Parasitism Flashcards
What is an ecological niche?
A multi dimensional summary of tolerances and requirements of species.
What is a fundamental niche?
A species has a fundamental niche which it occupies in the abscence of interspecific competition.
What is a realised niche?
Occupied in response to interspecific competition.
What is competitive exclusion?
As a result of interspecific competition, competitive exclusion can occur, where the niches of 2 species are so similar that 1 declines to local extinction.
Resource partitioning?
Where the realised niches are sufficiently different, potential competitors can co-exist by resource partitioning.
What is parasitism?
A symbiotic relationship between a parasite and its host (+/-). A parasite gains in terms of nutrients at the expense of its host.
Unlike a predator-prey relationship , the reproductive potential of the parasite is —— than that of the host.
Greater
Most parasites have a ——— as they are very host specific.
Narrow (specialised) niche
What is a word to describe parasites?
Degenerate
How are parasites degenerate?
As the host provides so many of the parasites needs, many parasites are degenerate, lacking structures and organs found in other organisms.
Ectoparasites?
Live in the surface of the host.
Endoparasites?
Lives within the tissues of its host
How many hosts do many parasites require to complete their life cycle?
More than 1
What is the definitive host?
The organism on or in which the parasite reaches sexual maturity
What is the intermediate host?
May also be required for the parasite to complete its lifecycle.
What is a vector?
Plays an active role in the transmission of the parasite and may also be a host.
What is malaria cause by?
Plasmodium
How does malaria work? (6 steps)
- 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 host.
What is schistosomiasis caused by?
Schistosomes.
Schistosomiasis (4 steps)
- 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.
What are viruses?
Parasites that can only replicate inside the host cell
What do viruses contain?
Genetic material in the form of DNA or RNA, packaged in a protective protein coat.
Some viruses are surronded by a ——— ——— derived from host cell materials.
Phospholipid bilayer.
The outer surface of a virus?
Contains antigens that a host cell may or maybe not be able to detect as foreign.
Viral 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.
Reteroviruses?
RNA reteroviruses use the enzyme reverse transcriptase to form DNA, which is then inserted into the genome of the host cell.
Viral genes can then be expressed to form new viral particles.
What is transmission?
The spread of a parasite to a host.
What is virulence?
The harm to a host species by a parasite.
Ectoparasites, how are they transmitted?
Generally through direct contact.
Endoparasites, how are they transmitted?
By vectors or by consumption of intermediate hosts.
Factors that increase transmission rates?
- overcrowding of hosts when they are at high density.
- mechanisms, such as vectors and waterborne dispersal stages, that allow the parasite to spread even if infected hosts are incapacitated.
Exploitation of host behaviour, why?
Host behaviour is often exploited and modified by parasites to maximise transmission
Parasites can alter…
- Host foraging
- Movement
- Sexual behaviour
- Habitat choice
- Anti-predator behaviour
What is the extended phenotype of the parasite?
Host behaviour
Parasites often suppress the host immune system and modify host size and reproductive rate in ways that benefit…
Parasite growth, reproduction or transmission.
Examples of non-specific defences?
- Physical barriers
- Chemical secretions
- Inflammatory response
- Phagocytes
- Natural Killer cells ~ destroying cells infected with viruses.
Epithelial tissues defensive purpose?
Blocks the entry of parasites
Hydrolytic enzymes in mucus, saliva and tears defensive purpose?
Destroy bacterial cell walls
Low pH environments of the secretions of stomach, vagina and sweat glands defensive purpose?
Denatures cellular proteins of pathogens.
Inflammatory responses defensive purpose?
Injured cells release signalling molecules. This results in enhanced blood flow to the site, bringing antimicrobial proteins and phagocytes.
Phagocytosis defensive purpose?
Killing of parasites using powerful enzymes contained in lysosomes, by engulfing them and storing them inside a vacuole
Natural killer cells defensive purpose?
Can identify and attach to cells infected with viruses, releasing chemicals that lead to cell death by inducing apoptosis.
A range of white blood cells constantly circulate, but why?
To monitor the tissues
If tissues become damaged or invaded, cells release?
Cytokines
What do cytokines do?
Increase blood flow resulting in non-specific and specific white blood cells accumulating at the site of infection or tissue damage.
Mammals contain many different lymphocytes, each possessing a receptor on its surface, which can potentially…
Recognise a parasite antigen.
Binding of an antigen to a lymphocytes receptor selects that lymphocyte to then…
Divide and produce a clonal population of this lymphocyte.
Some selected lymphocytes will —— ——others can —— —— in parasite infected cells
Produce antibodies ,, induce apoptosis
Antibodies possess regions where…
Amino acid sequence varies greatly between different antibodies.
What does the region of antibodies where amino acid sequence varies greatly between different antibodies give the antibody?
It’s specificity for binding antigen
What happens when the antigen binds to this binding site?
The antigen-antibody complex formed.
What does the antigen-antibody complex formed result in?
This can result in inactivation of the parasite, rendering it susceptible to a phagocyte or can stimulate a response that results in cell lysis
What else can happen other than cell lysis when the parasite is inactivated?
Memory lymphocyte cells are also formed
What does initial antigen exposure produce?
Memory lymphocyte cells specific for that antigen that can produce a secondary response when the same antigen enters the body in the future.
What happens when a secondary response occurs
When this occurs antibody production is enhanced in terms of speed of production, concentration in blood and duration.
How do Endoparasites evade the immune system?
Mimic host antigens to evade detection and modify host immune response to reduce their chances of destruction
Antigenic variation in some parasites?
Allows them to change between different antigens during the course of infection of a host
What else may antigenic variation allow?
Re-infection of the same host with the new variant.
How do some viruses escape immune surveillance?
By integrating their genome into host genomes, existing in an inactive state known as latency.
After going into latency, when do the viruses become active again?
When favourable conditions arise.
What is epidemiology?
The study of the outbreak and spread of infectious disease.
What is herd immunity?
The herd immunity threshold is the density of resistant hosts in the population required to prevent an epidemic.
Vaccines?
Contain antigens that will elicit an immune response.
What makes it difficult to find drug compound that only target the parasite?
The similarities between host and parasite metabolism.
What has been reflected in the design of vaccines?
Antigenic variation.
What makes it difficult to design vaccines?
Some parasites are difficult to culture in the laboratory
Challenges arise where?
Where parasites spread most rapidly as a result of overcrowding or tropical climates.
Where does overcrowding typically occur?
Refugee camps, that result from war or natural disaster or rapidly growing cities in LEDCs
These bad conditions make coordinated treatment and control programes ——— to achieve
Difficult
Civil engineering projects to improve sanitation combined with coordinated vector control may often be the only
Practical control strategy.
The importance of parasite control?
Improvements in parasite control reduce child mortality and result in population-wide improvements in child development and intelligence, as individuals have more resources for growth and development.
