helminthology

greek: helmis/ helminthos: intestinal worm

• collective term (not a taxon!) for parasitic worm like metazoans froma phyla platyhelmintes, nematoda and acantocephala

Species: Taenia solium, Taenis saginata, Echinococcus granulosus

e.g. diseases in humans: intestinal tapeworm infection, neurocystericercosis, echinococcosis

shape: segmentes, flat

body cavity: absent

body covering: tegument

digestive tract: absent

sex: hermaphroditic

attachment organs: sucker or bothridia and rostellum with hooks

number of species: 6000

number of species known to infect humans: 40

species: Schistosoma mansoni, schistosoma japonicum, fasciola hepatica

e.g. disease in humans: schistosomosis, swimmer’s itch

shape: unsegemented, flat

body cavity: absent

body covering: Tegument

digestive tract: incomplete (blind ending)

sex: Hermaphroditix, except schistosomes which are diecious

attachement organs: oral sucker and ventral sucker or acetabulum

number of species: estimated >15000 and 9000 regristed

number of species known to infect humans: 16

species: Ascaris lumbricoides, ochocera volvulus, trichuris trichiura, anchylostoma duodenale

e.g. diseases in humans: Ascariosis, drancunculiasis (guinea worm), elephantiasis, filariosis, hookworm infection, onchocercosis

shape: cylindrical

body cavity: present (pseudocoelom)

body covering: cuticle

digestive tract: complete

sex: diecious

attachment organs: Buccal capsule, lips, teeth and dentary plate

number of species: 800000 to 1mio estimated and 25000 registered

numbers of species known to infect humans: >12000

general structure:

• Flat, unsegmented, partially with adhesive organs

• no body cavity (parenchymatous)

• respiratory organs: absent - gas exchange through diffusion over tegument

• vascular system: absent

• alimentary system: blind ending (trematoda) or absent (cestoda)

• nervous system: simple (ganglia)

• excretory system : protonephridium

• sexual organs: complex, often hermaphroditic

• eggs: contain one oocyte, several yolk cells

• reproduction types:

  • oviparous (egg with oocyte)

  • ovoviviparous (egg with larva)

  • viviparous (live bearing)

• developemnt:

  • homoxenous (a single host)

  • heteroxenous (intermediate and definite host)

homoxenous: 1 host

heteroxenous: 2 or more hosts (di-, triheterocenous)

definite host: sexual reproduction of the parasite occurs

intermediate host; necessary for the development, but sexual maturity is not reached

parasites can be facultatively heteroxenous (can have a cycle in another host but doesnt need to)

paratenic host: stapelwirt; harbours sexually immature parasite life stages which dont develop further (not necessary for the life cycle, but source of infection)

• body: strobila, with several segements (proglottids)

• no intestine, nutrient absorbtion via body surface

• head: scolex with attachment strucutres

• hermaproditic

• mostly heteroxenous

pseudophyllida & Cyclophyllida

syncytial tegument with mcrotriches to increase the surface feeding, unterneath al layer of muscles (proglottids are mobile!)

general structure of adults

• scolex with adhesive organs (suckers, rostellum with (armed) and without hooks

scolex - region of proliferation - proglottids - genital pore - gravid proglottids

• adults : neck zone= zone of proliferation; number of proglottids on the genus: 3 (E. granulosus) up to 4000 (dibothricephalus latus), total length of tapeworm < 1cm up to several meters

• sexually mature segments: containing male and female reproductive organs, the male ones before female

• single set of reproductive organs: open in 1 sexual pore (median or lateral), a double set has 2 sexual pores

• at the end of strobila: gravid segments, reproductive organs regressed, uterus filled with reproductive products (eggs)

• pseudophyllida: uterus connected to the outer environemt, egg secretion from proglottids

• cyclophyllida: no connections to the outside, proglottids atr shed and release eggs when ruptured

• Evolutionary older than cyclophyllida

• scolex with 2 sucking groves (bothria)

• fertilized eggs with operculum

• eggs embryonate in the environment -> 1st larva =coracidium

• 2 intermediate hosts -> triheteroxenous

• eggs - coracidium - procercoid (1. IH) - plerocercoid (2-IH)

• Adults: develop in intestines of the defintive host (humans, mammals), release of eggs

• Egg: embryonates in envirnoment, larvae urrounded by cilia (coracididum) hatch and swim in the water

• uptake of coracidium by the 1st IH (copedod) -> percoid in the body cavity - subplanctos organism

