parasitology lecture 9: parasite's way of life pt. 5

why are high reproductive rates common for many parasites?

High investment in reproduction common when chances of progeny survival low.

High egg-laying capacity

why does being monoecious provide benefit for egg-laying capacity? what parasites fall into this category?

Cestodes and some trematodes (flukes) are monoecious.

◦ Proglottids of tapeworms equipped with

both testes and ovaries.

◦ Don't have to rely on both sexes being

present.

what kind of parasities use both sexual and asexual reproduction?

apicomplexans

what falls under sexual reproduction?

gamete formation

what falls under asexual reproduction?

sporogony and merogony

what are used to bring parasites into physical contact once they are at the same anotomical site?

chemoattractants

what are the three factors that can complicate understanding of parasite transmission?

- coinfection with other parasites

- multiple modes of transmission

- abiotic and biotic factors impacting transmission of parasites released by hosts

provide an example of coinfection with other parasites

Mice co-infected with Plasmodium and trematodes tend to produce more Plasmodium gametocytes → higher infectious load to mosquito → pass on more parasites to next mouse

what are some abiotic factors that can impact transmission?

temperature, pH, salinity

what are some biotic factors that impact transmission?

likelihood of hyperparasitism, predation on eggs/larvae, or encountering/entering an inappropriate host

what is the portal of exit?

Portal of exit - the anatomical structure through which

propagules move.

◦ For GI parasites, usually the anus

◦ For vector-borne parasites, usually the vector for both

ingress and egress

◦ Sexually transmitted parasites, ingress and egress via genital contact.

is the portal of exit always the same structure or tissue as where the parasite enters?

no

what is an example where the portal of exit is different from where the parasite entered?

Hookworm and schistosome larvae can burrow through

skin → intestine → eggs released in feces and/or urine

describe the trypanosome brucei developmental stages

change between slender and stumpy forms (the stumpy form is infectious to the tsetse fly)

Regulated by parasites themselves by monitoring their density in human blood blood.

Like quorum sensing, slender forms release Stumpy Induction Factor

(SIF).

◦ Threshold level of SIF ➔ slender to stumpy form

◦ Tsetse fly infection ➔ human immune system clears most parasites

➔ parasite surface

protein change to

increase parasite

numbers again

what is hypobiosis?

the cessation of development, during which the organism remains able to reinitiate

development in response to specific environmental

stimuli.

what are some examples of factors that can cause hypobiosis?

Stimuli are factors such as temperature, soil

moisture, changing photoperiod, other abiotic

factors.

◦ Hookworms and strongyloids good examples that can

undergo hypobiosis.

how is plasmodium falciparum an example of a parasite that must adapt to different environmental conditions?

they transition between mosquitoes and humans

Pre-made mRNA molecules held quiescent in gametocytes in P granules.

◦ Environmental changes between host induce translation for

needed proteins for new developmental stages.

• Drop in temperature

• Rise in pH

• Presence of xanthurenic acid

provide an example of differential gene expression during development

Many plants release a hormone through their roots called

strigolacone, which attracts fungi that establish a mutualistic

relationship.

► Striga seeds have around a dozen different strigolacone receptors.

► When the receptors bind the released hormone, it triggers

germination of the parasitic flowering plant.

QOTD: How do Trypanosoma brucei parasites

regulate a change between slender blood

forms and stumpy blood forms (and back

again)?

change between slender and stumpy forms (the stumpy form is infectious to the tsetse fly)

Regulated by parasites themselves by monitoring their density in human blood blood.

Like quorum sensing, slender forms release Stumpy Induction Factor

(SIF).

◦ Threshold level of SIF ➔ slender to stumpy form

◦ Tsetse fly infection ➔ human immune system clears most parasites

➔ parasite surface

protein change to

increase parasite

numbers again