Chapter 14:

Evolution and Human Health

• Objective: Understand the relationship between evolution, pathogens, antibiotic resistance, and their implications for human health.

Cholera Epidemics

• Historical Overview:

  • Cholera Epidemic (1854):

  • John Snow's mapping of infected individuals and water sources.

  • This was the first known epidemiological study.

  • Epidemiology:

  • Defined as the study of incidence, frequency, distribution, and control of infectious diseases in populations.

• Cholera in Haiti (2010):

  • Traced origins to Nepal; genetic analysis shows multiple substitutions over the years in various countries across outbreaks.

Germ Theory of Disease

• Key Contributors:

  • Charles Darwin’s publication of 'Origin of Species' (1859).

  • Louis Pasteur's formulation of the germ theory of disease (1858): diseases are caused by germs.

• Significance:

  • Paved the way for advancements in antiseptic surgery, discovery of antibiotics, and improvements in sanitation.

Evolving Pathogens

• Host-Pathogen Interaction:

  • An evolutionary arms race exists between pathogens and their hosts, engaging in constant recognition and defense mechanisms.

• Pathogen Characteristics:

  • Pathogens exhibit large population sizes, short generation times, and high mutation rates.

• Flu Virus Example:

  • The flu virus modifies to evade the host immune system, evidenced by antigenic variations (e.g., H and N proteins).

Antigenic Evolution in Influenza

• Historical Strains:

  • 1918 H1N1 (Spanish flu), 1957 H2N2 (Asian flu), 1968 H3N2 (Hong Kong flu), and 2009 H1N1 (swine flu).

• Antigenic Sites:

  • Specific regions of the flu virus proteins that the immune system recognizes; high mutation rates create selective advantages for novel strains.

• Study of Divergence:

  • Analysis between strains shows mutation patterns and survival characteristics.

Antibiotic Resistance

• Mechanism:

  • Antibiotics target and kill bacteria; those that resist are selected for in the population.

• Resistance Trends:

  • Evidence of increased resistance in cases of relapse, indicating the selective pressure imposed by antibiotic use.

• Cost of Resistance:

  • While resistance can be advantageous under antibiotic pressure, it may incur fitness costs in the absence of antibiotics.

• Preventive Measures:

  • Strategies that help avoid the evolution of resistant strains include careful antibiotic prescription practices, isolation of resistant patients, and promoting hygiene practices.

Evolution of Virulence

• Hypotheses on Pathogen Virulence:

  1. Recent Entrance Hypothesis: Pathogens evolve towards benignness over time.

  2. Coincidental Evolution: Accidental pathogens cause diseases but are not natural human pathogens.

  3. Short-sighted Evolution: Traits enhancing short-term fitness may detract from long-term success.

  4. Trade-off Hypothesis: Virulence level balances with transmission rate; respectively higher transmission rates permit higher virulence.

  • Historical Example:

• The 1918 flu epidemic showed how high transmission could correlate with high virulence due to close living conditions among soldiers.

COVID-19 & Coronaviruses

• Overview:

  • COVID-19 caused by SARS-CoV-2, which emerged in Wuhan, China in December 2019 and has had significant global impact.

• Coronaviruses:

  • A family typically causing mild illness; significant outbreaks from zoonotic origins, particularly from bats.

• Transmission:

  • Bats to humans or via intermediary hosts like pangolins.

• Spike Protein Mutation:

  • A critical mutation in the spike protein of SARS-CoV-2 enhances its ability to attach to human cells via ACE2 receptors.

Evolution in Human Populations

• Examples of Evolution:

  • Lactase production in certain populations; persistence allows the digestion of dairy post-weaning.

• Breast Cancer Research:

  • Evidence suggests relationships between viral infections and breast cancer susceptibility.

Adaptive Theories of Fever

• Two Hypotheses:

  1. Fever may be exploited by pathogens; reducing fever helps the host.

  2. Fever is an adaptive defense mechanism against infection.

• Research Findings:

  • Studies on iguanas indicate fever might improve survival during bacterial infection.

Evolution and Parenthood

• Theories of Parental Investment:

  • Evolutionary predictions suggest caregivers allocate care preferentially to biological over step-children, supported by observational studies.

