Practical 1

Subkingdom PROTOZOA

Subphylum SARCODINA

Phylum CILIOPHORA

Parasitology Winter 11/12

I. Parasites and Parasitism Definition and types

Parasitism:

• any receprocal association in which a species depends upon another for its existence

• Types of parasitism:

(1) symbiosis: both organisms cannot exist independently

(2) mutualism: both organisms are benefited

(3) commensalism: one partner is benefited, the other is unaffected

Parasitology Winter 11/12

PARASITE

a weaker organism that obtains food and shelter from another organism and derives all the benefit from the association

HOST

the harboring species that may show no harmful effects or may suffer from various functional and organic disorders

Parasitology Winter 11/12

I. Parasites and Parasitism

according to location in the host

• ectoparasites (infestation) • endoparasites (infection): extra- and intracellular

according to the time in which they contact the host • temporary • permanent

according to the degree of adaptability to parasitic life • facultative • obligate • pathogenic • pseudoparasites • coprozoic

Parasitology Winter 11/12

I. Parasites and Parasitism Types of parasites

• invasive form: the form that leads to infection • pathogenic form: the form of the parasite that

actually causes the disease • definitive host: harbors the adult or sexual stage

of the parasite • intermediate host: part or all of the larval or

asexual stage may take place in it • additional host: = secondary intermediate host • biohelminths: heteroxenous parasitic worms

(helminths) that go through their intermediate and definitive hosts directly independently of the environmental factors

• geohelminths: monoxenous helminths whose maggots become invasive in the external environment under strictly defined factors – t°, humidity etc.

Parasitology Winter 11/12

Parasitology Winter 11/12

Criteria Types of parasites Examples

location Ectoparasites Endoparasites – intra and extracellular

Mites, lice, fleas, mosquitoes, bugs Malaria plasmodium, toxoplasma, leishmania Trichomonas, amoeba

duration of parasitism

Temporary permanent

Lice, mosquitos, bugs, some mites Most endoparasites

degree of adaptation Facultative Obligate pseudoparasites

Leech, some round worms

number of hosts Monoxenous heteroxenous

Fleas, mites, most round worms Toxoplasma, malaria, flukes, tapeworms

Parasitology Winter 11/12

I. Parasites and Parasitism Parasitic infection and disease

Transmission of parasites involves three factors: (1) a source of infection (2) a mode of transmission (3) the presence of a susceptible host

Mechanisms by which parasites can damage the host: (1) mechanical effects (2) invasion and destruction of host cells (3) inflammatory reaction (4) competition for host nutrients

Parasitology Winter 11/12

II. Protozoa General features

(1) trilaminar unit membrane, supported by a sheet of contractile fibers

(2) homogeneous ectoplasm and granular inner endoplasm

(3) active feeding and growing stage: trophozoite (4) feeding by diffusion or active transport through the

plasma membrane, some species have cystosomes (5) several species have a cystic stage – enables survival

under unfavourable conditions (6) reproduction is usually asexual – binary fission by

mitotic division of the nucleus, followed by division of the cytoplasm

• Subkingdom (Type) PROTOZOA

• Subphylum SARCODINA

• Genus ENTAMOEBA

Parasitology Winter 11/12

III. Amoebae

• no fixed shape

• unit membrane surrounding the cytoplasm

• inner endo- and outer ectoplasm

• pseudopodia locomotion and engulfment of food by phagocytosis

• free-living or parasitic

• inhabit the alimentary canal

Parasitology Winter 11/12

III. Amoebae General features

trophozoite

– forma minuta

– forma magna

cystic stage

Parasitology Winter 11/12

III. Entamoeba histolytica Morphology

Parasitology Winter 11/12

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Parasitology Winter 11/12

III. Entamoeba histolytica Morphology

TROPHOZOITE – growing and feeding stage of the parasite • irregular shape • size: 12-60 µm, much smaller as a commensal in the lumen minuta form • protoplasm is differentiated into a thin outer layer of clear, transparent ectoplasm and an inner finely granular endoplasm • pseudopodia are formed by a thrusting movement of the ectoplasm in one direction, followed by the streaming of the whole endoplasm • the cell has to be attached to some surface or particle for it to move

• endoplasm: nucleus, food vacuoles, granules

• nucleus: not clearly seen in the living trophozoite, spherical, 4-6 µm, small central karyosome surrounded by a clear halo, karyosome is anchored to the nuclear membrane by fine fibrils called the linin network

• trophozoites divides by binary fission once in 8 hours

• killed by drying, heat, chemical disinfectants; they do not survive for any time in stools outside the body

Parasitology Winter 11/12

III. Entamoeba histolytica Morphology

Parasitology Winter 11/12

nucleus: not clearly seen in the living trophozoite, spherical, 4-6 µm, small central karyosome surrounded by a clear halo, karyosome is anchored to the nuclear membrane by fine fibrils called the linin network

Parasitology Winter 11/12

III. Entamoeba histolytica Life Cycle

infective stage: mature cyst passed in feces (remain viable under moist conditions for 10 days)

invasive mechanism: per os excystation metacyst optimum habitat: caecal mucosa , they lodge in the grandular crypts where they undergo binary fission some develop into precystic forms and cysts entire life cycle is completed in one host!!!

