MDD Microbiology (Protozoa)
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76 terms
Terms | Definitions |
|---|---|
 Four major groups of pathogenic protozoa for humans | Amoeba Flagellates Ciliates Apicomplexa |
| Amoeba | Move using pseudopodia |
| Flagellates | Move using flagella |
| Ciliates | Move using cilia |
| Apicomplexa | Motile structures such as flagella or pseudopods are present only in certain gamete stages Specialized organelles for cell invasion: apical complex |
| Host | Organism used by protozoan as source of nutrients and protection |
| Parasite | Organism that uses host, with harm to the host |
| Commensal | Uses host without harm |
| Reservoir | Organism from which parasite is transmitted to humans |
| Vector | Organism which transmits parasite to humans |
| Definitive host | Host in which parasite undergoes meiosis |
| Intermediate host | Host in which parasite multiplies only by mitosis |
| Trophozoite | Form of parasite which grows and multiplies |
| Cyst | Non-multiplying form, specialized for resistance and transmission |
| 4 methods for diagnosis of protozoan infections | Stool: "O&P" workup for ova and parasites Wet mount of fresh material, stained smears Blood or exudate: stained smears Tissue: histology Serology, PCR on increase |
| Pathogenic flagellates | Giardia lamblia Trichomonas vaginalis |
| Giardia lamblia | Natural habitat: intestinal tract of warm blooded animals How transmitted to humans: drinking sewage contaminated drinking water or water from mountain streams Non-human reservoirs: many rodents and beavers Disease produced and symptoms: trophozoite adheres to small intestinal wall, interferes with intestinal fat absorption, causing greasy frothy diarrhea along with abdominal gassy distention and cramps Methods for prevention and treatment: treat with metronidazole, prevent using sanitation measures Appearance under microscope: 2 nuclei, trophozoite looks like a kite |
| Trichomonas vaginalis | Natural habitat: vagina/urinary tract How transmitted to humans: sexually transmitted Non-human reservoirs: N/A Disease produced and symptoms: pruritis (itching), burning on urination, and copious vaginal secretions for females, males are usually asymptomatic Methods for prevention and treatment: treat with metronidazole, also provide for sexual partners Appearance under microscope: trophozoite is oval as well as flagellated, or "pear" shaped as seen on wet-mount slide |
| Hemoflagellates | Trypanosoma: blood & tissue infections; multiply outside cells Leishmania: tissue infections, multiply inside cells |
| Trypanosoma | Geographic range: eastern (T. b. rhodesiense) and western (T. b. gambesiense) Africa, and America (Trypanosoma cruzii) Vector and how transmitted to humans: transmitted by insect vectors through blood feeding Disease produced in humans: sleeping sickness (African), Chagas disease (American) Forms present in humans and the vector: African: epimastigotes multiply in gut and salivary glands of the Tsetse fly, trypomastigotes multiply in bloodstream of mammals; American: epimastigotes multiply in gut and salivary glands of Triatoma, amastigotes multiply intracellularly in mammalian tissue, migration to other sites via bloodstream by trypomastigotes Appearance in blood smear or tissue section: cells with or without flagella |
| Leishmania | Geographic range: South and Central America, Africa, Middle East Vector and how transmitted to humans: Sandfly bite Disease produced in humans: leishmaniasis Forms present in humans and the vector: promastigotes multiple in the gut of blood sucking sandfly, amastigotes multiply intracellularly in macrophages and RES, release into bloodstream by cell lysis Appearance in blood smear or tissue section: cells with or without flagella |
| Kinetoplast | Mitochondrion + basal body |
| Amastigote | No flagellum, kinetoplast central |
| Promastigote | Flagellum, kinetoplast anterior |
| Epimastigote | Kinetoplast migrates posteriorly; undulating membrane |
| Trypomastigote | Kinetoplast fully posterior |
| Leishman-Donovan body | Amastigotes in tissue - indicative of leishmaniasis |
