Endoparasites Flashcards
What is parasitism?
An ecological interaction where the parasite derives its nourishment from host, who is harmed.
Name the 2 major types of parasites
Endoparasitism
Ectoparasitism
Name and define 2 other types of parasites
Parasitoids = one part of life cycle is parasitic- eggs laid on host, larvae develop inside and eat host from inside out
Social parasities = one part of life cycle is parasitic- females lay eggs in nests of same or different species and the host bird of this nest raises offspring
What are some features of a parasite?
- smaller than host but have a rapid life cycle- so have a massive impact
What proportion of organisms are parasites?
1/3- potentially 1/2 of all species are parasites
What are some features of endoparasites?
= live inside host- can be extracellulary or intracellularly
- some of biggest killers on the planet- cause of disease
What are some challenges faced by endoparasites?
- Must evade host immune system
- Dispersal to different hosts is difficult as only adapted to live inside of host
What are the different types of parasitic hosts + how are they different?
Can be primary (=definitive) or secondary (=intermediate):
- Primary hosts:
long residency stage = parasites reach maturity here and often reproduce sexually
- secondary hosts
parasites stay a short time and often complete a developmental stage then activate exit strategy to primary/tertiary host
What are vectors?
Vectors transmit parasites between hosts = solve dispersal issue e.g. mosquitoes
What are reservoirs?
= long term hosts receiving little or no damage but cannot eradicate parasite
Name some types of intracellular parasites and what do they usually require?
Viruses
Bacteria
Fungi
Protozoa
- usually require vector to disperse
Describe the malaria life cycle.
- Mosquitoes = primary host of malaria as sexual stage is completed within it
- Mosquito takes up gametocytes and can also inject sporozoites released from oocysts
- Sporozoites enter secondary host (e.g. human) and go to liver
- Move out into asexual blood stage = clonal stage
- = 2 types of gametocytes produced and cycle continues
what are gametocytes?
cell that divides to form gametes
what are sporozoites?
motile, spore-like stage in life cycle of some parasites- usually infective agent
is malaria a successful parasite and why?
Yes- infects almost every group of vertebrates
and is present on every continent apart from Antarctica
Describe the life cycle of toxoplasma gondii in cats and their prey
- Infected mice seeks out cats
- New cats infected by eating mice- mice = vector
- New mice infected by eating food contaminated with cat poo or dead animals
Define oocysts
a zygote formed from a parastite
How is toxoplasma gondii so easily dispersed?
Sporulated oocysts = really tough egg that can survive in the environment for further transmission
Name some examples of extracellular parasites
- flatworms = Platyhelminthes
- tapeworms = Cestodes
- flukes = trematodes
- roundworms = nematodes
Describe the life-cycle of a tape worm
- larvae ensist into tissue to produce cysts- where they can emerge later or are consumed by primary host
- Digestion breaks down the cyst and can infect
- egg phase can end up in faeces which can result in transmission of eggs to secondary host
Are parasites morphologically complex and why?
There has been some loss of morphological complexity- no need for eyes, gut etc
- But there is a need for specialisation in different sensory receptors due to challenges
Describe the life-cycle of lyme disease
- relies on ticks as reservoirs and vectors- as they are small so are better for replication but do not move fast so new host required
- Ticks require 3 hosts to complete life cycle
What dies the cordyceps fungus do?
- Take over ants and force them to climb vertically up trees
- Before ant dies it is forced to bite down on vegetation
- Fruiting bodies burst and releases spores onto forest floor infecting more ants
why do mice seek out cats when infected with toxoplasma gondii?
Reduces mice fear of natural predators:
1. Forms cysts in brain which may increase dopamine production associated with the smell of cat urine
What % of humans and cats are infected with toxoplasma gondii?
cats = 40%
humans = 33%
What has been observed in humans when infected with toxoplasma gondii?
Increased risk taking- only correlation
What are gordian worms and what do they infect?
very long worm with 350 species belonging to the Nematomorpha phylum
- infect insects and crustaceans
How do gordian worms affect hosts?
- Stops any noise to prevent predators
- Non-aquatic hosts is forced to enter water
- Burrows out of body and lays eggs
- larvae infects secondary host
Define: immunomodulation
= controlling of the immune reponse
why do parasites use immunomodulation?
- reduce immune reponse to prevent worm being outed
- Host immune reactions reduces over time with length of residency of parasite to allow for long-term survival for reproduction and dispersal
What does the hygiene hypothesis suggest and where is the evidence for this?
Lack of parasties leads to a dysregulated immune system- as parasitites carry out immunomodulation to prevent overactivity
Increased prevalence in Western countries of allergies and diseases
What does the hygiene hypothesis suggest and where is the evidence for this?
Lack of parasties leads to a dysregulated immune system- as parasitites carry out immunomodulation to prevent overactivity
Increased prevalence in Western countries of allergies and diseases
