Vl 6 Toxoplasma

Question 1

Describe the 3 transmission risks of Toxoplasma? What are the respective infectious parasite stages?

Answer 1

• cat feces (Oocystes)
• contaminated water and vegtables (Oocystes)
• meat of infected animals (Bradyzoites)

Extra:
-blood transfusion or organ transplantation (Tachyzoites)

-transplacentally from mother to fetus (Tachyzoites)

Question 2

What is an apicoplast, how do we think it was acquired by apicomplexan parasites and how can we exploit this knowledge for therapy?

Answer 2

apicoplast: essential reduced plastid organelle (synthesis of fatty acids, isoprenoid, heme)
- may have been acquired by secondary endocytosis of the protozoa taking up a procaryot (cyanobacterium) and then an algae (endosymbiosis)

⇒ combination of antibiotics targeting the apicoplast is sufficient

Question 3

Which events can trigger reactivation of Toxoplasma bradyzoites in chronic infections?

Answer 3

• host gets immunosuppressed (e.g. AIDS/ HIV)
• when there is no immune response against the tachyzoites anymore
• Lack of immune responses ⇒ redifferentiation into tachyzoites by switching on tachyzoite-specific genes

Question 4

Describe the life cycle of Toxoplasma

Answer 4

• 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 5

Describe the mechanism of Toxoplasma tachyzoite locomotion and host cell invasion.

Answer 5

• locomotion via gliding motility, (actin-myosin contractions) + secretion of “Schleimspur”

Invasion:

• Attachment via microneme proteins
• Rhoptry protein secretion
• Junction formation
• Entry via actin-myosin motor
• Parasitophorous vacuole formation (formed from host cell membrane)
• closing of junction

Question 6

Why is Toxoplasma a neglected infection?

Answer 6

• generally silent infection
• doesn’t cause severe symptoms in immunocompetent individuals
• we can not treat encysted bradyzoites