HELMINTHS - philadelphia.edu.jo

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.


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.


Eggs


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


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


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)


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


Clonorchis sinensis

Biliary tract inflammation pigmented

gallstones

Associated with cholangiocarcinoma

Undercooked fish

Praziquantel

Nematodes (roundworms)


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


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



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



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)



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

https://www.academia.edu/30595207/Panikers_Textbook_of_Medical_Parasitology_7th_Edition_2013_PDF_








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