This document provides information about helminths (parasitic worms) that infect humans. It begins with objectives and classifications of helminths. Nematodes (roundworms) are then described in more detail, including their general features, habitats, life cycles and diseases caused like ascariasis, pinworm infection and whipworm infection. Hookworms are also discussed. Platyhelminthes (tapeworms and flukes) are then introduced, with descriptions of cestodes (tapeworms) like Taenia saginata and Taenia solium, and preventive measures for helminth infections are mentioned.

1. HELMINTHS
Human and Microbial Interaction
Unit VI
By
Muhammad Iqbal
Lecturer
KMU
Microbiology

2. OBJECTIVES
• At the end, the learners will be able to:
• Define key terms
• Discuss general characteristics of helminths
• Give their classification
• Identify helminthic diseases
• Discuss preventive measures
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3. Classification
Helminths
Phylum: Nemathelminthes (Round)
Class: Nematoda
Phylum: Platyhelminthes (flat)
Class: Cestoda & Trematoda
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4. General Features of Nematodes
Nematodes (Nema= thread) are commonly known as
Round worms. They include pinworms or thread wor
ms, Hookworms, Whipworms.
Shape: unsegmented, Round, elongated and tapered
at both ends. Hooks and suckers are absent.
Size: from 5 mm to 30 cm in length.
Digestive system: complete alimentary tract present.
Sex: dioecious, means male and female are separate.
Males are smaller than females.
Reproduction: Mostly are oviparous but some are vivi
parous.
Life cycle: Almost monogenetic; may take about 60 da
ys to complete their life cycle.
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5. Habitat
Regarding habitat there are two groups of Nemato
des:
1. Intestinal, and 2. Tissue or somatic Nematodes
1. Intestinal Nematodes:
a. Small Intestinal Nematodes:
e.g: Ascaris lumricoides (Round worm)
Ancyclostoma duodenale (hookworm)
Necator americanus (hookworm)
b. Large Intestinal Nematodes:
e.g: Enteroboius vermicularis (pinworm)
Trichuris trichiura (whipworm)
Infective stage: either fertilized egg or larva

6. Roundworms
Different species like Ascaris lumbricoid, etc are found.
Gk. Askaris=intestinal worm
► Size: Males 15-30 cm and females from 20-40 cm in l
ength
► Habitat: Small intestine
► Transmission: by ingestion of fertilized eggs via food
and water
► S/S
• GIT disturbance, N/V, Colic pain, anorexia, malnutritio
n, paleness, intestinal obstruction in heavy infection, fe
ver, liver abscess, pancreatitis and Loeffler’s syndrom
e due to their migration (ectopic infection).
Most infections (about 85%) are mild and symptomless.
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7. ► Diagnosis:
• The presence of adult worms in faeces or vomitus
• Microscopic stool examination for eggs and larvae
• Sputum microscopic examination
• Blood examination for Eosinophilia
► Treatment
1. Pharmacologic Treatment:
• Mebendazole and pyrantel pamoate are drugs of c
hoice. Other drugs are piperazine, albendazole, an
d Thiabendazole.
2. Surgery:
Is necessary in case of intestinal obstruction.
Note: Ascariasis in pregnancy should be treated afte
r 1st trimester.
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8. Pinworms
• Pinworm or threadworm is a common name. They in
clude different species like Enterobius vermicularis.
► Size: Small and can be seen with naked eyes. Male
s range from 2-5 mm and females from 8-12 mm in l
ength.
► Habitat: The adult worms remain attached to caecu
m, appendix and in ilium, ascending colon as well.
► Transmission: by Ingestion or inhalation of fertilize
d eggs.
• Female comes down and lays eggs in perianal area
during night which causes itching and irritation.
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9. Pinworm cont…
► S/S: perianal itching and irritation, pruritu
s ani.
►Laboratory Diagnosis:
• Graham sticky tape method for eggs on pe
rianal area.
• Microscopic stool examination
► Treatment: Mebendazole, pyrantel pamo
ate and should be repeated after two week
s
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10. Whipworms
• Whipworm (whip shaped) is a common name.
They include different species like Trichuris tri
chiura, etc.
► Size: Males range from 3-4 cm and females f
rom 4-5 cm in length.
• Females lay 2,000 to 6,000 eggs /day
► Habitat: Large intestine, caecum, appendex
► Transmission: Ingestion of food and water c
ontaminated with fertilized eggs.
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11. Whipworm cont…
► S/S: Abdominal pain, distention, mucous or
bloody diarrhea, anorexia, weight loss, eosin
ophilia, anemia.
► Laboratory Diagnoisis: Microscopic stool e
xamination.
► Treatment: Albendazole or Mebendazole
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12. HOOKWORM
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13. Hookworms
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14. Hookworm
• Hookworm is a common name. different speci
es are like Ancyclostoma duodenale (Gk. Anc
hylos=hooked), Necator americanus (Necator
=murderer means American murderer),etc. Ap
art from anthrophilic, there are zoophilic speci
es also.
► Habitat: duodenum and jejunum and ileum.
► Size: Male 10 mm and female 15 mm.
► Transmission: The entrance of rhabditiform
(rod shaped) larva through the skin of bare fo
oted man waking on contaminated soil.
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15. Hookworm cont…
► S/S: severe itching at penetration site known
as ground itch or ancylostoma dermatitis whic
h lasts for 2-4 weeks. Loeffler’s syndrome, an
emia as they suck blood and there secretions
also contain anticoagulant which leads to bloo
d loss.
► Laboratory diagnosis: Stool examination, S
tool occult blood, CBC.
► Treatment: Mebendazole or albendazole
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16. 2. Tissue or Somatic Nematodes
Somatic nematodes are filarial worms (Latin, filu
m means ‘thread’).
General features:
• Size: 2-10 cm in length
• Habitat: Lymphatic vessels, blood vessels, lung
s, and subcutaneous tissues
• Life cycle: They are digenetic, blood sucking in
sect.
• Vector: Filarial worms are transmitted by variou
s species of mosquitoes like Anopheles, Aedes,
and Culex. M. Iqbal

