parasitology lecture 8: parasite's way of life pt.4

what is site specificity?

the requirement of many parasites to arrive at a specific anatomical location on or within a particular host to grow or reproduce.

provide an example of site specificity

Plasmodiumrestricted to hepatocytes or erythrocytes depending on developmental stage in the mammal.

why have parasites evolved site-specific adaptations?

Each host offers several different habitat options.

- Each of these potential habitats differs in pH, nutrient

availability, oxygen concentration and other factors.

- Parasites are competing against the host's immune

system.

- Immune responses vary from location to location.

- Potential competition (especially with high infection levels) with other parasites.

*not all parasites are site-specific (ex: some cysts and tapeworms)

what kind of organisms is it easier to find a site?

Ability to "home in" less problematic

for ectoparasites.

◦ However, some sites are VERY specific!

provide an example of an ectoparasite that is very site-specific

Feather lice:

- Some lice attached to feathers with barbs of a certain diameter, matching the width

of their appendages.

Trematodes that parasitize fish:

- Attach to gill filaments of their host fish.

Even though a host's environment is complicated, it is usually _________.

predictable

due to anatomical similarities within hosts and homeostatic mechanisms in host that maintain relatively stable conditions

describe the migration of fasciola hepatica (liver fluke) from the intestine to the liver

1. violent spasms due to bile and excystation completes

2. continues spasms and release of lytic enzymes allow penetration of intestinal lining into preitoneal cavity

3. Larvae adhere to lining with suckers and begin

moving. Because peritoneal cavity is like a sphere,

movement in any direction leads to liver. Once liver

found, feed upon liver tissue.

what kind of parasites rely on affinity between surface molecules of host tissues and themselves?

parasites that are not highly mobile

what is an example of a parasite with high affinity for the host site? how does it do this?

toxoplasma gondii

Parasite initially binds intestinal epithelium of intermediate host via .

- Toxoplasma microneme protein 2 (mic2) binds to host protein

- Intracellular Adhesion Molecule-1 (ICAM-1). Leads to diapedesis (squeezing between epithelial cells) allowing the parasite to infect macrophages and dendritic

cells.

- Invasion with apical complex (actin/myosin motors)

- Phagocytic cells further disseminate parasite throughout host.

explain the mechanism controlling host specificity of toxoplasma gondii

Recall - definitive hosts of T. gondii are felines.

Several intermediate hosts (including mice).

the buildup of concentration of linoleic acid inside the cat causes toxoplasma to reproduce-> oocysts are able to be released into the environment

QOTD: List 2 reasons why parasites have

evolved to have site-specific adaptions.

1. access a particular tissue of the body

2. may not be super motile, so they need a way to have high affinity for the organ

what is a nematode?

round worm

what is a cestode?

tape worm

what is a trematode?

fluke/flatworm

how do intestinal parasites hold their positions within their host tissues?

Invasion of epithelial linings

◦ Adhere with adhesive disks or hook

on with proboscis or scolex

how do trematodes hold their positions within their host tissues?

Use of strong, ventral suckers

◦ Sexual reproducers - males and females form pairs

and male's powerful

musculature (coupled

with suckers)

explain plasmodium flaciparum adherence in the vasculature of the host

Inside erythrocytes, the parasite produces the protein Plasmodium

falciparum Erythrocyte Membrane Protein 1 (pfEMP1).

Along with other parasite and host proteins, causes formation of "knobs" that bind to capillary epithelial cells.

P. falciparum avoids transport to the spleen, where parasite- infected cells might be detected and destroyed.

Parasite-infected erythrocytes may accumulate in the capillaries of the central nervous or renal system, resulting in much of the severe pathology associated with P. falciparum .

provide an example of an ectoparasite adaptation to maintain positioning

Example: Pennella balaenopterae (parasitic copepod)

◦ External segmentation lost

◦ Locomotory appendages largely vestigial

◦ Females have developed anterior anchors

◦ Each anchor bifurcates, allowing her to embed tightly into blubber