HELMINTHS

Doç.Dr.Hrisi BAHARDoç.Dr.Hrisi BAHAR

HELMINTHSHELMINTHS

●The helminths are worm-like parasites.

● Helminths are separated according to their general external shape and the host organ they inhabit.

● The definitive classification is based

on the external and internal

morphology of egg, larval, and adult

stages

●Helminths are multicellular eukaryotes.

There are three classes of helminths

• Nematodes – "roundworms"

• Adult and larval roundworms are bisexual, cylindrical worms.

• They inhabit intestinal and extraintestinal sites.

• The nematodes include Trichinella, Ascaris, and Enterobius.

There are three classes of helminths

● Trematodes – "flukes"

● Adult flukes are leaf-shaped flatworms. Prominent oral and ventral suckers help maintain position.

● The life cycle includes an intermediate host.

● An example is the organism that causes schistosomiasis.

There are three classes of helminths

Cestodes – pig and cattle "tapeworms"

● Adult tapeworms are elongated, segmented, hermaphroditic flatworms that inhabit the intestinal lumen.

● Larval forms, which are cystic or solid, inhabit extraintestinal tissues

NEMATODESNEMATODES

• Some species require an intermediate host to complete development.

• Intestinal nematodes all mature into adults within the human intestinal tract.

NEMATODESNEMATODES

• The nematodes (nema: thread) are threadlike, nonsegmented parasites.,

• A few mm to 1m in length, with separated sexes.

• They possess a complex tegument and a digestive tract.

NEMATODESNEMATODES

• The males are usually smaller than the females and are equipped with copulatory organs that often show features specific to each species.

NEMATODESNEMATODES

● Development from the egg includes four larval stages andv four moltings before the adult stage is reached.

● The larval forms of many of these roundworms may be distributed widely throughout the body

NEMATODESNEMATODES

• Three of the intestinal nematodes are acquired by the ingestion of nematode eggs:

● Trichuris trichiura ("whipworm")

● Ascaris lumbricoides

● Enterobius vermicularis ("pinworm")

NEMATODESNEMATODES

• Two worms are acquired when their larvae penetrate through the skin, usually of the foot:

● Necator americanus ("hookworm")

● Strongyloides stercoralis

NEMATODESNEMATODES

• One is acquired by the ingestion of the encysted larvae in muscle (pork meat):

Trichinella spiralis

NEMATODESNEMATODES

Ascaris lumbricoides (Large Roundworm)

Causative agent

of

“ascariosis”

Ascaris lumbricoides

Occurrence

● The human large roundworm occurs worldwide.

● The main endemic regions, with prevalence rates of approx. 10–90%, include countries in Southeast Asia, Africa, and Latin America.

● Autochthonous infections are rare in central Europe.

Ascaris lumbricoides

Parasite and Lıfe Cycle

● The adult ascarids living in the small intestine are 15–40cm in length, about as thick as a pencil and of a yellowish pink color.

Enterobius vermicularis(Pinworm)

Causative agent of enterobiosis

(oxyuriosis)

Occurrence. The pinworm occurs in all parts of the world and is also a frequent

parasite in temperate climate zones and developed countries.

The age groups most frequently infected are five- to nine-year-old children and adults

Enterobius vermicularis

Parasite and Lıfe Cycle

Enterobius vermicularis which belongsto the Oxyurida has a conspicuous white color.

The males are 2–5mm long, The females 8–13 mm.

The long, pointed tail of the female givesthe pinworm its name.

Enterobius vermicularis

Class TrematodaClass Trematoda(Flukes)(Flukes)

• General characteristics

Most of the trematode species that parasitize

humans are dorsoventrally flattened with an

oval to lancet shape, although others have

different shapes such as the threadlike

schistosomes.

Class TrematodaClass Trematoda

• Most species are hermaphroditic.

• Snails are the first intermediate hosts;some species require arthropods or fish as second intermediate hosts

Class TrematodaClass TrematodaSchistosoma (Blood Flukes)

Causative agents of schistosomosis or bilharziosis.

Schistosomosis (bilharziosis) is one ofthe most frequent tropical diseases withabout 200 million infected persons.

The occurrence of schistosomosisdepends on the presence of suitableintermediate hosts (freshwater snails).

Schistosoma (Blood Flukes)

• Schistosomosis is also known as bilharziosis after the German physician Th. Bilharz, who discovered Schistosoma hematobium in human blood vessels in 1851.

• Schistosomosis occurs endemically in 74 tropical and subtropical countries of Africa, South America, and

Asia .The number of persons infected with schistosomes is estimated at 200 million(WHO 2008)

Schistosoma (Blood Flukes)

• Human infections result from contact with standing or slow-moving bodies of water (freshwater) when Schistosoma cercariae penetrate the skin.

• Schistosoma hematobium causes urinary schistosomosis.

S. mansoni, S. japonicum,S. intercalatum, and S. mekongi are the causative agents of intestinal schistosomosis and other forms of the disease.

Trematodes

Fasciola hepatica

Dicrocoelium dendriticum

Clonorchis spp

Paragonimus spp

Fasciola hepatica and F. gigantica are bile duct parasites of domestic ruminants.In their life cycle freshwater snails act as intermediate host Humans become accidentally infected when they eat plants to which

infectious parasite stages (metacercariae) adhere

Dicrocoelium dendriticum is a bile duct parasite in sheep,cattle, and other herbivores, Its life cycle includes two intermediate hosts (terrestrial snails and ants). Humans become infected accidentally when

they ingest ants containing infective metacercariae of the lancet liver fluke.

Fasciola hepatica

F. hepatica is a flattened,

leaf-shaped parasite about

2–5 cm long and at most

1 cm wide.

Dicrocoelium dendriticum

The lancet liver fluke

(0.5–1.0 ! 0.2 cm)

Fasciola hepatica egg Dicrocoelium dendriticum egg

Cestoda (Tapeworms)

Taenia saginata Taenia saginata

Taenia soliumTaenia solium

Echinococcus granulosusEchinococcus granulosus

Cestoda (Tapeworms)Cestoda (Tapeworms)

• General characteristics *Parasitize in the small intestine of humans.

* They are hermaphrodites and consist of the head (scolex), followed by an unsegmented germinative section (neck) and a posterior chain of segments (proglottids).

*There are no digestive organs, so nutrients are taken up through the absorptive integument.

Cestoda (Tapeworms)Cestoda (Tapeworms)

*The life cycle of cestodes include one or two intermediate hosts.

* Humans can also be infected by larval stages of various tapeworm species (cysticerci, metacestodes).

* These stages develop in body tissues and generally cause considerably greater pathological damage than the intestinal cestode stages.

Taenia speciesTaenia speciesCausative agents of

taeniosis and cysticercosis

*Taeniosis is a small intestine infection of humans caused by Taenia species.

*In T. saginata, the intermediate hosts are cattle.

*In the musculature of the cattle cysticerci develop and can be ingested by humans who eat raw beef.

* The cysticerci of T. solium develop in the musculature of pigs.

Taenia saginata (Beef Tapeworm)Taenia saginata (Beef Tapeworm)Causative agent ofT. saginata taeniosis

• Occurrence. This species occurs worldwide the number of infected humans is estimated to be between 40 and 60 million.

The parasite• * T.saginata grows as long as 10m and has a

scolex with four suckers.• * Proglottids at the posterior end of the chain are

longer than wide and each contains a treelike branched uterus containing 80 000–100 000 eggs.