BIO346 Lecture 2: The Amebae PDF

The Amebae  The Ameba Subphylum Sarcodinia Class Lobosea Intestinal Species Atrial Species Classification of the Amebae  Intestinal/Lumen-Dwelling Protozoa Flagellates...

The Amebae  The Ameba Subphylum Sarcodinia Class Lobosea Intestinal Species Atrial Species Classification of the Amebae  Intestinal/Lumen-Dwelling Protozoa Flagellates Apicomplexa – Giardia lamblia – Cryptosporidium parvum – Dientamoeba fragilis – Cryptosporidium hominis – Chilomastix mesnili – Cyclospora cayetanensis – Enteromonas hominis – Isospora belli – Retortamonas intestinalis – Trichomonas hominis Microsporidia – Trichomonas tenax (oral) – Enterocytozoon bieneusi – Trichomonas vaginalis (urogenital) – Encephalitozoon intestinalis Ameba Other – Entamoeba histolytica – Blastocystis hominis – Entamoeba dispar – Balantidium coli – Entamoeba coli – Entamoeba hartmanni – Entamoeba polecki – Entamoeba gingivalis – Endolimax nana – Iodamoeba bütschlii Intestinal/Lumen-Dwelling Protozoa Cont’d Numerous protozoa inhabit the gastrointestinal tract of humans The majority are non-pathogenic commensals or only result in mild disease The pathogenic ones can cause severe disease Transmitted by the fecal-oral route (i.e., ingestion of food and/or water contaminated with cysts Intestinal Protozoa: Life Cycle  Intestinal Protozoa Ameba – Entamoeba histolytica – Entamoeba dispar – Entamoeba coli – Entamoeba hartmanni – Entamoeba polecki – Entamoeba gingivalis – Endolimax nana – Iodamoeba bütschlii  Encystation Occurs when the environment is not conducive to trophozoite replication (i.e., overpopulation, pH change, availability of food and oxygen Trophozoites become more spherical in shape; 12-15 µm in diameter Ribsomes aggregate to form elongate chromatoid bodies Maturation involves two rounds of nuclear division; cb disappear Excreted cysts are infective; viable for weeks to months depending on environmental conditions due to the hard, protective cell wall  Trophozoite Stage Occurs through the process of excystation Unlike cysts, fragile Motile Replication occurs (via asexual binary fission)  Intestinal Protozoa: Symptoms/Diagnosis Most patients infected with ameba are asymptomatic Most common symptom is unexplained diarrhea Found in stool samples (trophozoites and/or cysts) Distinguishing factors/characteristics – Organism size – Number of nuclei (iodine wet preparations) – Location of nuclei (iodine wet preparations) – Cytoplasmic inclusions (iodine wet preparations) – Motility (saline wet preparations) Permanent stains – Make structures that are otherwise undetectable, visible and easier to identify  Intestinal Protozoa Ameba – Entamoeba histolytica – Entamoeba dispar – Entamoeba coli – Entamoeba hartmanni – Entamoeba polecki – Entamoeba gingivalis – Endolimax nana – Iodamoeba bütschlii  The Amebae Most amebae are free-living organisms in soil and water. A few species have become parasitic in vertebrates and may cause dangerous diseases in their hosts. Outbreak in 1933 World's Fair in Chicago caused by defective plumbing (cross connections between water lines and sewer lines) caused over 1000 cases of amebiasis resulting in 58 deaths  Entamoeba histolytica: Modes of Transmission Hand-to-mouth infection (via ingestion of infective (cyst) stage Food/water contamination Unprotected sex Vectors (flies and cockroaches)  Entamoeba histolytica Cont’d Can become highly virulent and invasive Infestation has the potential to lead to lethal, systemic disease After ingestion, cysts transform into trophozoites (exhibit active metabolism; usually motile) In the trophozoite stage, the parasite takes up nutrients and undergoes asexual replication Humans are the only host  Order Amoebida – Family Entamoebidae Entamoeba histolytica One of the most important and pathogenic parasites of humans Although pigs and primates may be infected, these infections are rare and unimportant. This parasite is transmitted from human to human; First seen in 1878 but not described until 1903 Causative agent of the disease intestinal amebiaisis (old name is Amebic Dysentery)  Entamoeba histolytica: General Characteristics Amorphous shape Trophozoites range in size from 8-65 µm in diameter (average 12-25 µm) ; cysts range from 12-18 µm At the trophozoite stage, move rapidly by extending fingerlike-projections called pseudopodia* * Distinguishing