Helminths Flashcards
Kingdom
Animalia
List the phylums
Phylum Platyhelminthes- ‘flatworms’, 2 classes the trematodes (flukes) and cestodes (tapeworms) Phylum Nematoda- ‘roundworms’, Ex. Toxocara canis, Dirofilaria immitis Phylum Acanthocephala- ‘thorny-headed worms’, ex. Macracanthorhynchus hirudinaceus (GI parasite)
Name the 2 classes in Phylum Platyhelminthes
Class Trematoda- the ‘flukes’, ex. Fasciola hepatica Class Cestoda- the ‘tapeworms’; 2 orders Cyclophyllidea and Pseudophyllidea Class Monogena- (monogenetic flukes)- ectoparasites, infesting the skin and/or gills of fish, amphibians and reptiles (not in domestic animals)
Name the 2 orders in Class Cestoda
Order Cyclophyllidea- ‘true tapeworms’, ex. Dipylidium caninum Order Pseudophyllidea- ‘peudotapeworms’, ex. Spirometra mansonoides
Subclass Digenea
(digenetic flukes)- endoparasites of domestic and wild animals, and humans; first life cycle requires more than one intermediate host; first intermediate host usually a snail; sexual and asexual generations; “leaflike” body shape; adult size 1 mm to 8 cm
Morphological features of Class Trematoda
-dorsoventrally flattened -some are long/narrow, some are leaf-shaped, some have thick fleshy bodies; schistosomes (blood flukes) are long and thin and resemble nematodes -have a tegument (outer skin) that may be smooth or covered with tiny spines -2 attachment organs: anterior feeding sucker (oral sucker); ventral attachment sucker called the acetabulum -digestive system: begins with a mouth surrounded by an oral sucker; muscular pharynx; esophagus with 2 blind ceca (unbranched- simple; highly branched-dendritic) -excretory system -nervous system -complex reproductive system: digenetics- hermaphroditic; male- 2 testes (tandem or parallel), vas deferens, seminal vescicle, prostrate, cirrus (penis), cirrus sac and genital pore; female- one ovary, seminal vesicle, vitelline/yolk glands, vitelline duct, ootype, Mehlis’ gland, uterus and genital pore
Morphological features of schistosomes
-tubular body -no 2nd IH -inhabit blood vessels, mature in the blood -not hermaphroditic -grossly resemble nematodes -female is slender, male carries female in a groove of his body called the gynecophoric canal -eggs are thin-shelled and have no operculum; some eggs have a lateral or terminal spine -important parasites in human beings - ex. Schistosoma hematobium- urinary Schistosoma mansoni- mesenteric vein Schistosoma japonicum- portal and mesenteric vein Schistosoma bovis- ruminant Heterobilharzia americana- canine blood fluke
Give examples of how flukes cause disease.
- Suck blood 2. Obstruct ducts/vessels 3. Egg accumulations 4. Destroy tissues/organs (from feeding, migration, pressure necrosis)
General progression of the typical fluke life cycle.
- Miracidium (ciliated, released into environment, penetrates snail) 2. Sporocyst (develops in the snail, produces rediae or cercariae) 3. Rediae (stage may be omitted, produces daughter rediae or cercariae) 4. Cercariae (resembles spermatozoan, leaves snail, 1/3 options: 1. infect/penetrate 2nd IH, 2. encyst on vegetation, 3. infect/penetrate DH directly) 5. Metacercaria (encysts in environment or a transport host, infects DH; INFECTIVE STAGE)
Typical diagnostic test used to detect fluke infections
- Necropsy 2. Sedimentation (eggs are either too large or too dense to float)
Fasciola hepatica
Designation: Platyhelminth->Trematoda->Fasciola hepatica (Liver Fluke) Identification: Adult 30x13 mm; eggs 130-150x63-90micrometers; highly branched internal morphology Lifecycle: egg in H2O-> miracidium-> infects snail/gastropod->sporocyst->rediae->cercaria->released onto plant or into H2O-> metacaria (infective stage)->passes into ruminant->gut->liver->bile ducts-> once mature (1 month) will release eggs into environment (H2O) Most pathogenic fluke in the US IH: aquatic snail Lymnaea sp. No 2nd IH Major cause of liver condemnation in slaughtered horses Diseases: Liver rot; Fascioliasis; Liver Fluke Disease Transmission: seasonal Primary lesions: liver parenchyma or bile ducts; can cause acute, subacute or chronic disease Sucks blood, obstructs ducts, egg accumulation Diagnositics: sedimentation (feces)-not helpful with acute cases, most helpful with young animals; necropsy