• 2nd IH (fish) feeds on 1st IH, plerocercoid in body cavity (paratenic hosts: rapacious fishes)

• scolex with 4 suckers

• eggs embryonate within the uterus of the proglottis

• release eggs contain the 1st larva (oncosphere) in so-called embryophore

• only one intermediate host -> diheterocenous

proglottids -> egg -> oncosphere -> metacestode in IH

size: ca 70 µm

form: polygonal

shell: irregular

contents: oncosphere in embryophore

inside empryo -> 6 hook larvae

oncosphere -> different forms of metacestodes (2nd larvae) in the IH, depending on the parasite genus

with or withous asexual reproduction

• Tetrahyridium - mesocestoides - simplest

• cystercoid - anoplocephalidae, dipylidium - cyst, round

• cysticerecus - most Taenia spp

• coenurus - T. multiceps, T. serialis - big fluid filled cyst and many cyst inside developing

• Echinococcus - E. spp - asexual reproduction

  
  

The adult tapeworm attaches to the small intestine wall -> head end or scolex

terminal proglottids break off and pass with feces

proglottids shed eggs on the groud

flea larvae eat the eggs

Cysticercoid - tapeworm larvae encyst in the flea and becomes infective

fleas are eaten to cause infection

subclass - aspidogastrea

subclass - digenea

• adults mostly dorso-ventrally flattend, with suckers

• blind endling alimentary tract

• usually hermaprodites (except schistosomas)

“two brids” - sex. reproduction as adults + asexual reproduction of the larvae

• parasites of vertebrates

• heteroxenous developemnt -> always molluscs as 1st )IH

• mostly dependent on water (exc. Dicroceoelium!)

• hermaphrodites with crossed-fertilization (allogamy) -> exc. schistosomatidae

• adult worms predominantly in the gastro-intestinal tract and its appendices (liver, gall bladder, pancreas)

• more rarely in nasal cavities, lungs, blood vessels etc.

• highly differentiated morphology and developemntal cycles

• obligate heteroxenous, with alternation of generations

• development most through 2 IH

• 1. IH - mostly gastropods

• 2. IH can be missed

• alternation of generations - sexual and asexual production

• alternation of hosts - final and IH

• 0.2mm - 13cm length

• dorsoventrally flattend

• non-segemented body

• oral and ventral sucker or acetabulum

• integument smooth or with spikes/scales

• oral sucker = mouth opening, digestive tube end in cecum

Schistosoma spp. -> schistosomiasis or Bilharziosis

• 250 to 300 mio humans affected

• 600 mio at risk

Fasciola hepatika - common liver fluke

dricocoelium dendriticum - lancet liver fluke

clonorchis sinensis - oriental liver fluke

ruminants and other mammals, including humans

2-5x 0.4 - 1.3cm

tegument with spikes

location of adults: bile ducts (bilidary duct)

Adult -> egg -> egg with miracidium -> miracidium -> sporocyst -> redia - cercaria (can develop daugter redia) -> metacercaria -> on plants ( infectious stage of definite host

asexual reproduction in the intermediate host!

cyst -> infectious stage

cercariae in slime of the first IH - terrestial snail

uptake of cercarie by 2nd IH - ant

Adult -> embryonated eggs are shed in the feeces -> Eggs are ingested by a snail IH (miracidia -> sporocyst-> cercariae) ->cercariae are released from the snail via the respiratory pore in a slime ball -> cercarie become metacercariae after being eaten by an ant -> Cow: Host becmoes infected by ingestion of infected ants -> adult in bile duct..

Human: uptake of cercarie via ant : adult in bile duct.

infective stage - > uptake

diagnosti stage -> eggs shed in feces

most cercariae develop into metacercariae

one cercaria migrate into the submandibular ganglion of the ant -> manipulation of ant behaviour

D. dendriticum

• 40-59 µm, brown, lid, thick eggshell

• content : miracidium

F. heptaica

• 120 - 140 µm, gold, smooth, thin eggshell with los

• content: yolk-cells

Trichobilharzioa and other species -> parasites of waterfowl

1- eggs are passed in feces of duck

2- eggs hatch and liberate miracidia

3- the parasite develops in a mollusan IH

4 - cercariae penetrate the skin of definitve hosts and migrate to blood vessels to complete the cycle

