Parasites

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Flagellate protozoa (list)

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Giardia lamblia, Dientamoeba fragilis, Trichomonas vaginalis

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Amoebae protozoa (list)

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Entamoeba histolytica (intestinal); free living (blood/tissue) - Naegleria species, Acanthamoeba species, Balabuthia species

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Apicomplexa protozoa (list)

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Intestinal and urogenital - Cryptosporidium species, Isospora belli, Cyclospora cayetanensis, Toxoplasma gondii
Blood and tissue - Plasmodium species, Babsesia species, Toxoplasma gondii as well

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Ciliated intestinal protozoa (list)

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Balantidium coli

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Kinetoplastids (list)

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Blood flagellates - Include the Trypanosome and Leishmania species

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Giardia lamblia

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Flagellated intestinal protozoa causing giardiasis (beaver fever); exists as both cyst (infectious form) and trophozoite (motile/feeding stage); Cysts ingested in contaminated water (wilderness distrubution - beavers, muskrats), gastric acid stimulates excysation producing 2 trophozoites which adhere to intestinal villi in duodenum and jejunum and reproduce by binary fission, they then may encyst and be excreted in feces. Noninvasive, usually asymptomatic, but produce malabsorption syndrome - acute disease include foul smelling watery diarrhea with abdominal cramps, flatulence and steatorrhea; Chronic infection may develop with IgA deficiency; cysts and trophozoites found in feces, passage is sporadic; Treated with Metronidazole

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Trichomonas vaginalis

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Flagellated urogenital protozoa; anerobic trophozoite (NO cyst stage); Sexually transmitted, lives and replicates in prostate, urethra and vagina where trophozoites adhere to epithelial cells, the secretion of cytotoxic lysosomal hydrolases lyse cells in contact iwth parasites, cell debris ingested by the trophozoites; presents with scant water vaginal discharge and vaginitis, men are primarily asymptomatic but urethritis, prostates and UTI problems may occur; diagnosed by trophozoite presence in discharge; treated with Metronidazole

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Dientamoeba fragilis

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Flagellate protozoa which was originally classified as an amoeba, no visible flagella; Has only a trophozoite stage, usually has 2 nuclei with a central karyosome arranged in granules

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Balantidium coli

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CILIATED protozoa; zoonotic disease with a reservoir in swine and monkeys; has mouth pore, micro- and micronucleus and a food vacuole; infection in human host ranges from asymptomatic carriage to ulceration of intestinal mucosa; diagnosed by presence of trophozoites or cysts in stool; treated with tetracycline

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Entamoeba histolytica

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Intestinal amoeba which exists as both cyst and trophozoite; ingestion of a single cyst is infectious, transmitted fecal-orally, passes through stomage where gastric acid stimulates trophozoite release into duodenum (producing 8 per cyst) carried via peristalsis to large intestine; Parasites penetrate the perimucosal space and attached to epithelial cells using lecitn-carbohydrate interactions, attachment is cytotoxic and they engulf cells; a galactose-inhibitable adherence protein is required for cytolysis and tissue distruction. Amoeba has a cytotoxin, the trophozoites multiply producing flask-shaped ulcers, they may erode the wall and disseminate (most common extraintestinal sites are liver and lungs); intestinal amebiasis is localized producing bloody diarrhea and abdominal pain; extraintestinal amebiasis is systemic, produces fever, and acute hepatitis or a liver abscess; cerebral amoebiasis is rare but also possible; must be distinguished from nonpathogenic E. dispar; Acute treated with metronidazole followed by iododquinol

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Cyclospora cayentanesis

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Apicomplexa intestinal protozoa; fecal-oral transmission of cysts; Presents with watery diarrhea, nausea, vomiting, stool reveals oocysts that fluoresce under UV light and are acid fast; treated with trimethopri-sulfamethoxazole (Bactrim)

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Isospora species

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Apicomplexa intestinal protozoa; fecal-oral transmission; oocyst is infective (and contains 8 sporozoites); causes severe diarrhea and malabsorption in AIDS patients; oocysts are found in stool, large enough to be seen without stain; treated with trimethopirim-sulfamethoxazole (Bactrim)

