2.5 Parasitism Flashcards
Define an ecological niche
An ecological niche is a multi dimensional summary of tolerances and requirements of a species
Define a fundemental Niche
A species has a fundamental niche that it occupies in the absence of any interspecific competition
Define a realised Niche
A realised niche is occupied in response to
interspecific competition
Define competative exclusion and its cause
As a result of interspecific competition, competitive exclusion can occur, where the Realised niches of two species are so similar that one declines to local extinction
What happens when the realised niches are sufficiently different?
potential competitors can co-exist
by resource partitioning
What is parasitism
Parasitism is a symbiotic interaction between
a parasite and its host (+/-)
What does a parasite gain from its host
Nutrients
Describe the reproductive potential in terms of parasites and hosts
Unlike in a predator–prey relationship, the
reproductive potential of the parasite is
greater than that of the host
What type of niche do most parasites have?
Most parasites have a narrow (specialised)
niche as they are very host-specific
Due to the hosts providing so many of the parasites needs, most parasites are……
degenerate, lacking structures and organs
found in other organisms
Define an ectoparasite
An ectoparasite lives on the surface of its
host
Define an endoparasite
an endoparasite lives within
the tissues of its host
Define the definitive host
The organism on/in which the parasite reaches sexual maturity
Talk about number of parasite hosts in terms of a lifecycle
Some parasites only require one host to complete a lifecycle, while most require more than one host.
What are the two types of hosts?
- intermediate host
- definitive host
Describe the role of a vector
A vector plays an active role in the transmission of the parasite and may also be a host (e.g. mosqitoes)
What Parasite is malaria caused by?
Plasmodium (endoparasite)
Describe the transmission of plasmodium into a human
- An infected mosquito, acting as a vector, bites a human.
- Plasmodium enters the human bloodstream.
- Asexual reproduction occurs in the liver and then in the red blood
cells. - When the red blood cells burst gametocytes are released into the
bloodstream. - Another mosquito bites an infected human and the gametocytes enter the mosquito, maturing into male and female
gametes, allowing sexual reproduction to now occur. - The mosquito can then infect another human host.
What parasite is the disease schistosomiasis caused by?
Schistosomes
Describe the transmission of Schistosomes
- Schistosomes reproduce sexually in the human intestine.
- The fertilised eggs pass out via faeces into water where they develop into larvae.
- The larvae then infect water snails, where asexual reproduction occurs.
- This produces another type of motile larvae, which escape the snail and penetrate the skin of a
human, entering the bloodstream
Viruses are parasites that can only replicate….
inside a host cell
What are the components of a virus?
Contain genetic material in the form of DNA or RNA which Is packaged in a protective protein coat
Some viruses are surrounded by……
a phospholipid membrane derived from host
cell materials
What does the outer surface of a virus contain?
The outer surface of a virus contains antigens that a host cell may or may not be able to detect as foreign
Describe the virus life cycle stages
- Infection of host cell with genetic material
- Host cell enzymes replicate viral genome
- Transcription of viral genes and translation of viral proteins
- Assembly and release of new viral particles
Describe the role of RNA retrovirus
RNA retroviruses use the enzyme reverse transcriptase to form DNA, which is then inserted into the genome of the host cell
Describe a function of viral genes
Viral genes can then be expressed to form
new viral particles
What is transmission
Spread of a parasite to a host
Define Virulence
Virulence is the harm caused to a host
species by a parasite
How are ectoparasites usually transmitted?
Ectoparasites are generally transmitted
through direct contact
How are endoparasites usually transmitted?
Endoparasites of the body tissues are often transmitted by vectors or by consumption of intermediate hosts
What are factors that increase transmission rates and why?
- The overcrowding of hosts when they are at high density
- vectors that allow transmission even if infected hosts are incapacitated
- waterborne dispersal stages, that allow the parasite to spread
What do parasites do to host behaviour sometimes?
exploit it to maximise transmission
What types of host behaviours would a parasite influence and give examples.
