INTRODUCTION TO

PARASITOLOGY

N.G.D. Martin, RMT,

30-21 Jan 2023
 Introduction to Parasitology
• Parasitology
– study of parasites
– Deals with the study of any organism that
depends on another organism for the purpose
of procuring food and securing protection.
• Parasite
• Host
• Vector
– organisms that acts as “carriers” responsible
for the spread of the disease
Symbiotic Relationships
• Symbiosis
– is the living together of unlike organisms
– may also involve protection or other advantages to
one or both partners

• Types of Symbiosis
• Mutualism
• Commensalism
• Parasitism
 Types of Symbiosis
1. Mutualism
– Two organisms both benefit from the
relationship
2. Commensalism
– One organism benefits from the relationship,
but does not affect the other.
 Types of Symbiosis
3. Parasitism
– One organism thrives into another organism for
survival at the expense of the host
– Parasite and the host
Chain of Infection
Organism

Host Reservoir

Mode of
Transmission
 Organism: Kinds of Parasites
• According to Habitat
• Effect of the Parasite on the Host
• Mode of Relationship
• Mode of Transmission
 Kinds of Parasites
A. According to Habitat
1. Ectoparasite – outside the body of host
(infestation)
2. Endoparasite – inside the body of host (infection)
B. Effect of the parasite on the host
1. Pathogenic- produces a disease pattern in man
2. Non-pathogenic – do not produce a disease
pattern in man
 Kinds of Parasites
C. Mode of Relationship between the parasite
and the host
1. Obligatory – need a host at some stage of
their life cycle to complete their development
and to propagate their species
2. Facultative – may exist in a free-living state or
may become parasitic when the need arises
3. Intermittent – only visit the host during
feeding time.
 Kinds of Parasites
C. Mode of Relationship between the parasite
and the host
4. Accidental or Incidental parasite- establishes
itself in a host where it does not ordinarily live
5. Permanent parasite- remains on or in the body of
the host for its entire life cycle
6. Temporary parasite - lives on the host only for a
short period
 Kinds of Parasites
D. Mode of Transmission
1. Soil-Transmitted
2. Snail Transmitted
3. Food Transmitted –developed in the fleah of
animals that man utilized as source of food
4. Contact-transmitted parasites –readily
infective upon contact
5. Vector-transmitted – develop in the body of
arthropods before they become infective
Chain of Infection
Organism

Host Reservoir

Mode of
Transmission
 Reservoir of Infection
• Reservoir
– transfers the parasite into the host
– each parasite has a specific reservoir
– Examples:
» Soil
» Snail
» Arthropods (bugs, fly)
» Animal/Food Borne
 Chain of Infection
Organism

Host Reservoir

Mode of
Transmission
 Mode of Transmission
1. Mouth
2. Skin Penetration
3. Arthropods
4. Congenital Transmission
5. Inhalation
6. Sexual Intercourse
 Chain of Infection
Organism

Host Reservoir

Mode of
Transmission
 Host
• Host represent a rich source and highly regulated
supply of nutrients

• Body fluids of animals are a good source of nutrition

• Ability of vertebrates to regulate body temperature

(37C)

• classified based on their role in the life cycle of the

parasite
 Kinds of Hosts
• Definitive or final host: is one in which the parasite attains
sexual maturity
– Humans are the definitive host in taeniasis

• Intermediate host: harbors the asexual or larval stage of the

parasite
– Pigs or cattle as intermediate hosts of Taenia spp. while snails are
hosts of Schistosoma spp.

• Paratenic host: one in which the parasite does not develop further
to later stages. However, the parasite remains alive and is able to
infect another susceptible host
– Paragonimus metacercariae in raw wild boar meat can pass through the
intestinal wall of humans and complete its development
 Kinds of Hosts
• Reservoir hosts:
– allow the parasite’s life cycle to continue and become
additional sources of human infection
• Pigs are reservoirs of Balantidium coli
• Field rats of Paragonimus westermani
• Cats of Brugia malayi
– Humans are not always the final host
– Man may be the most important host in the spread of the
disease or an incidental host of parasites prevalent in
other animals
Vectors - transmits the parasite from one host to
another
• Biologic vector: transmits the parasite only after the
latter has completed its development within the
host
– Aedes sucks blood from a patient with filariasis, the parasite undergoes
several stages of development from the first stage larva to 3rd stage larva
before it is transmitted to another susceptible host

• Mechanical or phoretic vector: transports the parasite

– Flies and cockroaches that feed on fecal material may carry
enteric organisms and transfer these to food
Infection vs Infestation
 Infection vs Infestation
Harm done inside the Harm done outside the
body of the host body of the host
Parasitic Infection
vs
Parasitic Disease
Parasitic Infection vs Parasitic Disease
• Shows mild symptoms • Develops pathologic
• Suffers little damage changes
• Exhibit symptoms of
varying degree
• High Fever
• Evidence of inflammation
• Generalized or localized
pain
Phases in the Course of Parasitic Infection
1. Exposure – an individual in a state risk of acquiring
the parasite
2. Inoculation – introduction of the parasite into the
host via portal of entry
3. Biologic Incubation Period – time from the entry of
the organism until they may be recovered in body
fluids , tissues or excretions without any
manifestation
4. Clinical Incubation Period – time of entry of a
disease-causing organism into the body of the host,
until the earliest sign and/or symptom of the
infection.
 Laboratory Diagnosis
• Specimens for parasitic infection
• Tools and Laboratory Techniques
 Laboratory Diagnosis
• Specimens for parasitic examination:
– Stool
– Blood
– Urine
– Sputum
– Cerebrospinal fluid
– Tissue aspirate
– Tissue biopsies
– Orifice swabs
 Laboratory Diagnosis
• Microscopy
• Concentration and Culture Methods
• Molecular Diagnostics : PCR
• Immunodiagnosis
– Detection of antigen or antibody from clinical specimens
 Parasitology
Nemat- Platyhelminthes Protozoan
helminthes
Nematodes Trematodes Cestodes Tubellaria Amoeba
-roundworms -flukes -tapeworms -free living,
marine waters
 Asynchronous Activity
Video Reference:
House MD, Season 1, Episode 1, “PILOT”

Take note for open discussion:

– Patient Symptoms
– Patient Exposure
– Final Diagnosis, Causative agent
 Next Meeting; 06/07 FEB 2022
• Short Quiz on Intro to Parasitology
– Yellow Filler as Quiz Booklet (Monday Class)
– Orange Filler as Quiz Booklet (Tuesday Class)
• Open Discussion on movie viewing
• Discussion on Nematodes (Roundworms)
Lesson 02: Part I
Nematodes

N.G.D.Martin, RMT
February 2023
 Nematodes
General Characteristics
• Roundworms, elongated,
cylindrical,unsegmented
• 2mm in length up to a meter
• Found everywhere
• Body Systems:
• No respiratory/circulatory system
• Digestive
• Muscular
• Nervous
• Excretory
• Reproductive
 Nematodes
Form and Function
• Bilaterally symmetrical, longated
and tapered at both ends.
• 3 germ layers, possess a
pseudocoelom
• Lumen of the pharynx is
characteristically triradiate
 Nematodes
Form and Function
• Body wall consists of:
• Cuticle
• Cortical: outermost zone, contains a highly resistant protein : Cuticulin
• Median – fine striations
• Basal zone – 2-3 fibrous layer
• Hypodermis
• Body wall musculature
 Nematodes
Nervous System
• Nerve ring or circumsophageal commissure
• Presence of ventral, lateral, and dorsal cephalic ganglia
• Presence of sensilla
 Nematodes
Digestive System
• Mouth – circular opening surrounded by a maximum of 6 lips
located in the anterior end
• Buccal cavity is tubular or funnel shaped which for some
specie is expanded for sucking purposes
• Food ingested moves into a muscular region of the tract
known as, esophagus, which is important for identification of
the specie
• Esophagus
• Rhabditiform – free-living
• Filariform –parasitic
 Nematodes
Excretory System
• Excretory Cells
• 2 types:
• Glandular
• Tubular
• Excretory Pore- Anus
• Median ventral duct and pore
 Nematodes
Reproductive System
• Sexes are dioecious
• Males –shorter, coiled tailed
• Female – longer, straight tail
 Nematodes
Classification of Female Nematodes
• Oviparous
-lays eggs outside the body
-ex: Ascaris lumbricoides
• Larviparous/Viviparous
-release larvae without egg cycle (juveniles)
-ex; Trichuris trichiura
• Parthenogenic
-release viable eggs even without males
-ex: Strongyloides stercoralis
Classification of Medically Important Nematodes
• Based on the presence and absence of caudal receptor.

• Class Enoplea
– caudal receptor and gland present
– Trichuris trichiura, Trichinella spiralis, Capillaria philippinensis

• Class Rhabditea
– with caudal receptor but without caudal gland
– Ascaris lumbricoides, Strongyloides stercoralis, Enterobius
vermicularis, Filarial worms, Hoookworms, Dracunculus medinensis,
Anglostrongylus cantonensis
Classification of Medically Important Nematodes
Based on Habitat
Small Intestine Large Intestine
• Capillaria philippinensis • Enterobius vermicularis
• Ascaris lumbricoides • Trichuris trichuira
• Strongyloides stercoralis
• Hookworms
 Ascaris lumbricoides
• Giant intestinal roundworm
• Human ascariasis
• Largest and most common
• Males : 15-30cm by 3mm;
Females: 20-40 cm by 5mm
• Contains lateral lines seen as
whitish streak along the entire
body length
• Terminal mouth with trilobate
lips with a small triangular
buccal cavity
 Ascaris lumbricoides Ova
Fertilized Ova Unfertilized Ova
• Broadly ovoid in shape • Longer, larger, sometimes
• Golden brown in color irregular in shape
• 3 thick transparent layers: • 2 layers present
• Vitelline membrane
• Glycogen membrane • Glycogen membrance
• Albuminous coat • Albuminous coat
• Types:
• Corticated
• Decorticated
Ascaris lumbricoides Ova
Ascaris lumbricoides Life Cycle
• Adult in small intestines
• Eggs are passed out in feces
• Embryonation in soil
• Fully embryonated eggs ingested
by man
• Large larva penetrates the
mucosa and enters the blood
circulation
• Heart to lung migration
• Larvae ascends the respiratory
tree and swallowed
 Ascaris lumbricoides Pathology
• Feeds on intestinal contents
• Abdomminal pain
• Diarrhea
• Nausea
• Loss of paetite
• Erratic Migration – may cause regurgitation and escape
through the nostrils
• Vomitted worms may pass the larynx and might lead to
suffocation or reach the lung to produce GANGRENE
• Might reach the eustachian tube to cause OTITIS MEDIA
 Ascaris lumbricoides Pathology
• Extra intestinal Pathology
• Bile duct, gall bladder, appendix
• Hemorrhagic pancreatitis
• Peritonitis
• Due to larva: non human ascariasis
• Visceral Larva Migrans
• Toxicara canis (dog ascariasis)
• Toxicara cati (car ascariasis)
• Ascaris suum (pig ascariasis)
• Ascaris pneumonitis or Loeffler’s Syndrome
• Due to adults
• Epigastric Pain
• Bolus : Diarrhea
• Malnutrition
 Ascaris lumbricoides
Diagnosis
• DFS
• Kato-thick
• Kato-katz
• Concentration technique (FECT, AECT)
Treatment
• Piperazine citrate
• Pyrantel pamoate
• Mebendazole
• Albendazole
 Trichuris trichuira
• Whipworm
• Trichuriasis
• 30mm to 50 mm
• Males are smaller than females
• Esophagus is long occupying 2/3 of
the body
• Contains stichocytes (glandular
cells surrounding the esophagus)
• No excretory system
• 3,000-10000 ova a day
 Trichuris trichuira Ova
• Unsegmented, barrel shaped,
lemon, football shaped
• Bipolar plugs
• Embryonation takes place in the
soil, first stage larve is formed
within 3 weeks
 Trichuris trichuira
• Treatment
• Pyrantel Pamoate
• Albendazole
• Mebendazole

• Life Cycle
• Adult worms attached to caecum wall
• Eggs ->feces
• Embryonation is soil
• Embryonated eggs ingestion
• Larvae hatch in the intestine
 Trichuris trichuira
• Pathology
• Diarrheic stool
• Abdominal pain, tenderness
• Nausea and vomiting
• Hypochromic anemia, IDA
• Rectal prolapse