5-> humans are exposed to dermatitis-producing cercariae

greek nema=thread

• free living or parasite

• between ~1mm and 1m in length

• cylindrical cross-section

• not segmented

• liquid filled body cavity (pseudocoel; without epithelial layer) with tubular inner organs

• body covering=collagenous cuticle, forms a hydroskeleton together with a longitudinal muscle layer

• developemtn with shedding of cuticle (ecdysis)

  • like athropodes

  • superphylum ecdysozoa

• structures digestive tract (foregut, midgut, rectum)

buccal capsule - strongyles

teeth - hookworms

lips - ascarids

dioecious (i.e. seperate sexes)

females:

• ovary (normally double; exception: Trichuridae), oviduct, uterus, receptaculum seminis, ovijector, vagina, vulva, some species vulva flap

males:

• normally only one testis, sperm duct (vas deferens) extended into seminal vesicle, ductus ejaculatorius opens into the cloaca

• accessory copulatory organs: 1 spiculum or 2 spicula, gubernaculum, telamon, bursa copulatric, pre-cloacal sucker

1. embrynation Eggs

2. Hatching Larvae

3. growth & moulting

4. Reproduction -adults

size: variable (small = 50 µm up to big ca 150 µm)

form: round, oviform, limoniform, with a pole-plug

shell: thick or thin, colorless, brown

contents: oocyte/blastomeres/larvae

post-embryonic phase:

LI exsheating -> LII -> exsheating -> LIII

the cuticle of the previous stages can be retained as a sheath (uvea) -> protection against envirnomental factos

• direkt (geohelminths): the p-e phases takes place in environment

  • in the egg (ascarids)

  • free living (strongyles)

• indirect development (biohelminths): the p-e phase take plave in an IH

  • warm or cold blooded e.g. filaria

1. Eggs passed in feces

2. vertical transmission to puppies / external environment - unembryonated egg into embryonated egg with L3 larva

3. ingestion of eggs

4. adults in small intestine of DH / ingestion of eggs in IH / paratenic host - Foodborn transmission on IH or L3 larvae in tissue of duck and uptake of dog.

5. L3 larvae migrates in tissue - diagnostic stage

1. infective L3 are transmitted during a blood meal to the next host

   (dogs are the primary host of the skin worm;; zoonotix risk, humans can be infected as well and develop a similar disease: worms develop on subcutaneous nodules and inner organs)

2. L3 moves to the subcutaneous tissue and grow in 5-9m to mature adults

3. adult worms live in module under the skin and release microfilaria which circulae in the blood

4. mosquito takes up microfilaria from an infected dog

5. the development from microfilaria to infective L3 happens inside the mosquito and takes approx. 10-30d

infectious stages for the DH are L1 or L3

• in the egg

• free living

• in paratenic, IH or DH

routes of infection in nematodes

• oral

• percutaneous

• lactogenic

• transplacental

development with body migration or without migration (but often with histothropic phase)

1. unembryonated egg in feces

2. infected egg with L3 in L2 cuticle

3. ingestion of infective egg

4. larvae mirate up the bronchi and are swallowed

5. hatched larvae penetrate the large intestinal wall and migrate via the liver to the lungs

6. larvae establish in the small intestine and become patent at week 6-8

dormant phase (arrested development)

induction via

• exogenous influence e.g. weather (ostertagia), alimentary deficiency (C. elegans)

• endogenous influences: e.g. overpopulation (cyathostominae), immunity of the host (ancylostoma)

purpose

• persistence of the population during unfavorable conditions

relevance

• synchronous reactivation-> severe pathology

• reactivation during getsation -> infection of offspring

• reactivation in spring -> contamination of envirnoment

pic 82

larvae inside nurse cells

no stages in environment

one DH infects another DH through predation

1. larvae are ingested in raw or undercooked meats

2. larvae enter small intestine, adults mature and live in small intestine

3. female sheds newborn larvae that enter lymph or bood

4. newborn larvae are carried throughout bloodstream

5. newborn larva enters skeletal muscle cell

6. nurse cell-larva comlex formed; normal and calcified nurde cell larvae complexes

• all species parasitic

• in the intestine of vertebrates (predominantly mammals and birds)

• heterocenous, IH: arthropods

• diecious

• no intestine

• proboscis with hooks

1. eggs shed in feces

2. eggs ingestes by arthropod IH (acanthro, ancanthella, cystacant)

3. DH becomes infected by ingestion of infected IH

4. Adults in small intestine

5. aberrant human infection - lives also in small intestine