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Cryptosporidium

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Apicomplexa intestinal protozoa; Fecal-oral, waterborne transmission, oocyst excreted in feces is infectious and contains 4 sporozoites; it exists in an extracytoplasmic, intracellular vacuole; they emerge form oocyst, attach to intestinal epithelial cell, are not invasive but exist within brush border of intestinal epithelium; Replicate by schizony, lyse and invade adjacent cells; sexual reproduction results in thick wall oocysts released into feces; may exist in swimming pools mucin like receptors mediate attachment to ileal mucus lining and degrade lining via enzymes; presents as asymptomatic carriage, acute (noninvasive diarrhea) or chronic disease (if immune deficient or child); oocysts in feces acid fast stain; No therapy needed in immune competent individuals, Nitazonzainide for children

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Leishmania species

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Flagellated blood protozoa (Kinetoplastid); Promastigotes in saliva of infected sandflies, bites to infect human where they are phagocytosed by macrophages, they there convert to amastigotes that replicated by binary fission in an acidified phagolysosome, the macrophages lyse and cycle continues. May be visceral (L. infantum, L. chagasi), cutaneous (L. tropica, L. major, L. mexicans) or mucocutaneous (L. braziliensis); congenital transmission is possible resulting in congential Kala-azar

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Visceral leishmaniais

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L. infantum or L. chagasi; incubation weeks to a year with fever, diarrhea and anemia; hepatosplenomegaly, weight loss and emaciation; kidney damage, fulminant disease if untreated; tisse biopsy showing amastigote stage; treated with Miltefosine

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Cutaneous leishmaniasis

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L. tropica, L. major, L. mexicana; most common leishmaniasis manifestation; 2 week to 2 month incubation, presents with red itchy papule at site of bite, enlarges and ulcerates, spreads outward; self heals but leaves scar; Rare manifestations include diffuse cuatneous leishmaniasis and leishmaniasis recidivous; biopsy of border of lesion shows amstigotes, ulcer tissue shos promastigoes; Treated with stibogluconate

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Mucocutaneous leishmaniasis

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Caused by L. braziliensis; 2 week to 2 month incubation, papule appears, involves destruction of mucous membrane and related tissue structures combined with edema and secondary bacterial infection; parasites disseminate to mucosa of nose and mouth and produce lesions; Treated with stibogluconate

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Trypanosoma brucei gambiense

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Blood flagellate protozoa; trypomastigote transmitted by tsetse fly via bite, replicated by binary or longitudinal fission in blood, lymph and spinal cord; densely packed variable surface proteins coat surface of parasite activatin B cells in a T-independet fashion and protecting other non-variant surface proteins from immune detection; leads to immune exhaustion, eventual CNS penetration and neuroogical damage; causes African Sleeping Sickness, ulcer at site of bite, lymph node enlargement with fever, myalgia and arthalgia; diagnosed by organisms in blood smears; acute treatment with suramin, chronic with melarsoprol

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Trypanosoma brucei rhodesiense

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Similar to T. b. amiense, found in wild game, and domestic animal host and reservoir; incubation period is short and diverse course if relatively rapid; acute disease results in death in 9-12 months if not treated, lymphadenopathy is uncommon and CNS invasion is more rapid; treatment similar to T. b. gamiense

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Trypanosoma cruzi

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Causes Chagas disease (american trypanosomes); transmitted by reduviid bug (kissing bug) feces, trpomastigotes migrate to tissues (cadiac, muslce, liver, brain), invade host cell, lyse vacuole and reside in cytosol, convrt to amastigotes, multiply by binary fission and lyse host cells and invade adjacent cells; may be asymptomatic, acute or chronic; Chagoma may be evident early at bit site followed by rash adn edema; acute infection shows fever, chills, malaise, myalgia and fatigue; Chronic chagas diease is hepatosplenomegaly, myocarditis, enlargement of esophagus and colon, heart block or brain damage causes death; detected in blood during acute stage but then only in tissues; treatment is limited (nifurtimox may only be effective during acute stage)

