Infectious Lecture

Question 1

Infection

Answer 1

Colonization of the human host

Question 2

Carriage

Answer 2

Establishment of a long term harmless relationship host and the bacteria

Question 3

Disease

Answer 3

Infections that result in pathology

Question 4

Pathogen

Answer 4

Biological agent (microbe) that can cause disease to its host

Question 5

Virulence

Answer 5

Relative capacity of a pathogen to cause disease

• Number of infecting microbes
• Entry route into body
• Effects of host defense mechanisms
• Virulence factors –> components of pathogen that damage the host

Question 6

Categories of infectious agents

Answer 6

Prions
Viruses
Bacteria
Fungi
Protozoa

Question 7

Prions

Answer 7

Abnormal form of host protein (PrP) via mutation
Found in neurons
Conformational change that confers resistance to proteases
Protease resistant PrP promotes conversion of the normal PrP to the protease resistant form

Question 8

Accumulation of abnormal PrP

Answer 8

Neuronal damage and spongiform changes

- Mad cow disease

Question 9

Skin entry

Answer 9

Barrier
Low pH
Fatty acids inhibit growth of microorganisms
Break in skins, burns, insect or animal bites

Question 10

GI tract entry

Answer 10

Contaminated food and drink
Defenses:
- acidic gastric secretion
- layer of mucus covering intestinal epithelium
- lytic pancreatic enzymes and bile detergents
- defensins
- normal flora disruptions by antibiotics

Question 11

Respiratory Tract Entry

Answer 11

Mucociliary defenses (secreted by globlet cells; cilia brush the virus down)
Small particles phagocytosed by alveolar macrophages
Influenza virus

Question 12

Influenza Virus

Answer 12

binding causes epithelial cells to be taken up into the cells
Virus multiples
Virus comes out and secretes neuraminidase so that the virus can spread (lowers the viscosity)

Question 13

Urogenital Tract Entry

Answer 13

Defenses: regular flushing, Low pH (lactobacilli; unfavorable to microbes), and local breaks in mucosa (STD; breaks allow entry)

Question 14

Spread and dissemination

Answer 14

APC picks up the infection
Takes it to the lymphatic (lymph and blood)
Can move into the blood stream and spread everywhere in the body
– Also can get spread via placental transfer or maternal milk

Question 15

Transmission

Answer 15

Skin shedding, coughing/sneezing, sex, urine/feces, insect vector (bug bites), animal to human (zoonotic) or nosocomical (acquired in hospital)

Question 16

How do microorganisms cause disease?

Answer 16

• Cause direct cell death
• Release toxins that kill cells at a distance or damage tissue (travels via blood)
• Induce host immune response- necessary to fight infection but may cause tissue damage (cannot turn off and on at the right time then it causes more damage than it is helping – inflammation)

Question 17

Viruses

Answer 17

Obligate intracellular parasites (can only live within the cell bc they need it to replicate)
Protein coat (capsid)
Aggregate within cells to form inclusion bodies (used for diagnostics)

Question 18

Diagnostic methods for viruses?

Answer 18

Inclusion bodies
Serologic testing (antibodies)
Molecular diagnostics (PCR; looks for certain DNA sequences)

Question 19

Viruses enter and replicate?

Answer 19

Damage the host cell

• Tropism (ten to infect certain cells)
• – Bc of certain receptors or machinery

Question 20

Once inside the host the viruses?

Answer 20

Direct cytopathic effects
Antiviral immune response – CD8 T cells go and kill the cell
Transformation of host cell into benign or malignant tumor

Question 21

Hep B

Answer 21

Sits in the liver while the immune system continuously attacks

Question 22

Immune evasion by microbes

Answer 22

When macrophage takes up the microbes, it destories them via phagosomes but the microbe can escape by changing their coat so they cannot be recognized, secreting a protein so that it will not be expressed on MHC, or developing a big capsule around it so they cannot be reached

Question 23

INF-gamma

Answer 23

First defense

- Bind INF-gamma and take it up so that it cannot act on it and get rid of it

Question 24

Acute Viral Infections

Answer 24

"transient"
Elicits effective immune response- eliminates the agent 
- Measles
- Mumps
- Poliovirus
- West Nile Virus

