Chapter 15 Flashcards
What is a parasite?
Lives in or on another organism (host)
Consumes host resources
Causes harm to host
A pathogen is a type of parasite that causes infecBous disease.
Ectoparasites
live on the outside of an organism.
Mostly arthropods (e.g., ticks, mites, lice, fleas)
Includes some leeches, lampreys
Nematodes
~4000 plants (e.g., mistletoe)
Endoparasites
live inside organisms.
Types of endoparasites
Viruses Prions Protozoans Bacteria Fungi Helminths
Prions
They begin as beneficial brain proteins.
A protein folds into an incorrect shape and becomes pathogenic.
It replicates by coming into contact with other proteins.
Transmission occurs through consumpBon of infected dead animals or their feces.
Bacteria
single-celled prokaryotes
Examples: “Shot hole” plant bacteria “Crown gall” Anthrax Plague Pneumonia Salmonella Leprosy
Fungi
Devastates many plant species
Examples:
Loss of American elm from Dutch elm disease
Loss of American chestnut from Cryphonectria parasitca
Batrachochytrium dendrobatidis
Fungus that lives in the outer layer of amphibian skin; causes ion imbalance.
It rapidly spread across Central America.
It is now the suspected cause of dozens of amphibian extinctions.
Helminths
Include several species of roundworms and flatworms
Examples:
Hookworms that feed on blood of intestines
Lungworms that live in the lungs
Echinostomes that live in kidneys
Liver flukes that infect livestock, resulting in death
Emerging infectious disease
a newly discovered or rare disease that increases in abundance.
Oben occurs when a mutaBon allows a pathogen to jump to a new host species.
Factors that influence the probability of host infection
Mechanism of transmission
Mode of entering the host
Ability of parasite to jump between specie
Existence of reservoir species
Counterahacks to host’s immune system
Horizontal transmission
When a parasite moves between individuals other than parents and offspring.
Vertical transmission
When a parasite is transmitted from a parent to its offspring.
Mode of entering the host
Piercing tissue (e.g., leeches) Reliance on a vector (e.g., malaria)
Ability of parasite to jump between species
A lethal parasite that specializes on one host may face exBncBon; soluBon is to infect mulBple species (e.g., bird flu, HIV)
Reservoir species
Species that carry a parasite but do not succumb to disease.
They can be a continuous source of parasites as other hosts become rare.
Counterahacks to host’s immune system
Avoiding detection by incorporating into chromosomes (e.g., HIV)
Form protective outer layer (e.g., schistosomes)
Vector
an organism that disperses a parasite between hosts.
Some parasites require multiple hosts to complete their life cycle.
Example: Lyme disease
Parasites can evolve adaptations that increase the probability of transmission…
Example:
The yellow dungfly is infected by a fungus.
The fungus causes the fly to perch upside-down on an upper leaf of a plant.
Spores are released, carried by the wind, and infect more flies.
The parasitic worm Acanthocephalus dirus
requires two hosts: an isopod and a fish.
Infected isopods increase their visibility to fish predators by spending more time in open water.
Worms develop in the fish, and parasites leave the fish with waste products that isopods consume.
Hosts have developed a range of responses to combat parasites.
Immune system responses
Production of antibacterial/antifungal compounds
Mechanical/biochemical defenses
Self-medication
When infected with nematode parasites, chimpanzees will consume Aspilia leaves, which are covered with any hooks that pull nematodes out of the digestive tract.
They also chew biher twigs from the Vernonia plant, which contain chemical compounds that kill parasites.
When two or more species continue to evolve in response to each other’s evolution
Invasive rabbit populations in Australia cause massive crop damage.
The government released a virus (Myxoma) into the populaBon that killed 99.8% of the rabbits.
This favored resistant rabbits and less lethal viruses.
Over time, both virus and rabbit populaBons coevolved and began increasing in abundance.
