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.