L16 - Disease

Question 1

What is a disease?

Answer 1

• An abnormal condition that negatively affects the structure or function of part or all of an organism, and that is not due to an external injury.
• A disease may be caused by external factors (e.g. pathogens) or by internal factors (e.g. autoimmune disorders).

Question 2

What are the types of causes of diseases?

Answer 2

1.Airborne (pathogens transmitted through air).
2. Food borne (foods w/pathogenic bacteria, viruses, or toxins).
3.Lifestyle (industrialized countries, unhealthy foods).
4. Non-communicable (can’t spread between ppl).
5. Infectious (presence and growth of pathogen in a host).

Question 3

What is the difference between contagious and communicable diseases?

Answer 3

• Both Infectious
• Contagious: infection that spreads commonly from one person to another (e.g. common cold).
• Communicable diseases: does not necessarily spread through everyday contact (e.g. ringworm).

Question 4

What is the difference between a parasite and a pathogen?

Answer 4

1. A parasite is an organism that lives on or in a host organism and gets its food from or at the expense of its host.
2. Pathogens are organisms that cause diseases within their host.
   ** A parasite can cause a disease in the host therefore a parasite can be a pathogen.

Question 5

What is an epidemic?

Answer 5

A widespread occurrence of an infectious disease in a community at a particular time

Question 6

What is an important driver of disease among humans?

Answer 6

• Community structure: Humans constantly created new ways of living and eating, and genetic changes evolved to minimize the effects of these diseases.

Question 7

What are virgin soil epidemics?

Answer 7

• 1500s: When Europeans began arriving on the shores of the Americas, the diseases they brought with them (measles, yellow fever)
  were diseases that INDG populations had no biological defense for
• Wiped out indigenous populations for the next 400 years
• 1535, Jacques Cartier noted that Iroquoians were dying
  of an illness he and his own men seemed
  immune to: SMALL POX
• By 1603, Stadacona was a ghost town

Question 8

What is the planned extinction of small pox?

Answer 8

• Highly contagious and destructive human disease
  
  • 30% mortality rate, highest mortality rate among children
• Planned extinction = worldwide immunization program
  
  • First (and only) successful attempt to eradicate a human disease.

Question 9

Explain the Black Plague (1347-1350) and its origins.

Answer 9

• Caused by a bacterium that circulates among wild rodents (e.g. rats) where they live in great numbers and density. It is transmitted to humans who are bitten by fleas that have fed on infected rodents or by humans handling infected animals.
• One of the most devastating epidemics in human history: 75-200M deaths
• It took 200 years for the world population to recover to its previous level.
• Thought to originate in Asia: cue to climate fluctuations, rodents began to flow the dried out grasslands to more populated areas, spreading the disease.

Question 10

Why were Jewish communities in Europe blamed for the outbreak of the Black Plague?

Answer 10

• Accusations spread that Jews had caused the disease by deliberately poisoning wells
  
  • A series of massacres and persecution of Jews
  • By 1351, 60 major and 150 minor Jewish communities had been exterminated
    
    • Eastward movement of Jews to Poland and Russia (where they remained for the next 6 centuries)
• Besides general anti-Semitism, Jews were accused because they were less impacted by the disease
  
  • Many Jewish laws that promote cleanliness and good hygiene practice = lower incidence of disease among Jewish communities

Question 11

Explain life after the Black Plague (recovered after 200 years)

Answer 11

Rising standards of living after the epidemic.

• Food prices dropped and labor wages increased
• More resources available
• Higher proportion of older adults, lower mortality risks (skeletal samples)

Question 12

What is influenza?

Answer 12

• An infectious disease caused by a virus
• There have been 9 influenza pandemics during the last 300 years

Question 13

Why was the 1918 influenza pandemic particularly bad?