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Naegleria fowleri

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Free living amoeba, trophozoite, cyst and flagellated stage; flagellated form when in water/deprived of nutrients, amoeba form in tissue; Infection occurs after simming in warm water that goes up nasal cavity; causes acute primary amoebic meningoencephaltitis which is almost always fatal; portal of entry is olfactory neuroepithelium, probably migrate along olfactor nerves into brain and CNS; 1-14 day incubation, headache, fever, nausea, comiting, death within 4-5 days; trophozoites in spinal fluid; amphotericin B with miconazole and rifanpin

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Acanthamoeba species

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Free living amoeba, ubiquitous in soil and water; infection is usually in a compromised host, is neurotropic and causes an encephalitis-like disease known as granulomatous amebic encephalitis which is slower progressing and more chronic; associated with lesions of cornea; entry through respiratory tract or lesions in skin

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Balamuthia species

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Free living amoeba causing granulomatous amebic encephalitis, can cause a subacute-to-chronic infection which is more rapidly processing, is more capable of infecting healthy individuals; primary lesion often respiratory tract or skin; almost always fatal

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Plasmodium vivax

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Benign tertian malaria, fever every 48 hrs; trophozoite stage moves freely inside RBC, merozoites only form able to invade reitculocytes (invades about 3%), may cause acute illness, not severe, does not usually cause death; splenomegaly, liver and kidney damage may occur; Reticulocytes are larger and more easily deformed; Duffy RBC antigen is imporantt in merozoite entry; hypnozoites form in liver allowing organism to survive and be releasted months to years later; trophozoites are ring shaped but ameboid in appearance; 12-20 day incubation, schizont forms 24 merozoites

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Plasmodium Malariae

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Quartan malaria, fever every 72 hours, incubation of 18-40 (potential longest); no hypnozoites so relapse does not occur but erythrocytic cycle may persist for years; does not usually cause an acute infection, symptoms are often mild, but immune complex glomerulonephritis and splenomegaly may develop as spleen removes abnormal RBCs; chimps may be a reservoir, invades only mature, aging RBCs so RBC numer is low, appear smaller than usual; schizont forms 8-12 merozoites; parasitemia of 1%

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Plasmodium ovale

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Tertian malaria invading reticulocytes similar to P. vivax, also has hypnozoite form in liver so relapses occur; heavier Schuffner dots on parasitized RBCs; schizont forms from 12 merozoites

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Plasmodium falciparum

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Malignant tertian malaria but fever may occur daily without obvious periodicity; 8-15 day incubation (shortest); No hypozoite forms, no true relapse, parasitemia may be 30-40% as RBCs of all ages are invaded; ring forms and crescent shape gametocytes may be seen in peripheral blood, other stages seen in capillaries; causes organ failure, coma and death, kidney damage associated, intravascular hemolysis with rapid destruction of RBCs produces dark urine (black water fever); mechanism of attachment is formation of knobs on surface of infected RBCs binding receptors on capillary endothelium, receptors increase in number in response to TNF-a, sequestration in capillaries keep them from being removed by the spleen; people with sickle cell trait have some protection; crescent shaped gametocytes is diagnostic

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Babesia microti

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Intraerythrocytic parasite related to malaria; sexual stage in tick, asexual stage in white-footed mouse; sporozoites develop in salivary gland of tick; sporozoites invade RBCs directly and divide, may form a Maltese cross, 4 merozoites, the RBC lyses and new cells are invaded; 1-4 week incubation; immunity develops after infection, symptoms overlap with Lyme disease, flu like illness, may be serious in immunocompromised and older patients; serious cases are treated with clindamycin and quinine

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Toxoplasma gondii

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Flagellated urogenital protozoa; single-celled, obligate intraceullar; 3 major stages - 1) oocysts contain diploid stage known as sporozoites (intestines of cat family), 2) cyst stage contains bradyzoites (tissues of infected individuals), and 3) tachyzoite is fast replicating stage responsible for parasite dissemination within a host and active form of disease; excreted in feces of cat and are infectious one day to several weeks later; transmitted through raw meat, cat feces, transplacentally to fetus, or by organ and bone marrow transplantation; bradyzoites and sporozotes penetrte intestinal lining, convert to rapidly replicating tachyzoite stage that infects and replicates within the host - invades all organs (muscles, heart, liver, spleen, lymph nodes, and CNS); cysts in retinal tissue, the brain and CNS and may reactive when immunosuppressed and cause encephalitis, chorioretinitis, pneumonia and sepsis; congenital transmission if infected for fist time during pregnancy (most severe if infected in first trimester); vast majority of infections are asymptomatic, in AIDS patients frequently localizes to basal ganglia in brain and often multiple foci are seen; One of most common causes of intraocular pressure in the world; diagnosed by antibody detection, IgM, IgG; Most common treatment based on a combination of folate inhibitors pyrimethamine and sulfadiazine

