Unit 2 KA5 Flashcards
Ecological Niche
Multi dimensional summary of tolerances and requirements of a species
Fundamental Niche
Occupies in the absence of interspecific competition
Realised Niche
Occupied in response to interspecific competition
Competitive Exclusion
Can occur where the niches of two species are so similar that one declines to local extinction
What can happen as a result of realised niches
Potential competitors can co-exist by resource partitioning
Parasitism
Symbiotic interaction between a parasite and its host (+/-)
What does a parasite gain from a host?
Benefit in terms of nutrients at the expense of its host
Reproductive potential if parasites
Greater than that of the host
Parasite Niche
Narrow as they are very host specific
Degenerate Parasites
As the host provides so many of its needs they lack structures and organs found in other organisms
Ectoparasite
Lives on surface of the host
Endoparasite
Lives within the tissue of its host
Definitive Host
Organism in which the parasite reaches sexual maturity
Intermediate Host
Required for the parasite to complete its life cycle
Vector
Plays an active role in transmission of the parasite and may also be a host
Malaria Life Cycle
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 red blood cells burst gametocytes are released into the blood stream
Another mosquito bites the infected humans and the gametocytes enter the mosquito
Matures into male and female gametes
Sexual reproduction can now occur
Mosquito can infect another human host
Schistosomes life cycle causing Schistosomiasis
Schistomes reproduce sexually in the human intestine
Fertilised eggs pass out via faeces into water where they develop into larvae
Larvae infect water snails
Asexual reproduction occurs
Produces another type of motile larvae
Escapes snail and penetrates skin of a human
Enters bloodstream
Viruses
Parasites that can only replicate inside a host cell
What do viruses contain
Genetic material (RNA or DNA) packed in a protective protein coat
What are some viruses surrounded by?
A phospholipid membrane derived from host cell materials
Outer surface of viruses
Antigens that a host cell may or may not be able to detect as foreign
Viral life cycle stages
Infection if host cell with genetic material
Host cell enzymes replicate viral genome
Transcription of viral genes
Translation of viral proteins
Assembly and release of new viral particles
Enzyme used by RNA Retroviruses
Reverse Transcriptase which forms DNA which is then inserted into the genome of the host cell
What can viral genes be expressed to form?
Viral particles
Transmission
Spread or a parasite
Virulence
Harm caused to a host species by a parasite
How are ectoparasites transmitted?
Direct contact
How are endoparasites of the body tissues transmitted?
Transmitted by vectors or by consumption of intermediate hosts
Factors increasing transmission rates
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
Maximising transmission
Host behaviour is often exploited and modified by parasites
What in the host is altered by parasites
Host foraging
Movement
Sexual behaviour
Habitat choice
Anti-predator behaviour
What becomes part of the extended phenotype of the parasite?
Host behaviour
What do parasites often do?
Suppress the host immune system
Modify host size and reproductive rate in ways that benefit the parasite growth, reproduction or transmission
Non-specific defences examples
Physical barriers
Chemical secretions
Inflammatory response
Phagocytes
Natural killer cells destroying cells infected with viruses
Non specific defences further examples
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 denatured cellular proteins of pathogens
What do injured cells release?
Signalling molecules that result in enhanced blood flow to the site bringing antimicrobial proteins and phagocytes
Phagocytosis
Killing of parasites using phagocytes contained in lysosomes by engulfing them and storing them inside a vacuole
Natural killer cells
Can identify and attach to cells infected with viruses, releasing chemicals that lead to cell death by inducing apoptosis
What happens when 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 do Iymphocytes possess
Possess a receptor on its surface which can potentially recognise a parasite antigen
Clonal population
Binding of an antigen to a lymphocyte receptor selects that lymphocyte to then divide and produce a clonal population
What can selected lymphocytes produce?
Antibodies which possess regions where the amino acid sequence varies greatly between different antibodies
What can lymphocytes induce?
Apoptosis I’m parasite infected cells
What does rhe variable region give the antibody?
Specificity for binding antigen
Antigen-antibody complex
When the antigen binds to the 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
Secondary Response
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
Endoparasites evading the immune system
Mimic host antigens to evade detection
Modify host immune response to reduce their chances of destruction
Re-infection of the same host with the new variant
How do viruses escape immune surveillance?
Latency - integrating their genome into host genomes existing in an inactive state
Virus becomes active again when favourable conditions arise
Epidemiology
Study of the outbreak and spread of infectious disease
Herd immunity threshold
Density of resistant hosts in the population required to prevent an epidemic
Vaccines
Contain antigens that will elicit an immune response
Why is it difficult to find drug compounds that only target the parasite?
Similarities between host and parasite metabolism
What must be reflected in the design of vaccines?
Antigenic variation
Factors that cause parasites to spread more rapidly
Overcrowding or tropical climates
Makes coordinated treatment and control programs difficult to achieve
How does overcrowding occur?
Refugee camps that result from war or natural disaster
Rapidly growing cities in LEDCs
Practical Control Strategy
Civil engineering projects to improve sanitation combined with co-ordinated vector control
Benefits of improving parasite control
Reduces child morality and result in population wide improvements in child development and intelligence as individuals have more resources for growth and development