feature of ameba Entamoeba histolytica trophozoites Entamoeba histolytica cysts uninucleate cyst binucleate cyst  Entamoeba histolytica cysts quadrinucleate or mature cysts – diagnostic in feces  Entamoeba histolytica Infection Common sources: Poor sanitation/contaminated water Use of human manure to fertilize vegetables Poor personal hygiene Exposure of food to flies and roaches https://www.cdc.gov/dpdx/amebiasis/index.html Entamoeba histolytica: General Characteristics Cont’d Nucleus has a small and central karyosome Peripheral chromatin is fine and usually evenly distributed around the nucleus Nucleus is invisible until stained Distinguishing feature: Red blood cells in the cytoplasm  Entamoeba histolytica Pathology Mucosa submucosa COLONIZATION OF THE LARGE INTESTINE  Entamoeba histolytica Pathology: Amebiasis Extra-intestinal lesions occur in 3 Ectopic sites: A. HEPATIC AMEBIASIS B. PULMONARY AMEBIASIS C. CEREBRAL AMEBIASIS Amebiasis  Amebiasis An estimated 50 million cases worldwide per year Up to 100,000 deaths per year Third leading cause of parasitic deaths (behind malaria and schistosomiasis) Associated with long-term (> 1 month) stays in an endemic area  Amebiasis On average, 1 in 10 people infected with E. histolytica becomes sick (asymptomatic intestinal amebiasis in 9 out of 10) Asymptomatic cases occur if: – Parasite is low virulence – Host inoculation is low – Patient’s immune system is functioning well  Amebiasis Cont’d Symptoms include diarrhea, stomach pain and cramping (symptomatic intestinal amebiasis/amebic colitis) – Secondary bacterial infections may develop – In severe cases, amebic dysentery results (stomach pain, bloody stools, and fever)  Amebiasis Cont’d In rare cases, invades the liver after invading the bloodstream and forms an abscess (symptomatic extraintestinal amebiasis) Diagnosis can only be performed serologically unless the trophozoite returns to the bloodstream  Amebiasis Cont’d Even less frequently, spreads to other parts of the body such as the lung or brain  Amebiasis: Presentation and Diagnosis On average, infected persons become ill 1-4 weeks after ingestion Diagnosis is very difficult because other cells and parasites have similar morphology and often leads to misdiagnosis – Analysis of stool samples – Blood tests (if believed to have invaded the intestinal wall) Usually treated with antibiotics  Entamoeba coli life cycle stages 1. TROPHOZOITE - 20 to 30 m in diameter - granular endoplasm is coarser than E. histolytica - lives in large intestine and feeds on bacteria and any other cells available to it; does not invade tissue  Entamoeba coli life cycle stages 2. CYST - encystment is similar to that of E. histolytica - immature cysts are rare in fecal smears - mature cyst is large, 10 to 33 m - chromatoidal bodies, if present, have splinter-like ends (disappear in most cysts) - cyst is released in the feces into the external environment https://www.cdc.gov/dpdx/intestinalamebae/modules/Intestinal_amebae_lg.jpg  Entamoeba gingivalis Also considered non-pathogenic Trophozoite lives on the surface of teeth and gums. Parasites feed on epithelial cells of the mouth, bacteria, food debris, and other cells available to them. Organisms are more common in persons with pyorrhea (gum disease) but they are not the cause of the condition. No cyst stage: Transmitted  Naegleria fowleri Found in warm environments in rivers, and hot springs, and soil The stages of the life cycle: cysts, trophozoites, and flagellated forms  Naegleria fowleri Stages: Flagellated trophozoites enter when a victim swims or dives into freshwater. - all victims have had a history of swimming in freshwater lakes or ponds or swimming pools a few days before the onset of symptoms - once it enters a human, the parasites always revert to the cyst  Naegleria fowleri Structures of the ameboid form:  Naegleria fowleri DIAGNOSIS – most cases have been diagnosed by identification of large numbers of amebae in the brain tissues Symptoms include a headache, fever, neck rigidity, and mental confusion followed by coma and death - Disease is so rare and the brain tissue destruction is so rapid that diagnosis is seldom made in time  Acanthamoeba spp. At least 5 species of Acanthamoeba have been identified in human tissues. Free-living trophozoites and cysts occur in both the soil and freshwater. Trophozoites occur only as ameboid forms:  Acanthamoeba spp. pathology Over 100 cases of granulomatous amebic meningoencephalitis caused by Acanthamoeba have been documented Most resulted in death in a few months. Mode of transmission is not known, as no history of swimming occurred in some cases.  