Parasitism Flashcards
What is an ecological niche?
Multi-dimensional summary of tolerances and requirements of species
What is a fundamental niche?
Niche that it occupies in the absence of any inter specific competition
What is a realised niche?
Niche that it occupies in response to interspecific competition
What is competitive exclusion?
Where the niches of 2 species are so similar that one will decline to local extinction
Competitive exclusion is a result of…
Interspecific
If species have sufficiently different realised niches…
Potential competitors can co-exist by resource partitioning
Parasitism is a… interaction between a…
Symbiotic, parasite and it’s host
Parasite gains benefit in terms of nutrients at expense of the host (+/-)
What is a symbiont?
An organism that lives in close association with another
Parasites have a greater…
Reproductive potential than their host (unlike predator-prey relationship)
Parasites are very host specific so they have a…
Narrow specialised niche
Because the host provides so many of their needs, many parasites are…
Degenerate ( lack structures/organs found in other organisms)
What is an ectoparasite?
Parasite which lives on the surface of its host e.g. ticks
What is an endoparasite?
Parasite which lives within tissues of its host
What is the definitive host?
The organism on or in the parasite reaches sexual maturity
What is the Intermediate host?
May also be required for the parasite to complete its life cycle
What is a vector?
Plays an active role in the transmission of the parasite and may also be a host
Key examples of parasites that require intermediate hosts to compete their lifecycle…
Plasmodium- causes malaria disease in humans
Schistosomes-cause disease schistosomiasis in humans
Stages in transmission of plasmodium
- An infected mosquito, acting as a vector, bites a human and plasmodium enters the bloodstream
- Asexual reproduction occurs in the liver and then in the red blood cells
- When the red blood cells burst, gametocytes are releases into the bloodstream
- Another mosquito bites an infected human and the gametocytes enter the mosquito, maturing into male and female gametes, allowing sexual reproduction to now occur
Stages in transmission of schistosomes
- Schistosomes reproduce sexually in the human intestine
- The fertilised eggs pass out via faeces into water where they develop into larvae
- 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 a human, entering the bloodstream
What are viruses?
Parasites that can only replicate inside a host cell
Viruses contain genetic material in the form of…
DNA or RNA packaged in a protective protein coat
The outer surface of viruses contains…
Antigens that a host cell may or may not be able to detect as foreign
Some viruses are surrounded by a…
Phospholipid membrane derived from host cell materials
What is transmission?
The spread of a parasite to a host
What is virulence?
The harm caused to the host species by a parasite
Ectoparasites are generally transmitted through…
Direct contact
Endoparasites of body tissues are ofter transmitted by…
Vectors or consumption of intermediate hosts
Factors that increase transmission rates
Overcrowding of hosts when they are at high density
Mechanisms that allow parasite to spread eve if infected hosts are incapacitated such as vectors and waterborne dispersal stages
Viral life cycle stages
- Virus antigens attach to host cell surface
- Infection of host cell with genetic material
- Host cell enzymes replicate viral genome
- Virus genes are transcribed to RNA which is translated to make viral proteins
- New virus particles are assembled and released
What is transmission?
The spread of a parasite to a host
What is virulence?
Harm caused to the host species by a parasite
Ectoparasites are generally transmitted through…
Direct contact
Endoparasites are often transmitted by…
Vectors or consumption of intermediate hosts
Factors that increase transmission rates
Overcrowding of hosts when they are at high density
Mechanisms that allow parasites to spread even if infected hosts are incapacitated e.g. vectors- mosquitos
waterborne dispersal stages- schistosomes
To maximise transmission…
Host behaviour is often exploited and modified by parasites (becomes part of the extended phenotype of the parasite)
Examples of alterations of host
Foraging
Movement
Sexual behaviour
Habitat choice
Anti-predator behaviour
Factors that increase virulence
Suppress the host immune system so parasites survive and reproduce in host without being attacked
Modify host size- grows larger to support asexual reproduction of more parasites
Reduce hosts’ reproductive rate so more energy is directed to parasite reproduction
Immune response in mammals has both…
Non-specific and specific aspects
What are the non-specific defences?
