I N F E C T I O U S D I S E A S E S

CHAPTER 12

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