Key Area 5 - Parasitism Flashcards
Niche
What is an ecological niche?
An ecological niche is a multi-dimensional
summary of tolerances and requirements of a species.
What does a species occupy in the absence of any interspecific
competition?
A species has a fundamental niche that it
occupies in the absence of any interspecific
competition.
How is a realised niche occupied?
A realised niche is occupied in response to
interspecific competition.
What occurs as a result of interspecific competition?
As a result of interspecific competition,
competitive exclusion can occur, where the
niches of two species are so similar that one declines to local extinction.
What can occur when the realised niches are sufficiently different?
Where the realised niches are sufficiently
different, potential competitors can co-exist
by resource partitioning.
The Parasite Niche
What is parasitism?
Parasitism is a symbiotic interaction between a parasite and its host (+/-).
What does a parasite gain from the expense of its host?
A parasite gains benefit in terms of nutrients at the expense of its host.
Unlike in a predator–prey relationship, the
reproductive potential of the parasite is
greater than that of the host.
Why do most parasites have a narrow niche?
Most parasites have a narrow (specialised)
niche as they are very host-specific.
As the host provides so many of the
parasite’s needs, many parasites are
degenerate, lacking structures and organs
found in other organisms.
What is an ectoparasite and endoparasite?
An ectoparasite lives on the surface of its
host, whereas an endoparasite lives within
the tissues of its host.
Parasitic Life Cycles
How many hosts are required for some parasites to complete their life cycle?
Some parasites require only one host to
complete their life cycle.
Many parasites require more than one host to complete their life cycle.
What is the definitive host?
The definitive host is the organism on or in
which the parasite reaches sexual maturity.
What are intermediate hosts required for the parasite to complete?
Intermediate hosts may also be required for the parasite to complete its life cycle.
Explain the role of the vector
A vector plays an active role in the
transmission of the parasite and may also be a host.
Explain the human disease malaria is caused by Plasmodium
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.
Explain how schistosomes cause the human disease 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?
Viruses are parasites that can only replicate
inside a host cell.
What do viruses contain?
Viruses contain genetic material in the form
of DNA or RNA, packaged in a protective
protein coat.
What are some viruses surrounded by?
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
Explain the viral life cycle stages:
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.
What do RNA retroviruses use to form DNA?
RNA retroviruses 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.
Transmission & Virulence
What is transmission?
Transmission is the spread of a parasite to a host.
What is virulence?
Virulence is the harm caused to a host
species by a parasite.
How are ectoparasites generally transmitted?
Ectoparasites are generally transmitted
through direct contact.
Endoparasites of the body tissues are often
transmitted by vectors or by consumption of intermediate hosts.
List 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.
How is host behaviour often exploited &
modified?
Host behaviour is often exploited and
modified by parasites to maximise
transmission.
Alteration of host foraging, movement, sexual behaviour, habitat choice or anti-predator behaviour.
What does the host behaviour become part of?
The host behaviour becomes part of the
extended phenotype of the parasite.
What do parasites often suppress and modify?
Parasites often suppress the host immune
system and modify host size and
reproductive rate in ways that benefit the
parasite growth, reproduction or transmission.
Defence Against Parasitic Attack
Immune response in mammals has what two aspects?
Immune response in mammals has both nonspecific and specific aspects.
Non-Specific Defences
Give examples of non-specific
defences
Physical barriers, chemical secretions,
inflammatory response, phagocytes, and
natural killer cells destroying cells infected
with viruses are examples of non-specific
defences.
Explain the action of physical barriers & chemical secretions
Epithelial tissue blocks the entry of parasites; hydrolytic enzymes in mucus, saliva and tears destroy bacterial cell walls; low pH environments of the secretions of stomach, vagina and sweat glands denatures cellular proteins of pathogens.
Explain the action of the inflammatory response
Injured cells release signalling molecules.
This results in enhanced blood flow to the
site, bringing antimicrobial proteins and
phagocytes.
Explain the action of natural killer cells
Natural killer cells can identify and attach to
cells infected with viruses, releasing
chemicals that lead to cell death by inducing apoptosis.
Explain the action of phagocytes
Killing of parasites using powerful enzymes
contained in lysosomes, by engulfing them
and storing them inside a vacuole in the
process of phagocytosis.
Specific Cellular Defences
What cells constantly
circulate & monitor the tissues?
A range of white blood cells constantly
circulate, monitoring the tissues.
What happens if tissues become damaged or invaded?
If tissues become damaged or invaded, cells release cytokines that increase blood flow resulting in non-specific and specific white blood cells accumulating at the site of
infection or tissue damage.
What is the action of different lymphocytes in mammals?
Mammals contain many different
lymphocytes, each possessing a receptor on its surface, which can potentially recognise a parasite antigen.
What occurs after an antigen binds to a lymphocyte’s receptor?
Binding of an antigen to a lymphocyte’s
receptor selects that lymphocyte to then
divide and produce a clonal population of this lymphocyte.
What can some selected lymphocytes produce or induce?
Some selected lymphocytes will produce
antibodies, others can induce apoptosis in
parasite-infected cells.
What do antibodies possess?
Antibodies possess regions where the amino acid sequence varies greatly between different antibodies.
This variable region gives the antibody its
specificity for binding antigen.
What is formed when an antigen binds to a binding site and what does this result in?
When the antigen binds to this binding site
the antigen-antibody complex formed can
result in inactivation of the parasite, rendering it susceptible to a phagocyte, or can stimulate a response that results in cell lysis.
What does initial antigen exposure produce? When this occurs, what becomes enhanced?
Initial antigen exposure produces memory
lymphocyte cells specific for that antigen that 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.
What cells are also formed?
Memory lymphocyte cells are also formed.
Immune Evasion
What have parasites evolved to evade?
Parasites have evolved ways of evading the
immune system.
What do endoparasites mimic?
Endoparasites mimic host antigens to evade detection and modify host immune response to reduce their chances of destruction.
What does antigenic variation in some parasites allow?
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.
How might some viruses escape immune surveillance?
Some viruses escape immune surveillance
by integrating their genome into host
genomes, existing in an inactive state known as latency.
When will a virus become active again?
The virus becomes active again when
favourable conditions arise.
Challenges In Treatment & Control
What is Epidemiology the study of?
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 can make it difficult to find drug
compounds that only target the parasite?
The similarities between host and parasite
metabolism makes it difficult to find drug
compounds that only target the parasite.
What do vaccines contain that will elicit an
immune response?
Vaccines contain antigens that will elicit an
immune response.
What has to be reflected in the design of vaccines?
Antigenic variation has to be reflected in the design of vaccines.
Why may it be difficult to design
vaccines?
Some parasites are difficult to culture in the
laboratory making it difficult to design
vaccines.
Where may challenges arise?
Challenges arise where parasites spread
most rapidly as a result of overcrowding or
tropical climates.
These conditions make co-ordinated
treatment and control programs difficult to
achieve.
How may overcrowding occur?
Overcrowding can occur in refugee camps
that result from war or natural disaster or
rapidly growing cities in LEDCs.
What may be the only practical control strategies to improve sanitation?
Civil engineering projects to improve
sanitation combined with co-ordinated vector control may often be the only practical control strategies.
What can improvements in parasite control reduce?
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.
