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  • Foundations in MicrobiologySixth EditionChapter 23The Parasites of Medical ImportanceLecture PowerPoint to accompanyTalaroCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

  • ParasitologyThe study of eucaryotic parasites, protozoa and helminthsCause 20% of all infectious diseasesLess prevalent in industrialized countries; increasingly common in AIDS patients

  • Typical Protozoan PathogensSingle-celled, animal-like microbes, most having some form of motilityEstimated 100,000 species, approximately 25 are important pathogensLife cycles vary Most propagate by simple asexual cell division of the active feeding cell (trophozoite).Many undergo formation of a cyst.Others have a complex life cycle that includes asexual and sexual phases.

  • Infective Amebas

  • Entamoeba histolytica and AmebiasisAlternates between a large trophozoite, motile by means of pseudopods and a smaller nonmotile cystTrophozoite has a large nucleus and lacks most other organelles.Humans are the primary hosts.IngestedCarried by 10% of world population

  • Entamoeba histolyticaCysts are swallowed and arrive at the small intestine; alkaline pH and digestive juices stimulate cysts to release 4 trophozoites.Trophozoites attach, multiply, actively move about and feed.Asymptomatic in 90% of patientsAmeba may secrete enzymes that dissolve tissues and penetrate deeper layers of the mucosa.Causing dysentery, abdominal pain, fever, diarrhea and weight loss

  • Entamoeba histolyticaLife-threatening manifestations are: hemorrhage, perforation, appendicitis, and tumorlike growths, amebomas.May invade liver and lungSevere forms of disease result in 10% fatality rate.Effective drugs are iodoquinol, metronidazole, and chloroquine.

  • Amebic Infections of the BrainCaused by Naegleria fowleri and AcanthamoebaOrdinarily inhabit standing waterPrimary acute meningoencephalitis is acquired though nasal contact with water or traumatic eye damage.Infiltration of brain is usually fatal.

  • An Intestinal Ciliate: Balantidium coliAn occupant of the intestines of domestic animals such as pigs and cattleAcquired by ingesting cyst-containing food or waterTrophozoite erodes intestine and elicits intestinal symptoms.Healthy humans are resistant.Rarely penetrates intestine or enters bloodTreatment tetracycline, iodoquinol, nitrimidazine or metronidazole

  • The Flagellates

  • Trichomonads: Trichomonas speciesSmall, pear-shaped4 anterior flagella and an undulating membraneExist only in trophozoite form3 infect humans:T. vaginalisT. tenaxT. hominis

  • Trichomonas vaginalisCauses an STD called trichomoniasisReservoir is human urogenital tract50% of infected are asymptomatic.Strict parasite, cannot survive long outside of host3 million cases yearly, a top STDFemale symptoms foul-smelling, green-to-yellow discharge; vulvitis; cervicitis; urinary frequency and painMale symptoms urethritis, thin, milky discharge, occasionally prostate infectionMetronidazole

  • Giardia lamblia and GiardiasisPathogenic flagellateUnique symmetrical heart shape with concave ventral surface that acts like a suction cupCysts are small, compact, and multinucleate.Reservoirs include beavers, cattle, coyotes, cats, and humans.Cysts can survive for 2 months in environment.Usually ingested with water and foodID 10 to 100 cysts

  • Cysts enter duodenum, germinate, travel to jejunum to feed and multiplyCauses giardiasis diarrhea, abdominal painDiagnosis is difficult because organism is shed in feces intermittently.Treatment: quinacrine or metronidazoleAgent is killed by boiling, ozone, and iodine.

  • Hemoflagellates: Vector-Borne Blood ParasitesObligate parasites that live in blood and tissues of human hostCause life-threatening and debilitating zoonosesSpread in specific tropical regions by blood-sucking insects that serve as intermediate hostsHave complicated life cycles and undergo morphological changesCategorized according to cellular and infective stages

  • Trypanosoma species and Tropanosomiasis Distinguished by their infective stage; trypomastigote is an elongate, spindle-shaped cell with tapered ends, eel-like motility2 types of trypanosomiasis:T. brucei African sleeping sicknessT. cruzi Chagas disease endemic to Central and South America

  • Trypanosoma brucei and African Sleeping SicknessSpread by tsetse fliesHarbored by reservoir mammalsTwo variants of disease caused by 2 subspecies:T.b.gambiense Gambian strain; West AfricaT.b. rhodesiense Rhodesian strain; East AfricaBiting of fly inoculates skin with trypomastigotes, which multiplies in blood and damages spleen, lymph nodes and brain.

  • Chronic disease symptoms are sleep disturbances, tremors, paralysis and coma.Trypanosomes are readily demonstrated in blood, spinal fluid or lymph nodes.Treatment before neurological involvement melarsoprol, eflornithineControl involves eliminating tsetse fly.

