Introductions

I can start this off. Then we can go around the room, thinking about

  • what you want to get out of the course
  • any worries/feelings/questions/concerns about the course
  • your favorite parasite

A bit about me

  • my background is quantitative disease ecology
  • started with ticks and small mammals
  • host-parasite interactions are incredibly interesting, parasites are gross.
  • lab research here

A bit about course structure

  • lecture (3 hrs) + lab (1 hr)
  • structure of lecture
  • structure of lab
  • course website

Syllabus

Work through syllabus, clarify structure, etc.

why is the website called “diseaseEcology” if this is a “parasitology” course?

Course website

Go through the course website and make sure everyone has easy access and is clear on how to get the lecture notes, readings, and homeworks.




End of lecture 1

What is parasitology?

  • The study of parasites and parasite-related disease

  • The difference between parasites and disease

  • Parasitology, disease ecology, and epidemiology

Parasitology, epidemiology, ecology

  • Parasitology: the study of parasites

  • Epidemiology: study of human infectious disease

  • Ecology: study of interactions with organisms and their environment

So how would we define disease ecology?

What’s the difference between disease ecology and epidemiology?

Raise your hand if you’ve taken an epidemiology course

  • What were the big takeaways?
    • Focus on mitigation, less on complexity?
    • Incorporating individual heterogeneity or environmental impacts?
    • Model environmental pathogen or vector populations, or were human case counts the main data?

What’s the difference between disease ecology and epidemiology?

  • Disease ecology uses some of the underlying theoretical models from epidemiology, but incorporates the role of species interactions and environmental drivers of infection dynamics

What this looks like in practice

  • Measles across England and Wales (1944-1994)

  • Time series of case counts in largest 10 cities reveals the clear effect the development and uptake of the vaccine

But it also changes the synchrony in case counts

  • synchrony is the tendency to have correlated fluctuations between two neighboring systems

  • here, the synchrony was driven by disease spreading across cities pre-vaccination

  • the synchrony went away after the vaccine was developed, because vaccine uptake through time tended to not be correlated between cities (and probably for other reasons)

What parts of that study are more epidemiological, and what parts are more ecological?

What about ecology and parasitology?

During a job interview I was once called a parasitologist

  • Why I am not a parasitologist
    • I don’t study individual parasites
    • I can’t identify parasites to species
    • I’ve rarely handled parasites
    • I don’t care about what many parasitologists care about

But you could call me a parasite ecologist

  • I care less about describing parasites and more about
    • how they infect their hosts
    • how this process is mediated by the environment
    • what the costs to host fitness are
    • if I can generalize across systems and gain common insight

How many parasites are there?

  • Around 40% of species diversity

  • Incredibly varied in life history

  • Tough to say

    • We keep finding more
    • Sampling is limited
    • Depends on what you want to call a parasite (viruses?)
    • Guesses range around 6 to 10 million species

What is the worst parasite?

5 minutes chatting in small groups

But every person gets 1 answer

I want

  • name of parasite

  • why it’s the worst

Microparasites

  • Generally microscopic

  • e.g., viruses, protozoans, bacteria, fungi

Macroparasites

  • Visible with naked eye

  • Generally rely less on the host for everything

  • e.g., helminths, ticks

Microparasites versus macroparasites

  • Microparasites mulitply within the host, macroparasites release juveniles outside

  • So…botflies are microparasites?

  • But enough people use this as a definition to where we should at least recognize it.

  • So macroparasite (e.g., cestode worm releases proglottids from host) different from microparasite (e.g., Yersenia pestis bacterial life cycle tons of times in same infected host).

Zoonotic parasites

  • A zoonotic parasite is a parasite that can infect humans.

  • A lot of the examples we’ll use in class will be on infectious diseases of humans

  • But this is not solely a human infectious disease course, so we’ll be pulling plenty of wildlife examples

  • Let’s name some zoonotic parasites

  • Let’s define some terms

    • spillover
    • emergence
    • re-emergence

The idea of parasite conservation

  • Parasites are incredibly diverse, and may represent a lot of extinctions

  • How/why do parasites go extinct?

  • Which parasites should be conserved?

    • tough to advocate for parasites which threaten human health or which threaten animal populations

What is the difference between parasites and disease?

  • Parasitism is being infected by a parasite.
  • Disease is defined as the expression of symptoms related to the parasite.

So the parasite causes disease, but these terms should not be confused.

Why do we care about infectious disease?

  • Impact on biodiversity

  • Economic importance

  • Impacts on humans

Impact on biodiversity

Fisher et al. 2020. Nature Reviews Microbiology

Economic importance

Cassella. 2022. High Country News

Impact on humans

Baker et al. 2022. Nature Reviews Microbiology

Koch’s postulates

  • Microorganism must be present in diseased individuals and absent in healthy individuals.

  • Microorganism must be isolated from a diseased organism and grown in pure culture.

  • Cultured microorganism should cause disease when introduced into a healthy organism.

  • Microorganism must be re-isolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent.

Limitations of Koch’s postulates

  • Super important when originally introduced for characterizing disease (TB, cholera, etc.)

  • Many infectious diseases subvert the postulates

    • some pathogens can’t be cultured yet (e.g., many prion diseases)
    • asymptomatic folks (e.g., Koch himself saw this with cholera)
    • low prevalence of infection given inoculation (hence the ‘should’ in postulate 3, which was previously ‘must’)

Even Koch had to bend his own postulates

  • Asymptomatic carriers of Vibrio cholera exist, so first postulate was already bent before it’s first application

Start of the wrap-up for the easy week 1 introduction

Welcome to parasite ecology or disease ecology

But we will also learn

  • some epidemiological modeling bits

  • a fair bit of ecology

  • a decent amount of human infectious diseases

  • some definite fun wildlife diseases

Let’s have a good semester

  • We’re going to learn a lot

  • Stay on top of readings

  • Ask when you have questions

  • Have fun