• Diagnosis
• DFS
• Kato-katz, Kato- thick
• FECT, AECT
 Strongyloides stercoralis
• Threadworm
• Cochin China Diarrhea
• Colorless, semi transparent
• Capable of free living and
parasitic cycles
 Strongyloides stercoralis
• Morphology
• Parthenogenic females reach a length of 2.0mm to 2.5 mm
• Small buccal capsules
• Ventrally curved pointed tails of males
• Long cylindrical esophagus – posterior bulb
 Strongyloides stercoralis Ova
• Thin shelled
• Transparent
• Partially embryonated egg
• Chinese lantern
• Eggs are seldom seen in feces
 Strongyloides stercoralis Larva
Rhabditiform Filariform
• Short buccal • Long, delicate
cavity esophagus
• Elongated • Tail is forked or
esophagus notched
with pyriform
posterior bulb
Strongyloides stercoralis Life Cycle
• 3 Life Cycles
• Indirect – filariform larvae skin penetration
• Direct
• Auto infection
Strongyloides stercoralis Life Cycle
 Strongyloides stercoralis
Pathology
• Pruritus and erythema at the site of penetration
• Pneumonitis due to larval migration to the lungs
• Weight loss, chronic dysentery accompanied by malabsorption
and steatorrhea
Diagnosis
• Harada Mori – recovery of rhabditiform larva
• Duodenal fluid -> aspiration
• Eggs can only be obtained by drastic purge of duodenal intubation
• ELISA
 Strongyloides stercoralis
Treatment
• Albendazole
• Thiabendazole
 RECAP
(short example of asynch activity)
Parasite Common Infective Stage Diagnostic Stage Final Host Mode of
name transmission

Ascaris Giant Embryonated Eggs, adult form Man Ingestion

lumbricoides intestinal eggs
roundworm
Trichuris Whipworm Embryonated Unembryonated Man Ingestion
trichuira eggs egg

Strongyloides Threadworm Filariform larva Rhabditiform Man Skin

stercoralis larva penetration
 Next Meeting
• Quiz #2
• Intro to Nematodes
• Ascaris lumbricodes
• Trichuris trichiura
• Strongyloides stercoralis
• Continuation of Nematodes:
• Hookworms
• Trichinella and Capillaria
• Filarial Worms
 Asynchronous Activity
Create a table that summarizes the first 3 parasites discussed.
• Scientific name
• Other name/Common Name
• Host
• Infective stage
• Diagnostic stage, tools
• Ova, adult characteristics
• Life cycle
• Pathology and Treatment
Lesson 02: Part II
Hookworms

N.G.D.Martin, RMT
February 2023
 Recap
Nematodes
Intestinal Roundworms Blood and Tissue Roundworms
• Capillaria philipinensis • Trichinella spiralis
• Ascaris lumbricoides • Angiostrongylus cantonensis
• Strongyloides stercoralis • Wuchereria Bancrofti
• Hookworms • Brugia malayi
• Enterobius vermicularis • Onchocerca volvulus
• Trichuris trichiura • Loa-loa
• Mansonella perstans
• Mansonella ozzardi
 Recap
Nematodes
Intestinal Roundworms Blood and Tissue Roundworms
• Capillaria philipinensis • Trichinella spiralis
• Ascaris lumbricoides • Angiostrongylus cantonensis
• Strongyloides stercoralis • Wuchereria Bancrofti
• Hookworms • Brugia malayi
• Enterobius vermicularis • Onchocerca volvulus
• Trichuris trichiura • Loa-loa
• Mansonella perstans
• Mansonella ozzardi
 Hookworms

Human Hookworms
• Necator americanus
• Ancylostoma duodenale

Animal Hookworms
• Ancylostoma braziliense
• Ancylostoma caninum
Morphology : Ova
• Hookworm ova are all alike
• Ovoidal, thin shelled and colorless
Morphology : Adult
• The hookworms are
characterized by the
presence of cutting
plates which may either
be teeth or semilunar
notch.
• Take Note:
• Buccal Cavity
• Copulatory bursa of
males
Necator americanus
• New world hookworm
• Nectoriasis, Uncinariasis, Tropical anemia
• “S” shaped
• Buccal capsule is provided by semilunar cutting plate.
• With an amphidial gland that secretes an anticoagulant
• Copulatory bursa is longer than broad with bipartite dorsal ray and a
long slender copulatory spicules that is fused at the tip forming a delicate
barb.
Necator americanus
Ancylostoma duodenale
• Old world hookworm
• Ancylostomiasis, miner’s anemia
• Stout, body contour into letter “C”
• 2 pairs of ventral teeth
• Copulatory bursa is bristle like with tridigidate dorsal ray
• With a pair of simple, long, bristle like copulatory spicule, plain and
free at the tip.
Ancylostoma duodenale
Ancylostoma braziliense
• Cat hookworm
• Cutaneous larva migrans, creeping
eruption
• Stratum germinativum – layer of the
skin where hookworms gets lost
• With a pair of teeth and a pair of
inconspicuous median teeth
• Copulatory bursa is broad and long
with short lateral rays
Ancylostoma caninum
• Dog hookworm
• Cutaneous larva migrans, creeping
eruption
• Also known to cause eosinophilic
enteritis
• With 3 pairs of ventral teeth
Hookworm Life Cycle
• Adults in small intestine
• Ova in Feces (diagnostic stage)
• Rhabditiform Larvae
• Filariform Larvae (infective stage)
• Skin Penetration of FL to host
• Larvae enters into circulation
• Larvae exits the circulation
through the lungs then coughed
up and swallowed
Hookworm Pathology
• Pulmonary lesion –”Wakana Disease”
• Creeping Reaction – dermatitis characterized by intracutaneous lesion
• Allergic reactions
• Ground itch or dew itch
• Hookworm anemia – microcytic, hypochromic anemia
• Intestinal Hemorrhage – heavy worm load
• Hypoalbuminemia – low levels of albumin due to combines loss of blood,
lymph and protein
Hookworm Diagnosis
• DFS
• Harada-mori
• The collection of larvae from eggs hatched on filter paper strips with one
immersed in water
• For surveillance, egg counting via stoll egg count and Kato Thick
• Larvae can be recovered by Baermann Funnel Method and Damp Gauze
Pad Method of Beaver
 The Unholy Trinity

