Parasitism Flashcards
What is an ecological niche?
A multi-dimensional summary of tolerances and requirements of a species
What is a fundamental niche?
The niche a species occupies in absence of any interspecific competition,
What is a realised niche?
Occupied in response to interspecific competition
What can happen as a result of interspecific competition?
Competitive exclusion can occur
When does competitive exclusion occur?
Where the niches of 2 species are so similar that one declines to local extinction
What can happen when realised niches are sufficiently different?
potential competitors can co-exist by resource partitioning
Parasitism is a ___________ relationship
symbiotic
How do parasite-host and predator-prey relationships differ?
Unlike in predator-prey relationships, the reproductive potential of the parasite is greater than that of the host
Why do most parasites have a narrow (specialised) niche?
because they are very host-specific
Why are many parasites degenerate?
Because the host provides so many of the parasite’s needs
What does degenerate mean?
lacking structures and organs found in other organisms
What is an ectoparasite?
Lives on the surface of its host
What is an endoparasite?
Lives within the tissues of its host
What is a vector?
A vector plays an active role in the transmission of the parasite and may also be a host
What causes the human disease Malaria?
Plasmodium
What causes the human disease schistosomiasis?
Schistosomes
What are viruses?
Viruses are parasites that can only replicate inside a host cell
Some viruses are surrounded by a
phospholipid membrane derived from host cell material
What do viruses contain?
genetic material in the form of DNA or RNA, packaged in a protective protein coat
What does the outer surface of a virus contain?
antigens that a host cell may or may not be able to detect as foreign
What is the importance of the enzyme reverse transcriptase?
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
What is the definitive host?
The organism in which the parasite reaches sexual maturity
What is the intermediate host?
May also be required for the parasite to complete its life cycle
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 generally transmitted?
Through direct contact
How are endoparasites generally transmitted?
By vectors or by consumption of intermediate hosts
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
Examples of how host behaviour exploited and modified by parasites to maximise transmission?
Alteration of host foraging, movement, sexual behaviour, habitat choice or anti-predator behaviour.
How do parasites modify the host’s behaviour in ways that benefit the parasite growth, reproduction or transmission?
Parasites often suppress the host immune system and modify host size and reproductive rate
Non-specific immune defences
Physical barriers, chemical secretions, inflammatory response, phagocytes, and natural killer cells destroying cells infected with viruses
What do epithelial tissue do?
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.
Specific cellular defences
A range of white blood cells constantly circulates, monitoring the tissues
What happens 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 does binding of an antigen to a lymphocyte’s receptor do?
selects that lymphocyte to then divide and produce a clonal population of this lymphocyte
Different types of lymphocytes
Some selected lymphocytes will produce antibodies, others can induce apoptosis in parasite-infected cells
Antibodies possess regions where the amino acid
sequence varies greatly between
different antibodies. This variable region gives the antibody its specificity for binding antigen
Endoparasites mimic host antigens to
evade detection and modify host immune response: to reduce their chances of destruction
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
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?
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
Vaccines contain
antigens that will elicit an immune response
Drug designing difficulties?
The similarities between host and parasite metabolism makes it difficult to find drug compounds that only target the parasite
Antigenic variation has to be reflected in the design of vaccines
Some parasites are difficult to culture in the laboratory making it difficult to design vaccines
What may be the only practical control strategies?
Civil engineering projects to improve sanitation combined with co-ordinated vector control
Parasites spread rapidly because of
Overcrowding, tropical environments
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
