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Home , Protoplasm, Pseudopodia

Medical Biology

Dr: Fadia Al-Khayat

Protozoa are unicellular animals in which the various activities like metabolism, locomotion…..are carried out by different of the .Also they have a well defined nucleus and don’t have a rigid which gave them a variation in size and shape.

Structure of protozoa 1- nucleus: usually only one is present 2- :which differentiated into a- outer cytoplasm() b- inner cytoplasm() Nutrition of protozoa

1-Holozoic protozoa: utilize preformed food material derived from living animals or plants. 2-Saprozoic protozoa:absorb nutrients. means that certain protozoa absorb predigested or soluble nutrients through their

3-Holophytic protozoa:like plants(chlorophyll). Locomotion of protozoa

Protozoa can be move by: , flagella, cilia and gliding

Reproduction of protozoa

1-Sexual a-Conjugation: two organisms exchange nuclear material and then separate. b-Syngamy:two gametes fuse together to form zygotes(microgametes+macrogametes)

2- Asexual reproduction a- Binary fission: the nucleus divide then the cytoplasm(1,2,4,8.16….) b- Multiple fission:the nucleus divide several times then the cytoplasm does. c-Budding:two or many daughter forms are produced from the parent cell. d-Sporogoy:occurs after the sexual reproduct(syngame),a process of multiple fission ,number of sporozoites are formed within the wall of a cyst. Four main groups of protozoa are recognized on the basis of their locomotion using specialized subcellular and cytoskeletal features

Amoebae use pseudopodia (singular: pseudopodium) to creep or crawl over solid substrates. Pseudopodia (or ‘false feet’) are temporary thread- like or balloon-like extensions of the cell membrane into which the protoplasm streams. Similar amoeboid motion has been observed in cells of many life-forms, especially phagocytic cells (e.g. human ).

Flagellates use elongate flagella (singular: ) which undulate to propel the cell through liquid environments. Flagella are ‘hair-like’ extensions of the cell membrane constructed of , hook and filament with an inner core of arranged in a specific 2+9 configuration (2 single central microtubules surrounded by 9 peripheral doublets). This configuration is conserved throughout eukaryotic biology, many organisms produce flagellated cells (e.g. human spermatozoa.

Ciliates use numerous small cilia (singular: ) which undulate in waves allowing cells to swim in fluids. Cilia are ‘hair-like’ extensions of the cell membrane similar in construction to flagella but shorter and present in much larger numbers. Ciliated cells are found in specialized tissues and organs in many other higher life-forms (e.g. human bronchial epithelial cells). Sporozoa (‘spore-formers’) were originally recognized not on the basis of their locomotion, but because they all formed non-motile spores as transmission stages. Recent studies, however, have shown that many pre- spore stages move using tiny undulating ridges or waves in the cell membrane imparting a forward gliding motion, but the actual mechanisms involved are not yet known. Human

Free-living protozoan groups that inhabit soils and natural are extremely diverse, not only in their structure but also in the manner in which they feed, reproduce, and move. The amoeboid group includes hundreds of different organisms, ranging in size from about .25 to 2.5 mm. Amoebas are considered the most primitive animals and are classified in the kingdom Protista. All amoeboid organisms have thin cell membranes, a semirigid layer of ectoplasm, a granular, jellylike endoplasm, and an oval nucleus Amoebas are identified by their ability to form temporary cytoplasmic extensions called pseudopodia, or false feet, by means of which they move about. This type of movement, called ,. Some species live on aquatic plants and some in moist ground; others are parasitic in animals and humans.

Amoeba contains food , food is taken in and material excreted at any point on the cell surface. During feeding, extensions of cytoplasm flow around food particles, surrounding them and forming a into which enzymes are secreted to digest the particles . contractile vacuoles involved in osmoregulation pumps excess out of the cell. Reproduction is asexual (binary fission).

Three groups of amoebas are concerned with human health.these groups are:

1-Amoebas live in the alimentary canal and able to invade , such as histolytica.

2-Amoebas live in the alimantry canal and unable to invade tissue,but dwell in the canal lumen such as , and Dientamoeba fraglis.

3-Amoebas live freely in water and can infect human brain while swimming in contaminated water such as .

