Theme: Medical protozoology

Symbiosis is the living together or close association of two dissimilar organisms. Commensalism is symbiosis in which one party (commensal) 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 is the study of human parasites of Protozoa. Medical Helminthology is the study of human parasitic worms of Trematoda, Cestoda, Nematoda. 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. Host is an organism that harbours or nourishes another organism (parasite). Definitive host (final h.) is a host that harbours the adult or sexually mature parasite. Intermediate host that 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.

Invasive diseases are caused by animals. Protozoan diseases are caused by Protozoa. Anthroponotic diseases are characteristic for humans. Anthropozoonotic diseases are characteristic for humans and animals. The ways of agent transmission of invasive diseases: contagion (by skin contact, sexual contact); alimentary or faecal-oral transmission (ingestion of raw or undercooked food or use of drinking water containing the infective stage of the parasite); by blood (by bite of vector containing the infective stage, blood transfusion); congenital (through the placenta)

Kingdom Animalia Subkingdom Protozoa Phylum 1. Sarcomastigophora Subphylum Sarcodina. Class Lobozea. Type species: Entamoeba histolytica, E. coli, E. gingivalis. Subphylum Mastigophora (or Flagellates). Class Zoomastigophorea. Type species: Trypanosoma brucei gambriense, T. b.rhodesiense, T. cruzi, Leishmania donovani, L. tropica, Lamblia intestinalis, Trichomonas vaginalis, T. hominis. Phylum 2. Apicomplexa. Class Sporozoa. Type species: Plasmodium vivax, P. malariae, P. falciparum, P. ovale, Toxoplasma gondii. Phylum 3. Ciliophora. Class Ciliata. Type species: Balantidium coli.

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 MMorphology: 1)forma magna; 2) forma minuta; 3) cyst.

Amebiasis Entamoeba histolytica trophozoite Entamoeba histolytica mature 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 ulcers 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.

Amebic Colitis: Severe dysentery with multiple ulcers in the large bowel, and a bloody diarrhea

Entamoeba histolytica trophozoites in section of intestine (H&E)

Gross pathology of liver containing amebic abscess

Amebic liver abscesses

Amoebiasis Laboratory diagnosis: Fresh stools are examined under the microscope. E. histolytica (forma magna and cysts with 4 nuclei) can be demonstrated in the stools. Prevention: 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.

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, P. malariae, P. falciparum, P. ovale, Toxoplasma gondii. PARASITESDISEASES Plasmodium vivaxtertian malaria Plasmodium malariaequartan malaria Plasmodium falciparumtropical (falciparum) malaria Plasmodium ovaletertian ovale-malaria MALARIA PARASITES OF MAN

Geographical distribution of malaria: in parts of Africa, Asia, Turkey, the West Indies, Central and South America, and Oceania

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: liver, blood Prevention: chemoprophylaxis and personal protective measures against the mosquito vector (Anopheles).

Blood stages of Plasmodium: 1) young trophozoites (ring forms); 2) growing trophozoites; 3) mature trophozoites; 4) mature shizonts; 5)macrogametocytes; 6) microgametocytes

Patient with malaria. Clinical manifestations: fever, anemia, splenomegaly, hepatomegaly

Laboratory diagnosis of malaria: Microscopy of thin and thick films blood smears. Different stages of the parasite (trophozoites, schizonts, and gametocytes) can be demonstrated in the blood.

Parasite: Toxoplasma gondii Disease: toxoplasmosis Intermediate hosts: birds and mammals, including humans Definitive hosts: cats 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 1) pseudocysts; 2) trophozoites; 3) cysts; 4) oocysts

T.g. human liver

lung heart

Congenital toxoplasmosis Clinical manifestations. Hydrocephalus, lesions in the organs of the vision (chorioretinitis), cirrosis of the liver and enlargement of the spleen.

Prevention of toxoplasmosis: washing of hands before meals and after handling animals and animal products, and the prohibition of preparing food from insufficiently cooked meat products, in particular liver. All women with a history of spontaneous abortion must be examined by laboratory methods for prevention of congenital toxoplasmosis.

Class Zoomastigophorea: 1)Motion is by flagella. 2)Reproduction is by longitudinal binary fission. 3) Complex life cycles include alternation of hosts. 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 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.

Morphology of trypanosoma: spindle-shaped cells with an undulatory membrane and pointed flagella at the ends. The organisms are motile, micro;m in length.

Scanning electron micrograph (5.500 × magnification) of African trypanosome (Trypanosoma brucei gambiense ) among host red blood cells

Tsetse fly (Glossina palpalis) is vector of Trypanosoma

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.

Parasite: Trypanosoma cruzi Disease: American trypanosomiasis, or Chagas’ disease Geographical distribution: South and Central America 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.

Trypanosoma cruzi was discovered in 1909 by C. Chagas in Brazil

Bug of family Triatomidae is vector of Trypanosoma cruzi

T. cruzi cardiac muscle

Clinical manifestation: fever, oedema of the face, and enlargement of the thyroid gland, lymph nodes, spleen, and liver, heart alterations

Parasite: Leishmania tropica Disease: Cutaneus leishmaniasis Geographical distribution: Asia, Africa, Europe Transmission: by sand fly vector - Phlebotomus sergenti (in Iran, Iraq, and India); Phlebotomus papatasi (in southern France, Italy, and certain Mediterranean islands) Hosts: man, dogs, wild rodents Localisation: cells of skin

Morphology of leishmania Intracellular amastigotes (without flagellum)2 - 6 micro;m; live in men Promastigotes (with flagellum) develop in the intestine of the sand fly

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. Prevention: early diagnosis, extermination of sandflies and dogs and rodents infected with leishmaniasis, and vaccination.

Parasite: Lamblia intestinalis Disease: lambliosis Geographical distribution: cosmopolitan Host: man Transmission: faecal-oral (alimentary) Infective stage: cyst Localisation: the small intestine (duodenum) and gall-bladder

Life cycle of Lamblia intestinalis

Lamblia intestinalis Morphology: Trophozoites are symmetrical, pear-shaped organisms with two nuclei. The body is micro;m with four pairs of flagella. Cysts are oval-shaped which are micro;m and have four nuclei.

Scanning electron micrograph (5.500 × magnification) of Lamblia intestinalis in duodenum.

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.

Parasite: Trichomonas vaginalis Disease: Urogenital trichomoniasis Geographical distribution: cosmopolitan. Morphology: Trophozoite is a pear-shaped (7-23 micro;m long) with four anterior flagella and a fifth forming the edge of an undularing membrane. The axostyle extends 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 micro;m, oval, with cilia. Cyst is micro;m. 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. Prevention: protection of foodstuffs and water from contamination with swine faeces and observation of individual hygiene when talking care of the domestic swine.