Chair of Medical Biology, Microbiology,
Virology, and Immunology
Theme:Medical Parasitology.
Lecturer As. Prof. O.V. Pokryshko
The main questions of the lecture are:
11. The forms of association between organisms
of
different species.
22. Medical Parasitology as a science.
33. Classification of parasites and hosts.
44. Protozoan diseases.
55. Classification of Protozoa.
66. General characteristic of Protozoa.
77. Parasites of different classes of Protozoa.
•Symbiosis is the living together or close association of two dissimilar
organisms. There are three forms of the symbiosis: mutualism,
commensalism and parasitism.
•Mutualism is symbiosis in which both parties benefit.
•Commensalism is symbiosis in which one party (commensalis) is
benefited and the other party (host) receives neither benefit nor harm.
•Parasitism [Gr.parasitios eating with another] is symbiosis in which
one party (parasite) benefits at the expense of the other (host).
•Parasitology [Gr. Parasitos parasite-logy] is the science of parasitism
and parasites.
•Medical Parasitology is the science or study of parasites of humans.
Medical Parasitology consists of: Medical Protozoology, Medical
Helminthology and Medical Arachnoentomology.
•Medical Protozoology is the study of human parasites of Protozoa.
•Medical Helminthology is the study of human parasitic worms of
Cestodes, Nematodes and Trematodes.
•Medical Arachnoentomology is the study of parasites of Arthropoda.
•Parasite lives upon or within another living organism (host) at whose expense
it obtains some advantage.
•External parasite (ectoparasite) lives on skin or hair of host.
Internal parasite (endoparasite) lives in body organs, body tissues, body cells,
body cavities of host.
•Facultative parasite is an organism which may be parasitic upon another but
which is capable of independent existence.
•Obligatory parasite can’t live apart from its host.
•Temporary parasite lives free of its host during part of its life cycle.
•Permanent parasite lives in its host from early life until maturity or death.
•Host is an organism that harbours or nourishes another organism (parasite).
The hosts divide into: definitive host, intermediate host and reservoir.
•Definitive host (final h.) is a host in which a parasite attains sexual maturity;
harbours the adult or sexually mature parasite.
•Intermediate host harbours the immature or asexual stages of the parasite.
•Reservoir host an animal that harbours the same species of parasites as man
and constitute a source of infection to him.
•Vector is an arthropod that carriers a parasite to its host.
Invasious diseases are caused by animals.
Protozoan diseases are caused by Protozoa.
Anthroponotic diseases are characteristic for humans.
Zoonotic diseases are characteristic for animals.
Anthropozoonotic diseases are characteristic for humans and
animals.
There are four ways of agent transmission
of invasious diseases:
1) contagion (by skin contact, sexual contact);
2) alimentary or faecal-oral transmission (ingestion of raw or
undercooked food or use of drinking water containing the
infective stage of the parasite);
3) by blood (by bite of vector containing the infective stage,
blood transfusion);
4) congenital (through the placenta).
•Kingdom Animalia
•Subkingdom Protozoa
Phylum 1. Sarcomastigophora
•Subphylum Sarcodina. Class Lobozea. Type species: Entamoeba
histolytica, Entamoeba coli, Entamoeba gingivalis.
•Subphylum Mastigophora (or Flagellates).
Class Zoomastigophorea. Type species: Trypanosoma brucei
gambriense, Trypanosoma brucei rhodesiense, Trypanosoma cruzi,
Leishmania donovani, Leishmania tropica, Lamblia intestinalis,
Trichomonas vaginalis, Trichomonas intestinalis, Trichomonas
buccalis.
Phylum 2. Apicomplexa. Class Sporozoa. Type species:
Plasmodium vivax, Plasmodium malariae, Plasmodium falciparum,
Plasmodium ovale, Toxoplasma gondii.
Phylum 3. Ciliophora. Class Ciliata. Type species: Balantidium
coli.
Morphology and Ultrastructure of Protozoa
1)Protozoa are unicellular animal organisms.
2)Each protozoon performs all functions of life.
3)Sizes is from 1 micro;m until 150 micro;m.
4)The protozoa have cytoplasm and nucleus.
5)The cytoplasm is differentiated into ectoplasm (the outer layer)
and endoplasm (the inner layer).
6)The ectoplasm functions in: protection, locomotion, ingestion of
food, excretion and respiration.
7)Locomotion either by pseudopodia, cilia and flagella.
8)The endoplasm encloses: organelles, contractile vacuoles for
osmoregulation, food vacuoles containing food during digestion.
9) The nutrition of all protozoa is holozoic. Absorption of liquid food
through the body surface, or ingestion of solid particles by the help
of pseudopodia or through the cytostome.
10) Reproduction may be asexual or sexual.
1) Motion is by pseudopodia.