| Winterbottom's sign | Swelling of lymph nodes (lymphadenopathy) along the back of the neck, in the posterior cervical chain of lymph nodes, as trypanosomes travel in the lymphatic fluid and cause inflammation - sign of African trypanosomiasis |
| Romana's sign | Eyelid swelling from Chagas disease - infection spread to conjunctiva |
| African trypanosomes | Three sub-species: T. b. brucei (ancestral form), T. b. rhodesiense (East Africa, rapidly progressive), T. b. gambesiense (West Africa, slowly progressive) Reservoirs/vector: T. b. brucei - wild ungulates (hoofed animals), T. b. rhodesiense - game animals and livestock, T. b. gambesiense - humans Three stages of disease in humans and symptoms: • Local inflammatory lesion. • Bloodstream phase, enlarged lymph nodes; systemic inflammatory/febrile illness. • CNS invasion: lassitude, weakness, motor problems, coma, death. Two drugs for treatment of early infections: suramin or pentamidine Two drugs for treatment of CNS disease: eflornithine and nifurtimox or melarsoprol |
| American trypanosomes | Disease produced: Chagas disease Reservoir/vector: mammals, wild or domestic, and include humans; vector is the reduviid bug Three stages of disease in humans and symptoms: • Primary lesion at site of infection • Spread to conjunctiva - eyelid swelling (Romaña's sign) and muscle - febrile illness. • Invasion of heart, CNS, abdominal viscera, smooth muscle dysfunction, megacolon |
| Leishmania | Disease produced by L. donovani: visceral leishmaniasis Two types of disease produced by dermotropic forms: cutaneous leishmaniasis - sore at the bite site, which heals in a few months to a year, leaving an unpleasant-looking scar, diffuse cutaneous leishmaniasis - widespread skin lesions which resemble leprosy, mucocutaneous leishmaniasis - skin ulcers spread, causing tissue damage to the nose and mouth |
| Entamoeba histolytica | How infections are contracted: fecal/oral transmission 2 key features observable under the microscope which distinguish it from other intestinal amoebas: nucleus with peripheral dark chromatin and central dot, ingested rbc distinguish it from commensal amoebae Damage produced to the intestine: cysts ingested - trophozoites in intestine which invade and ulcerate the intestinal wall Symptoms: 90% are asymptomatic, symptoms can range from mild diarrhea to dysentery with blood and mucus Best drug for treatment: metronidazole |
| 3 genera of free-living pathogenic amoeba and 2 types of infection produced | Naegleria, Hartmanella, Acanthamoeba Causes amoebic meningoencephalitis and severe keratitis |
| Important toxigenic flagellate and the group to which it belongs | Pfiesteria is a toxic dinoflagellate |
| Most important pathogenic ciliate, the disease it produces, and its appearance under the microscope | Balantidum coli Produces intestinal disease similar to that produced by Entamoeba (symptoms can range from mild diarrhea to dysentery with blood and mucus) Appears as a very large cell with micronuclei and a macronucleus |
| 3 major patterns of transmission of Apicomplexa to humans and 2 genera that use each of them | Insect vector: Plasmodium, Babesia Consumption of infected prey: Toxoplasma, Sarcocystis Feces of infected host: Cryptosporidium, Isospora |
| Apical complex | Involved in penetrating a host's cell Consists of a set of spirally arranged microtubules, a secretory body, and one or more polar rings |
| Trophozoite | The active, motile feeding stage of a sporozoan parasite |
| Schizont | A cell that divides by schizogony to form daughter cells |
| Schizogeny | Asexual reproduction by multiple fission, found in some protozoa, esp. parasitic sporozoans |
| Gametogeny | The development of merozoites into male and female gametes, which later fuse to form a zygote |
| Macrogametocyte | Undergo meiosis to form a single large gamete + polar bodies |
| Microgametocyte | Undergo meiosis to form motile gametes ("exflagellation") |
| Zygote | Oökinete - The motile zygote of the malarial organism that penetrates the mosquito stomach to form an oocyst under the outer gut lining |
| 3 ways that Plasmodium infections can be contracted from most to least frequent | Bite of Anopheles mosquito Blood transfusion Mother to fetus |