• Ascaris lumbricoides
• Trichuris trichiura
• Hookworms
Enterobius vermicularis
• Pinworm or Seatworm
• Enterobiasis or oxyuriasis
• Ova
Elongated with flattened lateral side, lopsided “D”
Two egg shell layer
1. Outer albuminous layer
2. Inner embryonic lipoidal membrane
 Embryonated when laid
Resistant to disinfectant
Remain viable for 13 days
Enterobius vermicularis
• Adult
Small whitish or brown in color
Male : 2-5mm coiled tail end
Female: 8-13mm pointed tail end
Diagnostic in the presence of cephalic alae and
distinct esophageal bulb
Enterobius vermicularis
• Life Cycle
 Adults in large intestine
(caecum)
Gravid females migrate to the
perianal area to deposit
embryonated egg
Ova are readily infective
(Diagnostic and infective stage)
Ova are ingested or inhaled by
man.
Larvae hatched at duodenum
Enterobius vermicularis
• Mode of transmission
Ingestion
Inhalation
Autoinfection
• Pathology
 Nocturnal pruritis ani
Insomnia
Loss of apetite
Irritation
• Diagnosis
Scotch tape swab
 Capillaria philippinensis
• Discovered in Ilocos, Norte Philippines
• Pudocworm
• Disease: Borborygamous, diarrheal disease,
dehydration
• Female Capillaria
1. Typical
 Oviparous
 8-10 eggs in the uterus in single row
 Gives rise to typical Capillaria
2. Atypical
 Larviparous
 40-45 eggs in 2-3 rows

• Male Capillaria with long spicule sheath

 Capillaria philippinensis
• Ova
Yellow, moderately thick
Peanut-shaped
striated egg with flattened bipolar
plugs
 Capillaria philippinensis
• Life Cycle
Male and atypical female in small intestine
2 weeks development of male and typical female
Eggs laid and pass out in feces in water
3-5 days embryonation in water
Embryonated egg ingested by freshwater fish
Infective larvae in intermediate hosts: bagsang,
bagsit, birot, ipon.(infective stage)
Ingestion of fish with infective larvae by final
host
Larvae to adult development in small intestine
Adult female in intestine may lay atypical eggs
resulting to autoinfection
 Capillaria philippinensis
• Pathology
 extreme persistent diarrhea that may lead to dehydration, rapid weight
loss, abdominal pain, gurgling of the stomach (Borborygamous), muscle
wasting, anorexia, vomiting, edema
Malabsorption of fats and sugar (intestinal malabsorption) and low plasma
levels of potassium, calcium, and total protein
Disease may develop hypotension and can eventually lead to death by
cardiac failure
• Diagnosis
DFS, AECT, FECT (worms, larvae, sometime even adult worms)
 Trichinella spiralis
• Trichina worm
• Trichinosis, Trichiniasis
• Smallest nematode to cause disease in man
• Whitish color
• The anterior end of the body is consist of esophagus with
stichosomes
• Males: 1.5 by 0.04mm with single testis
• Females: 3.5 by 0.06mm with single ovary, larviparous
 Trichinella spiralis
• Life Cycle
 Encysted in pig muscle
Ingestion of improperly cooked pork
Infected fleash is digested by gastic
juice
Adults in duodenum
Larviparous female burrows into
mucosa and deposit larvae
Larvae enters the circulation
Encysts in striated muscle
(diagnostic and infective stage)
Dead end cycle
 Trichinella spiralis
• Pathology
1. Incubation and intestinal invasion
• Diarrhea, constipation, vomiting, abdominal cramps
2. Larval migration and muscle invasion
• Fever, edema, pain and swelling
• Splenomegaly, gastric and internal hemorrhage
3. Encystment and encapsulation
• Fever, weakness, pain
• Diagnosis
1. Muscle Biopsy
2. Serological ELISA
END
Next Meeting (20 Feb 2023)
• Quiz on Hookworms, Pinworm, Pudocworm, Trichina Worm
• Discussion on Blood and Tissue Roundworms

Prelim Exam (27 Feb 2023)

• Intro to Parasitology
• Nematodes
PARASITOLOGY_LESSON II: PART 3
FILARIAL WORMS AND OTHER NEMATODES
N.G.D.MARTIN, RMT
 RECAP
Nematodes
Intestinal Roundworms Blood and Tissue Roundworms
• Capillaria philipinensis • Trichinella spiralis
• Ascaris lumbricoides • Wuchereria bancrofti
• Strongyloides stercoralis • Brugia malayi
• Hookworms • Onchocerca volvulus
• Enterobius vermicularis • Loa-loa
• Trichuris trichiura • Mansonella perstans
• Mansonella ozzardi
• Angiostrongylus cantonensis
• Drancunculus medinensis
FILARIAL WORMS
FILARIAL WORMS

Things to consider:
1. Nuclei arrangement
2. Sheath
3. Periodicity – time of hatching
or coming out
FILARIAL WORMS

 Arthropod transmitted (vector: Flies

and mosquitoes)
 Invades the circulatory system, muscle
and serous cavities, lymphatic system
 Size is about 2-50cm
 Males have 2 copulatory spicules
FILARIAL WORMS

 Viviparous females give birth to

pre-larval microfilaria
(microfilarial stage)
 Microfilaria is motile, snake like
with dark staining nuclei
occupying most of the entire
body
 Either with embryonic sheath or
without embryonic sheath
FILARIAL WORMS

 Periodicity
 Nocturnal – presence of microfilaria at night
 Diurnal - presence of microfilaria at day
 Subperiodic Diurnal -presence of microfilaria all day but abundant at day
 Subperiodic Nocturnal -presence of microfilaria all day but abundant at night
 Non-periodic –does not exhibit periodicity
FILARIAL WORMS : GENERAL LIFE CYCLE

1. Ingestion of microfilaria from the blood

or tissues by a blood sucking insect
2. Development of microfilaria in the
arthropod vector through two distinct
larval stages (1st and 2nd) before
reaching the infective stage, which is
the third stage filariform larva.
3. The transfers of the infective larva to
the skin of a new host by insect bite
4. The development and maturation of
the larva at its selection site.
 WUCHERERIA BANCROFTI

 Bancroft’s Filarial Worm

 Nocturnal
 Microfilaria:
 Sheathed
 With no terminal nuclei,
tapering tail
 2 vectors:
 Aedes poecillus
 Anopheles minismus flavorostis
 WUCHERERIA BANCROFTI

 Pathology
 Tropical eosinophilia
 Elephantiasis – enlargement of the scrotum,
vulva, genitals and lower lymphatics
 Granuloma of the spleen
 In the lymph nodes, they promote
pseudotubercular granulomatous reactions
which leads to edema, vascular and lymphatic
hyperplasia, fibrosis and caesation
 WUCHERERIA BANCROFTI

