helminths - philadelphia.edu.jo
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HELMINTHS LECTURE NO. 11
Course Name: PARASITOLOGY
Course Code: 0520442
Lecturer: Ms. Asma El-Shara’. MPH
Faculty Of Pharmacy,
Philadelphia University - Jordan
Introduction
The helminthic parasites are multicellular (metazoan).
bilaterally symmetrical animals having 3 germ layers
(triplobastic metazoa) and belong to the kingdom
Metazoa.
The term 'helminth' (Greek helmins-’worm’) originally
referred to intestinal worms, but now comprises many
other worms, including tissue parasites as well as
many free-living species.
Introduction (continued)
Helminths, which occur as parasite in humans belong to 2 phyla:
A- Phylum Platyhelminthes (flatworms) – It includes 2 classes:
1- Class – Cestoda (tapeworms).
2- Class – Trematoda ( flukes or digeneans)
B- Phylum Nemathelminthes – It includes class nematoda and 2
subclasses:
■ Subclass – Adenophoraea (Aphasmidia)
■ Subclass – Secernentea (Phasmidia).
Differences Between Cestodes, Trematodes, and Nematodes
Cestodes Trematodes Nematodes
Shape Tape-like, segmented Leaf-like, unsegmented Elongated, cylindrical, unsegmented
Head end. Suckers present; some have attached hooks
Suckers are present but no hooks
Hooks and sucker absent. Well-developed buccal capsule with teeth or cutting plates seen in some species
Alimentary canal
Absent Present but incomplete, no anus
Complete with anus
Body cavity Absent, but inside is filled with spongy undifferentiated mesenchymatous cells, in the midst of which lie the viscera
Same as cestodes Present and known as pseudocele. Viscera remains suspended in the pseudocele.
Sex Not separate: hermaphrodite (monecious
Not separate: hermaphrodite except Schistsoma
Separate (diecious)
Life cycle Requires 2 host except Hymenolepis (1 host) and Diphyllobothrum (3 host)
Requires 3 host except schistosomes (2 host)
Requires 1 host except flarial worms (2 host) and Dracunculus (2 host)
Important Features of Helminths
Adult Worms
■ Helminths have an outer protective covering, the cuticle or
integument, which may be tough and armed with spines or
hooks. The cuticle of live helminths is resistant to intestinal
digestion.
■ The mouth may be provided with teeth or cutting plates.
■ Many helminths possess suckers or hooks for attachment to
host tissues.
■ They do not possess organs of locomotion, but in some species
the suckers assist in movement.
■ Locomotion is generally by muscular contraction and relaxation.
■ Many helminths have a primitive nervous system.
■ The excretory system is better developed.
Important Features of Helminths
Adult Worms
■ The greatest development is seen in the reproductive system.
Helminths may be monoecious (with functioning male and
female sex organs in the same individual) or diecious (the two
sexes, male and female, separate).
■ In the hermaphroditic helminths, both male and female
reproductive systems are present in the same worm and self-
fertilization as well as cross-fertilization take place. (e.g. Taenia
solium).
■ In the dioecious species, males and females are separate, the
male being smaller than the female. (e.g. Ascaris lumbricoides) .
■ Rarely, the female is parthenogenic, being able to produce
fertile eggs or larvae without mating with males (e.g.
Strongyloides).
■ The eggs or larvae are produced in enormous
numbers— as many as 200,000 or more per
female per day.
■ Various helminths have distinct morphology of
eggs, which can be used to differentiate the
helminths.
Important Features of Helminths
Eggs
Important Features of Helminths
Larval Forms There are various larval forms of helminths found in man
and other hosts. These forms are as follows:
■ Cestodes: The various larval forms are cysticercus,
coenurus, coracidium, cystecercoid, procercoid, hydatid
cyst, and plerocercoid forms.
■ Trematodes: The various larval forms are miracidium,
cercaria, redia, metacercaria, and sporocyst.
■ Nematodes: The various larval forms are microfilaria,
filariform larva, and rhabditiform larva.
Cestodes: larval forms
Trematodes: The various larval
Nematodes: The various larval forms
Important Features of Helminths
Multiplication
■ Helminths differ from protozoans in their inability to multiply
in the body of the host.
■ Protozoans multiply in the infected person, so that disease
could result from a single infection. But helminths, apart
from very rare exceptions, do not multiply in the human
body, therefore, a single infection does not generally leads
to disease.
■ Heavy worm load follows multiple infections. Sometimes,
multiplication occurs within larval forms in Platyhelminths.
Life Cycle
■ Cestodes: They complete their life cycle in 2 different hosts,
except Hymenolepis nana, which completes its life cycle in a
single host and Diphyllobothrium latum which completes its life
cycle in 3 hosts.
■ Trematodes: They complete their life cycle in 1 definitive host
(man) and 2 intermediate hosts. Fresh water snail or mollusc act
as first intermediate host and fish or crab act as second
intermediate host except schistosomes which require 2 hosts – 1
definitive host (man) and other intermediate host (snail).
■ Nematodes: Nematodes require only 1 host to complete their life
cycle except filarial nematodes and Dracunculus medinensis,
which complete their life cycle in 2 hosts.
