DD Intro to Human Parasites: Protozoa and Helminths

Question 1

importance of infectious diseases for human health from a global perspective.

Answer 1

○ Infectious diseases cause 1/3 of all deaths
○ Infectious diseases cause 48% of all deaths in people under 45

Most of the infectious deaths could be prevented or treated

Question 2

How do protozoa and worms differ with regards to replication?

Answer 2

Most protozoan parasites can replicate and increase their numbers in humans.

In contrast, many worms undergo development but DO NOT DO NOT replicate in humans

Question 3

definitive host

Answer 3

species in which sexual reproduction occurs.

Question 4

intermediate hosts.

Answer 4

Hosts in which sexual reproduction does not occur

Question 5

taxonomic groups of protozoan parasites:

Answer 5

1. Amoebas
   
   2. Flagellates
   3. Ciliates
   4. Sporozoa
   5. Microsporidia

Question 6

taxonomic groups of helminths/worms/metazoan parasites:

Answer 6

1. Roundworms/Nematodes
   
   2. Flatworms/Trematodes/Flukes
   3. Tapeworms/Cestodes

Question 7

Which parasite is an important paradigm of helminthic infxn? Protozoan infxn?

Answer 7

Schistosomiasis as an important paradigm of helminthic infection

Malaria as an important paradigm of protozoan infection

Question 8

The life cycle of schistosomes

Answer 8

1) Humans poop/pee → schistosome eggs are in there
2) Eggs touch fresh water → hatch and release “miracidia”
3) Miracidia infect snails →
4) Develops as sporocysts in snails + generate successive generations (notice how replication event is outside of humans?)
5) Free-swimming cercariae are released by snail into the water
6) Humans go in the water → cercariae penetrate hu skin → initiate infxn
7) Cercariae lose their tails during penetration (hehe) and develop into schistosomulae in the tissues of the human host
8) Schistosomulae gain access to the circulation →
9) Migrate to the portal blood → mature into adult worms →
10) Male/female pair up → migrate to the mesenteric veins or to the venous plexus of the bladder → where mating occurs → eggs are released into intestine or urinary bladder
11) Eggs are released into environment (possibly water where they can start the cycle again!)

Question 9

What is the most important parasitic disease?

Answer 9

Malaria

-It affects > 1 billion people and causes 1-3 million deaths/year

Question 10

Four species of protozoa that cause malaria in humans:

Which causes the most deaths?

Answer 10

In genus Plasmodium:
- P. vivax, P. ovale, P. malariae, and P. falciparum.

P. falciparum sucks the most → causes most of the deaths.

Question 11

Life cycle of malaria parasites.

Answer 11

1. Infected mosquitos bite humans → inject sporozoites into the blood.
2. The asexual phase of development (schizogony) occurs in humans.
3. Sporozoites of all malaria parasites can infect liver cells and replicate
4. After primary replication in the liver (notice how replication is in the human?), merozoites are released from hepatic cells into the blood→ infect erythrocytes → undergo additional asexual replication.
5. Gametes (macro- and micro-gametocytes) are formed in infected erythrocytes.
6. Now gametes in infected humans are transmitted TO mosquitos
7. The sexual phase of development (sporogony) occurs in the infected mosquito where the gametes fuse in the intestine to form zygotes.
8. Development of the parasite in mosquitoes eventually leads to the production of sporozoites in the salivary gland.

Question 12

How does acquired immune response help malaria infxn?

Answer 12

After #8. Development of the parasite in mosquitoes and production of sporozoites in the salivary gland.

you are back at square 1 - Introduction of the sporozoites into a susceptible human by the bite of an infected mosquito initiates a repetition of the life cycle of the parasite.

But this time, acquired immune responses help to control the development of malaria parasites (the picture has it all)