Parasitology - Introduction and Protozoa

What is a parasite?

one who lives at another's expense

What hosts do parasites prefer?

Free living hosts

What is hyperparasitism

When a parasite has a parasite

What is the complex definition of a parasite?

an organism which is in continuous, intimate association with another organism but it is also metabolically dependent

What is a “direct” parasite lifestyle?

transmission of the parasites from one host to the next host occurs among members of the same species

What word describes a parasite which has one host (no intermediet hosts)

Monoxenous

What is an indirect life style?

when a parasite needs two or more different host species to complete its life cycle.

What is a definitive host?

host where parasites reach sexual maturity (sexual reproduction occurs)

What is an intermediate host?

host required for parasite development but where parasites do not reach sexual maturity.

Describe protozoa

unicellualar, eukaryotic organisims

Are protozoan parasites intracellular or extracellular?

both

What is a “resting stage” of a parasite?

cyst or spores

What is a metazoan cell?

a cell that belongs to a multicellular animal

How many nuclei do protozoans have?

Typically one

Which species of protozoans have 2 nuclei?

Ciliophora

Which species of protozoan has more than two nuclei?

Opalinata

Do protozoans have organelles?

Yes

How do protozoans asexually reproduce?

asexually via binary fission

How do protozoans sexually reproduce?

Fusion of the two sexual individuals, male and female

What is protozoan conjugation?

two stages fuse for a short while with each other and exchange DNA

How do protozoans move?

cillia, flagellum, pseudopods, gliding

What is the internal structure of flagellum and cillia?

an axoneme

Describe the structure of an aaxoneme

9 pairs of microtubules arranged in a circle

2 single microtubules in the centre

What class of amoebozoans typically demonstrate gliding locomotion?

Apicomplexa

Describe Giardia spp.

What are the two life stages of Giardia spp.

trophozite and cyst

Describe the Giardia spp. cyst

Oval, 4 nuclei

Describe the Giardia spp. trophozite

Pear shaped, Two nuclei, 4 pairs of flagella and 2 median bodies;

What is a median body?

a storage structure found in some protozoa (especially Giardia).

What occupies the ventral surface of a Giardian trophozite?

a ventral disk

What is the life cycle of giardia spp.?

Direct

How do you become infected by Giardia spp.?

ingestion of cysts with contaminated water or food

What is Excystation

where a parasite exits a cyst and becomes an active, feeding form again.

What triggers Excystation in Gastrula spp.?

triggered by exposure of cysts to gastric acid during their passage through the stomach and pancreatic secretions

What is encystation

When a parasite forms a protective cyst

When do Giardia spp. undergo encysation?

after exposure to the bile salts and pH

What is arguably the most successful parasite?

Toxoplasma gondii

What can Toxoplasma gondii infect?

All warm blooded animals

What makes Toxoplasma gondii cysts so sucessful?

can survive for up to 12- 18 months and are resistant to common disinfectants

can survive within immune cells (macrophages)

What are the effects of Toxoplasma gondii infection?

abortion/severe pathology in foetus

fatal for sea mammels and marsupials

change behaviour of intermediet hosts

severe pathology in immunocomprimised individguals

What is the definate host of Toxoplasma gondii

cats

What is the intermediet host of Toxoplasma gondii

Any warm blooded individgual

What cells are Toxoplasma gondii capable of infecting?

virtually any nucleated mammalian or avian cell

What is sporogony?

the stage where a parasite forms multiple infectious spores from a zygote.

Where does sporogony occur for Toxoplasma gondii?

in the enviroment

How do intermediate hosts become infected with Toxoplasma gondii

ingest sporulated oocysts with food/water;

Where does toxoplasma gondii?

What parasites immunosuppressant properties are being used to suppress autoimmune disease

What is included within phylum apicomplexia?

toxoplasma and plasmodium sp.

How do Toxoplasma gondii and Plasmodium spp sexually reproduce?

fusion of gamettes

How do Ciliophora sp. sexually reproduce?

conjugation

What protein is involved in gliding?

actomyosin

Where is gliding typical?

Plasmodium and toxoplasm sp.

What is the purpose of actomyosin?

secreted to achieve gliding locomotion

Which species sexually reproduce via conjigation?

Those with two nuclei

In conjugation which nuclei fuse?

The micronuclei

What is the structure which consists of a plasma membrane surrounding an axoneme

flagella

Describe the structure of a flagella

a plasma membrane surrounding an axoneme

What type of protozoan is this likely?

cilliate

What type of protozoan is this likely?

Ameoba sp.

How do Giardia spp. acheive locomotion?

flagella

Are giardia spp. zoonotic or not zoonotic?

zoonotic

What causes excytation in the small intestine of giardia cysts?

gastric acid and pancreatic secretions

How does an individual become infected with giardia spp.?

consumption of cysts in water or food

How do giardia trophozoites repoduce?

binary fission

Why do low pH and bile salts signal to giardia sp to encyst?

These are signals that the giardia are almost out of the host

What is the most successful parasite?

toxoplasma goondi

What can toxoplasma goondi oocysts survive

12-18 months, exposure to disinfectant

How can toxoplasma goondi be killed?

Temperature outside the range of 12-65 degrees

Why is toxoplasma goondi dangerous for mothers?

it is trans placental, can cause abortion/misarrange

Where is toxoplasma goondi found in the definitive host?

small intestine

Where is toxoplasma goondi found in the intermedeit host?

essentially anywhere

Describe the sporogony of toxoplasma goondi

occurs 1-5 days after exposure into enviroment

What is sporogony

asexual reproduction from cysts producing infective cells

How does toxoplasma goondi exit the cells of the intermediate host?

burst inside the host cell as a result of mass replication

What genus of mosquitoes transmits the protozoan plasmodium

Anopheles