| 4 species which cause human infections | P. falciparum (most virulent, most common) P. malariae P. vivax P. ovale |
| Life cycle of Plasmodium in mosquito | • Microgametocytes undergo meiosis to form motile gametes ("exflagellation"). • Macrogametocytes undergo meiosis to form a single large gamete + polar bodies. • Fertilization to form motile zygote = oökinete. • Invades gut wall, forms oöcyst. • Oöcyst enlarges, then divides to produce multiple sporozoites. • Sporozoites are the form that infects human hepatocytes. |
| Life cycle of Plasmodium in human | • Initial round of replication in liver by sporozoites from mosquito (exo-erythrocytic cycle). • Merozoites produced in liver are infectious only for red cells, not hepatocytes. • No re-infection of liver from blood. • Multiple rounds of infection in red cells. • Ultimately gametocytes are produced, infectious for mosquitos. |
| Exflagellation | The protrusion or formation of flagelliform microgametes from a microgametocyte in malarial parasites and some related sporozoa |
| Ookinete | Motile zygote |
| Oocyst | Zygote after invasion of gut wall |
| Sporogeny | Reproducing via spores |
| Sporozoite | A motile sporelike stage in the life cycle of some parasitic sporozoans (e.g., the malaria organism) that is typically the infective agent introduced into a host |
| Exoerythrocytic cycle | Involves infection of the hepatic system, or liver |
| Merozoite | Merozoites infect red blood cells and then rapidly reproduce asexually. The red blood cell host is destroyed by this process, which releases many new merozoites that go on to find new blood-borne hosts. Merozoites are non-motile |
| Hypnozoite | In some Plasmodium species, such as Plasmodium vivax and Plasmodium ovale, the parasite in the hepatocyte may not achieve maturation to a schizont immediately but remain as a latent or dormant form and called a hypnozoite |
| Erythrocytic cycle | The pathogenic portion of the vertebrate phase of the life cycle of malarial organisms that takes place in the red blood cells • Merozoite invades rbc. • Develops into vacuolated ring form. • Enlarges = trophozoite. • Nuclear division = immature schizont. • Cytoplasmic cleavage = schizont. • Cell lysis releases multiple new merozoites. |
| Ring form | Vacuolated form inside of rbc that develops from merozoites |
| Schizont | A cell that divides by schizogony to form daughter cells |
| Gametocyte | A cell that divides (by meiosis) to form gametes |
| Differential diagnosis of malaria by blood smear | P. vivax: ring form, dot nucleus; trophozoite: granules of precipitated hematin (Shuffner's dots); large gametocytes that fill the rbc - has a single nucleus P. falciparum: ring forms, multiple rings/cell, high level of parasitism, sickle-shaped gametocyte, trophozoites and schizonts not seen in the peripheral blood P. ovale: trophozoite (distorted 'fimbriated' host cell P. malariae: classic 'band' trophozoite |
| Four pathogenic species of Plasmodium (severity, fever cycles) | P. vivax/P. ovale: least severe, fevers at 48 hour intervals P. malariae: more severe, fevers at 72 hour intervals P. falciparum: most severe, fevers at 48 hour intervals |
| Prepatent period | Time from entry of a parasite into the body until the infection is manifested clinically or can be detected by routine diagnostic methods |
| Blackwater fever | A complication of malaria in which red blood cells burst in the bloodstream (hemolysis), releasing hemoglobin directly into the blood vessels and into the urine, frequently leading to kidney failure |
| Premunition | Resistance to infection by the same or closely related pathogen established after an acute infection has become chronic, and lasting as long as the infecting organisms are in the body |
| Why in falciparum malaria trophozoites and schizonts are seldom found in a smear of peripheral blood | It is unusual to see mature trophozoites or schizonts in peripheral blood smears, as these are usually sequestered in the tissues |
| 4 treatment regimens for malaria and when they should be used | Chloroquine - blood forms/primaquine - liver forms Quinine and doxycycline - cerebral malaria Fansidar (quinine and pyramethamine/sulfa) - areas of chloroquine resistance Artemisins - from a Chinese folk medicine - use for severe malaria |