Entamoeba histolytica

Entamoeba histolytica is a protozoan parasite responsible for a disease called amoebiasis. It occurs usually in the large intestine and causes internal inflammation as its name suggests (histo = tissue, lytic = destroying). 50 million people are infected worldwide, mostly in tropical countries in areas of poor sanitation. In industrialized countries most of the infected patients are immigrants, institutionalized people and those who have recently visited developing countries. Inside humans Entamoeba histolytica lives and multiplies as a trophozoite. Trophozoites are oblong and about 15–20 µm in length. In order to infect other humans they encyst and exit the body.

Life cycle

Entamoeba histolytica does not require any intermediate host. Mature cysts (spherical, 12–15 µm in diameter) are passed in the feces of an infected human. Another human can get infected by ingesting them in fecally contaminated water, food or hands. If the cysts survive the acidic stomach, they transform back into trophozoites in the small intestine. Trophozoites migrate to the large intestine where they live and multiply by binary fission. Both cysts and trophozoites are sometimes present in the feces. Cysts are usually found in firm stool, whereas trophozoites are found in loose stool. Only cysts can survive longer periods (up to many weeks outside the host) and infect other humans. If trophozoites are ingested, they are killed by the gastric acid of the stomach.

Mode of infection:

1- contaminated food and water containing the infective stage (mature cyst) 2- carriers(asymptomatic) 3- Homosexual men

Symptoms/Pathogenicity

Infections of E. histolytica vary in intensity from asymptomatic to severe or fatal invasions. Asymptomatic infections are responsible for the spread of the parasite with numerous cysts being passed in normal stools. Diarrheic stools primarily contain trophozoites which cannot persist in the environment.

• Infections of E. histolytica vary in intensity from asymptomatic to severe or fatal invasions. • Intestinal amoebiasis:The trophozoites come in contact with mucosa,secrete proteolytic enzymes ,which enable them to penetrate the epithelium and begin moving deeper.The intestinal lesion spreads in the intestinal wall as a duct like ulcer.Through these ulcers,blood escapes to the intestine lumen to demonstrate the important sign of amoebiasis. Trophozoite carried out by blood and lymph to form secondary lesion through out the body Extracellular amoebiasis:Invasive forms cause secondary lesion mainly in liver(hepatic or liver amoebiasis),in lung(pulmonary or lung amoebiasis),in brain,spleen.

Invasive forms of the disease lead to amoebic dysentery in which the trophozoites invade the intestinal wall, leading to the formation of amoebic ulcers. This results in severe diarrhea with blood and mucus present. In such cases it is important to identify E. histolytica in the stools to differentiate among other causes of dysentery.

If trophozoites penetrate the intestinal wall, serious problems can occur, including liver abcesses, or spread to the lungs and brain, usually resulting in death. Most Entamoeba histolytica infections are asymptomatic and trophozoites remain in the intestinal lumen feeding on surrounding nutrients. About 10–20 % of the infections develop into amoebiasis which causes 70 000 deaths each year. Minor infections (luminal amoebiasis) can cause symptoms that include:

 gas (flatulence)  intermittent constipation  loose stools  stomach ache  stomach cramping.

Severe infections inflame the mucosa of the large intestine causing amoebic dysentery. The parasites can also penetrate the intestinal wall and travel to organs such as the liver via bloodstream causing extraintestinal amoebiasis. Symptoms of these more severe infections include:

 anemia  appendicitis (inflammation of the appendix)  bloody diarrhea  fatigue  fever  gas (flatulence)  genital and skin lesions  intermittent constipation  liver abscesses (can lead to death, if not treated)  malnutrition  peritonitis (inflammation of the peritoneum which is the thin membrane that lines the abdominal wall)  stomach cramping  toxic megacolon (dilated colon)  weight loss.

Prevention

To prevent spreading the infection to others, one should take care of personal hygiene. Always wash your hands with soap and water after using the toilet and before eating or preparing food. Amoebiasis is common in developing countries. Some good practices, when visiting areas of poor sanitation:

 Wash your hands often.  Avoid eating raw food.  Avoid eating raw vegetables or fruit that you did not wash and peel yourself.  Avoid consuming milk or other dairy products that have not been pasteurized.  Drink only bottled or boiled water or carbonated (bubbly) drinks in cans or bottles.

