parasitology lecture 5: a parasite's way of life

what is a parasite life cycle?

a sequence of developmental events that occur over the course of an organism's lifetime

for a parasite, it requires at least one host and, for many, more than one host

In what fashion do life cycles occur?

a sequential fashion

what were the earliest infectious agents recognized in humans and animals?

helminths

what are some examples of the ancient helminths found?

Ancient Egyptian medical chronicles (1500 BC) describe

nematodes.

◦ Most likely hookworms and Ascaris .

In 400 BC, Hippocrates described what were likely

tapeworm segments in feces.

In 180 AD, Greek physician Galen noted positions of

helminth infections in intestines.

what was the worm believed to be the serpents around the medical staffs?

Dracunculus medinensis

◦ The guinea worm believed

to be the serpents around

the staffs.

◦ Removal of the worm.

who was considered the father of microbiology and why?

Antony Van Leeuwenhoek

◦ Dutch craftsman that was a skilled

lens maker.

◦ Considered Father of Microbiology

◦ 1681-described Giardia in detail.

who was considered the father of parasitology and why?

Francesco Redi

◦ Italian physician

◦ Considered Father of

Modern Parasitology

◦ 1684-his book described

over 100 different

animal parasites.

what was the first demonstration of parasite transmission by mosquito?

Elephantiasis, caused by filarial worms, was the first

parasite shown to be transmitted by mosquitoes.

what was the first parasite shown to be transmitted by an arthropod?

Smith and Kilbourne

first to show a protozoan

parasite (Babesia bigemina )

can be transmitted by an

arthropod (tick).

what are some characteristics of a direct life cycle?

Requires only a single host.

Even though these are relatively simple, the life

cycles are not always conventional.

Can reinfect the same host at different stages.

what is an example of the parasite infecting the same host but at different stages?

adult Ascaris may be residing in a person's intestines, and that same person may

then ingest eggs from contaminated water

what is an example of a direct life cycle?

Ancylostoma duodenale (and other hookworms)

Nematode

Adult worms are

only ~1cm long

what is another example of a direct life cycle?

Enterobius vermicularis

(pinworm)

Nematode

describe the hookworm life cycle

1. eggs in feces

2. rhabditiform larva hatches

3. development to filariform larva in environment

4. filariform larva penetrates skin

5. larva exit circulation in the lungs, they can then be coughed up and swallowed into the intestines

describe the pinworm life cycle

1. eggs on perianal folds

2. embryonated eggs ingested by humans

3. larvae hatch in small intestine

4. adults in lumen of cecum

5. gravid female migrates to perianal region at night to lay eggs