Unit 6--Microbiology

Chapter 19

continued

Viruses• Hard to classify as living, because:

• Contain only a protein coat (capsid) and a nucleic acid core (DNA or RNA)– May also contain a protein

envelope that protects virus from host organism recognition

• Reproduces only by infecting a host cell

Virologists consider viruses to be

acellular organisms.

• Bacteriophages: viruses that infect bacterial cells

• Viroids: naked RNA

• Prions: naked protein (protein infectious particles)

Viral Morphology (structural shape)

Lytic cycle

Lysogenic cycle:

may produce latent

(recurring) infections

Viruses leaving cell

Lytic vs lysogenic

• Viral infections that are lytic, destroy host cells quickly (& move on…)– Ex: Ebola, Chicken Pox

• Lysogenic infections destroy host cells slowly or not at all. Lysogenic viruses undergo lytic cycle when host cell becomes stressed (may be recurring)– Ex: HIV, herpes

Lytic or Lysogenic?

Proportional size of bacterium to virus

Epidemiology

• The study of diseases within a population

• Center for Disease Control Headquarters:

Atlanta, Georgia (US)

• World Health Organization

Headquarters:

London, England

Pandemic

• A global infection

Ex: • 1918 flu pandemic killed

25 million+• Bubonic plague (black

death) killed 24 million in 1300s

• Tuberculosis (white death) killed 2 billion in last 2 centuries

Outbreak• A sudden & unexpected increase in

numbers of infected individuals

Ex: West Nile Virus, Ebola, etc

Epidemic• A sudden increase in the occurrence of disease

above what was expected

Ex: • Swine flu (’76), • Polio (’50s), • Legionnaires

disease(’76)

Endemic

• A steady, low-level frequency that happens at regular intervals

Ex: • Common Cold,

chicken pox, etc

Morbidity rate

# of new disease in a population# of individuals in the population

Mortality rateMortality rate

# of deaths caused by disease in a # of deaths caused by disease in a populationpopulation # of individuals in the # of individuals in the populationpopulation

How might these numbers be useful?How might these numbers be useful?

Emerging infectious diseases

Medical students today are concerned that people misuse antibiotics and that Doctors over-prescribe antibiotics.

How can these 2 factors contribute to infectious disease emerging once again?

Ex: Tuberculosis, Smallpox, etc

Epidemiological Study

• Materials: – numbered containers for each student (test

tubes or small containers)– 2-3 drop of dilute sodium hydroxide in one– Distilled water in all the others– Paper numbered 1-5 to keep record of

“contacts”– Penolpthalein (1 drop in each beaker to test

after all contacts are complete)

Epidemiological study

• Procedure:– Only one container is contaminated with the

fluids from an infected individual– Select one container to represent your fluids– You need to exchange fluids with 5

individuals. Keep track of these people, in order of sharing

– Wait to be tested

Epidemiological study

• Challenge:– The entire class must work together in a

cooperative group…– You have to tell me who the original carrier

was.– You have only 2 guesses (asking me privately

counts as a guess)– If you guess correctly, you win!!– (if you do not take part in the problem-solving,

you will receive a zero for today)