2) Reproduction is by binary fission.
3) The production of a cyst is one of the stages in the life cycle.
4) The pathogenic species for man is Entamoeba histolytica, the non
pathogenic (commensal) species are E. gingivalis, E. coli.
Parasite: Entamoeba histolytica
Disease: Amoebiasis, or amoebic disentery
Geographical distribution: Cosmopolitan
Morphology: Three forms: 1) forma magna;
2) forma minuta;
3) cyst.
Life cycle of Entamoeba histolytica
Host: Homo sapiens
Transmission: faecal-oral (alimentary)
Infective stage: mature cyst
Localisation: large intestine
Pathogenicity:
1) Intestinal amoebiasis: formation of ulcerus of the wall of the
intestine, acute or chronic diarrhoea, stool containing blood and mucus;
may be asymptomatic infection.
2) Extra- intestinal amoebiasis: abscess of liver, lung, brain, skin.
Laboratory diagnosis: Fresh stools are examined under the
microscope. E. histolytica (forma magna and cysts with 4 nuclei) can be
demonstrated in the stools.
Prophylaxys: Treatment of patients and asymptomatic cyst carriers;
protection of foodstuffs and water from flies and contamination with
faeces, the staff of catering establishments must be examined for cysts
carriage, health education of the population.
Entamoeba coli. Cyst (8 nuclei)
Class Sporozoa:
1) lack locomotory organelles;
2) complex life cycles (sexual and asexual phases);
3) alternation of hosts;
4) the pathogenic species for man are: Plasmodium vivax, Plasmodium
malariae, Plasmodium falciparum, Plasmodium ovale, Toxoplasma
gondii.
MALARIA PARASITES OF MAN
PARASITES
DISEASES
Plasmodium vivax
Plasmodium malariae
Plasmodium falciparum
Plasmodium ovale
tertian malaria
quartan malaria
tropical (falciparum) malaria
tertian ovale-malaria
Geographical distribution: in parts of Africa, Asia, Turkey, the West
Indies, Central and South America, and Oceania
Blood stages of
Plasmodium:
1) young trophozoites
(ring forms);
2) growing
trophozoites;
3) mature trophozoites;
4) mature shizonts;
5)macrogametocytes;
6) microgametocytes
MALARIA PARASITES OF MAN
Intermediate host: Homo sapiens
Definitive host: Anopheles mosquito
Transmission: by bite of female Anopheles mosquito
Infective stage for man: sporozoite
Infective stage for mosquito: gametocyte
Localisation: blood, liver
Clinical manifestations: fever, anemia, splenomegaly,
hepatomegaly
Laboratory diagnosis: Microscopy of thin and thick films
blood smears.
Different stages of the parasite (trophozoites, schizonts, and
gametocytes) can be demonstrated in the blood.
Prophylaxis. Malaria may be prevented by chemoprophylaxis
and personal protective measures against the mosquito vector
(Anopheles).
LIFE CYCLE OF THE MALARIA PARASITE
E Exoerythrocytic schizogony (liver phase)
1. Mosquito bites man, takes blood meal and injecting sporozoites from its salivary gland
into the blood.
2. Sporozoites travel through blood to the liver, multiply asexually to form merozoites,
which upon liver cell rupture, are released into the bloodstream and infect erythrocytes.
Erythrocytic schizogony (blood phase)
1. Merozoites enter the erythrocytes, forming a ring-like trophozoite; mature trophozoites
asexually divide to form schizonts.
2. Schizont develops into merozoite daughter cells, then lyse the erythrocytes membrane,
leading to periodic paroxysms of disease due to resultant parasitemia. P. ovale, P. vivax, P.
falciparum —membrane lysis in 48 hours, P. malariae —membrane lysis in 72 hours.
3. Some merozoites develop into macrogametocyte and microgametocyte.
Sporogony
1. Mosquito ingests gametocytes with blood meal.
2. Gametocytes enter mosquito gut.
3. Zygote, formed from fertilization, invades gut wall to form an oocyst within 24 hours
following ingestion
4. Sporozoites are formed, released into the stomach, migrate to salivary glands, then
injected into human with blood meal.
Patient with malaria. Clinical manifestations: fever, anemia,
splenomegaly, hepatomegaly
Malaria. Blood smear
Parasite: Toxoplasma gondii
Disease: toxoplasmosis
Geographical distribution: Cosmopolitan
Morphology: Four forms:
1) pseudocysts;
2) trophozoites;
3) cysts;
4) oocysts
Intermediate hosts: birds and mammals, including humans
Definitive hosts: cats and other Felidae
Localisation: brain, eyes, skeletal and cardiac muscles, liver, and
lungs
Transmitted to humans by:
1) ingestion of undercooked infected meat (cysts and pseudocysts);
2) contamination of food or drink with infected cat faeces (oocyts);
3) transplacental (congenital)
Toxoplasma gondii
LIFE CYCLE OF TOXOPLASMA GONDII
1. Oocysts pass from cat intestine to cat faeces.
2. Oocysts sporulate in soil and are viable for longer than one year.
3. Humans ingest oocysts either from soil or cat raw tissue infected
with cysts. The alimentary route of infection takes place on
ingestion of meat, milk, and dairy products of animals sick with
toxoplasmosis, uncooked egges of affected birds, and water
contaminated by sick animals.