 Diagnosis and Treatment

 Blood smear – check periodicity ; Heparinized capillary method
 Knott’s concentration and the Millipore or membrane titration method
 Diethyl carbamazine
 BRUGIA MALAYI

 Malayan Filarial Worm

 Subperiodic Nocturnal
 Microfilaria
 2 distinct nuclei at the tip of the tail
 Angular curvature with secondary kinks
 Sheathed
 Vector : Mansonia uniformis
 BRUGIA MALAYI

 Pathology
 Malayan filariasis
 Tropical eosinophilia
 Elephantiasis – enlargement of the scrotum, vulva, genitals and lower lymphatics
 Granuloma of the spleen
 In the lymph nodes, they promote pseudotubercular granulomatous reactions which leads to edema,
vascular and lymphatic hyperplasia, fibrosis and caesation
 Diagnosis and Treatment
 Blood smear – check periodicity ; Heparinized capillary method
 Knott’s concentration and the Millipore or membrane titration method
 Diethyl carbamazine
 LOA LOA

 African Eye Worm

 Diurnal
 Microfilaria:
 Sheathed
 The tail is tapering gradually, caudal nuclei is
continuous with those of the trunk
 Vector:
 Chrysops sp. (Tabanid or Mango Fly)
 LOA LOA
 Pathology
 Subcutaneous tissue
 Calabar swelling
 Conjunctiva granulomata – non-
painful yellow itchy nodules
 Bung eye-painless edema of the
eyelids
 Protopsis – bug eye

 Diagnosis and Treatment

 Blood smear
 Diethyl carbamazine
 ONCHOCERCA VOLVULUS

 Convoluted filaria
 Non-periodic
 Microfilaria:
 Unsheathed
 Nuclei free anterior and posterior end
 Vector:
 Simulium sp. (Blackfly)
 ONCHOCERCA VOLVULUS
 Pathology
 River blindness
 Nodules in subcutaneous tissue
 Hyperkeratosis

 Diagnosis and Treatment

 Skinsnips
 Not found in blood can be found
in urine
 Surgical removal of nodule
 DEC treatment
 MANSONELLA PERSTANS

 Persistent filaria
 Non-periodic
 Microfilaria:
 Unsheathed
 Nuclei up to the tip of the
tail
 Vector:
 Culicoides sp.
 MANSONELLA PERSTANS
 Pathology
 Body cavities
 Recurrent pruritic subcutaneous lesions, fever, headaches and neurologic
manifestations
 Eosinophilia, fever, arthralgia (joint pains)

 Diagnosis and Treatment

 Blood smear
 Ivermectin as drug of choice
 MANSONELLA OZZARDI

 Ozzard’s filaria
 Non-periodic
 Microfilaria:
 Unsheathed
 Tail tapers into thin filament
 No nuclei at the tip
 Vector:
 Culicoides sp.
 MANSONELLA OZZARDI
 Pathology
 Body cavities
 Headaches, pruritis
 Lymphadenitis, adenopathy, hepatomegaly
 Eosinophilia, fever, arthralgia (joint pains)

 Diagnosis and Treatment

 Blood smear
 Ivermectin as drug of choice
OTHER NEMATODES
 ANGIOSTONGYLUS CANTONENSIS

 Rat lungworm  Accidental Host: Man

 Intermediate Host  Stays in the brain
 Eosinophilic
 Mollusks
Meningoencephalitis
 Rattus rattus
 Pila Africana
 Japanese Giant Snail
 Crabs/Talangka
 Definitive Host: Rat
 Infection to rats involves
lungs for development
 ANGIOSTONGYLUS CANTONENSIS

Life Cycle
 Adults in pulmonary arteries of rats
 Embryonate in blood for 6 days then
goes to respiratory tract, swallowed
and passed out through feces
 Penetration and ingestion of
mollusks
 Ingested by rats, parasite remain in
the brain
 No adult development in man
 ANGIOSTONGYLUS CANTONENSIS
Pathology
 Incubation period: 12-47 days
 Eosinophilic Meningoencephalitis
 Acute onset of severe headache, low grade fever, nausea and vomiting
 Stiffness of the neck, weakness of the hands and legs
 Abdominal pain
 Increased confusion coherence
 Disorientation or impairment of memory or profound coma

Diagnosis and Treatment

 Postmortem examination
 No treatment
 DRACUNCULUS MEDINENSIS

 Guinea Worm, Dragon Worm, Fiery Serpent Worm of the Israelites, Medina
Worm
 Inhabits the adult subcutaneous tissue
 Definitive Hosts : Man
 Intermediate Host: Copepods, cyclops
DRACUNCULUS
MEDINENSIS

Life Cycle
 Adults in cutaneous tissue
 Larva escapes from skin
blister
 Free swimming
(rhabditiform)
 Ingested by
cyclops/copepods
 Develop into filariform
 Ingested by man
 DRACUNCULUS MEDINENSIS

Pathology
 Vesicular lesions and ulcer for the
liberation of larval worms
 Erythema, Pain and allergic
reaction at the site of lesion
 Possibility of abscess formation
and secondary bacterial infection
Diagnosis and Treatment
 Flooding of the ulceration
 Metronidazole and thiabendazole
 END

March 6/7, 2023

Quiz on Lesson 2 : Part III
Discussion on Cestodes : Tapeworms
PARASITOLOGY_LESSON III: PART I
INTRODUCTION TO CESTODES
N.G.D.MARTIN, RMT
 PHYLUM PLATYHELMINTHES

General Characteristics
 Multi-celled animals
 Leaf-like structure = flukes
 Bilaterally symmetrical
 Possess an incomplete digestive tract
 Lack body cavity, circulatory and respiratory structures
 Has incomplete digestive tract
 Sexual organs are complicated: multi-lobe or single mass
 Life Cycle consists of a single obligatory host.
 PHYLUM PLATYHELMINTHES

Class Tubelaria Class Trematoda Class Cestoidea

Marine Waters Flukes Tapeworms
-leaf like -ribbon like
CLASS CESTOIDEA
CLASS CESTOIDEA

 Tapeworms, ribbon-like
 Hermaphroditic parasitic organisms
 No digestive tract
Two Important Classes

