parasite ecology. ecology the study of ecosystems –interaction between organisms and the...
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Parasite Ecology
Ecology
• The study of ecosystems– Interaction between organisms and the
environment• Biotic – living part of environment• Abiotic – non-living part of environment
Ecosystem
• A grouping of plants, animals, and microbes occupying an explicit unit of space and interacting with each other and their environment.
Ecological Niche
• The role and organism plays in an ecosystem.– Dependant on location of host in the
environment– Location within the host
• Dimensions on a resource
Distribution of Nematodes in the Eared Grebe
Site of Infection
• Coelozoic– Within a body cavity
• Lumen of intestine, peritoneal cavity, bladder…
• Histozoic– Within tissue
• Muscle, blood, skin…
Microenvironments
• Differ in:– Nutrients– Oxygen– pH– Mobility– Immune cells
Populations
• All the individuals of a distinct species living within a specific ecosystem.– Infrapopulation
• Within a single host
– Metapopulation• Within a single host species
– Suprapopulation• All stages all hosts
Population Terminology
• Intensity = # of parasites within a host.
• Mean intensity = average number of parasites within infected hosts.
• Prevalence = % infected.
• Incidence = New Infection/time uninfected at start time
• Density = total # in sampling unit.
Macroparasites
• Do not multiply in/on host.– Examples
• adult cestodes and trematodes.
– Aggregate populations• Crofton, 1970’s• Most parasites are within a few hosts.
Aggregate Populations
Microparasites
• Multiply in/on host.– Examples
• Plasmodium (malaria)• Trypanosomes (T. cruzi, Chagas disease)
Population Structure
• Which individuals are infected?
• How is the infection distributed in the population?
Susceptibility
• Some individuals are more susceptible to infection.
• Why?– Immune response?– Genetics?– Exposure?– Overall health and nutrition?
Parasite Community
• Multiple species of parasites within a host.
• Often in different microenvironments within host.
Reproduction
• Finding a host = limiting factor.
• Reproductive potential– Number of offspring
• Reproductive success– Chance offspring find host
• Low success = high potential
• High success = low potential
Increasing Reproductive Success
• Viviparity – live birth.– Some nematodes.
• Hermaphroditism– Insures fertilization and allows genetic
diversity.
• Asexual reproduction– Internal budding– Polyembryony– Schizogony
Adaptations for Transmission
• Altering appearance or behavior of host.
Ants infected with nematode
Epidemiology
• Study of disease distribution– Vectors – transmit parasites– Nidus – set of environmental conditions that
predict infection will occur.– Zoonoses – animal parasites that can infect
humans.
Co-evolution
• Parasite and host co-evolve
• Least virulent parasites can be very successful.
• Parasite must evolve ways to counter immune response.