parasitism Flashcards
what is an ecological niche
An ecological niche is a multi-dimensional summary of tolerances and requirements of a species
A species has a fundamental niche that occupies in the absence of what
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 happens 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 happens Where the realised niches are sufficiently different,
Where the realised niches are sufficiently different, potential competitors can co-exist by resource partitioning
what is parasatism
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
Unlike in a predator–prey relationship, the reproductive potential of the parasite is what?
Unlike in a predator–prey relationship, the reproductive potential of the parasite is greater than that of the host
what do most parasites have
Most parasites have a narrow (specialised) niche as they are very host-specific
what does degenerate means
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 the difference of ectoparasites and endoparasites
An ectoparasite lives on the surface of its host, whereas an endoparasite lives within the tissues of its host
what do parasites require 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. Intermediate hosts may also be required for the parasite to complete its life cycle.
what does a vector do
A vector plays an active role in the transmission of the parasite and may also be
a host
what is the human disease malaria is caused by
The human disease malaria is caused by Plasmodium
malaria parasite lifecycle
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.
Schistosomes cause the human disease schistosomiasis, henace explain the disease
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.
where can viruses and parasites replicate
Viruses are parasites that can only replicate inside a host cell
what is the form of genetic material that 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
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
what can viral genes can then be expressed to form
Viral genes can then be expressed to form
new viral particles
what are the factors that increase transmission rates
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
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
how are endoparasites of the body tissues often transmitted
Endoparasites of the body tissues are often transmitted by vectors or by consumption of intermediate hosts
how do parasites often maximise transmission
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.
The host behaviour becomes part of the extended phenotype of the parasite. true or false
The host behaviour becomes part of the extended phenotype of the parasite
what do parasites often suppress
Parasites often suppress the host immune system and modify host size and reproductive rate in ways that benefit the parasite growth, reproduction or transmission
what does Epithelial tissue block
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
what are some examples of non- specific defences
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
Immune response in mammals has both nonspecific and specific aspects
what is the result of injured cells releasing signalling molecules
Injured cells release signalling molecules. This results in enhanced blood flow to the
site, bringing antimicrobial proteins and phagocytes.
what is the process of phagocitosis
Killing of parasites using powerful enzymes contained in lysosomes, by engulfing them and storing them inside a vacuole in the process of phagocytosis.
what can 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 examples of Specific cellular defences
Specific cellular defences:
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
Mammals contain many different lymphocytes, each possessing a receptor on
its surface, which can do what?
Mammals contain many different lymphocytes, each possessing a receptor on
its surface, which can potentially recognise a
parasite antigen
what does binding of an antigen to a lymphocyte’s receptor do
Binding of an antigen to a lymphocyte’s receptor selects that lymphocyte to then
divide and produce a clonal population of this lymphocyte
what will some selected lymphocytes produce
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
what does the variable region give the antibody
This variable region gives the antibody its specificity for binding antigen
when the antigen binds to the variable region what is formed, and what is the result of this formation
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. Memory lymphocyte cells are also formed
what does initial antigen exposure produce
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
Parasites have evolved ways of evading the
immune system
why do endoparasites mimic host antigens
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 them to do
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 do 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 does the virus become active
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
why does the similarities between host and parasite metabolism make things difficult
The similarities between host and parasite metabolism makes it difficult to find drug compounds that only target the parasite
what does antigenic variation have to be
Antigenic variation has to be reflected in the design of vaccines
why is it difficult to design vaccines
Some parasites are difficult to culture in the laboratory making it difficult to design
vaccines
when do challenges arise (parasites)
Challenges arise where parasites spread most rapidly as a result of overcrowding or
tropical climates
what can overcrowding result in
Overcrowding can occur in refugee camps that result from war or natural disaster or
rapidly growing cities in LEDCs. These conditions make co-ordinated treatment and control programs difficult to achieve
what may often be the only practical control strategies
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
