parasitology platyheminths Flashcards
2 classes of platyhelminthes
cestoda (tapeworm)
trematoda (flukes)
platyhelminthes general characteristics
Flat mostly
Hermaphrodites
Definitive host diagnosis: eggs
At least 1 intermediate host
cestoda
phylum platyhelminthes (Flat mostly, Hermaphrodites, At least 1 intermediate host)
TAPEWORM
Segmented (can cut up and they will live), often long
Adults in host GI tract, almost always small intestine
Worms have no intestine, absorb nutrients across surface
Adults often nonpathogenic but people repelled
cestoda adults body divisions
Scolex (holdfast)
* Suckers and/or hooks NO MOUTH
* Attaches to gut wall
Neck
* Region of cell division, gives rise to proglottids
Proglottids (segments)
* Segments mature as they travel down the chain
* Oldest segments at the posterior end
cestoda segments
Each segment has at least one set of all reproductive organs of both sexes
Classified as:
* Immature
* Mature
* Gravid: contains fully developed eggs
Maturation occurs as moves down the chain
Common tapeworms shed gravid segments
Metacestode
General term for larval tapeworm
each species has its own name for this
INFECTIVE STAGE
cestodes general lifecycle
- eggs from adult tapeworm in definitive host passed into environment
- eggs eaten by intermediate host
- metacestode in intermediate host eaten by definitive host
taeniidae family
cestoda (platyhelmith)
Vertebrates are definitive and intermediate hosts
* Definitive host: predator mammal
* Intermediate host: herbivore or omnivore mammal—prey
Segments square to rectangular in shape
In general, larval stages (metacestode) most important, adults have little significance
Eggs passed from the host in segments
* Usually infection recognized from seeing segments
* Eggs seen infrequently in fecal exams
* Look the same for all family members
* Fecal flotation often negative because eggs in the segments
Two common/important metacestodes:
* Cysticercus
* Hydatid
non taeniidae families
cestoda (platyhelminths)
Invertebrate intermediate host, vertebrate definitive host
Cysticercus
metacestode (infective larvae) of taeniidae
Fluid-filled bladder
1 Inverted, invaginated scolex
1 Cysticercus produce 1 adult tapeworm in the DH
Infection/disease called cysticercosis
Hydatid
metacestode (infective larvae) of taeniidae
Fluid-filled bladder lines by a delicate parasitic membrane
Heads detach from wall into cyst fluid
Secondary cysts are formed as invaginations on the walls
1 hydatid produces up to thousands adult tapeworms
Infection/disease called hydatidosis
Taenia taeniaeformis
taeniidae (platyhelminths)
Common tapeworm of hunting cats
Eggs shed in segments
IH: Rodent, metacestode (Strobilocercus) in liver
CAT- MOUSE
Taenia pisiformis
taeniidae (platyhelminths)
Definitive host: canids
Egg shed in segments
IH: Rabbits
DOG- RABBIT
Echinococcus
taeniidae (platyhelminths)
Very small adults: 3-6 mm
* only 3 segments
Metacestode stage: Hydatid
Undergoes asexual reproduction
1 egg= Multiple scoleces formed
Potential for thousand of scolices to form
Echinococcus multilocularis
echinococcus, taeniidae (platyhelminths)
Life cycle
* Definitive host: Fox, sometimes dog, rarely cat
* Intermediate host: Small rodents, including lagomorphs
* Humans, dogs, and pigs: aberrant or accidental IH
* Metacestode: alveolar cyst (multilocular cyst)
Difficult to remove surgically because grows invasively
this is his fav parasite :)
Taenia saginata
5-15 m
Human/cattle
Cysticerci in bovine muscle (0.6 mm)
HUMAN-CATTLE
T/F? Tapeworms use their suckers for feeding?
