MICROIMM Lec 27: Protozoans

Explain the name "malaria"

mal = bad

aria = air

How is malaria transmitted?

Passed from one human to another by the bite of an infected mosquito

What parasite causes malaria?

Plasmodium parasites

What type of parasite is Plasmodium parasites?

Obligate; cannot survive independently as a free-living organism

How many hosts does Plasmodium parasites require?

2

List the 2 different hosts required for lifestyle

Vertebrate host

Arthropod vector

Asexual/sexual reproduction occurs in the vertebrate hosts

Asexual

Asexual/sexual reproduction occurs in the arthropod (mosquito) vector

Sexual

Which is the definitive host?

Mosquito

There are more than ___ species of Plasmodium

100

List the 4 species of Plasmodium that have long been recognized to infect humans in nature

P. falciparum

P. vivax

P. ovale

P. malariae

Which species is known to cause the most harm/death?

P. falciparum

Which region is P. falciparum most prevalent in?

Africa, tropical areas

Which two species are very similar in terms of parasite function?

P. vivax and P. ovale

How do P. vivax and P. ovale differ?

Geographic locations + type of blood group of host

Which regions are P. vivax found in?

Asia, Latin America, a bit in Africa

Which regions are P. ovale found in?

West Africa

Define tertian cycle

fever that occurs every 48 hours, or every third day

How is P. malariae different from the others?

Can cause chronic disease + slightly different life cycle

What is the fever cycle for P. malariae?

Quartan (every 72 hours)

P. knowlesi parasite travels from mosquito to which animal?

Macaques

What is the fever cycle of P. knowlesi?

Much shorter (24 hours)

Human malaria is transmitted only by mosquitoes of the genus ______

Anopheles

Human malaria is transmitted only by female or male mosquitoes?

Females

Of the ~430 Anonpheles spp., only ____ transmit malaria (ie. vectors) in nature

30-40

What do female mosquitoes need to eat for egg production?

Blood meal (+sugar)

What do male mosquitoes eat instead of blood meals?

Sugar

How long do males live for?

1 week

What nutrients do females require from blood meals?

- Iron

- Sugar

Where do females lay eggs?

Standing freshwater

What is the function of the proboscis?

Used by female mosquito to pierce skin, take up blood meal

What is the function of the salivary glands?

Contains many chemicals + proteins, saliva is injected at the site of blood meal

What is the purpose of saliva being injected at the site?

Numbs the site, thins the blood to prevent clot

What is the function of the crop area?

Storage area for sugar molecules from blood meal

What is the function of the Dorsal diverticulum?

digestion of the sugar meal

What is the function of the Anterior midgut junction organ?

Specialized function to help separate between sugar and blood meals

Which organ/pouch do blood meals get sent to?

Midgut

What is the Malpighian tube?

Like kidneys: helps with water balance/hydration

Do mosquitoes have a closed/open circulatory system?

Open

What is hemolymph?

Circulatory fluid in invertebrates, functioning like blood in vertebrates and circulating through their open circulatory system

Where does the mosquito pick up gametocytes of the parasite?

In peripheral blood (capillary) of the infected individual

Are macrogametocytes female/male?

Female

Are microgametocytes female/male?

Male

Does the mosquito pick up macro or microgametocytes?

Both female and male

Is the mosquito affected by the parasite?

No

What triggers a change in the gametocytes after ingestion with the blood meal?

Change in environment (from human to mosquito); different temperature, chemicals, etc

What event is triggered?

Exflagellation

Define exflagellation

Sperm comes out of male gametocytes

Where does fertilization occur in the mosquito's body?

Stomach

What is the ploidy of the zyote?

Diploid

What is the ookinete?

the motile zygote; formed after replication

What is the ploidy of the ookinete?

Tetraploid

Where does the ookinete move to?

Migrates between epithelial cells, to the lining of the stomach wall

Define sporogony

Asexual reproductive process of spore formation; mitosis

What is the ploidy of the spores?

Haploid

What structure does sporogony take place in?

Oocyst: formation occurs in wall of stomach

Where do the sporozoites travel to once division causes the oocyst to rupture?

Hemolymph

Which area of the mosquito body do the sporozoites travel to?

Salivary glands --> duct

What is the infective stage of the parasite?

Haploid sporozoites

Is the process that makes more copies of sporozoites asexual or sexual?

Asexual

Sporozoites are injected into humans with _____

mosquito saliva

What are the only cells that sporozoites can invade?

Hepatocytes (liver cells)

What triggers the conformation change from sporozoite to cryptozoite?

Change in environment

Are cryptozoites infective forms?

no

Cryptozoites undergo sexual/asexual reproduction in hepatocytes

asexual

Define schizogony

Asexual reproduction by multiple fission

During schizogeny, the schizont do not undergo _____. The progeny are all still attached

cytokinesis

When does cytokinesis occur?

When the hepatocyte ruptures

Define schizont

a cell that divides by schizogony to form daughter cells; the mass of cells

What is the name of the blood state of the parasite, after it leaves the liver?

Merozoite

What cells do the merozoites infect?

RBCs

Define invagination

the action or process of being turned inside out or folded back on itself to form a cavity or pouch.

What triggers the invagination of RBCs?

Merozoites invade RBCs

What stage forms when the merozoite invades the RBCs?

ring stage

Describe how the RBC changes after ring stage

- Own proteins are starting to be expressed

- RBC appearance changes

What causes the RBCs to become sticky and stick to the endothelium?

proteins and receptors expressed by the parasite on the RBCs

What happens if the RBCs become sticky?

Can create blockages in the vasculature

What happens to the merozoites after they are released from the RBCs?

Back into circulation; goes onto infect more RBCs

What does the parasite like to break down hemoglobin for?

For amino acids + sugar source

Explain how anemia is caused

Breakdown of RBCs

Can merozoites go back and infect the liver?

No

In ___ % of the merozoites, formation of male/female gametocytes is triggered

5-10%

What is the impact of mosquitoes taking up merozoites in their blood meal?

No impact, simply digested

Merozoites are pocketed inside a _____ upon entering the RBC

vacuole

What is the ring stage?

Early stage of trophozoite inside RBC

The trophozoites divide sexually/asexually to form the schizont in the RBCs

asexually

How many sporozoites are formed inside the oocyst?

thousands

When does the brief diploid phase occur?

In the mosquito

Which is the final/definitive host, the human or mosquito?

Mosquito

What phase is it briefly tetraploid?

Ookinete

What are the common symptoms of malaria?

fever, fatigue, muscle aches, nausea, and headaches

How long does it take between infection to feeling symptoms?

a few weeks

Describe the blood smear diagnosis technique

Smear blood across glass slide; stain; recognize different species of Plasmodium under light microscope

You can narrow your species diagnosis according to...

geographic location

Once you've been infected multiple times by malaria, are you able to build up immunity?

yes

What age is very susceptible to malaria?

children under 5

Explain in utero malaria infection

Vertical transmission: from mother to baby

When does transmission occur throughout the preganancy?

Placenta works to protect throughout pregnancy (in utero), but can be transmitted during birthing process

What are pregnant mothers treated with to protect their unborn babies?

anti-malarials

It is considered vertical transmission if the infant is infected within the first __ days of life

7