Question 25

Measles

Answer 25

ssRNA of paramyxovirus family

• One serotype (only one antigen)
• CD46 (all nucleated cells) and SLAM (cells of the immune system)
• Measles rash first
• Can cause transient but severe immunosuppression

Question 26

Mumps

Answer 26

Belongs to paramyxovirus family

• Enters via the upper respiratory tract
• Spreads via lymph nodes
• Replicates in T cells
• Spreads via blood to the salivary and other glands

Question 27

Poliovirus

Answer 27

Infects only humans via CD155

- Invades the CNS and replicates in motor neurons of the spinal cord or brain stem

Question 28

West Nile Virus

Answer 28

Flavivirus group

• Inoculated by a mosquito
• Replication in skin cells
• Migrate to lymph nodes where it again replicates
• Enters blood stream and cross BBB

Question 29

Chronic Latent Infections

Answer 29

Acute phase followed by a latent stage where the viruses persist in a non replicating and non infectious form with periodic reactivation and shedding of infectious virus
Herpes Simplex Virus
Varicella-Zoster

Question 30

Herpes Simplex Virus

Answer 30

Cold sores

• Spreads to sensory neurons at the site of infections and remains latent in neurons
• Can cause corneal blindess

Question 31

Varicella-Zoster Virus

Answer 31

Acute- chickenpox
Reactivation- shingles
- Latent in dorsal root ganglia is reactivated and infects sensory nerves supplying the skin

Question 32

Chronic Productive Infections

Answer 32

High mutation rate and escape control by immune system
Continued viral replication leads to persistent viremia
- Hep B

Question 33

Hep B

Answer 33

Acute and chronic liver disease
- Cellular injury from the immune response to infected liver cells rather than due to cytopathic effects of the virus – cannot control the infections (chronic infection develops – cirrhosis)

Question 34

Transforming infections

Answer 34

Viruses that cause cancer

Epstein-Barr Virus

Question 35

Epstein-Barr Virus

Answer 35

Infectious mononucleosis- Lymphomas in immunocompromised patients
- Atypical activated T cells
Transmitted via salvia
Tonsils- infections B cells
Productive/latent
EBNA2 and LMP1- B cell activation and proliferation
Heterophile antibodies (via B cells)- agglutinate RBCs

Question 36

Fungal infections

Answer 36

Fungi- eukaryotes with cell wall (chitin) and egosterol containing cell membranes

• Grow as multicellular filaments (molds)
• Grow as single cells/chains of cells (yeast)
• Asexual spores are “conidia”
• Diagnosed via histologic exam or culture

Question 37

Types of fungal infections

Answer 37

Superficial and cutaneous
Subcutaneous
Endemic (systemic; into the blood stream)
Opportunistic (immunocompromised)

Question 38

Candidasis

Answer 38

Thrush
Candida albicans
Benign commensals (one benefits another is not harmed)
Breach of skin or mucosal membranes
Shift between commensal and pathogen
Vaginitis Diaper rash
- Steroidal antibiotics = ^ susceptibility

Question 39

Candidasis invasion

Answer 39

Adhesions- adhesion to host cell is main virulence determinant
Aspartyl proteinases, catalase - help invasiveness

Question 40

Bacterias that cause different candidasis?

Answer 40

Candida esophagitis
Candida vaginitis
Cutaneous candidiasis
Invasive candidasis

Question 41

Cryptococcosis

Answer 41

Cryptococcus neoformans
- Encapsulated yeast that causes meningocencephalitis
Glucuronoxylomannin
- principal capsular polysaccharide - major viruelence factor

Question 42

Aspergillosis

Answer 42

Asperigillus fumigatus
- Responsible for allergies and sever infections
Aflatoxin (carcinogen)
- produced by aspergillus growing on peanuts - responsible for liver cancer

Question 43

Zygomycosis

Answer 43

Bread mold fungi - Zygomycetes

• Airborne asexual spore
• Immunocompromised individuals