Acute, Subacute and Chronic Fascioliasis
Acute: sheep, traumatic hepatitis, extensive destruction of liver parenchyma Subacute: less sudden onset, anemia/hypoproteinemia, death common, eggs present in feces Chronic: gradual onset of anemia, eggs in feces, hepatic fibrosis -Clinical signs sheep- lack of vigor, pale MM, “Bottle jaw”; cows- digestive disturbances, constipated/diarrhea
Platynosomum concinnum
Host: cats; mainly in Fl Habitat: Found in liver, bile and pancreatic ducts 2 intermediate hosts: terrestrial snails (Subulina spp., Eulata spp.), Anolis spp. lizards (also toads, geckos, skinks); Pill bug can act as a paratenic host “Lizard poisoning fluke” Identification: operculated; size 34-50 x20-35 micrometers (small but dense) Clinical signs: normally no severe disease/temporary inappetance Lifecycle: eggs leave host via feces->eggs containing miracidium are ingested by 1st IH (snail)-> miracidium hatches->sporocyst->cercariae-> 2nd IH (lizard gecko) or Pill bug then 2nd IH-> cecariae encyst in bile ducts of lizard-> metacariae remain in lizard until ingested by DH (cat)-> encyst in live/bile ducts and mature and then eggs leave host via feces Diagnostics: sedimentation(feces)- eggs rare if bile ducts occluded; necropsy
Paratenic host
host that ingests a stage of the parasite but there is no development of the parasite within that host; once ingested by DH, parasite will finish out life cycle
Heterobilharzia americana
“Canine blood fluke” Hosts: dogs, bobcat, raccoon; Common in gulf coast, Louisiana bayous, Mississippi delta Habitat: Mesenteric and hepatic veins IH: aquatic snail (Lymnaea cubensis” Identification: Appearance is “dark piece of lint coming out of the blood”; Size: Male- eggs hatch in water-> miracidium penetrates snail-> cercariae emerge from snail-> cercariae penetrate skin of DH (or MM)-> migrate to lungs-> liver->mesenteric veins->mature to adults->excrete eggs which make their way into feces Signs: often asymptomatic; diarrhea, vomiting, weight loss, lethargy, hypercalcemia; skin irritation (cercariae migrating); granulomatous inflammation (egg migration) Diagnostics: sedimentation, visual lesions on skin “swimmer’s itch”
Morphological features of tapeworms
-hermaphroditic, segmented -always endoparasitic (adults- GI/larva- extra-intestinal) -lack a body cavity and digestive tract; absorb food through their body wall (tegument) -body size ranges from a few millimeters to several meters -muscular system enables tapeworm to move inside/outside the host
Morphological features of Cyclophyllidean tapeworms
-scolex (head) normally containing four suckers called acetabula -can be armed and have hooks or rostellum (retractable nose) that may also be covered with backward facing hooklets or unarmed -scolex used to anchor tapeworm in place (holdfast organ) -short, unsegmented germinal neck -remainder of body-strobila, segments of proglottids, mature as they are “pushed away” +immature: most proximal, nonfunctioning repro organs +mature: centrally located, ‘teenagers’, mature, fully functioning repro organs +gravid: most distal, degenerated, nonfunctioning repro organs, contain eggs -proglottid contain complex excretory system, nervous system, 1-2 fully functional sets of male/female repro organs
Lifecycle of Cyclophyllidean
found in intestine of DH->eggs/gravid proglottids voided-> embryonate once in environment->oncosphere->ingested by IH->penetrate intestinal wall->migrate to predilection site->develop into larval tapeworm (metacestode)->migrates to extraintestinal site->fully develops (each metacestode contains one or more scolices)
Types of scolices
Cysticercoid: single scolex which is not invaginated into itself; ‘right side out’, tiny, fluid filled cavity, vesicle or bladder; found in mites/fleas Cysticercus: single scolex, invaginated into itself in a large, fluid filled cavity, vesicle or bladder; ‘inside out’, vertebrates such as ruminants, rabbits or mice Coenurus: large, fluid filled cavity, vesicle or bladder with many invaginated scolices, ‘multi-headed cystericus’ Hydatid cyst: large, fluid filled cavity, vesicle or bladder; develops other cysts called brood capsules, contain many protoscolices
