Transcript INTRODUCTION TO HELMINTHOLOGY ,GENERAL PROPERTIES

HELMINTHS
Doç.Dr.Hrisi BAHAR
HELMINTHS
●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
NEMATODES
• Some species require an
intermediate host to complete
development.
• Intestinal nematodes all mature
into adults within the human
intestinal tract.
NEMATODES
• 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.
NEMATODES
• The males are usually smaller than
the females and are equipped with
copulatory organs that often show
features specific to each species.
NEMATODES
● 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
NEMATODES
• Three of the intestinal nematodes
are acquired by the ingestion of
nematode eggs:
● Trichuris trichiura ("whipworm")
● Ascaris lumbricoides
● Enterobius vermicularis
("pinworm")
NEMATODES
• Two worms are acquired when
their larvae penetrate through
the skin, usually of the foot:
● Necator americanus
("hookworm")
● Strongyloides stercoralis
NEMATODES
• One is acquired by the
ingestion of the encysted
larvae in muscle (pork meat):
Trichinella spiralis
NEMATODES
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 belongs
to 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 gives
the pinworm its name.
Enterobius vermicularis
Class Trematoda
(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 Trematoda
• Most species are hermaphroditic.
• Snails are the first intermediate
hosts;some species require
arthropods or fish as second
intermediate hosts
Class Trematoda
Schistosoma (Blood Flukes)
Causative agents of schistosomosis or
bilharziosis.
Schistosomosis (bilharziosis) is one of
the most frequent tropical diseases with
about 200 million infected persons.
The occurrence of schistosomosis
depends on the presence of suitable
intermediate 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
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 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 egg
Dicrocoelium dendriticum egg
Cestoda (Tapeworms)
Taenia saginata
Taenia solium
Echinococcus granulosus
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)
*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 species
Causative 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)
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.