Pathogenesis

Question 1

What is putrefaction?

Answer 1

The decomposition of proteins by putrefying bacteria (anaerobic) resulting in the formation of polyamines with a putrid odour

Question 2

What is gnotobiology?`

Answer 2

Raising mammals under germ-free environments, or conditions with controlled spectra and numbers of microorganisms

Question 3

What is tetanus?

Answer 3

A disease caused by bacterium clostridium tetani

Question 4

What is pathogenesis?

Answer 4

A set of mechanisms by which an etiological factor (primary reason for a disease) causes a disease, pathos=disease, genesis=development

Question 5

What is epidemiology?

Answer 5

The study of the occurrence, distribution and control of diseases in populations

Question 6

What are the primary causal factors of diseases?

Answer 6

Genetic, physiological and environmental

Question 7

What are the three types of interactions between organisms? and give examples of each

Answer 7

Parasitic - measles, typhoid and Tb
Commensal - normal flora
Symbiotic - microflora that produces vitamins like B12

Question 8

What is the difference between true and opportunistic pathogens?

Answer 8

A true pathogen overcomes the host’s defences and causes disease easily while opportunistic pathogens cause disease in hosts with a reduced defensive capacity. Opportunistic pathogens are usually commensal organisms

Question 9

Are protozoa highly virulent?

Answer 9

The majority aren’t and are not able to replicate in the host, the extent of the disease is usually related to the infecting dose. They are often chronic

Question 10

What is virulence?

Answer 10

The extent of pathogenicity expressed by a pathogen can be expressed as a number of the pathogens cells sufficient for a pathogenic response. The smaller being the more virulent

Question 11

What is ID50 and LD50?

Answer 11

ID50 - The number of pathogen cells required for 50% of the host population to show signs of infection
LD50 - The number of pathogen cells required to kill 50% of a host population

Question 12

What are the transmission routes and what is meant by vehicles and vectors?

Answer 12

Respiratory tract, faecal-oral route, urogenital tract and mechanical transmission. Vehicle transmission is a means of transmission that involves riding along supposedly clean components such as food, water drugs etc. Vectors are arthropods that transmit pathogens, such as fleas, mosquitoes, ticks and lice

Question 13

What is the progression of a typical disease?

Answer 13

Infection, incubation period, acute period, decline period and convalescent period (or death in some cases)

Question 14

What are two ways of pathogenicity?

Answer 14

Toxicity - causing disease by different toxins that inhibit or kill host cells
Invasiveness - a pathogen that grows in a tissue to such amounts of cells that inhibit host functions and cause disease

Question 15

What are 3 factors that affect pathogenesis?

Answer 15

Pathogen factors, Host factors and environmental factors

Question 16

How can pathogens overcome host defenses?

Answer 16

They can overcome them through either passive defence, which is based on the structural components of the pathogen cell (cell wall) or by active defence, which is interfering with the host defences (toxins)

Question 17

What is the main passive defence that inhibits phagocytosis by host cells?

Answer 17

A bacterial capsule

Question 18

What material is present in cell walls of mycobacterium species?

Answer 18

A waxy material called mycolic acid, it inhibits the process if phagocytosis and the access of antibiotics into the cells

Question 19

What are exotoxins and what are the three sub-groups of them?

Answer 19

Exotoxins are toxic extracellular proteins secreted by gram +ve and -ve bacteria. The three groups are cytolytic toxins, A-B toxins and superantigen toxins

Question 20

What are the differences between the three sub-group exotoxins?

Answer 20

Cytolytic toxins - lyse host cells by enzymatic degrading cellular components (mostly membrane)
A-B toxins - consist of two covalently bonded subunits A(ctive) and B(inding). B subunit usually binds a cellular surface receptor that allows transferring A subunits through the membrane to the cell and damaging it
Superantigen toxins - stimulate large amounts of immune response cells that leads to massive inflammatory reactions

Question 21

What are enterotoxins?

Answer 21

Exotoxins that affect the host’s small intestines. They are often cytotoxic and kill epithelial cells in the intestinal wall by altering their permeability by forming pores in the cell membranes

Question 22

What are endotoxins?

Answer 22

Lipopolysaccharides produced in the outer layer of cell envelope of gram -ve bacteria, produced when they are dying

Question 23

What are factors that contribute to host innate resistance?

Answer 23

Nose and mouth
Ciliated epithelial cells of mucosal surfaces upward bacteria into mucous to be expectorated or swallowed and killed in the stomach
Stomach
Lumen of kidney and eyes that produce lysozyme
Blood that contains bacteriocidal beta-lysins that bind and disrupt bacterial cytoplasmic membranes

Question 24

How does killing host cells benefit the bacterium?

Answer 24

It allows the bacterium to use cellular products as nutrients and to release a space for further spreading into the tissue

Question 25

From what genus is anthrax originated and what does it cause in a host?

Answer 25

Bacillus anthracis, anthrax spores are highly resistant to physical and chemical agents and tend to deposit on the ground. It is an acute and severe disease and causes massive splenomegaly from the hyperfunction in destroying RBC, the host dies within a few days of infection. It has 3 toxins, protective antigen that mediates the entry of two other proteins, lethal factor and oedema factor into macrophages.

Question 26

What do anthrax toxins do to macrophages? (long answer)

Answer 26

Protective antigen (PA 83kDa) binds to a host cell surface receptor, PA83 is cleaved by a furin-like protease to yield a 63kDa form of Pa. PA63 oligomerizes into a heptameric receptor-bound pre-pore and binds to LF and/or EF. Inside the cell the complex endocytosis into acidic endosomal compartments, with the low pH inducing a conformational change of the pre-pore and releases LF and EF into the cytoplasm. EF increases cAMP to upset water homeostasis causing liquid accumulation. LF inactivates MAPK kinase causing a fail in cellular signalling, impairing macrophage function and causing a distorted immune system.

Question 27

What is botulism and what characterises it?

Answer 27

caused by botulinum toxin of anaerobic bacterium clostridium botulinum, it is characterised by a flaccid paralysis of muscles and respiratory failure

Question 28

How many antigenically distinct botulinum toxins are there and how many are associated with human botulism?

Answer 28

There are 7 from A-G. Types A, B, E and F are human

Question 29

How do botulinum toxins affect the body?

Answer 29

They bind to cholinergic peripheral nerves, blocking the release of the neurotransmitter acetylcholine, preventing muscle contraction causing resp and musculoskeletal paralysis (flaccid paralysis)

Question 30

What is the most common form of botulism?

Answer 30

Infant botulism, caused by the absence of competitive bowel microbes and digestions of the infant not being acidic enough

Question 31

What are symptoms of food-bourne botulism?

Answer 31

Symptoms occur after 1-2 days after consumption, causing weakness and dizziness, blurred vision, dry mouth, constipation and abdominal pain, no fever