Introduction to

Parasitology
rstuzon
BIOLOGICAL RELATIONSHIPS
• SYMBIOSIS - living together of unlike
organisms
1. mutualism
2. commensalism
3. parasitism
DEFINITION OF TERMS
• endoparasite • incidental parasite
• ectoparasite • permanent parasite
• infection • temporary parasite
• infestation • definitive host
• intermediate host
• erratic parasite
• paratenic host
• obligate parasite
• reservoir host
• facultative parasite • vectors
STOOL ANALYSIS
• final digestions happens in the small intestines and is
usually the lodging site of parasites
• the most common test used to identify parasites
• stercobilin
• 20-40 grams
DIARRHEA
• causes:
1. parasites
2. bacteria
3. virus

• types:
1. secretory
2. osmotic
3. intestinal hypermotility
FECALYSIS
• diagnostic stage
• routine fecalysis - anything • infective stage
that pertains to the study
of stool

• parameters needed:
1. volume
2. color
3. consistency
METHODS
• Direct Fecal smear
PROTOZOANS
AMOEBA
• Entamoeba histolytica • Endolimax nana
• Entamoeba hartmanni • Iodamoeba butschlii
• Entamoeba gingivalis • Naegleria fowleri
• Entamoeba coli • Acanthamoeba sp.
• Entamoeba polecki
GENERAL CHARACTERISTICS
• presence of hyaline foot like
extrusions from the ectoplasm called
pseudopodia
• intestine dwellers (except E.
gingivalis)
• commensal organisms (except E.
histolytica)
• undergo excystation except D. fragilis
and E. gingivalis
Four stages in life cycle:
1. trophozoite form
2. precystic form
3. cystic form
4. metacystic form
Entamoeba histolytica
• most pathogenic
• ingests rbc
• intestinal amoebiasis
• mucous layer of the intestine
• bull’s eye karyosome
• cigar-shaped chromatoidal body
• flask-shaped ulcer
TYPES OF AMOEBIASIS
• Intestinal
1. asymptomatic
2. acute amoebic dysentery
• Extraintestinal
1. ALA
2. pulmonary amoebiasis
3. amoebic pericarditis
4. cerebral amoebiasis
5. cutaneous amoebiasis
6. genital amoebiasis
Entamoeba coli
• whisk-broom appearance
• plenty of vacoules with ingested
bacteria
• “dirty-looking cytoplasm”
Entamoeba hartmanni
• Resembles E. histolytica but
nonpathogenic
• no ingested RBC
• “small race”
Entamoeba gingivalis
• oral cavity
• “Pyorrhea”
• with ingested WBC
Endolimax nana
• found in intestine
• “comma-shaped”
• ground-glass cytoplasm
• punched-out/crossed-eyed
nuclei
• smaller than E. histolytica
Iodamoeba butschlii
• Glycogen mass
• Stained deep-mahogany brown
by Lugol’s Iodine
• With achromatin granules
• “Basket of Flowers”
• mistaken as Blastocystis hominis
Naegleria fowleri
• Opportunistic amoeba
• primary amoebic encephalitis (PAM) - purulent spinal fluid without
bacteria
• stagnant water
• swimming
• 3 stages:
1. amoebic trophozoite
2. flagellate trophozoite
3. cyst
 Acanthamoeba sp.
• granulomatous amoebic encephalopathy
• associated with amoebic keratitis
• spine-like projections

• acanthopodia (locomotion)
1. culbertsoni - slightly wrinkled ectocyst
2. polyphaga - delicate looking
acanthopodia
3. castellani - wrinkled ectocyst
4. astronyxis - folded ectocyst
FLAGELLATES
• Giardia lamblia • Trichomonas vaginalis
• Chilomastix mesnili • Trichomonas tenax
• Trichomonas hominis
• Dientamoeba fragilis
Giardia lamblia
• Traveller’s diarrhea/Leningrad’s
curse
• pear-shaped trophozoite
• falling leaf motility
• oldman with eyeglass
• causative agent of Giardiasis
• duodenum and jejunum
Laboratory diagnosis:
• steatorrhea and jaundice • string test
• duodenal aspirate-specimen of chouce
• DFS
Chilomastix mesnili
• Pear-shaped trophozoite
• cork-screw motility
• nipple-like cyst
• Lemon-shaped trophozoite
• shepherd’s crook (safety pin)
Trichomonas spp.
• T. vaginilis - GUT
• T. hominis - instestines
• T. tenax - oral cavity
T. vaginalis
• Pyriform shape
• undulating membrane
• jerky-tumbling motility
• found in urine
• Trichomoniasis
• frothy, creamy, mucopurulent
vaginal discharge
• dysuria
• most common std
• pingpong infection
Dientamoeba fragilis
• irregular-shaped with leaf-likr
pseudopodia
• tetracoccic karyosome
• co-infection with Enterobius
vermicularis
HEMOFLAGELLATES
Leishmania donovani
Trypanosoma rhodesiense
Trypanosoma cruzi
Trypanosoma gambiense
Leishmania donovani
• Amastigote - infective stage to
sandfly
• Promastigote - infective stage to
man

• Disease:
1. Visceral leishmaniasis
2. Kalaazar
3. Death fever
4. Dumdum fever
Trypanosomes
• Trypanosoma cruzi - “Chaga’s disease”

• Trypanosoma
gambiense/Trypanosoma rhodesiense
• Diseases: Mid and West african
sleeping sickness/East-African
sleeping sickness

Trypomastigote - infective stage to man

• Tse-tse fly (glossina sp)
• Signs and symptoms of acute infection:
• Winterbottom’s sign - swelling of lymph nodes
• Kerandal sign - delayed sensation to pain
• Sleeping sickness - parasite invades the CNS

