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