This document provides an introduction to helminthology, the study of parasitic worms. It defines key helminth terminology and discusses the classification, characteristics, life cycles and examples of the three main classes of helminths: nematodes, cestodes, and trematodes. Nematodes are roundworms, cestodes are tapeworms, and trematodes are flukes. The document highlights some important helminth infections including ascariasis, trichuriasis, hookworm infections, and hymenolepiasis and their effects on human health. It also discusses the life cycles and pathogenic stages of intestinal nematodes like whipworm, hookworms, and roundworm.

1. INSTITUTE OF PULIC HEALTH, DHAKA
Department of Laboratory Medicine
BSc in Health Technology (Laboratory)- 1st Year
HELMINTHOLOGY
Lecture No. 01(Introduction)
By
Sk. MIZANUR RAHMAN
Assistant Bacteriologist, MBL, IPH
MS in Biotechnology & Genetic Engineering (UODA)
MS in Microbiology (SU)
MPH in Epidemiology (SUB)

2. Norman Stoll, President of the
American Society of
Parasitologists
1947 inaugural address
“This wormy world”
Called for a world-wide
effort to control worm
infections

3. Method of Learning
• Terminology
• Introduction
• Classification
• Characteristics
• Differences between the classes
• Example and Life cycles

4. HELMINTH/WORM TERMINOLOGY
• Adults: sexually reproductive life cycle stage
• Larvae: developmental or asexually reproductive life
cycle stage
• Eggs: stage protective of zygote &/or embryo
• Cysts: usually a larval stage encapsulated in tissues
of an intermediate host
• Hypobiosis: worms in temporary developmental
arrest
• Monoecious/hermaphroditic: both sexes 1 body
• Dioecious: sexes separate; males & females
• Parthenogenesis: ability to produce offspring
without fertilization of eggs

5. Helminths, continued
Worm-terms, continued
• Oviparous: production of eggs, discharged from
uterus of female
• Ovoviviparous: production of eggs which hatch
prior to discharge from uterus of female
• Viviparous: production of embryos/L1 larvae, no
rigid encapsulation of embryo

6. Introduction to helminth
• Helminth means worm. Their motile activity is
accomplished by wriggling movement. The helminth of
medical importance belong to 3 classes: Nematoda,
Trematoda and Cestoda.
• Helminthology is the study of parasitic worms and their
effect on their hosts.
• Geohelminths refer to the helminths which complete
their life cycles not requiring the processes of the
development in intermediate hosts. They have only one
host and a simple life cycle, such as ascarid, hookworm,
pinworm and etc.
• Biohelminths refer to those that have to undergo the
development in intermediate hosts to complete their life
cycle , such as filaria, liver fluke, pork tapeworm and so on.

7. Taxonomic classification of helminths
Sub
kingdom
Phylum Class Genus – examples
Metazoa Nematodes
Round worms; appear round in
cross section, they have body
cavities, a straight alimentary
canal and an anus
Ascaris (roundworm)
Trichuris (whipworm)
Ancylostoma (hookworm)
Necator (hookworm)
Enterobius (pinworm or
threadworm)
Strongyloides
Platyhelminthes
Flat worms; dorsoventrally
flattened, no body cavity and, if
present, the alimentary canal is
blind ending
Cestodes
Adult tapeworms are found in the
intestine of their host
They have a head (scolex) with
sucking organs, a segmented body
but no alimentary canal
Each body segment is
hermaphrodite
Taenia (tapeworm)
Trematodes
Non-segmented, usually leaf-
shaped, with two suckers but no
distinct head
They have an alimentary canal and
are usually hermaphrodite and leaf
shaped
Schistosomes are the exception.
They are thread-like, and have
separate sexes
Fasciolopsis (liver fluke)
Schistosoma (not leaf
shaped!)

8. HELMINTHS (WORMS)
Characteristics
Eukaryotic (N+CW), multicellular animals that usually have
digestive, circulatory, nervous, excretory, and reproductive
systems.
Worms with bilateral symmetry, head and tail, and tissue
differentiation (endoderm, mesoderm, and ectoderm).
Parasitic helminths spend most or all of their lives in host
and usually have the following specializations:
– May lack a digestive system. Absorb nutrients from host’s food,
body fluids, or tissues.
– Have a reduced nervous system.
– Means of locomotion is reduced or absent.
– Complex reproductive system. Individuals produce many eggs that
can infect another host.

9. Helminthes
Cestodes Trematodes Nematodes
Shape Segmented plane Unsegmented plane Cylindrical
Body cavity No No Present
Digestive tube No Ends in cecum Ends in anus
Sex
Hermaphroditic -
Taenia
(tapeworm)
Hermaphroditic, except
Schistosoma which
are dioecious
Dioecious-
Ascaris
(roundworm)
hook organ
component
Oral sucker, botridias,
and double
Rostellar hooks
Oral sucker and ventral
sucker
Lips, teeth, filariform
extremities, and
dentary plates

10. Helminths (Worms): Some Important Ones
Most acquired from ingestion of or contact with feces-contaminated soil or
food
• Nematodes (Roundworms):
– Ascaris lumbricoides GI illness; pneumonitis
– Trichuris trichuria chronic GI
• Hookworms:
– Ancylostoma duodenale chronic anemia
– Necator americanus chronic anemia
– Strongyloides stercoralis chronic anemia
• Cestodes (tapeworms):
– Hymenolepis nana GI illness
Worm burdens tend to be low in the United States; little illness occurs
Still major causees of illness in developing countries

11. Examples of important metazoa – intestinal nematodes
• Trichuris (whipworm)
– A soil transmitted helminth
– prevalent in warm, humid conditions
– Can cause diarrhoea, rectal prolapse
and anaemia in heavily-infected
people
• Ancylostoma and Necator (hookworms)
– A major cause of anaemia in the
tropics
• Strongyloides
– inhabits the small bowel
– infection more severe in
immunospressed people (e.g.
HIV/AIDS, malnutrition, intercurrent
disease)
• Enterobius (pinworm or threadworm)
– prevalent in cold and temperate
climates but rare in the tropics
– found mainly in children
• Ascaris (roundworm)
– Found world-wide in conditions of
poor hygiene, transmitted by the
faecal- oral route
– Adult worms lives in the small
intestine
– Causes eosinophilia
Heavy intestinal infections may occur
with Ascaris. Adult worms can be
several cms long.

12. Infective name Pathogenesis
stage route Prevention
mode
Life cycle Pathogenic name Pathogenesis
stage localization Treatment
migration Diagnosis
Diagnostic stage-morphology Diagnosis
stage methods
stage outside name Epidemiology
(vector, other host) name Prevention
Learning method