Lecture 28

Question 1

Evolution of New Diseases

Answer 1

• ecological changes
• change of host
• genetic changes

Question 2

Evolution of Virulence

Answer 2

-change in existing disease organism

Question 3

Evolution of Antibiotic Resistance in Previously Sensitive Disease Bacteria

Answer 3

• misuse of antibiotics
• selection for resistance
• roles of institutions in promoting resistance (livestock raising, hospitals)

Question 4

What makes viruses, bacteria, and protistan parasites evolve so quickly?

Answer 4

• molecular adaptations
• rapid replication
• huge population sizes
• gene transfer between species
• mutations
• strong selection

Question 5

Where do new diseases come from?

Answer 5

• changes in host from animal to human, with evolution of ability to transmit from human to human
• changes in microbes already involved with humans to produce a different and more virulent disease

Question 6

Human Factors in Promoting New Diseases

Answer 6

• land clearing/settlement and contact with new animals
• human-promoted spread of animal/insect disease hosts
• transportation and travel
• crowding in cities
• poverty
• multiple sexual contacts
• dangerous behavior (sharing syringes)

Question 7

Ebola

Answer 7

• primate virus
• breaks out in parts of Africa every year
• most serious human outbreak was in Zaire in 1970’s with a 90% fatality rate
• chills, fever, terrible joint, muscle, and throat pain hemorrhage by 4th day and vomit and excrete blood and bleed from gums
• death due to shock from fluid loss
• breaks down lining of veins which then leak fluid
• if fluid is administered it leaks into lungs and patient drowns

Question 8

Filovirus

Answer 8

• RNA virus-7 genes
• likely carrier is fruit bats which aren’t affected
• drop partly eaten fruit that’s eaten by animals which humans may eventually eat

Question 9

Problems With Eradication

Answer 9

• difficult to deal with because of contact between western medical concerns and cultural customs
• customs and poverty amplify problems with containment
• i.e. burial customs-want to kiss and wash loved ones before laying them to rest

Question 10

Lyme Disease

Answer 10

• painful chronic disease with arthritis and neurological symptoms
• tick borne
• mouse reservoir for spirochaete (reproduces in mice)
• tick rests on mouse then breeds on deer
• huge deer populations caused by deforestation and destruction of predators then deer pass ticks to humans

Question 11

Selection: The Host Immune System

Answer 11

-variation arises from point mutations, recombination, and change of host

Question 12

Influenza

Answer 12

• 1918 millions died; mostly young people
• two modes of evolution: antigenic drift and antigenic shift
• segmented genome can recombine with pig or bird viruses if replicated in the same cell to produce a novel genome
• highly dangerous and is the source of new flue viruses

Question 13

Antigenic Drift

Answer 13

-drift of antigenic groups by single amino acid substitution

Question 14

Antigenic Shift

Answer 14

• dramatic sudden large change, sudden appearance of a new version of the virus
• becomes completely unrecognizable to the antibodies in the population

Question 15

Spanish Flu (1918)

Answer 15

• evolved by drift and in humans by shift thus human flu H1N1 shifted to H2N2 and to H3N2 because humans live a long time so so do immune responses
• very different than other flues
• typically flu epidemics kill very young and very old people
• the 1918 flu produced a peak in the mid 20-30’s so the most healthy and vital people in the population were getting sick and dying
• then it disappears for a couple years

Question 16

Pigs

Answer 16

• life is a year in agriculture so pig flu evolves much more slowly
• remained H1N1
• eventually new flu might get passed to humans

Question 17

2009 Flu

Answer 17

• H1N1 similar to 1918

- recognized by same antibodies

Question 18

Why was 1918 flu so deadly to young people?

Answer 18

• probably ironically because young people are the healthiest
• cytokine stimulated death response genes are highly activated in infected mice
• younger patients might have mounted a stronger cytokine response to flu pneumonia than younger and older patients

Question 19

Controversial Research Project

Answer 19

-dug up flu victims and reconstructed flu virus using the fragments of virus RNA-highly virulent and mice died rapidly

Question 20

Darwinian Evolution at Work

Answer 20

• selection in evolution of antibiotic resistance by pathogenic bacteria
• components: bacteria and selection–>try to kill those bacteria by exposing them to antibiotics lethal to most bacterial cells and heritable variation among bacterial cells in resistance to antibiotic

Question 21

Antibiotic Resistance Genes

Answer 21

• lots of mutations available in large bacterial population
• antibiotic use produced great drop in US infectious diseases
• medicine ignored evolution-no thought about ability of bacteria to evolve-despite early warnings that bacterial strains resistant to antibiotics were turning up in hospitals
• all microbes evolve rapidly

Question 22

How Antibiotic Resistance Spreads

Answer 22

• misapplication of antibiotics in agriculture not to treat disease but to promote growth
• three mechanisms: inactivation of antibiotic by modification or destruction
• blocking access of antibiotic to target
• alteration of antibiotic target site
• there has been an emergence of clinically important antibiotic resistance

Question 23

Resistance Transfer Factors on Bacterial Plasmid

Answer 23

• bacterial cell with chromosomal DNA and plasmid DNA
• plasmid DNA much smaller than bacterial chromosome and is capable of transfer to other bacteria, and capable of recombination with other plasmids

Question 24

Why do antibiotics and antibiotic resistance methods exist in nature?

Answer 24

• both are part of arms race between microbes that supplies selective pressures-tough competition
• number of bacteria and fungi produce antibiotics-that’s how discovered and produced

Question 25

Resistance Mechanisms

Answer 25

- organism that makes antibiotic evolves self-protection - target organism is under selection - bacteria readily share genes for resistance across species - when exposed to low doses of antibiotics they grow better

Question 26

What do bacteria do with antibiotics and resistance in their lives in nature?

Answer 26

- original idea: inhibit growth of competition - play roles at non therapeutic levels - modulation of interactions within bacterial communities - intermicrobial signaling

Question 27

Where does antibiotic resistance come from?

Answer 27

- huge numbers of antibiotic resistance genes in environment - self protection from own antibiotics suggested by universal multidrug resistance efflux pumps - antibiotic resistance genes may have arisen as general environmental detoxifiers

Question 28

Big Evolutionary Shift

Answer 28

- use of antibodies in clinical settings at very high levels - resistance genes switch in control from fine tuned to constitutive under strong promoters - easier transfer to plasmids