Lecture 27: Infectious Diseases

Question 1

What is the normal defense mechanism against pathogens in the skin?

Answer 1

There are physical and chemical barriers as well as innate/adaptive immunity.

Skin:
-Dense, keratinized outer layer
-Low pH (5.5)
-Content of fatty acids that inhibit microbial growth

Question 2

What are the common routes of infection?

Answer 2

Skin

Respiratory

Intestinal

Urogenital

Question 3

How do pathogens break the normal defenses of the skin?

Answer 3

Release of enzymes to break skin barrier

Cute, wounds, burns and pressure-related foot sores

Intravenous catheters in hospitalized patients

Question 4

How do pathogens disseminated into various organs and tissues?

Answer 4

Depending on the organism, the pathogen can break through the skin, lungs, thoat, intestine and urinary tract to get into the lymph node. Through the lymph vessel the pathogen can get into the bloodstream and from there go almost anywhere. To the CNS, skin, lungs, kidney, salivary gland, liver and even the placenta.

Question 5

What are the four major mechanisms by which microbes can evade immune defense?

Answer 5

1. Remaining inaccessible to the host immune system.
   -EX: bacteria propagate in the lumen of the intestine
2. Constantly changing antigenic repertoires.
   -EX: HIV
3. Inactivating antibodies or complement, resisting phagocytosis, or growing within phagocytes from ingestion.
   -EX TB
4. Suppressing the host adaptive immune response.
   -EX: CMV and EBV can inhibit production of MHC class 1 proteins

Question 6

What are the mechanisms of viral entry?

Answer 6

1. Host-cell receptors for a particular virus
   -EX: HIV, Rhinoviruses, SARS-CoV-2
2. Cell-type specific transcription factors that recognize viral enhancer adn promoter sequences
   -EX: JC virus
3. Physical barriers
   -EX: Enteroviruses replicate in the intestine resisting inactivation by acids, bile and digestive enzymes

Question 7

What are the mechanisms of bacterial injury?

Answer 7

1. The ability of bacteria to cause disease depends on ability to
   -adhere to host cells
   -invade cells and tissues
   -deliver toxins that damage cells and tissues

2.

Question 8

How can diphtheria inhibit toxin protein synthesis?

Question 9

What is the normal defense mechanism against pathogens in the respiratory tract?

Answer 9

There are physical and chemical barriers as well as innate/adaptive immunity.

Respiratory tract:
-Mucus, swallowing, cilia
-Phagocytic killing by alveolar macrophages
-Secreted antibodies (IgA)

Question 10

What is the normal defense mechanism against pathogens in the intestinal tract?

Answer 10

There are physical and chemical barriers as well as innate/adaptive immunity.

Intestinal tract:
-Acidic gastric pH
-Viscous mucus secretions
-Lytic pancreatic enzymes and bile detergents
-Antimicrobial peptides called defensins
-IgA
-Normal gut flora

Question 11

What is the normal defense mechanism against pathogens in the urogenital tract?

Answer 11

There are physical and chemical barriers as well as innate/adaptive immunity.

Urogenital tract:
-Frequent urination to flush out pathogens
-Low pH in the vagina resulting from catabolism of glycogen in the normal epithelium by commensal lactobacilli

Question 12

How do pathogens break the normal defenses of the respiratory tract?

Answer 12

Express molecules adhere to the respiratory tract

Question 13

How do pathogens break the normal defenses of the intestinal tract?

Answer 13

Bacteria release enterotoxins, exotoxins, invade and damage the internal mucosa and lamina propria causing ulceration, inflammation and hemorrhage

Viruses (nonenveloped) are resistant to bile and digestive enzymes

Fungi in immunocompromised patients

Intestinal protozoan use cysts for transformation

Intestinal helminths cause obstruction of the gut

Question 14

How do pathogens break the normal defenses of the urogenital tract?

Answer 14

Easier for women to get a UTI them men due to length of urethra.

Antibiotics can kill lactobacilli and make the vagina susceptible to infection.

Certain microorganism develop specific mechanism for attaching to vaginal or cervical mucosa or for entering local breaks in the mucosa during sexual intercourse. (genital warts, syphilis)

Question 15

What are the mechanisms of viral injury?

Answer 15

Once viral proteins have been synthesized, there are multiple pathways for injury.

Lysis of host cells

Immune cell-mediated killing

Alteration of apoptosis pathways

Induction of cell proliferation and transformation, resulting in cancer

Inhibition of host cell DNA, RNA or protein synthesis

Damage to plasma membrane

Damage to cells involved in antimicrobial defense, leading to secondary infection.