Biological Sciences 318 - Parasitology Lab Platyhelminthes 2.
Parasitology lab notes
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Transcript of Parasitology lab notes
Lab 5: Trematodes!
Flukes
Trematodes: General Info• Phylum: Platyhelminthes – the
flatworms• Unsegmented, leaf-like bodies• 2 subclasses: Monogenea
(monogenetic trematodes) & Digenea (digenetic trematodes)
• Monogenetics usually parasitize fish, reptiles & amphibians
• Digenetic trematodes parasitize wild & domestic animals & humans
Trematodes: Morphological Features
• Mouth connects to pharynx, leads to esophagus, bifurcates into 2 ceca
• No anus: releases cecal contents back through mouth into tissue it infects
• Cecal contents can be seen in histopathologic section and are colloquially referred to as “fluke puke”
• Also possess and acetabulum, or ventral sucker – holdfast organ not associated with feeding
• Near anterior end, mouth is surrounded by muscular oral sucker
Trematodes: Reproduction
• With exception of schistosomes (blood flukes) all flukes are hermaphroditic
• Each fluke possesses both sex organs
• Self-fertilization usually takes place, but cross-fertalization can also occur
Flukes: General Life CyclePart 1
• Operculated eggs pass in feces• Egg comes in contact w/ water – hatches and becomes
motile miracidium• Miracidium seeks out and penetrates skin of aquatic snail
(1st intermediate host) • In snail, develops into sporocyst – sack in which next
stage redia develops• Each sporocyst contains many redia, each redia many
cercaria• Cercarial stage usually has a tail and will emerge from
snail & swim in water.
Flukes: General Life CyclePart 2
Cercarial stage takes 1 of 3 paths:1. Cercaria may directly penetrate the skin of definitive
host2. Cercaria may attach to vegetation, lose its tail, secrete a
thick cyst wall around itself and develop into a metacercaria. Vegetation w/ attached metacercaria is ingested by definitive host
3. Cercaria may lose its tail, penetrate the 2nd intermediate host, secrete thick cyst wall & become metacercaria in 2nd intermediate host. In this case, the 2nd intermediate host w/ encysted metacercaria is ingested by primary host
Fluke: Life Cycle
Identification of Trematode Ova
• Singly operculated oval shaped eggs
• Very distinctive
Dicrocoelium dendriticum: Lancet Fluke
• Definitive hosts: sheep, goats & cattle
• Tiny ~ 6-10mm long• Live in the fine braches of bile duct
– can produce biliary hyperplasia• Produces brown, embryonated,
operculated ova• Intermediate hosts: snail then ant• Can be zoonotic if eat chocolate
covered ants!• Found on fecal sedimentation or in
bile ducts at necropsy
Fasciola hepatica:Liver Fluke
• Definitive hosts: ruminants, cattle• Most pathogenic fluke of cattle in US,
very common• Lives in liver & bile ducts, causes
liver rot• Eggs are large & heavy, should use
fecal sedimentation to find• Intermediate host: snail – develops
into metacercaria on vegetation• Can be zoonotic if eat fress watercress • Can be found as spurious eggs in dog
& cat feces (coprophagy)
Fascioloides magna:Deer Liver Fluke
• Definitive host: White-tailed deer
• May also use sheep, cattle & pigs as incidental hosts
• Adults found in liver parenchyma
• Adults are Unique in appearance
• Eggs may be found on fecal flotation of deer feces, but not incidental hosts feces
Platynosomum fastosum:Lizard-poisoning Fluke
• Definitive host: cats• Intermediate hosts:
snail then lizard• Seen frequently in
Southeastern US (FL)• Adults found in liver,
gall bladder, bile ducts• Signs: v/d, icterus, &
anorexia, fever, death
Nanophyetus salmincola:Salmon-poisoning fluke
• Definitive hosts: dogs, cats, wild carnivores
• Intermediate host: snail then fish (trout & salmon)
• Signs begin 5-7 days after ingestion
• Fluke causes minimal damage, severity is due to rickettsial parasite carried on fluke – causes damage to capillaries, rash, fever, fatal enteritis in dogs
• Zoonotic potential if eat undercooked fish
Paragonimus kellicotti:Lung fluke
• Definitive hosts: dogs & cats• Intermediate host: snail, crayfish• #1 most common small animal fluke• Can be found in float of feces or
sputum• Adults live in lung parenchyma but
are known for getting “off track” – can end up in brain, other organs
• Immature flukes encyst and penetrate intestinal wall, migrate to diaphragm & penetrate into pleural cavity – mature in lungs
Schistosomes of wild birds:Swimmer’s Itch
• Swimmer’s Itch or schistosome cercarial dermatitis caused by cercarial stage of schistosomes of migrating aquatic birds
• Cercaria penetrate skin of human, causing severe pruritic dermatitis.
• Only true zoonotic degenetic fluke