Order Pseudophillidea Order Cyclophillidea

Scolex is unarmed Scolex with 4 suckers and usually centrally

Equip with a dorsal and ventral groove placed apical rostellum
Scolex is spatulate Armed with hooks
Scolex is quadrate
Sex pores open laterally
CLASS CESTOIDEA

 Parts of an adult tapeworm:

1. Scolex – head, site of
attachment to the host
2. Neck – Site of development
3. Strobila – a series of proglottids;
an elongated body
CLASS CESTOIDEA

 Length varies from 3mm to 10m

or more.
 The number of proglottids ranges
from 3 to 4000
 Gravid proglottids are located at
the distal portion of the scolex
wherein the primary genitalia
have been atrophied and consist
essentially of a uterus distented
with eggs
CLASS CESTOIDEA

 Proglottids may be described as:

1. Craspedote –overlapping
2. Acraspedote- non-overlapping
3. Apolytic- detaches with eggs
4. Anapolytic – releases eggs first
then detaches.
CLASS CESTOIDEA

 Eggs are stirred in the uterus

 Pseudophillidea eggs are
discharged from the uterus via
uterine pore
• Ovoid, operculated and immature
when passed in the feces.
• Requires incubation in water
before they become mature
CLASS CESTOIDEA

 Cyclophillidea eggs are non-

operculated
• Spherical, and almost fully
embryonated when discharged
from the proglottids
CLASS CESTOIDEA

 Larvae of Tapeworms:

Solid Type Cystic Type

Plerocercus/Procercoid Cysticercoid
-Globular with the scolex invaginated into the -with a slightly developed bladder anteriorly
body of the larva

Plerocercoid/Sparganum Cysticercus
-elongated with head free or invaginated only to -true bladder larva
the neck -head invaginated into the proximal portion of the
tapeworms
MEDICALLY IMPORTANT SPECIES OF TAPEWORMS

Pseudophillidea Cyclophillidea

Diphyllobotrium latum Taenia solium

Taenia saginata
Dipylidium caninum
Hymenolepsis diminuta
Hymenolepsis nana
Echinococcus granulosus
Echinococcus multilocularis
Spirometra mansoni
 END

March 13/14, 2023

Quiz on Lesson 3 : Intro to Cestodes
Discussion on D. latum, D.caninum,
Taenis sp.
Phylum
Platyhelminthe
s
Phylum Platyhelminthes
Referred to as FLATWORMS
Three Classes:
◦Class Turbellaria
◦Class Trematodes
◦Class Cestodes
CESTODES
Parts:
◦ Scolex -Recovery in stool means successful treatment
◦ Neck – site of development
◦ Strobila -Chain of segments/proglottids
◦ Immature segment
◦ Mature segment
◦ Ripe/Gravid Proglottid
 Tapeworms
• The body plan of adult
scolex cestodes includes a scolex
(looks like the “head”), a
neck
neck and strobila that can
extend for only a few
proglottids or thousands
• The strobila - Proglottid:
each individual segment
strobila • Most worms are very long:
occupying the entire length
of small intestine
The Tegument

Cestodes do not have a mouth or

any form of intestine
In reflection of this important
role in uptake the absortive
surface is highly enlarged by
small microvilli or microtriches
Microfilaments (actin polymers
are the molecular backbone of
microtriches)
 Diphyllobothrium latum
Common Name: fish/broad tapeworm
The largest tapeworm of man
Scolex: spatulate, almond-shaped; SPOON-SHAPED
The segments are square-shaped and the uterus is
highly coiled (coiled rosette uterus) located at the
middle of the gravid proglottid
Has 2 bothria or sucking grooves
 D. Latum Ova
Yellowish brown in color
With thick shell and an inconspicuous
operculum; terminal knob on opposite end
Approximately, 1,000,000 ova are released
daily
Diphyllobothrium latum
Egg: Operculum
(D. latum’s egg is operculated
when laid)

Aboperculum
(Thickened area opposite the
operculum)
Diphyllobothrium latum
MOT: ingestion of fish with PLEROCERCOID
LARVA
Infective Stage: PLEROCERCOID LARVA
First Intermediate host: various
crustaceans
Second Intermediate host: fish
Habitat: small intestine
Diphyllobotrium latum - the fish tape worm

http://www.dpd.cdc.gov/DPDx/HTML/Diphyllobothriasis.htm
Diphyllobotrium latum - the fish tape worm
• Diagnosis through detection of
characteristic eggs in feces
• These eggs are oval or
ellipsoidal an operculum
(arrows) at one end that can be
inconspicuous. At the opposite
end there is a small knob that
can be barely discernible
• The eggs are passed in the
stool unembryonated. Size
range: 58 to 76 µm by 40 to 51
µm.
• Treatment with praziquantel

• Proglottids of
Diphyllobothrium latum.
These proglottids tend to be
passed in strands of variable
length in the stool. The
proglottids tend to be broader
than long. Image contributed
by Georgia Division of Public
Health.
D. Latum scolex
D. Latum proglottid
PATHOLOGY DUE TO ADULT WORM:
By products by the adult worm absorbed into the host
tissue may create a systemic toxemia at times with
anemia, bothriocephalus anemia or tapeworm
pernicious anemia, Vit B12 Deficiency
Large number of worms may cause mechanical
obstruction of the intestines when they tangled
together
Patients may experience nervous disturbances, digestive
disorders, abdominal discomfort, weight loss, weakness
DIAGNOSIS:
Recovery of eggs in stool; proglottids may be
vomited
For sparganosis, dx is usually not made until after
surgical removal of the worms and drainage of
the involved sites
Kato technique
 Dipylidium caninum
Common Name: Dog Tapeworm; Double-
Pored Tapeworm, Pumpkin seed
tapeworm; Cucumber tapeworm
Adult worm is pale reddish & measures
10-70cm in length
Proglottids are narrow & have double set
of reproductive organs; with two genital
pores (bilateral)
Gravid proglottid is described as “melon-
shaped; pumpkin-seed shaped or
shaped like rice granules
 Dipylidium caninum
•The scolex is small & globular and contains
four suckers.
•Club-shaped armed rostellum (with 1-7
circlets of spines)
•The EGG is described as “MOTHER
PACKET” (8-15 eggs or 5-30 eggs) ;
spherical, thin shelled & six-hooked
oncosphere
Dipylidium caninum
Mode of Transmission: Ingestion of infective stage
Infective stage: cysticercoid larva
Definitive Host: Dogs
Intermediate Host:
• Dog flea (Ctenocephalides canis)
• Cat flea (Ctenocephalides felix)
• Human flea (Pulex irritans)
• Dog louse (Trichodectes canis)
PATHOLOGY
Depends upon the intensity of infection
In children, usually there is only a single worm infection without
or with mild to severe manifestations
Symptoms consist of slight intestinal disturbances, epigastric
pain, indigestion, loss of appetite due to metabolic waste of
worm
There can also be diarrhea, anal pruritus, allergic reactions
Some are asymptomatic, moderate eosinophilia has been
reported
Taenia solium
Taenia saginata
Difference Taenia saginata Taenia solium
Common Name Beef tapeworm Pork tapeworm
Intermediate Cattle Pig
Host
Scolex No rostellar hooks Rostellum armed with 2 rows of
large and small hooklets
Length 25 meters 7 meters
Number of 1000-2000 Less than 100
Proglottids
Gravid proglottid 15-20 lateral branches 7 to 13 lateral branches
“dichotomous or tree-like” “dendritic or finger-like”
Eggs same Same
Infective Stage Cysticercus bovis Cysticercus cellulosae
Pathogenesis Bolus obstruction Neurocysticercosis
T. saginata
scolex
T. solium scolex
Taenia life-cycle