| 4 drugs for malarial prophylaxis | Chloroquine - if no resistance locally Mefloquine (Larium) - liver toxicity, sleep/psychiatric disturbances Doxycycline (sensitizes to sun, not to pregnant women) Malarone (fewer side effects) |
| Babesia | Areas of endemism: NE United States including NJ Reservoir: white-footed mouse, microtus voles, and the white-tailed deer Vector: tick-borne Disease produced: irregular fevers, chills, headaches, general lethargy, pain and malaise. In severe cases, hemolytic anemia, jaundice, shortness of breath, and hemoglobinuria are documented due to the lytic effects of parasitic multiplication Technique for diagnosis: blood smear and indirect fluorescent antibody tests Key feature for identification: protozoa with varying shapes and sizes, the potential to contain vacuoles, and the lack of pigment production. Trophozoites within an erythrocyte that appear in a tetrad formation are also indicative of Babesia. Best drug for treatment: oral Atovaquone with oral azithromycin |
| Isospora | How infection is transmitted to humans and groups (if any) with especially severe disease: ingestion of sporulated oocysts, chronic in HIV+ patients Illness produced: diarrhea Methods for prevention: hygiene Drug for treatment: Bactrim |
| Sarcocystis | How infection is transmitted to humans and groups (if any) with especially severe disease: infection occurs when undercooked meat is ingested Illness produced: a rare invasive form with vasculitis and myositis and an intestinal form that presents with nausea, abdominal pain, and diarrhea Methods for prevention: infection can be prevented by cooking the meat before eating. Alternatively freezing the meat at -5C for several days before ingestion will kill the sporocysts Drug for treatment: metronidazole |
| Cryptosporidium | How infection is transmitted to humans and groups (if any) with especially severe disease: AIDS patients are at risk Illness produced: diarrhea Diagnose by fecal smear - cysts may be acid fast Methods for prevention: boil all water used for drinking Drug for treatment: no effective therapy |
| Cyclospora | How infection is transmitted to humans and groups (if any) with especially severe disease: outbreaks from contaminated fruit and vegetables, oocysts can be present due to using contaminated water or human feces as fertilizer Illness produced: diarrhea Diagnose by fecal smear - cysts may be acid fast Methods for prevention: cook food and try to avoid drinking stream water while outdoors Drug for treatment: Bactrim |
| Toxoplasma | Reservoir/vector and how infection is transmitted to humans: natural cycle between rodent and carnivore - infected cats shed oocysts in feces, humans can also acquire infection by eating undercooked meat Types of illness produced in healthy persons, immunocompromised persons, and fetus with infection in utero: non-specific febrile illness Two techniques for diagnosis: difficult to distinguish from primary central nervous system lymphoma, and as a result, the diagnosis is made by a trial of therapy (pyrimethamine, sulfadiazine + leucovorin), followed by a brain biopsy if the drugs produce no effect clinically and no improvement on repeat imaging, also PCR Two drug regimens for treatment: acute - pyrimethamine, sulfadiazine, clindamycin, spiramycin; latent - atovaquone, clindamycin (need to kill cysts) |
| Life cycle of Sarcocystis | Many infections may be asymptomatic The life-cycle of a typical member of this genus involves two host species, a definitive host and an intermediate host. Often the definitive host is a predator and the intermediate host is its prey. The parasite reproduces sexually in the gut of the definitive host, is passed with the feces and ingested by the intermediate host. There it eventually enters muscle tissue. When the intermediate host is eaten by the definitive host, the cycle is completed. The definitive host usually does not show any symptoms of infection, but the intermediate host does. Infection occurs when undercooked meat is ingested |
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