4. Transmitted via placenta when mother develops infection during
gestation-congenital infection.
5. Invade intestinal wall after entering host (usually orally) and
disseminate via lymphatics and bloodstream forming trophozoites.
Toxoplasma gondii can spread to many host cells (of the
histophagocytic system, nerve tissue, liver, placenta, etc).
Class Zoomastigophorea:
1) Motion is by flagella. The flagellum arises from kinetoplast. The
kinetoplast is composed of the blepharoplast and the parabasal body.
2) Vesicular nucleus with central karyosome.
3) Reproduction is by longitudinal binary fission.
4) Complex life cycles include alternation of hosts.
Intermediate hosts commonly serve as vectors, which transport
developing parasites from one definitive host to another.
Parasitical species parasites of tissues and blood:
a) Trypanosoma
b) Leishmania
Their transmission requires a biological vector.
Species living in the digestive tract and genitals:
a) Lamblia intestinalis
b) Trichomonas vaginalis
c) Trichomonas hominis
Their transmission does not require a biological vector.
Parasites: Trypanosoma brucei gambiense and
Trypanosoma brucei rhodesiense
Disease: African trypanosomiasis, or sleeping sickness
Geographical distribution: West and Central Africa
Morphology: spindle-shaped cells with an undulatory
membrane and pointed flagella at the ends. The
organisms are motile, 25-40 micro;m in length.
Transmission: by bite of infected tsetse flies (Glossina
palpalis)
Reservoir hosts of T.b.gambiense are: man, domestic pig,
cattle, dog, antelope.
Reservoir hosts of T.b.rhodesiense are: hartebeest, lion,
hyena.
Localisation: blood, lymph nodes, cerebrospinal fluid,
brain, muscles.
Trypanosoma brucei gambiense
Scanning electron micrograph (5.500 × magnification)
of African trypanosome (Trypanosoma brucei
gambiense ) among host red blood cells.
Tsetse fly (Glossina palpalis) is vector of T. b. gambiense
and T. b. rhodesiense
Pathogenicity:
1) From the site of bite trypanosomes reach the blood
and lymphatics where they multiply.
2) There is perivascular infiltration with chronic
inflammation, leading to meningoencephalitis.
3) The patient suffers from fever, rash, headache,
lymphadenopathy, oedema of the brain. There are
alternating periods of fever and apparent recovery.
This is followed by depression and progressive
lethargy.
4) Rhodesien form develops within weeks to months,
Gambian form develops within years. The disease
becomes chronic and persists for months and even
years.
Laboratory diagnosis:
1) microscopic examination of blood and of
material obtained by puncture of the enlarged
lymph nodes;
2) examination of the cerebrospinal fluid
(availability of trypanosomes).
Prophylaxis:
1) treatment of patients;
2) protection of the population from the bites of
tsetse flies (Glossina palpalis);
3) the use of insect repellents, extermination of
vector flies.
Trypanosoma brucei gambiense in blood.
Parasite: Trypanosoma cruzi
Disease: American trypanosomiasis, or Chagas’ disease
Geographical distribution: South and Central America
Morphology: typical, small (20 micro;m) trypomastigotes (with
flagella) are found in peripheral blood and amastigotes
(intracellular without flagella) - in tissues.
Transmission: 1) by bite of infected bug species of the family
Triatomidae ; 2) congenital; 3) by blood transfusion.
Reservoir hosts: armadillos, opossums, rodents, monkeys, dogs, cats.
Localisation: blood (in acute phase), cells of lymph nodes, spleen,
liver, brain, muscles.
Clinical manifestation: fever, oedema of the face, and enlargement of
the thyroid gland, lymph nodes, spleen, and liver, heart alterations.
Laboratory diagnosis: 1) examination of patient’s blood;
2) guinea pig inoculation with 5-10 ml of patient’s blood;
3) serologic tests.
Prophylaxis: 1) extermination of bugs;
2) chemoprophylaxis with special preparations in endemic areas.
American trypanosomiasis (Chagas’ Disease) was
discovered in 1909 by C. Chagas in Brazil.