  • Trypanosoma cruziCauses Chagas diseaseReduviid bug (kissing bug) is the vector.Infection occurs when bug feces is inoculated into a cutaneous portal.Local lesion, fever, and swelling of lymph nodes, spleen, and liverHeart muscle and large intestine harbor masses of amastigotes.Chronic inflammation occurs in the organs (especially heart and brain).Treatment nifurtimox and benzonidazole

  • Leishmania species and LeishmaniasisLeishmaniasis - zoonosis transmitted among mammalian hosts by female sand flies that require a blood meal to produce eggsEndemic to equatorial regionsPromastigotes are injected with sand fly bite, convert to amastigote and multiply; if macrophage is fixed the infection is localized; systemic if macrophage migrates.

  • Cutaneous-oriental sore, Baghdad boil - localized ulcerated soreEspunda skin and mucous membrane infection of the head; chronic infectionSystemic-visceral - high intermittent fever; weight loss, enlarged spleen, liver, and lymph nodesKala azar is the most severe and fatal form if untreated.

  • Apicomplexan parasitesSporozoansLack locomotor organelles in the trophozoite stateAlternate between sexual and asexual phases and between different animal hostsMost form specialized infective bodies that are transmitted by arthropod vectors, food, water, or other means.PlasmodiumToxoplasma Cryptosporidium

  • Plasmodium: The Agent of MalariaDominant protozoan diseaseObligate intracellular sporozoan4 species: P. malariae, P. vivax,

    P. falciparum and P. ovaleFemale Anopheles mosquito is the primary vector; blood transfusions, mother to fetus300-500 million new cases each year2 million deaths each year

  • 2 distinct phases of malarial parasite development:asexual phase human host Infected female mosquito injects asexual sporozoite which localizes in liver; it then undergoes schizogony generating 2,000-40,000 merozoites which enter circulation in 5-16 days depending on species.Merozoites attach to and enter red blood cells, convert to trophozoites and multiply; red cell bursts releasing merozoites that differentiate into gametes.

  • Sexual phase mosquito hostMosquito draws infected RBCs; gametes fertilize forming diploid cell which forms sporozoites in stomach.Sporozoites lodge in salivary glands; available to infect human host

  • PlasmodiumSymptoms include episodes of chills-fever-sweating, anemia, and organ enlargement.Symptoms occur at 48-72 hour intervals as RBCs rupture; interval depends on species.P. falciparum most malignant type; highest death rate in childrenDiagnosis by presence of trophozoite in RBCs, symptomsIncreasing drug resistanceTherapy is chloroquine, quinine, or primaquine.

  • Coccidian ParasitesZoonotic in domestic animals and birds

  • Toxoplasma gondii and ToxoplasmosisIntracelllular apicomplexan parasite with extensive distributionLives naturally in cats that harbor oocysts in the GI tractAcquired by ingesting raw meats or substances contaminated by cat fecesMost cases of toxoplasmosis go unnoticed except in fetus and AIDS patients who can suffer brain and heart damage.Treatment: pyrimethamine and sulfadiazine

  • Sarcocystis and SarcocystosisSarcocystis parasites of cattle, swine, and sheepDomestic animals are intermediate hosts; they pick up infective cysts while grazing on grass contaminated with human feces.Humans are infected when the meat is consumed.Symptoms include diarrhea, nausea, and abdominal pain.No specific treatment

  • Cryptosporidium: A Newly Recognized Intestinal PathogenAn intestinal pathogenInfects a variety of mammals, birds, and reptilesExists in tissue and oocyst phases1990s 370,000 cases in Milwaukee, WI due to contaminated water; filtration required for removalIngestion of oocysts which give rise to sporozoites that penetrate intestinal cellsCauses gastroenteritis, headache, sweating, vomiting, abdominal cramps, diarrheaAIDS patients may suffer chronic persistent diarrhea.No effective drugs

  • Isospora belli and CoccidiosisIntracellular intestinal parasite with oocyst stageTransmitted in fecally contaminated food or drinkInfection usually asymptomatic or self-limitedSymptoms include malaise, nausea and vomiting, diarrhea, fatty stools, abdominal cramping, and weight loss.Treat with sulfadiazine and pyrimethamine, when required

  • Cyclospora cayetanensis and CyclosporiasisEmerging protozoan pathogen; causes cyclosporiasisOral-fecal transmission; fresh produce and waterOocysts enter small intestine and invade the mucosa.Symptoms of watery diarrhea, stomach cramps, bloating, fever, muscles achesDiagnosis can be complicated.Treatment: trimethoprim and sulfamethoxazole

  • Babesia species and BabesiosisFirst protozoan found to cause a disease r


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