Acanthamoeba spp. Pathology Incriminated in a number of cases of keratitis (inflammation and opacity of the cornea). Most of these ocular infections were in contact lens wearers who used home-made saline It appears that swimming with contact lenses were necessary for invasion Diagnosis by identifying amebae in corneal scrapings Drug treatment has been successful in most cases  New facultative Ameba Recently Identified A new freshwater ameba called Balamuthia has been incriminated is some 80 cases of amebic meningoencephalitis in humans since 2001. Only 2 survivals Easily misidentified so some of the cases of granulomatous amebic meningoencephalitis believed to have been caused by Acanthamoeba may well have been caused by Balamuthia  Summary Parasitic infections are widespread but the majority take place in tropical/developing countries Infections with pathogenic intestinal ameba account for approximately 100,000 deaths per year The life cycle intestinal ameba includes the reproductive (trophozoite) and infective (cyst) stages Only one pathogenic intestinal ameba (Entamoeba histolytica); however, Entamoeba dispar is morphologically similar Distinguishing feature of E. histolytica is the presence of red blood cells in the Miscellaneous Protozoa  The Ciliates Subphylum Class Sarcodina Lobosea Phylum (amebas) Sarcomastigophora Subphylum Class Mastigophora Zoomastigophora (flagellates/ hemoflagellates) Phylum Class Ciliophora Kinetofragminophorea (ciliates) Order Class Blastocystida Blastocystea Phylum Class Apicomplexa Sporozoa  The Ciliates: Balantidium coli Exists in trophozoite and cyst forms Considered the largest protozoan; measures 28 μm up to 152 μm (avg length = 35 μm to 50 μm) Typically exhibits rotary, corkscrew-like motility Balantidium coli: Life Cycle  Balantidium coli: Trophozoite Ovoid to sac-shaped Tapers at the anterior end Contains two nuclei A micronucleus is located adjacent to the macronucleus 1-2 vacuoles visible Small cytosome Has a layer of cilia all around (used for motility)  Balantidium coli: Cyst Spherical to oval in shape Avg size = 52 µm – 55 µm Micronucleus not visible even in stained preparations 1-2 vacuoles Double cyst wall with cilia in between Mature cysts lose their cilia Balantidium coli  Balantidium coli: Mode of Transmission Ingestion of contaminated food and water Via fecal-oral and person-person routes Also possible reservoir host transmission  Balantidium coli: Symptoms Asymptomatic/Carrier State Balantidiasis – Mild colitis – Diarrhea (may contain pus, mucus, and blood) – Abcesses and ulcers may form in the mucosa of the large intestine – Secondary bacterial infections result – Can invade the liver, lungs, urogenital tract, etc.  Balantidium coli: Laboratory Diagnosis Analysis of stool specimens for trophozoites and cysts – Trophozoites recovered from runny stools – Cysts recovered from normal/formed stools Wet and stained preparations should be analyzed  Balantidium coli: Prevention and Control Personal hygiene Sanitary water conditions  Pneumocystis Carinii: Stages Cyst – Avg size = 4 µm – 12 µm – 4-8 nuclei (intracystic bodies) – Nuclei are either arranged in a rosette or scattered throughout the infected cell Pneumocystis Carinii: Stages  Pneumocystis Carinii: Life cycle not fully understood – It is believe that it infects the alveolar spaces in lung tissue – When mature cysts rupture, trophozoites are released – Also infects the spleen, lymph nodes, and bone marrow  Pneumocystis Carinii: Transmission Believed to be via person-person contact through the transfer in pulmonary droplets (water vapor we exhale) Known to be transmitted through the placenta; can result in stillbirths Those at greatest risk of contracting the infection are the immunocompromised, e.g., AIDS patients, young children  Pneumocystis Carinii: Symptoms PneumocystoisAtypical Interstitial Plasma Cell Pneumonia – Leading cause of death in AIDS patients – Non-productive cough – Fever – Rapid breathing – Cyanosis (bluish tinge in skin indicative of decreased oxygen in the blood)