Theme:Medical Parasitology. 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.

of invasious diseases: 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.

Class Lobozea: 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)

Plasmodium falciparum tropical (falciparum) malaria Plasmodium ovale 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 tertian malaria Plasmodium malariae quartan malaria Plasmodium falciparum tropical (falciparum) malaria Plasmodium ovale 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

Intermediate host: Homo sapiens Definitive host: Anopheles mosquito 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 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 Tsetse fly (Glossina palpalis) is vector of T. b. gambiense and T. b. rhodesiense

Pathogenicity: 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 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 gall-bladder.

of Lamblia intestinalis Life cycle of Lamblia intestinalis

Pathogenicity: chronic duodenitis, enterocolitis; 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).

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