17. • Microfilaria: The adult females are vivipar
ous and give birth to larvae called microfila
ria. The vectors transmit microfilaria into h
uman blood.
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18. Lymphatic Filariasis
• Three filarial worms are responsible for lymph
atic filariasis. They are Wucheria bancrofti, Br
ugia malayi, Brugia timori. The most common
is Wucheria bancrofti which is responsible for
90 % of infections. It causes elephantiasis.
• Wucheria bancrofti
• Habitat: lymph nodes and lymph vessels
• Size: male 2-4 cm x 0.1 mm
female 8-10 cm x 0.2 mm
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19. They affect different tissues as:
a. Lymphatic vessels as lymphatic filariasis cau
sed by, for example, Brugia malayi
b. Subcutaneous tissues (e.g Loa loa)
c. Conjunctiva (e.g Loa loa)
d. Lungs (e.g Trichinella spiralis)
Transmission:
Somatic nematodes are mostly transmitted to
man in the form of larvae by mosquito bite.
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20. Lymphatic Filariasis
A female Anopheles mosquito t
aking a blood meal
Elephantiasis of the leg (sou
rce: WHO)

21. Platyhelminthes
(Tapeworms)
Platyhelminthes are classified into C
estodes and Trematodes
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22. Platyhelminthes
Cestodes Trematodes
1. Tape-like, segmented
2. Monocious /Hermaphrodite
3. Suckers often with hook
4. Alimentary canal absent
1. Leaf-like, unsegmented
2. Monocious except schistosomes
3. Suckers but no hook
4. Alimentary canal present but inco
mplete
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23. Cestodes
Gk. Kestos=ribbon, means tape-like
► General Features:
• Shape: dorsoventrally flattened.
• Habitat: Intestine and other body tissues.
• Size: ranges from 1 cm to 15 meters.
• Body structure: Consists of
a) scolex: containing suckers (organs of att
achment)
b) neck: (germinal centre from which new pr
oglottids or segments keep generating)
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24. Cestodes general features cont…
c) Strobila: Trunk or body of tapeworm
• Proglottid: three types ---immature, mature, gravid.
Each mature proglottid contains both male and fema
le reproductive organs
• Digestive system: No digestive system
• Sex: hermaphrodites
• Life cycle: Digenetic, using intermediate and
definitive host.
They cause both intestinal as well as systemic i
nfections
There are different species of cestodes.
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25. Taenia saginata (beef tapeworm)
• Distribution: Worldwide
• Size: usually 5-10 meters but may exceed ev
en 20 meters. It is white in color.
• Habitat: Adult tapeworms live in the small int
estine of man attached to the mucosa by sc
olex.
• Life span: It may live for about 10 years.
• Proglottids: The strobila (trunk) consists of
1000-2000 proglottids (segments). Each seg
ment has opening to discharge fertilized egg
s.
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26. Cont….
• Testes: 300-400 in each mature proglottid
• Ovaries: Two in number. Each segment contai
ns about 80,000 eggs.
• Life cycle: It requires two hosts to complete its
life cycle.
• Intermediate host: Cattle (cow or buffalow) har
bours larval stage
• Definitve host: Man who harbours adult worm.
• Transmission: Ingestion of cysticercus cyst lar
vae by man in raw or undercooked meat of cattl
e or contaminated food or water.
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27. • Development in man: the larvae cysticerci g
row into adult in man. They discharge fertilize
d eggs through human faeces. The eggs are
viable upto 8 weeks in soil and are infective f
or cattle only.
• Development in cattle: The cattle ingest the
eggs during grazing. The eggs pass from inte
stine into muscles via blood circulation. In mu
scles,the eggs develop into larvae called cyst
icercus bovis. This larva is ingested by man i
n raw or undercooked beef.
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28. • S/S: Nausea, abdominal discomfort, pain, i
ndigestion, diarrhea alternating with consti
pation.
• Diagnosis: Microscopic stool examination
for segments and eggs
• Treatment: Praziquantel or Niclosamide
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29. Taenia solium (pork tapeworm)
• Size: 2-3 meters in length.