30
PATHOLOGY ( T. solium)
Adult – negligible
May cause mild transitory intestinal obstruction and
may give rise to vague abdominal pain similar to hunger
pain
Larva- lodge practically in every organ and tissues of the
body
Most commonly located in striated muscle
May lodge in the brain, subcutaneous tissues, spinal
cord, heart, liver, eyes giving rise to pressure symptoms.
Cysts may survive up to 5 years
 Human cysticercosis
When humans plays the role of the
Intermediate Host
• Larval stages develop in the human host
• Humans acquire cysticercosis through faecal-oral contamination with T. solium
eggs
• The oncosphere in the eggs is released by the action of gastric acid and
intestinal fluids
• Cross the gut wall and enter the bloodstream
• They are carried to the muscles and other tissues
• They encyst as cysticerci at small terminal vessels (1 cm) (A) and (B)
• Neurocysticercosis and ophtalmic cysticercosis serious

MRI of multiple
cysts. Image
courtesy of the
Centers for Disease
Control and
Prevention.
Racemose Cysticercosis-MRI
 Neurocysticercosis

Neuroimaging: MRI of viable (A) and degenerating (B) cysts and CT of

calcified cysticerci. The Lancet (2003) 361: 547

• The parasite infects the CNS

• Epileptic seizures (58-80% when parenchymal
brain cysts).
• Intracranial hypertension, hydrocephalus, or
both. This syndrome is related to the location of From: NEJM (2001) 345:879
parasites in the cerebral ventricles or vasal
cisterns.
• Occasionally a cyst may grow larger (giant cyst)
 Cysticercosis pathology

Cysts degenerate: the fluid becomes opaque and dense and edges irregular
and shrink.
Calcification starts in the cephalic portion and leaves a whitish calcified
nodule
Racemose form: high mortality. Large translucent vesicle lobulated without
scolex which develops in the basis of the brain or in the ventricles.
Sometimes several small vesicles surround a pedicle like a bunch of grapes.
The death of the larva leads to inflammation of the affected region
Convulsions are the most common manifestation of cerebral cysticersosis
CSF may show elevated protein, decreased glucose and increased
mononuclear cells
Half of the cases may present CSF eosinophilia without peripheral
eosinophilia
DIAGNOSIS
Demonstration of eggs in stool or by scotch tape
method; Formalin ether concentration technique
Differentiation of gravid segment pressed between the 2
slides
Serologic tests: ELISA, Electron –immunotransfer blot or
Western blot (IgG & IgM)
Cysticercosis: CAT – computed axial tomography scan ;
MRI- magnetic resonance imaging
TREATMENT, PREVENTION AND CONTROL
Praziquantel & niclosamide
Proper disposal of human excreta
Avoid eating insufficiently cooked pork
Freezing at -20 C for 10 days will kill the cysticerci
For cysticercosis:
Good personal hygiene
Avoidance of drugs which cause disintegration of the gravid segment
PATHOLOGY ( T. saginata)
No cysticercosis in man
Pathology is mainly due to the large size which is
frequently responsible for disturbances in the normal
functioning of the digestive tract; obstruction in the bile,
pancreatic ducts and appendix
Absorbed by products may also cause systemic
intoxication
Epigastric pain, vague discomfort, hunger pangs,
weakness, pruritus ani, diarrhea and anorexia
Hymenolepsis nana
Hymenolepsis
diminuta
Difference Hymenolepsis nana Hymenolepsis diminuta
Common Name Dwarf tapeworm Rat tapeworm
Intermediate Only human tapeworm that does not Insects
Host require an IH. However, insects may
act as an intermediate host in some
occassions
Scolex With rostellum armed with a ring of With unarmed rostellum
20-30 spines
Eggs Eggs contain an oncosphere Eggs contain an oncosphere
enclosed in an inner membrane with enclosed in an inner
two polar thickenings, from each of membrane with two polar
which arise 4-8 filaments thickenings without
filaments
Infective Stage Eggs, Cysticercoid larvae Cysticercoid larva
Final Host Man Rat
Hymenolepis nana -
the dwarf tape worm
Hymenolepis nana occurs
relatively frequently
world wide and is usually
an infection of children