• penetration of the columnar epithelial cells facilitated by the tissue lytic substances released by amoebae and by the motility of the trophozoite

• histolysain – degrades the intercellular matrix and facilitates tissue invasion

• lipophilic protein – lyses host cells by forming pores in their membranes

• phospholipase – enhances the cytolytic activity of the amoebae

Parasitology Winter 11/12

III. Entamoeba histolytica Pathogenicity

Intestinal Amoebiasis

• typical manifestation: amoebic dysentery

• stools: large, foul smelling, brownish black, often with bloodstreaked mucus intermingled with faeces; red blood cells are clumped and reddish brown

• trophozoites contain ingested erythrocytes

• patient is aferbrile and nontoxic

• quite often: only diarrhoea or vague abdominal symptoms

Parasitology Winter 11/12

Extraintestinal Amoebiasis

• most common complications:

hepatic involvement (amoebic hepatitis),

amoebic abscess in the brain

Parasitology Winter 11/12

• demonstration of trophozoites or cysts in stools, tissues or discharges from the lesions

• identification of enzymes secreted by the parasite in blood

• invaded carriers – identification of quadrinucleate cyst in fecal probes

Parasitology Winter 11/12

III. Entamoeba histolytica Laboratory diagnosis

• invasive form: cyst (forma cystica)

• pathogenic form: trophozoite (forma magna)

• invasive strategy: ingestion of contaminated food or water

• host: human

• location in the host: intestinal epithelium, mucosa of large intestine

• vector: flies

• disease: amoebiasis

• pathogenicity: histolyasin, lipophilic protein, phospholipase

Parasitology Winter 11/12

• nonpathogenic commensal intestinal amoeba

• medical importance - it has to be differentiated from E. histolytica

• larger – 20-50 µm

• sluggish motility

• No differentiation between endo- and ectoplasm

• contains ingested bacteria but no red cells

• cysts are larger – 10-30 µm, and have 8 nuclei

• lumenal commensal, no tissue invasion, nonpathogenic

Parasitology Winter 11/12

IV. Entamoeba coli

• Subkingdom (Type) PROTOZOA

• Phylum CILIOPHORA

• Genus BALANTIDIUM

Parasitology Winter 11/12

V. Balantidium coli

CYST

TROPHOZOITE

• the only ciliate protozoan parasite

• the largest protozoan parasite

• present worldwide

Parasitology Winter 11/12

V. Balantidium coli Life cycle

• infection is acquired from pig and other animal reservoirs or from human carriers

• infective form CYST • excystment – in the

small intestine

• liberated trophozoites feed and multiply as lumen commensals in the large intestine

TROPHOZOITE

• lives in the large intestine, feeding on cell debris, bacteria, starch grains and other particles

• large ovoid cell – 60-70 µm (length), 40-50 µm (breadth)

• anterior end (narrow) – cystosome and cytopharynx

• posterior end (broad) – cytopyge (anal pore)

• cell has two nuclei – a large kidney-shaped macronucleus and a small micronucleus

• several food vacuoles and two contractile vacuoles

• motile being propelled by vigorous motion of the cilia

Parasitology Winter 11/12

V. Balantidium coli Life cycle

Parasitology Winter 11/12

Pathogenicity

• trophozoites penetrate the submucosaof the intestines and „digest“ epithelial cells with the help of the enzyme hyaluronidase

• parasites can penetrate into the muscle layer of the mucosa and destroy blood vessels

• clinical disease (balantidiasis) results only when trophozoites burrow into the intestinal mucosa, set up colonies and initiate inflammatory reaction

Parasitology Winter 11/12

V. Balantidium coli

Clinical features

• invasion is usually asymptomatic, cyst carrier

• main manifestations: diarrhoea or frank dysentery with abdominal colic, tenesmus, nausea and vomiting

• very rarely: mucus and blood in the feces

• ocassionaly: intestinal perforation with peritonitis and rarely involment pf genital and urinary tracts

Parasitology Winter 11/12

V. Balantidium coli

Parasitology Winter 11/12

V. Balantidium coli

Diagnosis • demonstration of the parasite in faeces

motile trophozoites in diarrhoeic faeces cysts found in formed stools

Parasitology Winter 11/12

• invasive form: cyst

• pathogenic form: trophozoite

• invasive strategy: per os, cysts are excreted in pig´s faeces

• host: human, pig

• location in the host: submucosa of the intestines

• vector: flies

• disease: balantidiasis

• pathogenicity: „digestion“ of intestinal epithelial cells with the help of the enzyme hyaluronidase