PHMP Helminths

helminthic parasites

are multicellular (metazoa) bilalerally symmetrical animals having 3 germ layers (triplobastic metazoa) and belong to the kingdom Metazoa.

'helminth' (Greek helmins-’worm’)

originally referred to intestinal worms, but now comprises many other worms, including tissue parasites as well as many free-living specie

Phylum Platyhelminthes

The platyhelminths are tape-like, dorsoventrally attened worms.

Phylum Platyhelminthes

They either lack alimentary canal (as in cestodes) or their alimentary canal is incomplete, lacking an anus (as in trematodes). Body cavity is absent, viscera is suspended in gelatinous matrix.

They are mostly hermaphrodites (monoecious)

Class – Cestoda (tapeworms)

Class – Trematoda ( ukes or digeneans)

Phylum Platyhelminthes includes 2 classes:

Class Cestoda

have tape-like, dorsoventrally attened, segmented bodies.

They do not possess an alimentary system.

The head carries suckers and some also have hooks

Class Cestoda

They possess scolex, neck, and proglottids.

They are monoecious and body cavity is absent.

They are oviparous

Class Trematoda

have flat or fleshy, leaf-like unsegmented bodies.

The alimentary canal is present but is incomplete i.e., without an anus

Class Trematoda

They possess suckers but no hooks.

The sexes are separate in the schistosomes, while the other flukes are hermaphroditic.

They are oviparous

Phylum Nemathelminthes (Nematoda)

are elongated, cylindrical worms with an unsegmented body. They possess a relatively well-developed complete alimentary canal, with an anus.

Body cavity is present.

Phylum Nemathelminthes (Nematoda)

The head does not have suckers or hooks, but may have a buccal capsule with teeth or cutting plates.

The sexes are separate (diecious).

They are either oviparous or larviparous

Cestodes

Trematodes

Nematodes

Cestodes (Greek kestos—girdle or ribbon)

re multisegmented, dorsoventrally flattened tape-like worms whose sizes vary from a few millimeters to several meters. The adult worms are found in the small intestine of humans

Head (scolex)

Neck

Trunk (strobila)

The adult worm consists of 3 parts:

Head (scolex)

It is the organ of attachment to the intestinal mucosa of the definitive host, human or animal

4 suckers (or acetabula)

In parasites of the order cyclophyllidea, the scolex possesses

rostellum

In some cyclophyllidea like Taenia solium, scolex has an apical protrusion called as the ____,may or may not be armed with hooks.

v

Neck

It is the part, immediately behind the head and is the region of growth from where the segments of the body (proglottids) are being generated continuously

Trunk (strobila)

also called as strobila is composed of a chain of proglottids or segments The proglottids near the neck, are the young immature segments, behind them are the mature segments, and at the hind end, are the gravid segments.

are hermaphrodites (monoecious) and every mature segment contains both male and female sex organs. In the immature segments, the reproductive organs are not well-developed. They are well-developed in the mature segments. The gravid segments are completely occupied by the uterus filled with eggs

Tapewrorms

do not have a body cavity or alimentary canal

Rudimentary excretory and nervous systems are present

Tapeworm

do not have a body cavity or alimentary canal

Rudimentary excretory and nervous systems are present

Metazoans

They are multicellular eukaryotic organism

As animals, they have organ systems

Metazoans

However, the parasitic species often have limited digestive tracts, nervous systems, and locomotor abilities.

May have complex reproductive cycles with several different life stages and more than one type of host.

monoecious

having both male and female reproductive organs in a single individua

dioecious

each having either male or female reproductive organs.

intestinal species

those primarily involved with the intestinal tract,

intestinal tissue species

those that migrate into the tissue following initial contact with the intestinal tract

Nematodes

Unsegmented

Have full digestive system 

Dioecious – Female usually larger than male in size

Some species migrates and or take up residence outside the intestine

definitive host

The adult stage of a parasitic helminth is found in the

intermediate host

Each larval stage of a parasitic helminth requires an

Rhabditiform larva

early developmental stage or juvenile stage

Filariform

short and pointed, penetrates the skin

Enterobius, Ascaris, Trichuris

Ingestion of eggs:

Skin penetration:

Strongyloides, Necator, Ancylostoma

Trichinella spiralis (usually by undercooked meat e.g. pork containing the larvae) (penetrates through the muscle)

Ingestion of larvae:

Wuchereria, Loa, Mansonella, Onchocerca, Drancunculus

Larvae transmission via insect bite:

Enterobius vermicularis

Pinworm, seatworm, Oxyuriasis

Yellowish white in color, pointed, resembles pinhead

Trichuris trichiura

Whipworm

Pinkish gray, resembles whip itself, males possess prominent curled tail

Ascaris lumbricoides

Roundworm of man

Creamy white, pink tint, female has lead thickness, male has prominent incurved tail

Strongyloides stercoloaris

Threadworm

Colorless, transparent body, finely striated cuticle, short buccal cavity

Necator americanus

New world hookworm

Contains pair of cutting plates, Male has prominent copulatory bursa

Ancylostoma duodenale

Old world hookworm

Contains actual teeth, Male has prominent copulatory bursa

Trichinella spiralilis

Trichina worm

Thin anterior end females are blunt and round posterior end, males are curved

Dracunculus medinensis

Guinea worm

Female has prominent rounded anterior end, male coils its anterior end at least once

Enterobius vermicularis

Colorless, double-layered thick shell

Trichuris trichiura

Yellow brown color, barrel or football shape, hyaline polar plug each end

Ascaris lumbricoides

Rounded (fertilized) or oval (non-fertilized), corticated

Strongyloides, Necator, Ancylostoma

Smooth and colorless shell, 2,4-8 embryonic cleavage

Filarial Nematodes

Thread-like parasitic nematodes that are transmitted by arthropod vectors

Adults are threadlike and creamy in appearance

They are formed in different lymphatics or body cavities

Filarial Nematodes

Classified as “Sheathed or unsheathed”

They are vector-borne parasitic nematodes ( Female mosquito)

mosquitoes (Anopheles minimus flavirostris-rural; Aedes poecilusurban; Culex pians quinquefasciatus

Filarial Nematodes

W. bancroft

mosquitoes (Mansonia spp., Anopheles spp.)