Bug of family Triatomidae is vector of Trypanosoma cruzi
Parasite: Leishmania tropica
Disease: Cutaneus leishmaniasis
Geographical distribution: Asia, Africa, Europe
Morphology: Intracellular amastigotes (without
flagellum) 3 to 6 micro;m long by 1.5 to 3 micro;m
in diameter live in men. Promastigotes (with
flagellum) develop in the intestine of the sand fly.
Transmission: by sand fly vector - Phlebotomus
sergenti (in Iran, Iraq, and India); Phlebotomus
papatasi (in southern France, Italy, and certain
Mediterranean islands).
Reservoir hosts: man, dogs, wild rodents.
Localisation: cells of skin.
Phlebotomus sandfly is vector
of Leishmania tropica.
Clinical manifestation: development of a
cutaneous papule that evolves into a nodule,
breaks down to form an indolent ulcer, and
heals, leaving a depressed scar.
Laboratory diagnosis: detection of the
Leishmania parasites in cells of skin.
Prophylaxis: early diagnosis, extermination
of sandflies and dogs and rodents infected
with leishmaniasis, and vaccination.
Parasite: Leishmania donovani
Disease: Visceral leishmaniasis, or kala-azar
Geographical distribution: India, Pakistan, China, and
Central Africa, Central America.
Transmission: by sand fly vector Phlebotomus
Reservoir hosts: man, dogs (except in India), cats, rodents.
Localisation: cells of visceral organs (liver, spleen, lymph
nodes, bone marrow).
Clinical manifestation: hepatosplenomegaly, irregular fever,
chills, vomiting, anemia, an earth-grey color of the skin.
Laboratory diagnosis: examination of sternal bone marrow
obtained by sternal puncture.
Prophylaxis: early diagnosis, opportune treatment, rodent
control, and extermination of sandflies and of dogs infected
with leishmaniasis.
Parasite: Lamblia intestinalis
Disease: lambliosis
Geographical distribution: cosmopolitan.
Morphology: Trophozoites are bilateral, symmetrical,
pear-shaped organisms with an elongated posteriоr and
two symmetrically placed nuclei. The body of the parasite
is from 10 to 18 micro;m long with four pairs of flagella.
Cysts are oval-shaped which are 10-14 micro;m and have
four nuclei.
Host: man.
Transmission: faecal-oral (alimentary).
Infective stage: cyst.
Localisation: the small intestine (duodenum) and gallbladder.
Life cycle
of Lamblia
intestinalis
Pathogenicity: chronic duodenitis, enterocolitis;.
cholecystitis and hepatitis.
Laboratory diagnosis: microscopic examination
of the duodenal contents or faeces.
Prophylaxis: Treatment of patients and
asymptomatic cyst passers; protection of
foodstuffs and water from flies and
contamination with faeces, the staff of catering
establishments must be examined for cysts
carriage, health education of the population.
Lamblia
intestinalis
Scanning electron micrograph (5.500 × magnification)
of Lamblia intestinalis in duodenum.
Parasite: Trichomonas vaginalis
Disease: Urogenital trichomoniasis
Geographical distribution: cosmopolitan.
Morphology: Trophozoite is a pear-shaped (7 to 23 micro;m
long) with four anterior flagella and a fifth forming the edge of
an undularing membrane. The axostyle extends the length of
the body.
Host: man
Transmission: by sexual contact; otherwise (through contact
with toilet seats and towels, for example).
Localisation: vagina, urethra, prostate.
Clinical Manifestations: vaginitis in women, more commonly
asymptomatic in men, but may lead to prostatitis or urethritis.
The main symptoms are dysuria, pruritis, yellow and frothy
discharge.
Laboratory diagnosis: microscopic examination of the vaginal
fluid, scrapings, or washing.
Trichomonas vaginalis
Class Ciliata
1) Move by cilia, which are numerous
and cover most of the body.
2) Have 2 nuclei, macronucleus
containing vegetative chromatin and
micronucleus containing generative
chromatin.
3) Reproduce by transverse binary
fission, and sometimes by conjugation.
Parasite: Balantidium coli
Disease: Balantidiasis
Geographical distribution: cosmopolitan.
Morphology: The trophozoite is from 75 to 200 micro;m in
length, asymmetrical, oval, with cilia, a cytostome, anal pore,
the macronucleus, the micronucleus, two contractile vacuoli.
Cyst with a double-layer membrane, from 30 to 60 micro;m in
diameter.
Hosts: man, domestic swine
Transmission: faecal-oral (alimentary)
Localisation: large intestine
Clinical Manifestations: colitis, ulcers and abscesses of colon,
diarrhoea, blood and mucus in the stool.
Laboratory diagnosis: microscopic examination of the faeces.
Prophylaxis: protection of foodstuffs and water from
contamination with swine faeces and observation of individual
hygiene when talking care of the animals (domestic swine).
Thank you for attention!