Differences between Cyclophyllideans and Pseudophyllidean tapeworms
Pseudo -2 narrow, deep, weakly muscular grooves at anterior end, holdfast organelle (bothria) -only 1 set of male/female repro organs per proglottid -produce operculated eggs, release ciliated hexacanth embryo -2 IH- 1st aquatic crustacean contain “procercoid stage”; 2nd usually vertebrate “plerocercoid stage”
Dipylidium caninum
Host: dogs, cats, other canids and felids, humans-zoonotic! Habitat: small intestine Identification: adults gravid proglottids voided in feces->egg packets released when proglottids rupture->eggs are ingested by IH-> develop into infective cysticercoid->IH then ingested by the DH->cysticercoid releases the scolex-> attaches to the small intestine and begins to grow Signs: not very harmful, heavier infections produce non-specific abdominal signs (constipation/diarrhea, unthriftiness, pot-bellied appearance); may scoot due to irritation Diagnostics: proglottids in feces, break open and add saline, examine under microscope, fecal floatation-egg packets rarely seen (not uniformly distributed) Treatment: praziquantel, epsiprantel, fenbendazole Control and prevention: control fleas and lice
Anoplocephala perfoliata
Hosts: Equids (horses, donkeys, mules, zebras); worldwide Habitat: A. perfoliata- Lappeted tapeworm, most common, small and large intestine Identification: A. perfoliata- 5-9 cmx1.2cm, small scolex, lappets, pyriform apparatus, 65-80 micrometers Life cycle: hermaphrodidtic found in small intestine of equine DH->gravid proglottids break free releasing eggs possessing pyriform apparatus->free living grain mites ingest these eggs->cysticercoid develop in mites (2-4 months)->horse ingest the mites on grains and grasses-> cysticercoids emerge, noninvaginated scolex will attach, one tapeworm grows (2 months) Clinical signs: light infestations-no signs; large-may result in death; A. perfoliata- most pathogenic, poor growth, chronic ill thrift, recurring diarrhea, anemia, progressive weight loss
Spirometra mansonoides
Host: dogs, cats, raccoons Habitat: small intestine Identification: large (operculated eggs shed in feces->contact water, coracidium develops within and emerges from egg->1st IH ingests coracidium, develops into procercoid stage->2nd IH ingests infected copepod->bores through intestinal wall->migrates to muscles/connective tissues, develops into plerocercoid stage (sparganum)->when plecocercoid is ingested by DH, digested out of muscle tissue and attaches to small intestine-> tapeworm grows and matures (7-14 days) Signs: Zoonotic potential-> human ingests copepod (migrates to periorbital area; dogs/cats-asymptomatic, some vomiting, weight loss, diarrhea Diagnostics: fecal float/sedimentation Treatment: praziquantel (higher dose than other tapeworms) Control/Prevention: prevent predation/avoid feeding cats and dogs raw/undercooked meat
Where would you find the cercarial stages of F. hepatica? What is the next step in the lifecycle?
The cercaria develop in the aquatic snail lymnaea spp., emerge from the snail, then settle at the bottom of a pond/body of water. They then shed their tail and encyst as metaceracariae which are eaten by the DH (sheep/goats/cattle)
Draw the adult of Fasciola hepatica. Label the oral sucker, acetabulum and blind seca. Describe the seca and tegument of F. hepatica. Why are the internal organs difficult to differentiate from each other?
Seca- esophagus divides into 2 blind ceca
Tegument-skin, covered with tiny spines
Internal organs are difficult to differentiate because they are highly branched
You have smashed open a proglottid recovered from the surface of a canine fecal sample in saline and examined the contents on a microscope slide using a compound microscope. You see a large packet with several eggs inside, each with a set of 6 hooklets. Name the genus and species of the parasite ova you are seeing. Why is this a good way to diagnose this parasite?
The parasite ova are from Dipylidium caninum. These egg packets are unique to D. caninum and each egg has a hexacanth embryo with 6 hooklets.