An intermediate host is
not required and
autoinfections occur
frequently

Cysticercoids develop in
the lymphatics of villi

Alternatively infection
through cysticercoids in
insects that contaminate
grains or cereal
PATHOLOGY (H. nana)
Metabolic waste of the worm absorbed into the host’s system produced
generalized toxemia
Headache, dizziness, anorexia, inanition, pruritus of nose and anus, periodic
diarrhea, vomiting and abdominal distress, pallor, weight loss
Patients are restless and irritable some have epileptic form convulsions and
eosinophilia
Rarely, convulsions occur
Heavy infection may result in enteritis due to necrosis and desquamation of
the intestinal epithelial cells
DIAGNOSIS
Demonstration of eggs in stool, concentration of stool
Eggs are susceptible to heat and dessication, cannot
long survive outside the host
H. diminuta
PATHOLOGY ( H. diminuta)
Similar to other tapeworm infections; no autoinfection
Infections are usually light and multiple infetions are
exceptional; the highest # recorded is 19 worms
Life span in a person is short, experimental infections in
adult person lasting only for 5-7 weeks
DIAGNOSIS
Recovery of eggs in stool; distinguished from H. nana by
its circular shape, larger size and lack of bipolar
filaments
Echinococcus
granulosus
Echinococcus
multilocularis
 Echinococcus granulosus
Common Name: Hydatid Worm causing Hydatid
disease; Dog tapeworm
Shortest tapeworm, measuring only 3-6 mm
The scolex is quadrate, pyriform with 4 cup-like
suckers; armed rostellum (30-36 hooks) with three
segments
The eggs cannot be differentiated from that of
Taenia
E. granulosus
scolex(hooks)
E. granulosus entire worm
 Echinococcus granulosus
Infective stage: hydatid cyst
Definitive Host: dog or wild canine
Intermediate host: sheep;
cattle;goats; horses; camels
Man’s role: Man is only an accidental
intermediate host
The Hydatid Cyst
Thousands of protoscolices can
fill the hydatid (hydatide sand)
Protoscolices are the infective
stage for dogs
Hydatides usually grow slowly
but steadily (1-5 cm per year)
They are usually well tolerated
until their size becomes a
problem or they rupture
Cyst rupture or leakage can result
in allergic reactions and
metastasis
Echinococcosis:
Cystic hydatid disease
Liver cysts cause liver
swelling, right epigastric pain,
nausea, vomiting
Obstruction of bile ducts and
blood vessels can cause
cholangitis, jaundice, cirrhosis
and portal hypertension

This upper abdominal CT scan shows multiple cysts in the liver, caused
by echinococcus. Note the large circular cyst (seen on the left side of
the screen) and multiple smaller cysts throughout the liver.
http://www.drkoop.com/ency/93/ImagePages/1177.html
Echinococcosis:
Cystic hydatid disease
Lung cyst are often well tolerated but obstruction
and or rupture can cause chestpain, cough and
dyspnea
The first symptoms of brain cyst is often focal
epilepsy
Diagnosis is by serology, radiology, CT scans and
sonograms.
Treatment is surgical. Prognosis depends on size and
location of hydatide (mortality is around 5-10%)
Hydatide is often injected with sterilizing fluids to
avoid “metastases”
Benefit of chemotherapy is inconsistent
DIAGNOSIS
Unilocular cysts are diagnosed later in life only after they
have grown to tremendous size
Hydatid cyst may be diagnosed by:
1. roentgenogram
2. biopsy samples
3. exploratory cyst puncture
4. ultrasound scan
5. immunologic test ( intradermal, precipitin, complement
fixation, hemaglutination, bentonite flocculation, latex
slide agglutination and flourescent antibody test, ELISA, CT,
Western blot )
 Echinococcus granulosus
Diagnosis:
◦X-ray
◦Immunological (Bentonite Flocculation
Test) same with T. spiralis
◦Casoni’s Intradermal test
PREVENTION AND CONTROL
Surgical removal of the hydatid cyst is helpful only in
operable sites
When surgery is employed precausionary measures
should be employed to prevent spillage of the cyst fluid
of hydatid sand into the operative cavity
Personal hygiene/ health education
Dogs should be prevented from eating carcasses of
sheep, cattle and hogs in endemic areas
Dogs should be dewormed
 Echinococcus multilocularis
Hydatid worm -Alveolar hydatid disease
Called alveolar cyst; with many minute cavities
containing crumpled or discolored hyaline membrane, all
enclosed in avascular fibrous adventitia
The cavities contain little or no fluid, scolices are rarely
seen
Intermediate hosts- field mouse, vole, squirrel and
shrew
PATHOLOGY
Common site of development is the liver, next the lungs,
and then other organs
The hepatic disease clinically resembles a slowly
developing mucoid carcinoma with hepatomegaly,
splenomegaly, jaundice and ascites in the later stages
In some cases, the cyst metastasize to other organs
When found in the brain, it is always fatal
DIAGNOSIS
Immunologic test- similar to E. granulosus
Usually made later in post mortem examination
 Spirometra spp.
SPARGANOSIS is the larval infection with the
plerocercoid larva ( spargana)
Spirometra mansoni, Spirometra erinacei,
Spirometra ranarum
Intestinal parasites of cats, dogs and other
carnivores
Gravid proglottids have a spiral uterus
Eggs are operculated and immature,
similar to D. latum but smaller
Larvae- opaque and glistening white (3.5
cm in length)
Spatulate scolex
Sparganum removed from the chest wall of
a patient. The worm measured about 70
mm long.
HUMAN SPARGANOSIS MAY RESULT FROM:
Ingestion of infected cyclops containing the
procercoid stage, which penetrates the intestinal
wall, migrates to the subcutaneous tissues and
muscle fascia and develop into sparganum
Drinking water containing Cyclops or Copepods
infected with plerocercoid larva
When man ingest raw infected flesh of amphibia,
reptiles, birds or mammals containing sparganum
HUMAN SPARGANOSIS MAY RESULT FROM:

Use of poultice or local application of the flesh of

infected vertebrates to the skin and other parts
of the body (eye, vagina) resulting in the
migration of the sparganum out of the flesh into
the human tissues
Ingestion of raw pork, since sparganum develop
also in pigs
The larva may be found in the eyes, subcutaneous and muscular tissues of the
thorax, abdomen, thighs, inguinal region and the viscera
Patient may complain of painful edema due to migrating larva also known as
migrating tumor
Local indurations, periodic giant urticaria, edema, erythema with chills, fever and
high eosinophilia may be seen in patients
Tissues infected with spargana become edematous and
very painful to touch
Death of the worm produces intense local inflammation,
eosinophilia and charcot leyden crystals
Ocular sparganosis is characterized by intense pain,
irritation and edematous swelling of the eyelids with
excessive lacrimation
Spargana in lymph channels may result in elephantiasis
In subcutaneous tissues, acniform pustules may develop/
pulmonary artery may become infarcted
 Diagnosis, Treatment
Recovery of plerocercoid larvae from infected tissues
Surgical removal of the larvae from infected tissues
Praziquantel but its efficacy in human has not been proven
END
NEXT MEETING: 27/28 March 2023
Online Classes
Agenda:
Quiz on Cestodes via Google Form
The quiz will be open for an hour only.
• 3-4PM for Monday Group
• 9-10AM for Tuesday Group
• Secure your internet connection.
Lecture on Trematodes