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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
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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:
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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
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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