Parasitism 2.5 Flashcards
what is an ecological niche?
a multi-dimensional summary of tolerances and requirements of a species
a species has a fundamental niche that it occupies in what?
in the absence of any interspecific competition
a realised niche is occupied in response to what?
interspecific competition
what can occur as a result of interspecific competition?
competitive exclusion - where the niches of two species are so similar that one declines to local extinction
what happens where the realised niches are sufficiently different?
potential competitors can co-exist by resource partitioning
what is parasitism?
a symbiotic interaction between a parasite and its host in which the parasite benefits (+) in terms of nutrients at the expense of its host, which loses these (-)
a parasite gains benefit in terms of what?
nutrients at the expense of its host
the reproductive potential of the parasite is greater than that of the host unlike in what relationship?
in a predator–prey relationship
most parasites have a narrow (specialised) niche because?
they are very host-specific
what is symbiosis?
an intimate co-evolved relationship between two species that can be notated:
- + for benefits
- - for detriment
- 0 for neutral
many parasites are degenerate, what does this mean?
they have lacking structures and organs such as digestive systems found in other organisms
where does an ectoparasite live?
it lives on the surface of the host
where does an endoparasite live?
it lives within the tissues of it host
what is the definitive host?
the organism on or in which the parasite reaches sexual maturity
what is the intermediate host?
the organism which may be required for the parasite to complete its life cycle
what is a vector?
it plays an active role in the transmission of the parasite and may also be the host
what is malaria caused by?
the parasite Plasmodium
describe how plasmodium enters humans
- infected mosquito (acts as a vector) bites human and plasmodium enters bloodstream
- asexual reproduction occurs in the liver and then in the red blood cells - burst to release gametocytes into bloodstream
what happens if a mosquito bites a human infected with malaria?
gametocytes enter mosquito - maturing into male and female gametes and allowing sexual reproduction to occur
what do schistosome parasites cause?
schistosomiasis
describe the life cycle of schistosomes
- schistosomes reproduce sexually in the human intestine
- fertilised eggs pass out via faeces into water where they develop into larvae that infect snails
- once they infect the snails, they reproduce asexually which produces another type of motile larvae
- motile larvae escape the snail and penetrates the skin of humans - enters blood stream
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 by?
phospholipid membrane derived from host cell materials
what does the outer surface of a virus contain?
antigens that a host cell may or may not be able to detect as foreign
describe the life cycle stages of a virus
- infection of the host cell with genetic material
- host cell enzymes replicate viral genome
- viral genome is then transcribed and translated into viral proteins
- new viral particles are assembled and released from host cells
how do retroviruses work?
they use the enzyme reverse transcriptase to form DNA
- the DNA is then inserted into the genome of the host cell - allowing new viral particles to be formed
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?
through direct contact or by consumption of intermediate hosts
how are endoparasites of the body tissues transmitted?
by vectors
what are some factors that increase transmission rates?
- overcrowding of hosts when at a high density
- mechanisms such as vectors and waterborne dispersal stages - allows parasite to spread even if infected hosts are incapacitated
how do parasites maximise transmission?
by exploiting and modifying its hosts behaviour
what becomes part of the extended phenotype of the parasite?
the alteration of:
- host foraging
- movement
- sexual behaviour
- habitat choice
- anti-predator behaviour
in what ways do parasites often suppress the host immune system and modify host size and reproductive rate?
in ways that benefit parasite growth, reproduction or transmission
what do immune responses in mammals involve?
- non-specific defences
- specific cellular defences
what are examples of non-specific defences?
- physical barriers
- chemical secretions
- inflammatory response
- phagocytes
- natural killer cells destroying cells infected with viruses
how do skin and epithelial tissue act as physical barriers?
by blocking the entry of parasites
what do chemical secretions include and how do they work?
- include hydrolytic enzymes in mucus, saliva and tears
- they destroy bacterial cell walls
how do secretions of the stomach, vagina and sweat glands work?
they create low pH environments that denature cellular proteins of pathogens
what happens when cells become injured?
- they release signalling molecules that enhance blood flow to the site
- brings antimicrobial proteins and phagocytes
how can phagocytes kill parasites?
by using powerful enzymes contained in lysosomes by engulfing them and storing them inside a vacuole in the process of phagocytosis
how do natural killer cells work?
by identifying and attaching to cells infected with viruses, releasing chemicals that lead to cell death by inducing apoptosis
what do a range of white blood cells do?
they constantly circulate in the blood, monitoring the tissues
what happens if tissues become damaged or invaded?
cells release cytokines that increase blood flow - results in non-specific and specific white blood cells accumulating at the site of infection or tissue damage
what do mammals contain many different types of and what are its properties?
lymphocytes
- each of them possess a receptor on its surface that can potentially recognise a parasite antigen
what happens when an antigen binds to a lymphocytes receptor?
it selects that lymphocyte to divide and produce a clonal population of this lymphocyte
what can selected lymphocytes do?
- some produce antibodies
- some induce apoptosis in parasite-infected cells
what do antibodies possess and what does it do to them?
- regions where the amino acid sequence varies greatly between different antibodies
- this variable region gives the antibody its specificity for binding antigen
what happens when an antigen binds to a binding site and what does it result in?
the antigen-antibody complex formed can result in
- the inactivation of the parasite
- rendering it susceptible to a phagocyte
- stimulate a response that results in cell lysis
what do 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 in a secondary response?
antibody production is enhanced in terms of speed of production, concentration in the blood and duration
how have parasites evolved?
in ways of evading the immune system
how do endoparasites reduce their chances of destruction?
by mimicking host antigens to evade detection and modify the host immune response
what does antigenic variation in some parasites allow?
allows them to change between different antigens during the course of infection of a host - may also allow reinfection 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 active state known as latency
when do viruses emerge from latency (their inactive state)?
when favourable conditions arise
what is epidemiology?
the study of the outbreak and spread of infectious disease
what is the herd immunity threshold?
the density of resistant hosts in the population required to prevent an epidemic
what do vaccines contain?
antigens that will elicit an immune response
why is it difficult to find drug compounds that only target the parasite?
because of the similarities between the host and parasite metabolism
what has to be reflected on in the design of vaccines?
antigenic variation
how do parasites make it difficult to design vaccines?
because they are difficult to culture in a laboratory
what happens as a result of overcrowding or tropical climates?
the arise of challenges where parasites spread most rapidly
where can overcrowding occur?
- in refugee camps that result from war or natural disasters
- rapidly growing cities in less economically developed countries (LEDCs)
what do overcrowded conditions make it difficult to achieve?
co-ordinated treatment and control programmes
what may often be the only practical parasite control strategies?
civil engineering projects to improve sanitation, combined with co-ordinated vector control
what do improvements in parasite control and what can it result in?
- controls the reduce of child mortality
- results in population-wide improvements in child developments and intelligence as individuals have more resources for growth and development
