Pathogenesis And Clinical Aspects Of Tropical Infe
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FOODBORNE HELMINTHS: FASCIOLA AND TAENIA SPP. (24/02)
INTRODUCTION
• Parasites = organisms that, in order to complete their natural life cycle, must live temporarily
or permanently in or on another living organism (the host), from which they derive nutrients
• Most human parasites belong to the protozoa (unicellular) or helminths (worms)
HELMINTHS AND THEIR LIFE CYCLE
• There are 4 main types but this lecture will mainly focus on Fasciola (fluke) and T. solium
(tapeworm)
• Helminths have complex life cycles: eggs, larvae, adult worms
• Definitive host: harbors adult stage; production of eggs or larvae that leave the host via
feces, urine, etc.
• Intermediate host/environment: development of infective larvae, with or without (asexual)
multiplication; infection of host, through skin or orally, etc.
FOODBORNE HELMINTHS
• Infection with foodborne helminths can happen through fish consumption, contaminated
plants, water, eating of wild meat, …
• Consumer: stage where people get infected
• It’s mainly zoonoses: animal as food source/contaminator of food source
o But also often an important environmental factor
, • One Health approach!: Is the idea that the health of people is connected to the health of
animals and our shared environment
FASCIOLA
INTRODUCTION
• Taxonomy: it belongs to the class of the Trematoda (flukes) and
the subclass of the digenea (flukes with an indirect life cycle)
• It’s a liver fluke
• Causes disease in humans: Fasciolosis
o Historically fasciolosis was considered an animal disease
• It was added to the list of neglected tropical diseases (NTD) by
WHO in 2010
• 2.6 million are affected and >180 million at risk
• It also has an economic impact on livestock sector
TRANSMISSION
LIFE CYCLE-DEVELOPMENTAL STAGES
• Cattle and sheep are definite host: when infected
they pass yellow eggs in the feces which are
unembryonated (a)
• For embryonation they need an aquatic
environment (b)
• Miracidium (which is inside the egg) will now hatch
from the egg and actively seek a snail (c)
• Miracidia are free-living in the water will actively
penetrate the snail
• Next: Sporocyst (d)→ redia (e)→ cercaria (f)
• Cercaria are released from the snail host in the
water and will seek vegetation where they encyst and transform into metacercaria (don’t
have a tail anymore)
• Humans can become infected as definitive host: they penetrate the intestinal wall and
migrate to the liver → in the liver parenchyma juvenile F. hepatica (first stage in final host)
can be found → adult flukes in bile duct
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