Describe the posterior end of the male Ostertagia ostertagi nematode
It has a copulatory bursa to wrap around the female and spicules to deposit sperm in the vagina of the female; trichostrongyloidea small mouth; copulatory bursa wraps around female, spicules deposit sperm in vagina of female
Draw the encysted Trichinella spiralis larvae. a) Where are these encysted larvae found in the host? b) What protects them (specifically) from the immune system of the host? c) How do they complete their lifecycle from this encysted stage?
a) T. spiralis larvae are found encysted in striated muscle of the host (IH) b) they are protected from the immune system because they are in the host’s own muscle cell, nurse cell c) from here they encyst in the small intestine of the DH when the IH or its raw meat is eaten
Look at the microfilariae of Acanthocheilonema reconditum and Dirofilaria immitis. How would you differentiate them?
To differentiate, measure them Acanthocheilonema reconditum: 250-288 micrometers, curved body, blunt head, “button hook” tail Dirofilaria: 307-322 micrometers, straight body to tapered tail
Draw the mouth (anterior end) of Ancylostoma caninum. How many pairs of teeth does A. caninum have? (get picture)
A. caninum has 3 pairs of teeth
Describe the egg of a typical Ascarid. What is the infective stage of Toxocara canis and how might the new definitive host become infected? (get picture)
Ascarid eggs are very large (non-larvated) with a thick, rough body wall to protect them for passage to a new host. The infective stage is the egg with L2 inside. The new DH may be infected by various routes: direct transmission (ingestion), prenatal/transuterine, colostral/lactogenic, ingestion of paratenic host
Give a distinguishing characteristic of the F. hepatica egg.
eggs are operculated
Where would you find the redial stages of F. hepatica? What is the next step in the lifecycle?
Aquatic snail, Lymnaea spp.; next step is cercaria
How does the mouth of A. caninum differ from Osteragia ostertagia? How are the posterior ends of male A. caninum and O. ostertagi similar? What other ways are A. caninum and O. ostertagi similar? (morphologically and/or biologically)
Mouth differences: O. ostertagi has a small mouth while A. caninum has a large buccal cavity with three pairs of teeth along the ventral margin Posterior similarities: copulatory bursa with 2 evenly sized spicules Other similarities: direct lifecycles, non-larvated eggs in feces
In the typical trematode lifecycle, what stage is infective to the final vertebrate host?
Metacercariae
The intermediate host for Fasciola hepatica is: a) terrestrial snail, Subulina spp. b) Anolis spp. lizards c) aquatic snail, Lymnaea spp. d) none of the above, they have a direct lifecycle
C) aquatic snail, Lymnaea spp.
Where in the feline host can adults of Platynosomum concinnum be found?
bile ducts and liver
An armed scolex indicates the presence of ________ and ___________.
hooks; rostellum
A large, fluid filled bladder containing multiple invaginated scolices is characteristic of which tapeworm metacestode stage? a) cysticercoid b) cysticercus c) coenurus d) hydatid cyst
C) coenurus
Proglottids of Dipylidium caninum are unique in that they have: a) a single uterine pore b) two, lateral uterine pores c) a single genital pore d) two, lateral genital pores
D) two, lateral genital pores
Name the metacestode stage of Spirometra mansonoides that encysts in the muscle of the second intermediate host.
plerocircoid or sparganum
Type I Osteragiasis is caused by: a) large numbers of eggs acquired from pasture b) large numbers of L3 larvae acquired from pasture c) ingested L3 larvae that go into a hypobiotic state d) hypobiotic larvae that simultaneously resume development
B) large numbers of L3 larvae acquired from pasture
What stage of Toxocara canis is infective to the definitive host?
L2 larvated eggs
T/F: Occult infections of Dirofilaria immitis are best diagnosed using a Modified Knott’s test in order to visualize circulating microfilariae.
False
Match the parasite scientific name on the left with the common name on the right 1. Platynosomum concinnum A Barberpole 2. Dirofilaria immitis B. Hookworm 3. Ancylostoma caninum C. Lizard poisoning fluke 4. Haemonchus contortus D. Whipworm 5. Dipylidium caninum E. Rumen fluke F. Heartworm G. Bankrupt worm H. Double-pored tapeworm
- C 2. F 3. B 4. A 5. H
The final host, where sexual reproduction occurs and/or adult or mature stages are seen:
definitive host
The host in which asexual reproduction occurs and/or developing stages of the parasite are found:
intermediate host
The host that harbors encysted larval stages- no further development occurs:
paratenic host
Infection is parasitism by this type of parasite:
endoparasite
Infestation is parasitism by this type of parasite:
ectoparasite