Physical barriers
Chemical secretions
Inflammatory response
Phagocytes
Natural killer cells
Physical barriers
Epithelial tissue blocks the entry of parasites
Chemical secretions
Hydrolytic enzymes in mucus, saliva and tears destroy bacterial cell walls and low pH environments of secretions of the stomach, vagina and sweat glands denatures cellular proteins of pathogens
Inflammatory response
Injured cells release signalling molecules (histamine) which enhance blood flow to the site, priming antimicrobial proteins and phagocytes
Phagocytes
Killing of parasites using powerful enzymes contained in lysosomes, by engulfing them and storing them inside a vacuole in the process of phagocytosis
Natural killer cells
Can identify and attach to cells infected with viruses, releasing chemicals that lead to cell death by inducing apoptosis
What are specific cellular defences produced in response to?
Specific antigens
What constantly circulates, monitoring the tissues?
A range of white blood cells
What happens if tissues become damaged or invaded?
Cells release cytokines
What do cytokines do?
Increase blood flow resulting in non-specific and specific white blood cells accumulating at the site of infection or tissue damage
What are lymphocytes?
White blood cells found mainly in lymph glands
Mammals contain many different…
Lymphocytes each possessing a receptor (can potentially recognise a parasite antigen) on its surface
What are memory lymphocytes?
Type of white blood cell
Initial antigen exposure produces…
Memory lymphocyte cells specific for that antigen
What happens when the same antigen enters the body in the future?
Memory lymphocytes can produce a secondary response
What does the secondary response increase?
Speed of antibody production
Concentration of antibody in blood
Duration of time antibody is in blood
(enhanced antibody production)
What is clonal selection?
When binding of an antigen to a lymphocyte’s receptor selects that lymphocyte to divide and produce a clonal population of this lymphocyte
What can selected lymphocytes do?
Produce antibodies- possess regions where amino acid sequence varies greatly between different antibodies
Induce apoptosis in parasite infected cells
(this variable region gives the antibody its specificity for binding antigen)
Stages of clonal selection
Antigen binds to binding site
Antigen-antibody complex formed
Results in inactivation of parasite
How can an antigen-antibody complex result in the inactivation of a parasite?
Renders it susceptible to a phagocyte
Stimulates a response that results in cell lysis
3 ways parasites have evolved to evade immune system
Mimic host antigens
Antigenic variation
Integration with host genomes
How do parasites mimic host antigens?
Endoparasites mimic host behaviour to evade detection by modifying the host immune response and reducing their chances of destruction
Antigenic variation in some parasites allows them to…
Change between different antigens during the course of infection of a host, may allow reinfection of the same host with a new variant
Some viruses escape immune surveillance by…
Integrating their genome into host genomes, existing in an inactive state known as latency
Virus becomes active again when favourable conditions arise
What is epidemiology?
Study of outbreak and spread of infectious disease
What is the herd immunity threshold?
Density of resistant hosts in there population required to prevent an. edidemic
How is herd immunity achieved/threshold reached?
Through vaccinations
What is herd immunity?
When a new infection in a population can be contained because susceptible hosts are too dispersed for parasite to continue to spread
What are the challenges in parasite treatment?
- 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 (e.g. influenza-new vaccines)
- Some parasites are difficult to culture in the laboratory so difficult to design vaccines
- Rapid spread of parasites as a result of overcrowding or tropical climates
Overcrowding can occur in…
Refugee camps resulting from war or natural disaster
Rapidly growing cities in LEDC’s (less economically developed countries)
Overcrowded conditions make…
Co-ordinated treatment and control programs difficult to achieve
How can parasites be controlled?
Civil engineering projects to improve sanitation
Co-ordinated vector control
(combination may often be the only practical control strategy)
Improvements in parasite control results in…
Reduced child mortality
Population-wide improvements in child development and intelligence as individuals have more resources for growth and development