• Human Behavior Studies:

  • Findings from rural Trinidad indicate discrepancies in care received between biological and step-children.

• Conclusion: Understanding the evolutionary dynamics of diseases and antibiotic resistance is crucial in modern health contexts. It highlights the intricate interplay between pathogens, host defenses, and human health outcomes.

Did you hear the tea on cholera? Back in the 1850s, there was this major scandal during the cholera epidemic when John Snow, a smart guy who was like the Sherlock Holmes of disease, literally mapped out where everyone was getting sick. Can you believe he figured it all out just by looking at their water sources? That was the first time epidemiology came into play, which is all about studying how diseases spread in populations. Fast forward to 2010, and we had another cholera drama, but this time in Haiti. Scientists traced it back all the way to Nepal! Crazy, right? Genetic tests showed that the germ has been mutating while traveling the globe, kind of like the ultimate game of telephone.

Now, let’s spill some tea on germ theory! Back in the late 1800s, this hot topic was ignited by none other than Charles Darwin—yes, that Darwin—a fellow who basically changed how we think about evolution with his 'Origin of Species.' But wait, it was Louis Pasteur who really spilled the beans, asserting that germs were the culprits causing diseases! This revelation was scandalous because it paved the way for modern medicine, leading to antiseptic surgery and the discovery of antibiotics. Imagine the hush-hush conversations in surgical theaters meeting the concept of cleanliness!

When it comes to pathogens, oh boy, we’re talking about a real cat-and-mouse game. These tiny villains grow in numbers, reproduce faster than we can blink, and mutate like they’re in some wild competition. Think of the flu virus as the ultimate diva that constantly changes to dodge the immune battles in our bodies—ever heard of H and N proteins? Those are the famous names of the flu virus that always keep us guessing!

Oh, and let’s spill the beans on the flu’s historical drama. We’ve had some nasty strains in the past: the notorious 1918 H1N1, the Asian flu of 1957 (H2N2), and who could forget the Hong Kong flu of 1968? The list goes on! The more these strains mutate, the more they thrive, leaving scientists up at night wondering how to handle these diva viruses.

Now, let's switch to the hot-button issue of antibiotic resistance! Antibiotics are supposed to be our superhero allies, but these resistant bacteria? They are like the rebels who refuse to follow the rules. When antibiotics kill the weak bacteria, the strong ones just multiply! It’s like a bad reality show unfolding right in our bodies. Interestingly enough, research shows that while these tough bacteria might thrive under pressure, reducing their fitness when antibiotics aren’t around—such a dramatic life!

Then there's the evolution of virulence—that’s a spicy subject! Scientists have thrown around theories about how pathogens might tone down their aggressive behavior over time. But some diseases can’t help but be ruthless, just like the 1918 flu that took advantage of dense military living conditions during WWI. Can you imagine the whispers among soldiers as they battled against both the enemy and their own ferocious flu?

Now, can we talk about COVID-19? It burst onto the scene like a reality TV star, taking over our lives when it emerged in Wuhan in December 2019. SARS-CoV-2, the villain behind this saga, has been causing chaos worldwide. The buzz is all about how this virus, which is usually mild and cozy, might have come from bats. What’s more juicy is that it can jump from bats to humans or even through intermediary hosts—like those cute little pangolins. The drama intensified with a game-changing mutation in its spike protein, making it super clingy to our cells!

When it comes to evolution in human populations, there’s more juicy gossip—like the fact that some people have really thrived thanks to their ability to digest dairy beyond childhood, all due to an adaptation enabling lactase production. And let’s not forget the ongoing chatter around breast cancer research suggesting that viral infections might be a hidden culprit behind increased susceptibility!

And, oh! The adaptive theories around fever have also sparked debates! Some say fever helps pathogens thrive, while others swear it’s our body’s way of fighting back like a champion. It’s like the ultimate drama unfolding in the immune system!

Finally, let’s wrap up with parental investment theories. Here’s the scoop: scientists say caregivers might give preferential treatment to their biological kids over step-kids. Observations in rural Trinidad have hinted that there could be actual differences in care. Talk about a family feud!

In summary, understanding the evolution of diseases and antibiotic resistance is like reading a riveting novel, filled with incredible twists and turns that highlight the complex relationships between humans and pathogens, all affecting our health outcomes!