Consumption (parasitism) exam 3 (3)

definition of parasitism

• Occurs when parasite consumes some, but not all, of a host

• host usually does not die, but does suffer a cost (lower fitness)

Ectoparasite

a parasite that lives on the outside of an organism

example of an ectoparasite

ex. Chiggers can transmit the Orientia tsutsugamushi, bacteria causes scrub typhus-Ulcer-Fever-Headaches

Plants having ectoparasites?

Nematodes that act as plant ectoparasites live in the soil and feed on plant roots. These 1-mm-long worms attach to a plant root, inject digestive enzymes that break down root cells, and then consume the resulting slurry.

Endoparasite 

A parasite that lives on the inside of an organism 

Example of an endoparasite

Plasmodium sp. (protist)

• Causes malaria in humans

• Kills over 1 million people per year

Endoparasite(intracellular) def/ characteristics

live inside of the cells of a host

very small 

Endoparasite (intercellular) 

-live in the spaces between cells

-large

Life cycle of the malaria parasite 

• Mosquitos inject parasite (protozoan)

• Reproduces asexually (liver), sexually in red blood cells

• Destroys red blood cells

• Mosquito consumes parasite from infected human

graph the compares the consequences of edoparasite and ectoparasite lifestyles

Emerging Infectious Disease

a disease that is newly discovered or has been rare and then suddenly increases in occurrence

Susceptible-Infected-Resistant (S-I-R) Model

the simplest model of infectious disease transmission that incorporates immunity

What does the SIR-model not include?

doesn’t show vaccines

doesnt show pop. of ppl who couldnt recover/die

it expects that everyone recovers

SIR- model with COVID

The number of infected individuals decreased but the duration of infectivity was prolonged by >200 days

2/3 of the population would need to be immunized to stop the epidemic

Prions

1. Prions are NOT living organisms

• They are not viruses or bacteria.

• They contain no DNA or RNA.

• They are simply misfolded proteins.

How do prions replicate

• They replicate by touching normal proteins and causing them to misfold.

• The original prion acts as a template.

• This creates a chain reaction → more prions → more tissue damage.

What is the effect of prions

4. What prions do

• They cause cell death and brain tissue damage.

• All prion diseases are fatal.

what reduces the abundance of the forest tent caterpillars

VIRSUES

When the tent caterpillar population is high, the virus can more easily spread from one host to another, so each caterpillar is more likely to get the virus. Under these conditions, large numbers of caterpillars die. As host population density decreases, it becomes harder for the viruses to find a new host and the prevalence of the disease declines. Since fewer caterpillars become infected and die, the caterpillar population starts to increase again.

how does the parasite–host model differ from the predator–prey model

Parasites — unlike predators — do not always remove host individuals from a population, and hosts — unlike prey — may develop immune responses that make some individuals resistant to the pathogen.

what does each letter stand for in S-I-R

100 percent of the individuals begin as susceptible to the pathogen (S).

Of those, some percentage becomes infected (I).

Of the infected individuals, some percentage develops resistance via immunity (R).

the rate at which a pathogen spreads through a population depends on two opposing factors

One factor is the rate of transmission between individuals (b), which includes both the rate of contact of susceptible individuals with an infectious individual and the probability of infection when there is contact. The other factor is the rate of recovery (g), which is the period of time from when an individual is infected and can transmit the infection to when the individual’s immune system clears the infection and the individual becomes resistant to any future infections.

PROBABILITY of contact between susceptible and infected individuals’ equation

S times I

RATE of infection between susceptible and infected individuals

S times I times b

What does Ro stand for

the reproductive ratio of the infection (𝑅0)

(𝑅0)= S times b/g

Assumptions of the S–I–R Model

assumes that there are no births of new susceptible individuals and that individuals retain any resistance they develop.