Unit 2 - Parasitism Flashcards
What is a ecological niche?
An ecological niche is a multi-dimensional
summary of tolerances and requirements of a
species
What is a fundamental niche?
A species has a fundamental niche that it
occupies in the absence of any interspecific
competition
What is a realised niche?
A realised niche is occupied in response to
interspecific competition
What is competitive exclusion?
where the niches of two species are so similar that one declines to local extinction
What is resource partitioning?
Where the realised niches are sufficiently
different, potential competitors can co-exist
by resource partitioning
What is paratitism?
Parasitism is a symbiotic interaction between
a parasite and its host (+/-). A parasite gains benefit in terms of nutrients
at the expense of its host
What is the difference in the reproductive potential of the host to parasitise?
Unlike in a predator–prey relationship, the
reproductive potential of the parasite is
greater than that of the host.
What do parasites have?
a narrow (specialised)
niche as they are very host-specific
What does degenerate mean?
lacking structures and organs found in other organisms
What does the host provide?
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?
An ectoparasite lives on the surface of its
host,
What is an endoparasite?
lives within the tissues of its host
What is the definitive host?
The definitive host is the organism on or in
which the parasite reaches sexual maturity.
Intermediate hosts may also be required for
the parasite to complete its life cycle
What is a vector?
A vector plays an active role in the
transmission of the parasite and may also be
a host
What is the life cycle of 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
What is the life cycle 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.
What is the definitive host in plasmodium?
In the mosquito
What is the intermediate host in plasmodium?
Human where asexual reproduction takes place
What is the definitive host of the schistosomes?
Human
What is the intermediate host of the schistosomes?
Snail
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 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
What is the viral life cycle stages?
- Infection of host cell with genetic material
- host cell enzymes replicate viral genome
- transcription of viral genes
- translation of viral proteins
- assembly and release of new viral particles
What is RNA retroviruses?
RNA retroviruses use the enzyme reverse
transcriptase to form DNA, which is then
inserted into the genome of the host cell
What can viral genes do?
Viral genes can then be expressed to form
new viral particles
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 transmitted?
through direct contact
How are endoparasites transmitted?
Endoparasites of the body tissues are often
transmitted by vectors or by consumption of
intermediate hosts
What are the factors that increase transmission rates?
- the 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
Why are host behaviours exploited?
exploited and
modified by parasites to maximise
transmission
What does the host behaviour become?
The host behaviour becomes part of the
extended phenotype of the parasite
How are host behaviours altered?
- host foraging
- movement,
- sexual behaviour
- habitat choice
- anti-predator behaviour.
What can parasites do to supress the host immune system?
- Modify host size
- Modify reproductive rate (benefit the
parasite growth, reproduction or transmission)
What do defence against pathogens do humans have?
nonspecific and specific aspects
What are the non-specific defences?
Physical barriers, chemical secretions,
inflammatory response, phagocytes, and
natural killer cells
What are natural killer cells?
natural killer cells destroying cells infected
with viruses
What does the epithelial tissue do?
Epithelial tissue blocks the entry of parasites;
What do chemical secretions do?
- 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.
What happens when cells are injured?
Injured cells release signalling molecules. This results in enhanced blood flow to the site, bringing antimicrobial proteins and phagocytes.
What is the process of phagocytosis?
Killing of parasites using powerful enzymes contained in lysosomes, by engulfing them and storing them inside a vacuole in the process of phagocytosis
What do natural killer cells do?
Natural killer cells can identify and attach to
cells infected with viruses, releasing
chemicals that lead to cell death by inducing
apoptosis.
What are the specific defences?
A range of white blood cells constantly
circulate, monitoring the tissues
What happens if a tissue becomes 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 do different lymphocytes have?
each possessing a receptor on
its surface, which can potentially recognise a
parasite antigen
What happens when an antigen binds to a lymphocytes receptor?
lymphocyte’s receptor selects that lymphocyte to then
divide and produce a clonal population of this
lymphocyte
What are the two types of things lymphocytes can do?
- Some selected lymphocytes will produce
antibodies - others can induce apoptosis in parasite-infected cells
What do antibodies possess?
regions where the amino acid sequence varies greatly between different antibodies
What does the variable region do?
gives the antibody its
specificity for binding antigen
What happens when an antigen binds to the 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 do memory lymphocyte cells do?
- 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 do endoparasites do to evade the immune system?
- mimic host antigens to evade detection and modify host immune response to reduce their chances of destruction
- It may also 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.
- The virus becomes active again when
favourable conditions arise
What is epidemiology?
Epidemiology is the study of the outbreak
and spread of infectious disease
What is 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 makes it difficult to find drugs that only target the parasite?
The similarities between host and parasite
metabolism
What must be reflected in vaccines?
Antigenic variation has to be reflected in the
design of vaccines
Why is it often difficult to design vaccines?
Some parasites are difficult to culture in the
laboratory making it difficult to design
vaccines
What are some of the challenges with parasites spreading?
- overcrowding or tropical climates
- Overcrowding can occur in refugee camps
that result from war or natural disaster or
rapidly growing cities in LEDCs.
How do you reduce the rates of transmission?
- Civil engineering projects to improve
sanitation combined with co-ordinated vector
control may often be the only practical control
strategies - 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
What happens when secondary exposure occurs?
When this occurs antibody production is enhanced in terms of speed of production, concentration in blood and duration
How are memory cells formed?
Initial antigen exposure produces memory
lymphocyte cells specific for that antigen