- Foraging (mosquito is more likely to feed on the blood of more than one person)
- Movement (frogs develop additional back leg therefore moving slower and easily caught by next prey)
- Sexual behaviour (in mayfly parasite has to return to water to find next host and so females go to lay egg’s even if they have no eggs and males act as females and try and lay eggs)
- Habitat choice (Ant climbs to top of blade instead of going to next so it is easily eaten by next host)
- Anti-predator behaviour (rats seek out cat urine so they are eaten by cat and the parasite is ingested by new host)
What does the host behaviour become in terms of the parasite?
The host behaviour becomes part of the
extended phenotype of the parasite
How does the parasite modify the host so that parasite growth, reproduction or transmission is increased?
- Parasites often suppress the host immune system
- Modify host size
- Reduce host reproductive rate
What are two categories of immune response in mammals
specific and non specific
Non specific defence: Physical Barriers
- Epithelial tissue blocks entry of parasites
- nasal hair traps parasites
Non specific defence: Chemical Secretions
- Hydrolytic enzymes in mucus, saliva and
tears destroy bacterial cell walls - Low pH environments of the secretions of stomach and sweat glands denatures cellular
proteins of pathogens
Non specific defence: Inflammatory Response
- Injured cells release signalling molecules.
- This results in enhanced blood flow to the
site and recruitment of antimicrobial proteins and phagocytes.
Non specific defence: Phagocytosis
- Phagocytes engulf parasites and store them inside a vacuole
- Powerful enzymes in the lysosome then digest the parasite
Non specific defence: Natural Killer Cells
- Natural killer cells can identify and attach to
cells infected with viruses - Then release chemicals that lead to cell death by inducing apoptosis.
What is the role of white blood cells
A range of white blood cells constantly circulate, monitoring the tissues
Describe the role of a lymphocyte
Try and recognise a parasite antigen using the receptor on its surface
Describe what happens when a lymphocyte binds to an antigen
- Antigen binds to a lymphocyte’s receptor
- Lymphocyte then divides and produces a clonal population of itself
What two defence stratagies do lymphocytes have?
- Produce antibodies
- induce apoptosis in parasite-infected cells
Why are antibodies specific to their binding antigen
Antibodies have a amino acid sequence that is special to that antibody.
What happens when an antigen binds to its binding site
- Antigen-antibody complex is formed
- This can result in inactivation of the parasite, rendering it susceptible to a phagocyte, or can stimulate a response that results in cell lysis
Describe how memory cells are produced
- Initial antigen exposure produces memory lymphocyte cells specific for that antigen
- Can produce a secondary response when the same antigen enters the body in the future.
- When this occurs antibody production is enhanced in terms of speed of production, concentration in blood and duration.
Describe how endoparasites evolve to avoid destruction
- Mimic host antigens to evade detection
- Integrating their genome into host genomes, existing in an inactive state known as latency
(The virus becomes active again when favourable conditions arise) - Antigenic Variation
Describe antigenic variation in parasites
Antigenic variation in some parasites allows them to change between different antigens during the course of infection of a host
It may also allow re-infection of the same host with the new variant
Define Epidemiology
Epidemiology is the study of the outbreak
and spread of infectious disease
What is the herd immunity threshold?
The herd immunity threshold is the density of resistant hosts in the population required to prevent an epidemic
What do vaccines contain
Vaccines contain antigens that will elicit an
immune response
What problem does similarities between hosts and parasite metabolism cause?
difficult to find drug
compounds that only target the parasite
What has to be reflected in the design of vaccines
antigenic variation
One reason why it may be difficult to design vaccines
Some parasites are difficult to culture in the laboratory making it difficult to design vaccines
Challenges in treatment and control arise when
Parasites spread rapidly as a result of overcrowding or tropical climates
Common area of overcrowding
Refugee campsthat result from war or natural disaster or rapidly growing cities in LEDCs.
What may often be the only practical control stratagy for outbreaks of parasite infections?
Civil engineering projects to improve sanitation combined with co-ordinated vector control
Improvements in parasite control also improves in child development and intelligence, how?
- Reduces child mortality
- individuals have more resources for growth and development
