Parasitism Flashcards
What is an ecological niche
A multi-dimensional summary of tolerances and requirements of a species
What is a fundamental niche
A niche a species occupies in the absence of any interspecific competition
What is a realised niche
A niche in response to interspecific competition
What is competitive exclusion
The niches of two species are so similar that one declines to local extinciton
What is resource partitioning
When potential competitors co-exist since realised niches are sufficiently different
What type of interaction is parasitism
Symbiotic (+/-)
Does the parasite or the host have a greater reproductive potential
The parasite does
What kind of niche does a parasite have
A very narrow, specialised host specific niche
What makes parasites degenerate
The way the host provides so many of the parasite’s needs that it lacks in structures and organs found in other organisms
Where does an ectoparasite live
On the surface of its host
Where does an endoparasite live
In the tissue of its host
What is the definitive host
The organism on or in which the parasite reaches sexual maturity
What is a vector
Something that plays an active role in the transmission of the parasite and also may be a host
Explain the transmission of the disease malaria
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 blood cells
Blood cells burst releasing gametocytes into bloodstream
Another mosquito bites an infected human and gametocytes enter the mosquito, maturing into males and female gametes, allowing sexual reproduction to now occur.
The mosquito can then infect another human host.
Explain the transmission of schistosomiasis
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 a host cell
What do viruses contain
Genetic material in the form of DNA or RNA, packaged in a protective protein coat
What are some viruses surrounded in
A phospholipid bilayer derived from host cell materials
What allows viruses to be detected by host cells
The outer surface of a virus contains antigens that a host cell may or may not be able to detect as foreign
Describe the viral life cycle stages
Infection of host cell with genetic material
Host cell enzymes replicate the viral genome
Transcription of viral genes and translation of viral proteins
Assembly and release of new viral particles
What enzyme do RNA retroviruses use
Reverse transcriptase to form DNA
What happens to the DNA once it has been converted
It is inserted into the genome of the host cell which forms new viral particles
What is transmission
The spread of a parasite to a host
What is virulence
The harm caused to a host species by a parasite
How are ectoparasites transmitted
Via contact
How are endoparasites transmitted
By vectors or by consumption by intermediate hosts
Name 2 factors that increase transmission rates
Overcrowding of hosts when at high density
Mechanisms such as vectors and waterborne dispersal stages, that allow the parasite to spread even if infected hosts are incapacititated
How do parasites maximise transmission
They exploit and modify hosts to max transmission
Name 5 examples of when host behaviour is exploited
Alteration of host foraging Sexual behaviour Habitat choice Anti-predator behaviour Movement
What becomes part of the extended phenotype of a parasite
The host’s behaviour
How can parasites increase their own growth, reproduction and transmission
By suppressing the host immune system and modify host size and reproductive rate
Give 4 examples of non-specific defences
physical barriers chemical secretions inflammatory response phagocytes NK cells destroying cells
What does epithelial tissue do in terms of defence
blocks the entry of parasites
What does hydrolytic enzymes in mucus, saliva and tears do
Destroy cell walls
What does low pH of stomach, vagina and sweat glands do
dentures cellular proteins of pathogens
Explain inflammatory response
Injured cells releasing signalling molecules (cytokines), resulting in enhanced blood flow to the site, bringing antimicrobial proteins and phagocytes (specific and non-specific white blood cells)
Explain phagocytosis
The killing of parasites using powerful enzymes contained in the lysosome, by engulfing them and storing them inside a vacuole in the process of phagocytosis
Describe how NK cells work
They identify and attach to cells infected with viruses, releasing chemicals that lead to cell death by inducing apoptosis
What makes a lymphocyte specific to a parasitic antigen
The receptor
What happens upon binding of a lymphocyte to the antigen of a parasite
The lymphocyte divides and produces a clonal population of lymphocytes
What are the 2 possible roles of lymphocytes
Some will produce antibodies and others will induce apoptosis in parasite -infected cells
What gives each antibody its specificity for the binding antigen
The variation in amino acid sequence in particular regions
What is the effect of antibody binding
Inactivation of the parasite, rendering it susceptible to a parasite
Stimulating a response that results in cell lysis (breaking down of a cell membrane)
What is the use of memory cells
When the same antigen enters the body in future a secondary response is produced
The secondary response is enhanced in terms of speed of production, concentration in blood and duration
How do endoparasites evade detection
They mimic host antigens
How do endoparasites reduce their chances of destruction
They modify host immune response
What is antigenic variation in terms of parasites
It is when parasites change between different antigens during the course of infection of a host
What is the cause of reinfection of the same host by a parasite
antigenic variation
How can viruses escape immune surveillance
By integrating their genome into host genomes, existing in an inactive state known as latency. The virus then becomes active again when favourable conditions arise
What is epidemiology
The study of the outbreak and spread of an infectious disease
What is the herd immunity threshold
The density of resistant hosts in the population required to prevent an epidemic
How do vaccines work
They contain antigens that will elicit an immune response
What makes it difficult to find drug compounds that only target the parasite
The similarities between host and parasite metabolism
What are 2 considerations when designing vaccines
Antigenic variation
Some parasites are difficult to culture in the lab