Cestodes (tapeworms)
ORGANISM DISEASE TRANSMISSION TREATMENT
Taenia solium Intestinal tapeworm Ingestion of larvae encysted in undercooked pork
Praziquantel
Cysticercosis, neurocysticercosis (cystic CNS lesions, seizures)
Ingestion of eggs in food contaminated with human feces
Praziquantel; albendazole for neurocysticercosis
Cestodes (tapeworms)- continued
ORGANISM DISEASE TRANSMISSION TREATMENT
Diphyllobothrium latum
Vitamin B12 deficiency (tapeworm competes for B12 in intestine) megaloblastic anemia
Ingestion of larvae in raw freshwater fish
Praziquantel
Echinococcus granulosus
Hydatid cysts (“eggshell calcification”) in liver E; cyst rupture can cause anaphylaxis
Ingestion of eggs in food contaminated with dog feces
Sheep are an intermediate host
Albendazole
Trematodes (flukes)
ORGANISM DISEASE TRANSMISSION TREATMENT
Schistosoma
Liver and spleen enlargement (S mansoni, egg with lateral spine A ), fibrosis, inflammation, portal hypertension Chronic infection with S haematobium (egg with terminal spine B) can lead to squamous cell carcinoma of the bladder (painless hematuria) and pulmonary Hypertension
Snails are intermediate host; cercariae penetrate skin of humans in contact with contaminated fresh water (eg, swimming or bathing)
Praziquantel
Trematodes (flukes)- continued
ORGANISM DISEASE TRANSMISSION TREATMENT
Clonorchis sinensis
Biliary tract inflammation pigmented
gallstones
Associated with cholangiocarcinoma
Undercooked fish
Praziquantel
Nematodes (roundworms)
ORGANISM DISEASE TRANSMISSION TREATMENT
INTESTINAL
Enterobius vermicularis (pinworm)
Causes anal pruritus (diagnosed by seeing egg via the tape test) A
Fecal-oral Pyrantel pamoate or bendazoles (because worms are bendy)
Ascaris lumbricoides (giant roundworm)
May cause obstruction at ileocecal valve, biliary obstruction, intestinal perforation, migrates from nose/mouth
Fecal-oral; knobby-coated, oval eggs seen in feces under microscope B
Bendazoles
Bendazoles
Albendazole Mebendazole
Nematodes (roundworms) - continued
ORGANISM DISEASE TRANSMISSION TREATMENT
INTESTINAL
Strongyloides stercoralis (threadworm)
Autoinfection: rarely, some larvae may penetrate the intestinal wall to enter the bloodstream without leaving the body
Larvae in soil penetrate skin; rhabditiform larvae seen in feces under microscope
Ivermectin or bendazoles
Ancylostoma duodenale, Necator americanus (hookworms)
Cause anemia by sucking blood from intestinal wall Cutaneous larva migrans—pruritic, serpiginous rash from walking barefoot on contaminated beach
Larvae penetrate skin Bendazoles or pyrantel pamoate
Nematodes (roundworms) - continued
ORGANISM DISEASE TRANSMISSION TREATMENT
INTESTINAL
Trichinella spiralis
Larvae enter bloodstream, encyst in striated muscle muscle inflammation Trichinosis—fever, vomiting, nausea, periorbital edema, myalgia
Undercooked meat (especially pork); fecal-oral (less likely)
Bendazoles
Trichuris trichiura (whipworm)
Often asymptomatic; loose stools, anemia, rectal prolapse in children (heavy infection)
Fecal-oral Bendazoles
Nematodes (roundworms) - continued
ORGANISM DISEASE TRANSMISSION TREATMENT
TISSUE
Toxocara canis Visceral larva migrans—nematodes migrate to blood through intestinal wall inflammation and damage. Often affects heart (myocarditis), liver, eyes (visual impairment, blindness), and CNS (seizures, coma)
Fecal-oral Bendazoles
Onchocerca volvulus
Skin changes, loss of elastic fibers, and river blindness (black flies, black skin nodules, “black sight”); allergic reaction to microfilaria possible.
Female blackfly Ivermectin (ivermectin for river blindness)
Nematodes (roundworms) - continued
ORGANISM DISEASE TRANSMISSION TREATMENT
TISSUE
Loa loa Swelling in skin, worm in conjunctiva
Deer fly, horse fly, mango fly
Diethylcarba-mazine
Wuchereria bancrofti
Lymphatic filariasis (elephantiasis)— worms invade lymph nodes inflammation lymphedema C ; symptom onset after 9 mo–1 yr
Female mosquito Diethylcarba-mazine
References
■ Paniker’s Textbook of Medical Parasitology. Paniker CKJ. and
Ghosh S. 7th ed. Jaypee Brothers Medical Publishers (P) Ltd, 2013.
ISBN: 978-93-5090-534-0. ONLINE REFERENCE:
https://www.academia.edu/30595207/Panikers_Textbook_of_Me
dical_Parasitology_7th_Edition_2013_PDF_. Retrieved on October
15, 2018.
■ First Aid for the USMLE Step 1 2018. Le T et al., 28th Edition.
McGraw Hill Education, 2018. ISBN: 978-1-26-011613-7. ONLINE
REFERENCE:
https://drive.google.com/file/d/1cIL8zyNUIfpT1IwDdekZN7tAMsFp
PG7p/view . Retrieved on January 15, 2019.
■ https://www.autism.com/statement_helminths