Filarial Nematodes

Brugia malayi

Chrysops spp.( deer flies)

Filarial Nematodes

L. loa

Simulium damnosum (black flies)

Filarial Nematodes

O. volvulus

Wuchereria bancrofti (Peripheral blood)

Brugia malayi (Peripheral blood)

Loa loa (Peripheral blood)

Sheathed species

Onchocerca volvulus (Lymph spaces of skin, subcutaneous nodules)

Mansonella species (Peripheral blood)

Unsheathed species

Wuchereria bancrofti

Bancroft’s filaria

Tip of tail free of nuclei

Brugia malayi

Malayan filaria

Presence of two distinct nuclei in the tip of the tail

Loa loa

Eye worm

Distinct continuous row of nuclei extent to tip of tail

Onchocerca volvulus

Blinding filaria

Nuclei do not extend to tip of tail

Mansonella ozzardi

New world filaria

Numerous nuclei, do not extend to tip of tail

Mansonella perstans

Perstans filaria

Numerous nuclei, do not extend to tip of tail

Cestodes

As compared to other parasitic worms, ____are characterized by a long, flat body (ribbon-like) that can grow to over 20 meters in length depending on the species.

Cestodes

They are also characterized by a segmented body that plays an important role in their life cycle

Cestodes

The immature segment lies proximal to the neck and is composed of immature reproduction organs, this is followed by the middle or mature segments which contain the well- developed reproductive organs; the distal most portion is the gravid segment which characterized by its uteri filled with eggs

Cestodes

Hermaphrodites (Monoecious)

No digestive tract – nutrition mainly derived from absorption 

Required at least 1 intermediate host for transmission (Except D. latum where 2 intermediate host are required and H. nana where no intermediate host is needed.)

Cestodes

The egg consist of a hexacanth embryo (Oncosphere) – defined as the motile

First larval stage characterized by the presence of six small hooks called hooklets – for attachment

Scolex

Part of adult tapeworm

anterior end

Proglottids

Part of adult tapeworm

individual segments in their mature form

Strobila

Part of adult tapeworm

reproductive organs

Suckers

Part of adult tapeworm

attachment

Rostellum

Part of adult tapeworm

extension of scolex

Tegument

Part of adult tapeworm

excreted waste products

Taenia solium

Pork tapeworm

Four suckers, rostellum and hooks are present (Double crown hooks) 7-15 branches per segment

Taenia saginata

Beef tapeworm

Four suckers, rostellum and hooks not present 15-30 branches per segment

Hymenolepis diminuta

Rat tapeworm

Four suckers, rostellum is present but no hooks Sac-like uterus filled with eggs

Hymenolepis nana

Dwarf tapeworm

Four suckers, rostellum is short hooks are present in one row Saclike uterus filled with eggs

Dipylidium caninum

Dog/Cat tapeworm Pumpkin seedtapeworm

Four suckers, Club-shape rostellum with 1-7 spines, hooks not present Pumpkin seed-shape proglottid

Diphyllobothrium latum

Broadfish tapeworm

Two sucking grooves with almond shape, hooks and rostellum not present Centrally located rosette shape uterus

Echinococcus granulosus

Dog tapeworm

Hyadatid tapeworm Scolex contains 4 suckers and approx. 36 hooks, small neck and three proglottids

Trematodes

they are a group of animals that belong to the phylum Platyhelminthes, specifically to the class Trematoda. They are flattened worms, with a typically leaf-shaped flattened bod

Trematodes

The are broadly oval or leaf like in shape with an oral sucker, a prepharyngeal tube, a pharynx and esophagus and a bifurcated intestinal ceca which ends blindly except in the blood flukes

Trematodes

They are hermaphrodites except for the human blood flukes (Schistosoma spp)

Sexually mature trematodes found in the definitive host

Trematodes

Requires two intermediate host, mollusks (Snail) and shellfish/fish except Schistosoma spp (one intermediate host needed)

Manner of transmission is through ingestion of infective stage except Schistosoma spp (through skin penetration)

Trematodes

Early stage developed inside the mollusks

Infective stage is metacercaria

Fork-tailed appearance

Cercaria in Schistosoma spp –

Fasciola hepatica

Fasciolopsis buski

Presence of distinct operculum

Clornochis sinensis

Presence of distinct shoulders and presence of small knob opposite operculum

Heterophyes heterophyes

Metagonimus yokogawai

Operculum present, shoulder is also present but not discrete, small knob may be present

Paragonimus westermani

Prominent operculum with shoulders; obvious terminal shell thickening opposite operculum

Schistosoma mansoni

Appearance of large lateral spine

Schistosoma japonicum

Appearance of small lateral spine

Schistosoma haematobium

Appearance of large terminal spine

Fasciola hepatica

Liver fluke

Equipped with so called shoulders

Fasciolopsis buski

Large intestinal fluke

Oblong, fleshy, No shoulders

Clonorchis sinensis

Chinese liver fluke

Each end is narrower than the midportion of the body