cough/sneeze) • Transmission occurs when people inhale droplets • M. bovis passed from cattle meat and milk, although this transmission is now extremely rare in developed countries TB • Recent increase in TB cases due to: • • • • Strain of TB becoming antibiotic resistant HIV/AIDS pandemic Poor housing in inner cities and homelessness Breakdown of TB control programms TB TREATMENT • Sample of mucus from lungs easy to identify TB • If pos., infected is isolated ASAP and treated with antibiotic regiment • Very long treatment (6-9 months) • People who do not complete treatment may facilitate drug resistance in TB bacteria • Multiple-drug-resistant forms of TB (MDR-TB) now widespread; resistant to at least 2 main drugs used to treat TB • Can take two years to treat PREVENTING TB • Avoiding contact with active TB patients • BCG vaccine protects against M. bovis strain of TB • Effectiveness decreases with age • Cattle routinely tested for TB and destroyed if positive • TB bacteria killed when milk is pasteurized ANTIBIOTICS • Can be used to treat or cure bacterial or fungal infections • Show selective toxicity, killing the pathogen but no effect on host cells • Can be derived from living organisms or man made HOW ANTIBIOTICS WORK • • • • Stop synthesis of bacterial walls Stop protein synthesis Interfere with cell membrane function Stop enzyme action ANTIBIOTICS • NOT effective on viruses • Broad spectrum effective against wide range of bacteria • Narrow spectrum effective against only a few