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Congenital toxoplasmosis

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Retinochoretinitis, encephalomyelitis, hydrocephalus, microcephaly and abortion; cerebral calcifications; Newborns can have fever, pneumonitis, convulsions, hepatosplenomegaly

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Trichuris trichirua

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A nematode: Whipworm - Ingested eggs hatch into a larval worm in small intestine, migrate to and attach to the cecum; large worm burdens may produce abdominal pan, distension, bloody diarrhea, weakness and weight loss. Prolapse of rectum may occur; anemia and eosinophilia are seen in severe infections; there is characteristicdark bile staining, barrel shaped eggs wiht polar plugs in stool. Treated with albendazole or mebendazole

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Ascaris lumbricoides

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Largest nematode to infect humans; eggs ingested, larval worm penetrates duodenal wall to enter bloodstream where it is carried to liver, heart and pulmonary circulation; larvae break free in lung alveoli, grow and molt; they reenter the intestine by a trachea route and are swallowed and returned to small intestine; may be asymptomatic, can migrate into bile duct and liver and damage tissue or perforate intestine; mgiration may produce pneumonitis resembling an asthma attack; eggs in stool are bile-stained, oval; adult worms pass in stool or vomit. Treated with albendazole or mebendazole

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Necator americanus

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Filariaform larva penetrate intact skin, enter circulation, carried to lungs, coughed up and swollaowed to develop into adulthood in small intestine. Hooklike head attaches to small intestine and sucks blood from injured intestinal tissue; may produce allergic rxn and rash at site of skin penetration, may produce pneumonia, anemia and nutritional deficiencies may occur; stool examination reveals characteristic non-bile stained segmented eggs; Treatment is albendazole or mebendazole

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Strongyloides stercoralis

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Threadworm - small intestine; larva penetrates intact skin, enters circulation and goes to pulmonary system, coughed up, swallowed, adults develop in small intestine; eggs hath into larvae in intestine before being passed in feces, can cause autoinfection; pneumonitis in migration, blood eosinophilia, hyperinfection syndrome can occur in immune-compromised individuals and if often fatal; May be sexually transmited or from pets; Eggs not typically seen, multiple samples and concentration of stool required; treated with lvermectin with albendazole or mebendazole

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Enterobius vermacularis

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Small, white pinworms; eggs ingested and larvae hatch in small intestine and migrate to large intestine where they mature; migrating female deposits eggs in perianal skin where they hatch and release larvae within hours, autoinfection can occur; often asymptomatic carriers; people allergic to secretions of migrating worms experience severe pruritus which may lead to secondary bacterial infection; most common helminth infection in US; confrimation by detection of characteristic eggs on anal mucosa, rarely seen in fecal samples; treated with albendazole or mebendazole

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Toxocara canis and cati, Baylisacaris pocyonis

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Ascarid intestinal worms of either dogs (T. cantis) or cats (T. cati) or raccoons (B. procyonis); infect humans causing visceral larva migraines, toxocariasis ocular larva migrans and neural larva migrans; eggs ingested, hatch into larval forms which penetrate gut, enter blooods tream and migrate as larvae to human tissue; organs involved include lung, heart, kidney, muscle, eyes, CNS; death may develop from respiratory failure, cardiac arrhythmia or brain damage; Eosinophilia and serological confirmation; Treatment is primarily symptomatic

