1. Chapter 12
Infectious Diseases

2. 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

3. 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.

4. 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

5. Treating cholera IV salt and glucose solution to rehydrate body
Oral rehydration
Glucose solution

6. 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)

7. 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

8. 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)

9. 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

10. 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

11. 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)

12. 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

13. 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

14. 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)

15. AIDS Spread through direct exchange of body fluid NOT spit or sweat!!!
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)

16. 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

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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

26. How antibiotics work Stop synthesis of bacterial walls
Stop protein synthesis
Interfere with cell membrane function
Stop enzyme action

27. antibiotics NOT effective on viruses
Broad spectrum effective against wide range of bacteria
Narrow spectrum effective against only a few