F
What is the general name used for cestode larval stages?
metacestodes
Where will you find metacestodes?
intermediate host
Non taeniids
platyhelminths, cestodes
Belong to several different families (we’ll only see Dipylidiidae and Anoplocephalidae)
Use arthropod as intermediate hosts
Metacestode stage called cysticercoid: small cyst with invaginated single scolex, no fluid filled bladder
cysticercoid
Metacestode stage of non taeniids
small cyst with invaginated single scolex, no fluid filled bladder
Dipylidium caninum
non taeniid (cestode, platyhelminth)
15-70 cm
Most common tapeworm of dogs and cats in the US
Gravid segments released containing egg packets
Indirect life cycle, IH: fleas. Lice an uncommon IH
Flea larvae ingest egg packets, cysticercoid develop before flea become adult
Infection of DH follows ingestion of flea
PPP: 2-3 weeks
usually non pathogenic
diagnosis of Dipylidium caninum
but tapeworm segments in perianal area or around feces, where animal sleeps
eggs not seen on fecals
Dipylidium caninum - Clinical importance
Infection generally subclinical
Zoonotic, young children most likely to be infected, but very uncommon
Flea control critical to prevent reinfection
Ruminant and equine tapeworm life cycle
- Gravid segments released containing eggs
- Eggs are ingested by the IH: Oribatid mites in pasture (coprophages)
- Cysticercoid in mites
- DH infected when ingest infected mites while grazing
Anoplocephala perfoliata
equine tapeworm
Very common infection
Short tapeworm cluster at ileocecal junction
Usually asymptomatic
* Occasionally causes inflammation and ulceration
* In most severe cases associated with perforation, intussusception
Difficult to diagnose
* Surprisingly, segments not seen in manure
* Eggs usually not present on fecal exam
* Because diagnosis is difficult, horses routinely treated at least once/year
* Infection can’t practically be prevented
Moniezia benedeni
cattle tapeworm
non taeniiae
Moniezia expansa
small ruminant tapeworm
non taeniiae
ruminant tapeworms
Moniezia benedeni (Cattle) and Moniezia expansa (Small ruminants)
Very common infection
Diagnosis
* Frequently see segments in manure, especially young animals
* Eggs in fecal exams: shape square
M. benedeni: square
M. expansa: triangular
trematoda
platyhelminths
flukes
dignena
trematoda (flukes), platyhelminths
Leaf shaped
Unsegmented
1-2 suckers
Operculated eggs passed in feces: usually diagnosed with fecal exam
Usually 2 IH, first IH is ALWAYS a snail
trematode life cycle
- Most fluke eggs must hatch in water
- Larvae (miracidium) swim to specific snail host
- Some flukes use land snails, egg ingested by snail
- Asexual development in snail (sporocysts and redias)
- Next larval stage produced by snail (cercaria)
- Usually swims to pasture
- Become the infective stage (metacercaria) – sometimes in environment, sometimes in second IH
- Metacercaria can be ingested by a paratenic host
- DH is infected when ingests metacercaria
eggs > miracidium > sporocyst> redias > cercaria > metacercaria >DH
miricidium
1st larval stage of trematodes
swim to snail
Fasciola hepatica and Fascioloides magna
ruminant liver flukes
Adults in liver and bile ducts of host
Fasciola: ruminants, rabbits, humans, dogs, others
Fascioloides: white-tailed deer
Fasciola hepatica - Life cycle
trematode, platyhelminth
1. Adults release eggs that hatch in water
2. First IH: Lymnaeid snails (asexual reproduction)
3. Cercariae encyst on vegetation and become in metacercaria
4. Ingested by DH
5. Larval fluke migrate to liver
6. After several weeks enter bile and mature
PPP: 3-4 months
Fasciola hepatica - Clinical importance
In ruminants can cause chronic poor doing
May have acute disease (especially small ruminants) associated with liver migration (mechanical damage)
Diagnosis by egg detection—sedimentation technique
Control difficult because hard to eradicate snails
Fascioloides magna
trematode, platyhelminth
normal host: deer
Larvae cause serious disease in sheep and goats because keep migrating around liver until animal dies
Sheep and goats are abnormal hosts
Hard to control