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Ancylostoma braziliense

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Canine and feline hookworm; filariaform lavae penetrate intact skin but fail to develop in human hosts; larvae remain trapped in skin migrating through subcutaneous tissue creating surpentine tunnels; human disease is cutaneous larva migraines; severe erythematous and vesicular reaction leading to secondary bacterial infection; patients can develop transient pulmonary infiltrates with peripheral eosinophilia (Loftier's syndrome); diagnosis by clinical appearance of tunnels in skin adn contact with infected dog or cat feces. Treated with albendazole

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Trichinella spiralis

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Trichinosis; infectious larval form is found in striated muscles of carnivorous and omnivorous mamals. Humans ingest encysted larvae and these develop into adult worms in small intestine. Larvae migrate from the intestine into the circulation and to striated muscle sites where they encyst. Disease ranges from asymptomatic to fatal depending on location of migrating larva and tissue burden. Eosinophilia is common. Treatment is primarily symptomatic

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Wuchereria bancrofti and Brugia malayi

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Mosquito introduces infective larvae during a blood meal, larvae migrate to lymphatic system where they mature into adult worms; 3-12 months after injection the adult male fertilizes the female and she produces sheathed larval microfilariae that enter the circulation; early acute symptoms are fever, lymphangitis, lymphadenitis with chills and recurrent fever; may be due to inflammatory response to molting adolescent worms or dying adults in lymphatics; disease progression leads to persistent obstruction of lymph vessels and fibrous proliferation; recurrent bacterial infections or allergy to dead worms exacerbate tissue damage; may progress to filarial elephantiasis; only detectable in blooda t night; treated with diethylcarbamazine

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Onchocerca volvulus (Onchocerciasis)

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River blindness - blackfly inroduces larvae during a bite, larvae migrate to subcutaneous tissue and develop into adult worms that encase in fibrous subcutaneous nodules; after fertilization, female worms produce as many as 2000 non sheathed microfilariae daily that migrate to skin, eyes and other tissue; subcutaneous ndules develop on skin and chronic infection induces severe skin damage, may cause blindness in eyes; diagnosed with microfilariae in skin snip preparations; treated with surgical removal and ivermectin

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Loa loa (loiasis)

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Similar life cycle to W. bancrofti but vector is fly called Chrysops or mango fly; calabar swellings are produced as worms migrate through subcutatneous tissue creaitng painful, pruritic nodules; eosinophilia common; isolated from blood during the day; diethylcarbamazine, corticosteroids to prevent allergic reaction to dying parasites, surgical removal of ocular parasites

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Drancunclus medinesis

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Guinea Worm disease; Long and thin tissue-invading nematode; human disease due to ingestion of water contaminated with microcustcean; larvae released in stomach, penetrate the digestive tract, fertilized female migrates to subcutaneous tissue; gaivd female aligns anterior end near skin and induces a blister that opens on contact with water to release larvae; Treated by removal of female worm from lesion

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Schistosomes (S. manosoni, S. japonicum, S. haematobium)

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Flukes; a ciliated free living Schistosome cercaria in fresh water penetrates intact skin, enters the circulation and develops in the intrahepatic portal circulation (mansoni, japonicum) or in the vesicle, prostatic, rectal and uterine plexuses and veins (haematobium); males and females pair up and migrate together to their final locations where egg production occurs; S. mansoni and S. japonicum are found in mesenteric veins and produce intestinal schistosomaiasis, S. haematobium resides in veins around urinary bladder and causes vesicular schistosomiasis; eggs elicit intense inflammation and produce enzymes that induce sufficient tissue destruction to allow the eggs to pass through the mucosa into the lumen of the bowel and bladder; passed in feces or urine, hatch upon reaching free water; pruritic papular skin rash may occur at site of cercaria penetration; Liver damage; japonicum also frequently involves cerebral structures when eggs reach brain and induce granulomas causing neurological manifestations; fibrosis of bladder, ureters and associated tissue; Can be differentiated from each other based on egg characteristics in addition to their large size and golden color; treated with praziquantel

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Fasciola hepatica

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Sheep liver fluke; parasite of herbivores and humans; ingestion of watercress inected with encysted metacercariae; larvae migrate through the duodenal wall, across the peritoneal cavity, penetrate the liver capsule and mature in the bile ducts; characteristic operculated eggs in stool; treated with bithionol