• Trypanosoma cruzi
• Metacyclic trypanosomes - infective stage to man
• Reduviid bugs - kissing bugs
• s/s: Romanas sign - edema of face
CILIATES
• largest protozoa pathogenic to man
• cecum
• ulcer formation leading to dysentery
• kidney-shaped macronucleus trophozoite
COCCIDIA AND HEMOSPORINA
• Cryptosporidium parvum
• Cyclospora cayetanensis
• Isospora belli
• Sacrocystis hominis
• Toxoplasma gondii
Cryptosporidium parvum
• animal parasite
• major opportunistic parasite in AIDS patient
• intestine
• sheater’s sugar floattion method
• DFS for ID of oocyst
Isospora belli
• Human coccidiosis
• charcot-leyden crystals
(eosinophilia)
• zinc sulfate method
Toxoplasma gondii
• toxoplasmosis
• resembles infectious mononucleosis
• mother to fetus transmission
• bradyzoites - latent form
• cat - definitive host
• man - intermediate host
Cyclospora cayetanensis
• post-consumption of fresh
produce
MALARIAL PARASITES
Plasmodium species
FEATURES
• target tissues and blood cells
• undergo sexual (sporogony) and asexual (schizogony) reproduction
• other stages: oocyst, sporozoite, trophozoite, schizont, merozoite,
and gametocyte
Genus: Plasmodium
• life cycle is composed of:
Schizogony
• in RBCs (human)
• other tissue cells of human host
• pigment derived from hemoglobin of infected RBCs
Sporogony
• gametocytes
• sporozoites
Plasmodium falciparum
• most common in the Philippines
• Malignant tertian malaria (or quotidian)
• ring trophozoites with applique form
• maurer’s dots
• sausage/crescent shape
Plasmodium vivax
• second most common in the Philippines
• Benign tertian malaria
• schuffner’s dots
• round shape
Plasmodium malariae
• Occasionally seen in the Philippines
• Quartan malaria
• ziemann’s dots
• ovoid shape
Plasmodium ovale
• Endemic in Africa, West coast, Etiopia
• Ovale malaria
• james dots
• round shape
2 kinds of RELAPSE
• Recurrence/true relapse (PvPo)
• s/s: parasites coming from the liver
• P. vivax and P. ovale

• Recrudescence (PfPm)
• s/s: surviving parasites in RBCs
• P. falciparum and P. malariae
Manner of Transmission
• mosquito bite (Anopheles spp)
• blood transfusion
• contaminated syringes and needles
• across the placenta during delivery
Diagnosis
• history of travel
• hepatosplenomegaly and/or anemia
• malarial smear:
• thin smear examined within 15mins
• thick smear-examined within 5 minutes
• trophozoite, schizonts, and gametocytes are seen in PBS
Babesia microti
• infects RBC
• transmitted by ticks (Ixodes sp)
• simultaneous transmission with
B. burgdorferi
• Mistaken for Plasmodia
• Anemia
• Malaise, fever, chills
HELMINTHS
WORMS OF MEDICAL IMPORTANCE
•NEMATODES (round worms)
•CESTODES (tape worms)
•TREMATODES (flukes)
NEMATODES
Hookworms
Threadworm
Whipworm
Trichina worm
etc.
• hosts:
• stages of development:
• infective stage to human:
• route of transmission:
• adult male: tail end expanded due to COPULATORY BURSA
• adult female: tail end straight and pointed
• adult male and female: with buccal cavity with teeth of cutting plates
Necator americanus
• “new world hookworm”, “american hookworm”, “american murderer”
• no teeth, but with semi-lunar cutting plates
• S curvature
Ancylostoma duodenale
• “old world hookworm”, “urcinaria”
• with two pairs of teeth
• C curvature
Nonhuman Hookworms
• A. caninum (dog) - longest hookworm
• A. braziliense (cat) - smallest hookworm

• cutaneous larva migrans - creeping eruption

- reddish itchy papules
Strongyloides stercoralis
• “threadworm”
• cochin-china diarrhea, Vietnam
diarrhea
• notched tail end
Trichuris trichiura
• whipworm
• adult male: tail end is coiled 360
degrees
• adult female: tail end is more or
less straight
• egg-football or barrel-shaped
with protruding bipolar mucus
plugs
Trichinella spiralis
• Trichina worm
Ascaris lumbricoides
• giant intestinal roundworm
Capillaria philippinensis
• mystery disease
• flattened bipolar
• pudok’s disease
Enterobius vermicularis
• seatworm/pinworm
Small Nematodes
Important properties of Microfilaria
1. It exhibits periodicity
2. Microfilaria may be sheathed or unsheathed
1.

Microfilariae Periodicity

Wuchereria bancrofti Nocturnal

Brugia malayi Nocturnal

Loa loa Diurnal

Onchocerca volvulus Non periodic

2.
PARASITE SHEATHED MICROFILARIA
W. bancrofti Nuclei do not extend to the tip of the tail
B. malayi With two distinct terminal nuclei
L. loa Nuclei extend to the tip of the tail

PARASITE UNSHEATHED MICROFILARIA

O. volvulus Nuclei do not extend to the tip of the tail
M. ozzardi Nuclei extend to the tip of the tail
M. perstans Nuclei do not extend to the tip of tail
Angiostrongylus cantonensis
• rat lung worm
• meningoencephalitis in man
Dracunculus medinensis
• medina worm, guinea worm,
serpent worm, dragon worm,
fiery dragon worm
• chopstick method