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.