Parasitism Flashcards
What is a niche?
An ecological niche is a multi-dimensional summary of tolerances and requirements of a species
What are fundamental and realised niches ?
A species has a fundamental niche that it occupies in the absence of any interspecific competition
A realised niche is occupied in response to interspecific competition
What is competitive exclusion ?
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 is resource partitioning ?
Where the realised niches are sufficiently different, potential competitors can co-exist by resource partitioning
Species exploiting different components of the resource
What is parasitism ?
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 aspects are more unique about a parasite ?
Unlike in a predator–prey relationship, the reproductive potential of the parasite is greater than that of the host
Most parasites have a narrow (specialised) niche as they are very host-specific
What does degenerate mean ?
As the host provides so many of the parasite’s needs, many parasites are degenerate, lacking structures and organs found in other organisms.
Production of unused tissue would be a waste of resources.
What are the types of parasite ?
An ectoparasite lives on the surface of its host, whereas an endoparasite lives within the tissues of its host
How many hosts do parasites need ?
Some parasites require only one host to complete their life cycle
Many parasites require more than one host to complete their life cycle
What are the types of parasite hosts ?
The definitive host is the organism on or in which the parasite reaches sexual maturity. (produces gametes, undergoes sexual reproduction, meiosis, egg laying, etc)
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
Explain malaria
The human disease malaria is caused by Plasmodium
1) An infected mosquito, acting as a vector, bites a human. Plasmodium enters the human bloodstream.
2) Asexual reproduction occurs in the liver and then in the red blood cells.
3) When the red blood cells burst gametocytes are released into the bloodstream.
4) Another mosquito bites an infected human and the gametocytes enter the mosquito, maturing into male and female gametes, allowing sexual reproduction to now occur.
5) The mosquito can then infect another human host
Explain Schistosomiasis
Schistosomes cause the human disease schistosomiasis
1) Schistosomes reproduce sexually in the human intestine.
2) The fertilised eggs pass out via faeces into water where they develop into larvae.
3) The larvae then infect water snails, where asexual reproduction occurs.
4) 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
Describe the structures of a virus ?
Viruses contain genetic material in the form of DNA or RNA, packaged in a protective protein coat
Some viruses are surrounded by a phospholipid membrane derived from host cell materials
The outer surface of a virus contains antigens that a host cell may or may not be able to detect as foreign
What are the stages of the viral life cycle ?
1) Infection of host cell with genetic material
2) Host cell enzymes replicate viral genome
3) Transcription of viral genes and translation of viral proteins
4) Assembly and release of new viral particles
What are retroviruses ?
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 are transmission and virulence ?
-Transmission is the spread of a parasite to a host
-Virulence is the harm caused to a host species by a parasite
How are ecto and endoparasites transmitted ?
Ectoparasites are generally transmitted through direct contact
Endoparasites of the body tissues are often transmitted by vectors or by consumption of intermediate hosts
What are 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 exploited by parasites to maximise transmission ?
Host behaviour is often exploited and modified by parasites to maximise transmission, including;
-Alteration of host foraging
-Movement
-Sexual behaviour
-Habitat choice
-Anti-predator behaviour.
The host behaviour becomes part of the extended phenotype of the parasite
What is modified by parasites ?
-Parasites often suppress the host immune system
-Often modify host size and reproductive rate, in ways that benefit the parasite growth, reproduction or transmission
What aspects does the immense response of mammals against parasitic attack have ?
Immune response in mammals has both non-specific and specific aspects
What are the non-specific defences ?
1) Physical barriers,
2) Chemical secretions,
3) Inflammatory response
4) Phagocytes
5) Natural killer cells destroying cells infected with viruses
What are specific examples of non-specific defences ?
-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 the non-specific defences ?
1) Physical barriers
-Epithelial tissue blocks the entry of parasites
2) Chemical secretions
-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.
3) Inflammatory response
-Injured cells release signalling molecules. This results in enhanced blood flow to the site, bringing antimicrobial proteins and phagocytes
4) Phagocytes
-Killing of parasites using powerful enzymes contained in lysosomes, by engulfing them and storing them inside a vacuole in the process of phagocytosis.
5) Natural killer cells destroying cells infected with viruses
-Natural killer cells can identify and attach to cells infected with viruses, releasing chemicals that lead to cell death by inducing apoptosis.
What happens if tissues becomed damaged or invaded ?
A range of white blood cells constantly circulate, monitoring the tissues
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
How can lymphocytes recognise a parasite ?
Mammals contain many different lymphocytes, each possessing a receptor on its surface, which can potentially recognise a (specific) parasite antigen
What happens when a lymphocytes receptor binds to an antigen?
-Binding of an antigen to a lymphocyte’s receptor selects that lymphocyte to then divide and produce a clonal population of this lymphocyte
-Some selected lymphocytes will produce antibodies, others can induce apoptosis in parasite-infected cells
Why are antibodies specific ?
Antibodies possess regions where the amino acid sequence varies greatly between different antibodies
This variable region gives the antibody its specificity for binding antigens
What do antibodies do ?
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 are memory lymphocyte cells ?
-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.
Antigen bind to lympho receptor, clonal population, some clones r memory
What is immume evasion and methods to achieve this ?
Parasites have evolved ways of evading the immune system
-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 ?
Epidemiology is the study of the outbreak and spread of infectious disease
What is the herd immunity
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 are challenges in the use of medicine against parasites ?
-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.
Where do parasites spread most rapidly and what does this mean ?
-Challenges (in treatment and control) arise where parasites spread most rapidly as a result of overcrowding or tropical climates
-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 is an example of a control strategy of parasites, and what are the effects of this ?
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.
Civil engineering projects r expensive, more resources for biological and physical g&d
