Transcript Parasite Ecology

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.