Life-Cycles

Question 1

Describe the life cycle of Trypanosoma brucei. How does the parasite adapt
to acquired immunity in the vertebrate host?

Answer 1

1) Tsetse fly injects metacyclic trypomastigotes into skin tissue
2) parasites enter lymphatic system and pass into bloodstream
3) bloodstream trypomastigotes multiply by binary fission (slender form)
4) tsetse fly infected during bloodmeal (stumpy form)
5) develop to procyclic trypomastigotes in gut
6) migrate to salivary glands, transform to epimastigotes (continue multiplying)
7) transform to metacyclic trypomastigotes ⇒ injected in host

long slender form has vsg-switching ⇒ adaption to aquired immunity via antigen variation

Question 2

Describe the life cycle of Trypanosoma cruzi

Answer 2

1) triatome bug bites human and leave feces next to bite
2) scratching get’s trypomastigotes into blood stream
3) macrophage and muscle cell invasion
4) amastigote transformation (asexual replicate life stage)
5) trypomastigote transformation free in blood again
6) triatome bug takes up parasite
7) conversion to epimastigote followed by trypomastigote conversion in bug gut

Question 3

Describe the life cycle of Leishmania in the vector and mammaiian host

Answer 3

1) Sandfly injects promastigotes
2) attach to phagocytes, get taken up, proliferate as amastigotes and lyse the cell to reinvade other host cells or be taken up again by another sandfly, proliferating there attached to the gut wall
3) conversion to promastigotes (extracellular in vector, intracellular in host)

Question 4

Describe the life cycle of Entamoeba

Answer 4

• Entamoeba transfered only between humans, fecal-oral
• 4-nuclei cyst (Dauerform) is infectious
• trophozoit bursts out of cyst, starts eating
• have multiple nuclei ⇒ single nucleus amoeba splits of
• multiplies and encysts

Question 5

Describe the life cycle of Toxoplasma

Answer 5

• oocysts are taken up through contaminated ground or raw flesh
• cysts transform to tachyzoites and proliferate in host gut
• Tachyzoites travel to muscle and neural tissue and encyst to bradyzoites
• infect cats when host gets consumed (e.g.birds)
• develop into unsporangulated oocyst and are passed through cat feces (sporangulate after 1-5 days ⇒ infective)
• infectious stage for humans and others through contaminated water, food, soil
• convert into static tissue cysts in heart (problematic), brain, eye etc. and can convert back to tachyzoites

Question 6

Describe the life cycle of Ascaris lumbricoides

Answer 6

1) embryonated eggs ingested with contaminated food
2) L2 larvae hatch in small intestine
3) larva penetrate intestinal wall, enter blood stream and travel through heart and liver to lungs
4) conversion to L3 and break out into alveolus, actively migrate up the bronchi, are coughed up and swallowed again
5) grow into adults in small intestine
6) mate and produce eggs
7) unembryonated eggs passed through feces
8) in environment, eggs embryonate within 3 weeks

Question 7

Describe the life cycle of Onchocerca volvulus

Answer 7

1) blackfly bite transmits L3
2) mature into adults in subcutaneous knot
3) adults produce microfilariae (found in skin and lymphatics of connective tissues)
5) filariae taken up by Blackfly
6) penetrate midgut and migrate to thoracic muscle
7) develop to L3, migrate to head and proboscis

Question 8

Describe the life cycle of Wucheria bancrofti.

Answer 8

1) mosquito injects L3 larvae into skin
2) develop to adults (reside in lymphatics)
3) produce microfilariae (migrate into lymph and blood channels)
4) filariae ingested by mosquito⇒ penetrate mosquitos midgut and migrate to thoracic muscles
6) develop to L3 larvae
7) migrate to head and proboscis

Question 9

Describe the life cycle of Paragonimus westermani

Answer 9

1) infection by eating undercooked crustacean with parasite metacercariae
2) metacercariae excyst in the duodenum (zwölffingerdarm)
3) penetrate through intestinal wall, travel into the lungs, encapsulate and develop into adults - lay eggs (can also invade other tissues, but lifecycle can not be completed since eggs cant leave)
4) eggs excreted unembryonated in the sputum, or alternately swallowed and passed with stool
5) eggs embryonate in the external environment
6) miracidia hatch and invade the first intermediate host
(snail)
7) Miracidia go through several developmental stages inside the snail
8) cercariae emerge from snail⇒ invade second intermediate host (crustacean) encyst and become metacercariae⇒ infective stage for mammalian host

Question 10

Describe the aquatic part of the life cycle of Schistosoma spp.

Answer 10

eggs excreted via urine or feces⇒ hatch releasing miracidia⇒ swim and infect snail (intermediate host) ⇒ 2 different sporocyst stages in snail⇒ develop into cercariae⇒ released from snail, free swimming, can penetrate human skin

find host via lipids and fatty acids⇒ body temperature irrelevant