Genus and Entamoeba histolytica species

Etiologic Amoebiasis; amoebic dysentery; extraintestinal amoebiasis, usually agent of: amoebic liver abscess; amoebic lung abscess

Infective Tetranucleated cyst (having 4 nuclei) stage

Definitive Human host

Portal of Mouth entry

Mode of Ingestion of mature cyst through contaminated food or water transmission

Habitat Colon and cecum

Pathogenic

Trophozoite stage

Locomotive Pseudopodia ("false foot”") apparatus

Mode of Binary fission reproduction

Lytic necrosis (it looks like “flask-shaped” holes in Gastrointestinal Pathogenesis tract sections (GIT)

Lab Most common is direct fecal smear (DFS) and staining (but does not diagnosis allow identification to species level); enzyme immunoassay (EIA); indirect hemagglutination (IHA); Antigen detection – monoclonal antibody; PCR for species identification. Sometimes only the use of a fixative (formalin) is effective in detecting cysts. Culture: From faecal samples - Robinson's medium, Jones' medium

Metronidazole for the invasive trophozoites pluse a lumenal amoebicide for those still in the intestine, 750 mg three times a day Treatment orally, for 5 to 10 days. Followed by Paromomycin, 30 mg/kg/day orally for 5 to 10 days (Humatin) is the luminal drug of choice.

Entamoeba coli

is a non-pathogenic species of Entamoeba that frequently exists as a commensal parasite in the human gastrointestinal tract. Clinically, E. coli (not to be confused with the bacterium Escherichia coli) is important in medicine because it can be confused during microscopic examination of stained stool specimens with the pathogenic Entamoeba histolytica. While this differentiation is typically done by visual examination of the parasitic cysts via light microscopy, new methods using molecular biology techniques have been developed. The presence of E.coli is not cause in and of itself to seek treatment as it is considered harmless. However it should be noted that when a person becomes infected with this benign entamoeba, other pathogenic organisms may have been consumed at the same time.

Entamoeba gingivalis

Entamoeba gingivalis is a non-pathogenic protozoa and is known to be the first in humans to be described. It is found only in the mouth between the gingival pockets and near the base of the teeth. Entamoeba gingivalis is found in 95% of people with gum disease and in 50% of people with healthy gums. The cyst formation is not present, therefore transmission is occure through the droplets of saliva, direct from one person to another by kissing, or by sharing eating utensils. Only the trophozoites are formed and the size is usually 10 micrometer to 20 micrometer in diameter and morphologically resembles that of E. histolytica Entamoeba gingivalis trophzoites characteristically exhibit active . The multiple pseudopods vary in their appearance as the trophozoite moves . The pseudopods may appear long when seen at one point in time and short and blunt the next time they are seen . The single nucleus contains a central karyosome surrounded by peripheral chromatine that is for the most part fine and evenly distributed .Achromatic granules arranged in strands may be visible extending from the karyosome to the peripheral chromatin ring . Anumber of inclusions are typically found in the finely granular cytoplasm , including : food vacuoles containing phagocytosed and partially digested white blood cells ( leukocytes ) and epithelial cells of the host , bacteria , and ingested RBCs . It is important to note that E. gingivalis is the only ameba that ingests white blood cells . . Entamoeba gingivalis have pseudopodia that allow them to move quickly. Their spheroid nucleus is 2 micrometer to 4 micrometer in diameter and contains a small central . There are numerous food vacuoles and contain cellular debris, blood cells and bacteria. Entamoeba gingivalis, as the name implies typically lives around the gum line of the teeth and gingval pokets of unhealthy mouths, It is non pathogenic and isolated from healthy mouth but mainly it is isolated from diseased mouth with oral abscesses ,dental carries and other inflammatory conditions in the mouth. In addition, the E. gingivalis trophozoites have been known to inhabit the tonsillar crypts and the bronchial mucus. E. gingivalis may also be found in the mouths of individuals who practice good oral hygiene .. This amoebae is actively motile by multiple pseudopodia . Ectoplasm is clear, well differentiated from granular endoplasm. Endoplasm contain many food vacuoles, some of them with diagnostic rounded dark – staining bodies represent the nuclei of ingested white blood cells and epithelia cells. The nucleus is histolytic type.