06 infectious disease basics

[Disease] Parasites vs predators

Parasites don't immediately kill victims and usually reproduce faster than hosts

[Disease] Pathogen

A parasite that causes disease

[Disease] Microparasites

Bacteria, viruses, protozoans; often direct transmission; infected or not; acquired immunity; short infections

[Disease] Macroparasites

Nematodes, fleas, ticks, mites; often multi-host or environmental stage; harm depends on load; no acquired immunity; chronic

[Disease] Microparasite examples

Cholera, plague, Ebola, measles, coronaviruses, malaria Plasmodium

[Disease] Macroparasite examples

Guinea worm, fleas, ticks, mites

[Disease] Ectoparasite

Lives outside host; disperses readily and shielded from immune system; vulnerable to enemies and environment (corn smut, velvet mite)

[Disease] Endoparasite

Lives inside host; protected from environment and enemies; vulnerable to immune system, hard to disperse (tapeworm, TB)

[Disease] Serengeti wildebeest parasites

Nasal bot flies (Oestrus), eye-fly larvae (Gedoelstia) reaching the braincase, nematodes, cestodes, trematodes (Talbot and Talbot 1963)

[Disease] Transmission modes

Direct contact (STDs), airborne (TB, measles), fecal-oral (typhoid, cholera), vector-borne (malaria, Lyme)

[Disease] Vector

Organism (e.g., mosquito) that carries a pathogen between hosts, as in malaria

[Disease] Endemic

Small fluctuations, persistent disease (e.g., TB)

[Disease] Epidemic

Intense outbreaks followed by disappearance (plague, SARS, measles)

[Disease] American chestnut blight

Fungus Cryphonectria parasitica introduced with Japanese chestnuts in the late 1800s; devastated American chestnut

[Disease] Chytrid fungus

Batrachochytrium dendrobatidis (Bd); amphibian-specific; caused huge biodiversity loss; first detected in Australia, now worldwide

[Disease] Harlequin frogs

Two-thirds of Atelopus species have vanished since the 1980s

[Disease] Zoonotic

Disease that spills over from animal reservoirs; most emerging diseases are zoonotic

[Disease] Zoonotic examples

Nipah (fruit bats), avian influenza (aquatic birds), Ebola (mammals)

[Disease] Take-home messages

Parasites are diverse; SIR helps guide vaccination; herd immunity; disease affects populations and biodiversity; most novel diseases come from wildlife