Introduction to infectious Diseases

Question 1

leading causes of death in 1900

Answer 1

1 pneumnia or influenza
2 tuberculosis
3 gastrointestinal infections

Question 2

leading causes of death in 2010

Answer 2

1 heart disease

2 cancer

Question 3

leading causes of death globally in 2019

Answer 3

1 heart disease

2 stroke

Question 4

noncommunicable vs communicable

Answer 4

able to transfer from human to human

Question 5

Innate/ specific IR is not 100% effective

Microbes possess numerous characteristics to evade / overcome defenses such as

Answer 5

evolution, microbes&raquo_space;»> faster than host
average gen time for bacteria (1 h) vs host (20 y)

gene exchange (on plasmids/ transposons) 
e.g. antibiotic resistance gees and virulence genes

Question 6

Host-pathogen relationship

Answer 6

speed of host acquired IR

Microbes ability to multiply, spread and cause disease vs hosts ability to contain and eliminate

delayed response=disease + shedding

Question 7

Adaptation and balanced pathogenicity

example in humans

Answer 7

adaption of both microbe (parasite) and host over time

• without extensive damage
• longer the relationship -> less damage

e.g. Myxoma virus-spread by mosquitoes -infects rabbits

it was introduced in 1950s to control the rabbit population, initially 99% died, but more rabbits survived over time: less lethal strain of virus replaced original and rabbits adapted

HIV, CJD

Question 8

types of infections 3

Answer 8

microbial attachment/ penetration mechanism

biting arthropod

skin wound

Question 9

what are the steps of infection? 6

Answer 9

1) attachment and possible entry into body
2) local or general spread in body
3) multiplication
4) evasion of host defenses
5) shedding from body (exit)
6) damage to host -not a requirement but some damage usually required for shedding

Question 10

what are Koch’s Postulates

Answer 10

1) the suspected germ must be present in every case of the disease
2) the germ must be isolated and grown in pure culture
3) the cultured germ must cause the disease when it is inoculated into a healthy, susceptible experimental host (animal or plant)
4) the same germ must be reisolated from the diseased experimental host

Question 11

challenges to koch’s postulates (1980s)

Answer 11

unculturable organisms
-traponema pallidum pallidum* (cultured later when technology advanced)

Host immunologic factors
-Rheumatoid arthritis (?)

involvement of more than one pathogen
-HDV

Infections only in humans
-HIV

Question 12

The life cycle of the CTX phage

Answer 12

the CTX phage attaches to the pili on the surface of Vibrio cholerae

the phage injects its genetic code and now the CTX gene is incorporated into its genetic code.

now virulent the bacterium produces a toxic chemical that alters the epithelial cells of the small intestine

Question 13

Molecular evolution of Koch’s postulates

Answer 13

1. the virulence trait under study should be associated much more with pathogenic strains of the species than with nonpathogenic strains
2. inactivation of the gene or genes associated with the suspected virulence trait should substantially decrease pathogenicity
3. replacement of the mutated gene with the normal wild-type gene should restore pathogenicity
4. the gene should be expressed at some point during infection and disease process
5. antibodies or immune system cells directed against the gene products should protect the host

Question 14

severity of the infection depends on

Answer 14

dose and route of infection
age 
sex
nutritional status 
genetic background