Parasitism Flashcards
What is an ecological niche
An ecological niche is a multi-dimensional summary of tolerances and requirements of a species.
What is a fundamental niche
A species that 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 and how can it occur
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.
When can potential competitors coexist by resource partitioning
Where the realised niches are sufficiently different, potential competitors can co-exist by resource partitioning.
What is parasitism
Parasitism is a symbiotic interaction between a parasite and its host.
How does a parasite gain benefit
A parasite gains benefit in terms of nutrients at the expense of its host.
What has greater reproductive potential, a parasite or its host
Unlike in a predator-prey relationship, the reproductive potential of the parasite is greater than that of the host.
What niche do parasites have and why
Most parasites have a narrow niche as they are very host-specific.
Are parasites degenerate and why
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 and an endoparasite
An ectoparasite lives on the surface of its host, whereas an endoparasite lives within the tissue of its host.
How many hosts does a parasite need to complete its life cycle
Some parasites require only one host to complete their life cycle; however, others may need more.
What is the definitive host
The definitive host is the organism on or in which the parasite reaches sexual maturity.
What would an intermediate host be used for
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.
How is malaria caused by 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 the male and female gametes, allowing sexual reproduction to now occur. The mosquito can then infect another human host.
How do Schistosomes cause the human disease schistosomiasis
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 the human, entering the bloodstream.
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 some viruses surrounded by
Some viruses are surrounded by a phospholipid membrane derived from the 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 are the viral life cycle stages
- Infection of the 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
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 be expressed to form
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
Ectoparasites are generally transmitted through direct contact or by consumption of intermediate hosts.
How are endoparasites transmitted
Endoparasites of the body tissues are often transmitted by vectors.
What increases 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 the infected hosts are incapacitated.
How do parasites maximise transmission
Alteration of host foraging, movement, sexual behaviour, habitat choice, and anti-predator behavior.
What becomes part of the extended phenotype of the parasite
The host behaviour becomes part of the extended phenotype of the parasite.
Why do parasites often suppress the host immune system and modify host size and reproductive rate
Parasites often suppress the host immune system and modify host size and reproductive rate in ways that benefit the parasite’s growth, reproduction, or transmission.
What type of aspects do immune responses in mammals have
Immune response in mammals has both nonspecific and specific aspects.
What are some non-specific defences
Physical barriers (epithelial tissue blocks the entry of parasites), Chemical secretions (hydrolytic enzymes in mucus), Inflammatory response (saliva and tears destroy bacterial cell walls), Phagocytes (injured cells release signalling molecules which result in enhanced blood flow to the site, bringing antimicrobial proteins and phagocytes), natural killer cells (NKC can identify and attach to cells infected with the virus releasing chemicals that lead to cell death by inducing apoptosis) destroying cells infected with viruses are examples of non-specific defences.
What are specific cellular defences
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 the infection or tissue damage.
How do mammals recognize a parasite antigen and kill them
Mammals contain many different lymphocytes, each possessing a receptor on its surface, which can potentially recognize a parasite 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.
Where do antibodies possess regions
Antibodies possess regions where the amino acid sequence varies greatly between different antibodies. This variable region gives the antibody its specificity for binding antigen. 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.
How are memory lymphocytes formed
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 and production, concentration in blood and duration.
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 allows change between different antigens during the course of infection in a host
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 a 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 do viruses become active again
The viruses become 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 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 cause an immune response.
What makes it difficult to find drug compounds that only target the parasite
The similarities between host and parasite metabolism makes it difficult to find drug compounds that only target the parasite.
What has to be reflected in the design of vaccines
Antigenic variation has to be reflected in the design of vaccines.
What does some parasites being difficult to culture mean for designing vaccines
Some parasites are difficult to culture in the laboratory making it difficult to design vaccines.
In terms of parasite spread when do challenges arise
Challenges arise where parasites spread most rapidly as a result of overcrowding or tropical climates.
Where can overcrowding occur
Overcrowding can occur in refugee camps that result from war or natural disaster or rapidly growing cities in LEDCs (Lower Economically Developed Countries).
How does overcrowding and tropical climates affect treatment and control programs
These conditions make coordinated treatment and control programs difficult to achieve.
How can we control parasite spread
Civil engineering projects to improve sanitation combined with coordinated vector control may often be the only practical control strategy.
Why are improvements in parasite control good
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.