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Opisthorchis sinensis

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Oriental or Chinese Liver fluke; two intermediate hosts, eggs have to be eaten by a snail, then infect a fish where they encyst and develop into infective metacercariae; human ingestion of infected fish, fluke develop in duodenum and migrate to the bile ducts; biliary obstruction may occur; may lead to adenocarcinoma of bile duct; recovery of characteristic eggs from stool is diagnostic; treated with praziquantel

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Paragonimus westermani

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lunk flukes; two intermediate hosts; muscles and gills of freshwater crabs and crayfish are second and source of infective stage; larvae hatch in stomach, migrate through intestinal wall, abdominal cavity, diaphragm, plural cavity and set up residence in lungs; eggs liberated from ruptured bronchioles to the sputum or swallowed and released in feces; inflammation and fibrosis of lungs, cough, pneumonia and chest pain; last years and may be fatal; stray flukes may enter spinal fluid; sputum viscous with brown or red streaks due to eggs or blood; treated with Triclabendazole

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Fasciolopsis buski

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Intestinal flukes; humans ingest encysted larval stage (metacercaria) from aquatic vegetation, parasites attach to mucosa of small intestine; operculated eggs pass in feces and exposure to water releases free-swimming larvae capable of penetrating the soft tissue of snails, which then the snails release the final stage that are free swimming and encyst on aquatic vegetation. Marked eosinophilia, characteristic large golden bile-stained eggs with an operculum in stool; treatment is praziquantel

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Taenia solium

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Pork tapeworm; swine ingest eggs that develop into a six-hooked larvae form that penetrates the intestinal wall, migrates in the circulation to tissues and develops into a cysticercus (blader worm). Humans ingest swine muscle containing cysticercus and parasites attach to the small intestine through their scolex, they can become several meters long. Sexually mature proglattids contain eggs and are released into the feces. Intestinal parasites cause few symptoms, extraintestinal phase can cause serious disease; cystericercosis is due to human ingestion of egs or autoinfcetion due to fecal-oral transmision or regurgitation of proglattid. Can be fatal. Presence of proglattids in feces or free eggs on perianal skin are diagnostic; treated with niclosamide, steroids for allergic reaction to dying worms

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Taenia saginata

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Beef tapeworm; Similar to T solium but intermediate host is cattle and does not cause cysticercosis in humans; often asymptomatic or abdominal pain; presence of proglattids in feces or free eggs on perianal skin is diagnostic, treated with niclosamide; steroids for allergic reaction

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Diphyllobothrium latum

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Fish tapeworm; one of the largest, two intermediate hosts: freshwater crustaceans and fish; larvae in fish and are ingested in humand and mature in intestine; prolattids/eggs released in feces develop into free-swimming larvaein freshwater that are ingested by crustaceans; occasional intestinal discomfort, pernicious anemia due to competition for vit B12; operculated eggs in feces diagnostic, treated by niclosamide

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Echinococcus granulosus and E. multilocularis

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Hydatid disease - humans act as incidental end stage hosts; adult tapeworm in anine inestine releases infectious eggs into feces, ingestion by huan results in release of a six hooked larval sat that penetrates the intestine and enters circulation spreading to tissues including liver, lungs, CNS and bone; Larvae form a unilocular hydatid fluid-filled cyst that grows slowly like a tumor and is encased by a laminated germinative membrane; daughter cysts reproduce within parental cysts; pathology in humans results from cyst expansion and pressure within tissues, inflammation and potentially anaphylactic shock upon cyst rupture and dissemination to vital cyts; surgical resection is treatment

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Hymenolepis nana and H diminuta

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dwarf tapeworm (first); no inermedaite host, ingestion of embryonatd eggs leads to development of larval cysicercoid in intestinal villi that develop into adults that release infectious eggs in the feces; heavy infection can induce diarrhea, abdominal pain anorexia and headaches; characteristic egg in feces; treated with praziquantel

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Dipylidum caninum

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Pumpkin seed tapeworm; larval worms develop in dog and cat fleas; parasites are stransmited by ingestion adn reside in intestine; heavy worm burdens can cause abdominal discomfort, anal pruritis from active migration of the proglattids and diarrhea; characteristic eggs in stool; treated with niclosamide