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)