Answer 13

• It was not more agressive than previous influenza, but that the special circumstances of the epidemic (malnourishment, overcrowded medical camps and hospitals, poor hygiene) promoted bacterial superinfection that killed victims.
• Occurred during WW1: close quarters and massive troops movement fuelled the disease.
• Prevention and treatment methods for flu were limited.
  
  • No vaccine, no antiviral drug, no antibiotics.

Question 14

Why was it also referred to as the “Spanish Flu”?

Answer 14

• It didn’t originate in Spain
• Because that nation had remained neutral during WWI, it freely reported news of flu numbers, whereas for nations involved in the war, communications about the severity of the disease were kept quiet

Question 15

What were the impacts of the Spanish Flu (1918)?

Answer 15

• Virus disproportionately affected young men = labor shortage
  
  • More women in the workforce = helped to advance women’s rights.

Question 16

Explain Malaria

Answer 16

• Mosquito-borne infectious disease that affects humans and other animals - not spread from person to person.
• Caused by eukaryotic microorganism (not bacteria) that is parasitic to insects.
• Mosquito bite introduces the parasite from mosquito’s saliva to person’s blood - the parasites travel to the liver where they mature and reproduce.
• Prevalent in tropical/subtropical regions.
  
  • Consistent high temperatures + high humidity + stagnant waters = perfect breeding grounds.
• Symptoms: fever, tiredness, vomiting, headaches

Question 17

Explain malaria and the Panama Canal.

Answer 17

• Isthmus of Panama was an ideal environment for mosquitos. The control of malaria was vital for the construction of the Panama Canal.
• Big sanitation campaign to rid the Isthmus of mosquitos. Death rate and yellow fever reduced.
• Once the barrier of disease had been removed, the Panama Canal was competed in 1914.

Question 18

What is virulence?

Answer 18

• Virulence is a pathogen’s ability to infect or damage a host
• A highly virulent pathogen can do a lot of damage to a host.
  
  • However, if the host’s illness is too severe, it will prevent the pathogen from being transmitted to a new host = low evolutionary fitness
• A less virulent pathogen could spread to far more hosts because hosts will feel well enough to come into contact with many others

Question 19

Explain sexually-transmitted pathogens?

Answer 19

• These pathogens cannot immobilize their host too soon
• Latency period of these pathogens are long enough so that the host can find a new sexual partner to unwittingly pass on the pathogen to

Question 20

Explain cholera?

Answer 20

• Caused by eating food or drinking water contaminated with bacterium
• Cholera has evolved a high level of virulence and may kill its host just a few hours after symptoms begin (even in previously healthy people)
• Cholera victims are rapidly immobilized by the disease, but they are tended by others who in this process get infected

Question 21

Explain the link between climate change and diseases.

Answer 21

• Humans and animals are forced to compete for dwindling habitat and resources.
• Rising temperatures and changing rainfall patterns: Insect vectors tend to be more active at higher temperatures
  
  • Increased prevalence of malaria in places experiencing much warmer and wetter weather

Question 22

Explain the threat that mosquitos have on native Hawaiian birds.

Answer 22

• Rising temperatures allowed for mosquitoes to expand into birds’ high elevation ranges
  
  • Native birds are no longer safe from diseases (they are very susceptible due to isolation).
• Some birds retreated to higher grounds where its too cold for mosquitoes.
• With climate change and rising temperatures, the birds are no longer safe.

Question 23

How is ebola linked to climate change?

Answer 23

1. Increase in weather events plays a role in Ebola outbreaks.
   - Dry seasons followed by heavy rainfalls produce an abundance of fruit.
   - Fruits = bats and apes eat together, which provides opportunities for the disease to jump between species (fruit bats carry diseases).
   - Humans can contract the disease by eating or handling the infected animals.
2. Climate change increases severe dry spells that hit agricultural yields and drive humans into the forest for food (bushmeat).
3. Deforestation leads to habitat loss and more people entering the forest, which forces animals like bats to find new habitats and hunt for food near humans.