• Habitat: Small intestine.
• Life span: upto 25 years
• Transmission: Ingestion of cysticerci by ma
n (definitive host) in raw or undercooked pork
.
• Proglottids: 800-900
• Intermediate host: pig
• Defenitive host: man
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30. • Life cycle is similar to that of T. saginatta.
• Transmission is same with that of T. saginatta
• It causes both intestinal as well as systemic inf
ections
• S/S:
• In Intestinal taeniasis there is abdominal disco
mfort and pain.
• Systemic infections include subcutaneous tiss
ues, skeletal muscles and brain infection
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31. ►Diagnosis
a) For Intestinal taeniasis:
• Microscopic stool examination
b) Tissue cysticercosis (tissues affected by cyst
icercus larvae is called cysticercosis) is diagnos
ed by:
• Radiography, biopsy
• CT scan, MRI
• Treatment:
• Same as T. saginatta infection
• For cysticercosis, prazequantel and albendazol
e are effective.
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32. Other systemic/tissue cestodes
They ineter body tissues in larval forms.
Examples are:
• Echinococcus granulosus (dog tapeworm) cau
ses hydated disease
• Echinicoccus multilocularis (rodent tapeworm)
causes alveolar and hydated disease
- Hydatid disease occurs when the larval stage
s of these organisms are ingested
- The larvae may develop in man and cause le
sions in several organs, e.g. liver, brain
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33. Trematodes
• Trematodes have suckers with a hole (Gk. Trema, h
ole; edios, appearance) appears in the middle of suc
kers, and hence are called trematodes.
• General characteristics:
• Leaf-shaped
• Unsegmented
• Size is 1 mm to several cm
• Found in intestine, liver, lung, blood vessels
• They are mostly hermaphrodites
• Either monogenetic or digenetic
• Their infective larvae are cercaria, metacercaria and
miracidium. M. Iqbal

34. • They are named according to the organs t
hey infect like liver fluke, lung fluke, etc.
Liver fluke Lung fluke

35. Prevention
• Education
• Safe disposal of faeces
• Avoid contact with contaminated soil
• Good personal hygiene
• Adequate sanitation
• Avoid bare footed walking
• Control measures for mosquitoes and flies
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36. References
• Textbook of Medical Parasitology by P.Ch
akabrty
• Tortora, microbiology, ed 10th
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37. M. Iqbal

38. • Annelid worms such as leeches all have an anterior (oral) sucker for
med from the first six segments of their body, which is used to conne
ct to a host for feeding. It also releases an anaesthetic to prevent the
host from feeling pain while it sucks blood. They use a combination
of mucus and suction (caused by concentric muscles in those six se
gments) to stay attached and secrete an anti-clotting enzyme, hirudi
n, into the host's blood stream. The medicinal leech (Hirudo medicin
alis) has two suckers, one at each end, called the anterior and poste
rior sucker. The posterior is mainly used for leverage while the anteri
or sucker, consisting of the jaw and teeth, is where the feeding takes
place.[12] During locomotion directional movement of the body is don
e by successive attachment and detachment of the oral sucker and t
he acetabulum.[2]
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39. • A medicinal leech with its oral sucker
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40. Schistosoma (blood fluke)
• Morphology
• Adult schistosomes share all the fundamental features of
the digenea. They have a basic bilateral symmetry, oral
and ventral suckers, a body covering of a syncytial tegu
ment, a blind-ending digestive system consisting of mout
h, oesophagusand bifurcated caeca; the area between th
e tegument and alimentary canal filled with a loose netw
ork of mesoderm cells, and an excretory or osmoregulat
ory system based on flame cells. Adult worms tend to be
10–20 mm (0.4–0.8 in) long and use globins from their h
osts' hemoglobin for their own circulatory system.
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41. Schistosoma
• Schistosoma indicum
• Schistosoma datta
• Schistosoma japonicum
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