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Protozoan Parasites


ENTAMEOBA HISTOLYTICA (amoeba-->amoebiasis)
--Chicago World's Fair outbreak in 1933 caused by sewage contaminated drinking water, 1,000 cases, 58 deaths
--motile protozoan very highly infectious
--trans: fecal-oral (modern cases in US usu due to food handlers), dogs and cats may have it but do not shed cysts in feces, can be trans via sexual activity (frequently diagnosed among homosexual men)
--common in food & water, found worldwide, more in tropics and more in poverty
--the trophozoite (active form) is only in host and fresh feces
--cysts survive outside but need some moisture, then excyst in gut after being swallowed
--pathogenicity: ingest cysts-->become trophozoite in ileum-->set up house in cecum & colon-->invasion of colonic epithelium by its own digestive enzymes causing necrosis-->teardrop lesions form when parasite infests muscularis layer-->can enter portal circulation and form abscesses in the liver
--S/Sx: infections can be asymptomatic for years or vague GI issues, or amoebic dysentery incl bloody mucousy diarrhea wtih abdominal pain, cramping and farts, may alternate with constipation over months/years
--Complic: ulcers (less than 16% of cases) or abscesses (usu liver), intestinal blockage (rare), masses are rare, may combine with other infx, fatalities infrequent
--Dx: three stool samples, microscopic fecal analysis (find cysts via floating/sedimentation, trophozoites only in major infx), false negatives are common
--Dx: more: stains incl fluorescent antibody test, or aspiration of pus from a liver abscess, can recover cysts from contaminated food of water via filtration

GIARDIA LAMBLIA (flagellated protozoan-->giardiasis)
--has become one of the most common water bourne disease in US, aka "beaver fever"
--trans: fecal-oral, usu from people drinking untreated spring/creek water
--incidence: high in mental hospitals, day care centers, and among male homosexuals
--pathogenicity: ingested-->infects only GI tract-->cyst in duodenum, trophozoites attach anywhere along gut wall-->cause inflammation-->decreased nutrient absorbtion
--Dx: microscopic fecal analysis, may require more than one sample to find either trophozoite or cyst, may also be present in urine sample, can also use immunoflourescent assay or ELISAs to find parasite in stool
--S/Sx: gastroenteritis (onset usu around 7 days after ingestion): nonbloody, foul-smelling diarrhea w/ cramping, distention, flatulence, nausea, vomiting, possible low fever

TRICHOMONAS VAGINALIS (flagellated, single celled protozoan-->trichomoniasis)
--trans: sex (STD), also any contact incl: towels, benches, etc.
--no cyst form
--infection increases HIV transmission risk, both ways
--Dx: microscopic exam of urine, vaginal or urethral discharge, prostatic secretions
--four anterior flagellae and a 5th on the margin
--S/Sx: symptoms more common in the female: vaginitis or trichomoniasis, men usu asymptomatic but may have penile irritation or burning on urination, women usu have white to yellow-green frothy discharge with a strong odor, and may have itching and discomfort with sex

TRYPANOSOMES (flagellated protozoa) (see lengthy separate post, back in the winter, for the full scoop on these bugs and African sleeping sickness)
--African sleeping sickness trans: tsetse flies
--T. brucei gambiense in West & Central Africa
--T. brucei rhodesiense in East Africa
--T. cruzi --> Chagas dz, trans via triatomine bugs (reduvid, kissing, assassin bugs in all Americas)

AFRICAN SLEEPING SICKNESS (flagellated protozoan)
--see an old post on this
--African sleeping sickness trans: tsetse flies
--T. brucei gambiense in West & Central Africa
--T. brucei rhodesiense in East Africa
--pathogencitiy: flybite-->1 week later, trypomastigotes in blood and lymph-->multiply until immune system lyses organisms-->some change surface antigens and survive-->new multiplication cycle-->cycle can repeat many times-->late in infx trypanosomes are in many organs esp myocardium and CNS-->DEATH at 9mo to 2 years after onset of dz
--Dx: trypanosomes in wet mount or Giemsa stained thin smear of peripheral blood or fluid from enlarged lymph node. Also look for anemia, monocytosis, elevated serum polyclonal IgM
--monocytosis = elevated monocytes in blood

CHAGAS DISEASE (flagellated protozoan)
--T. cruzi
--trans via triatomine bugs (reduvid, kissing, assassin bugs in all Americas)
--pathogenicity of Chagas: kissing bug shits in a bite on skin-->trypomastigoes enter wound-->invade macrophages-->transform into amastigoes and multiply-->lyse macrophage and are released as trypomastigotes-->infect other cells esp nervous sys, myocardium and muscle.
--Dx: typically asymptomatic at first, may go acute 1-2 weeks later with fever, hepatomegaly and lymphadnopathy, chronic infx-->cardiomyopathy, apical aneurisms, heart failure, stokes-adams attacks, thromboembolism, mgaesophagus, megacolon
--stokes-adams attack = transient syncope = LOC due to low blood/o2 in brain

LEISHMANIA spp. (hematoflagellated, unicellular, obligate intracellular zoonotic parasite)
--4 sp cause dz: tropica, mexicana, braziliensis, donovani
--200+ million people infected, ostly in tropics & subtropics
--1 million new infx annuals
--largely ignored by temperate nations
--in culture, stain reveals intracellular amastigoes as Leishman-Donovan bodies
--Leishman-Donovan bodies = Small, oval protozoans lacking flagella and undulating membranes, found within macrophages of the skin, liver, and spleen in leishmanial infections such as kala-azar and mucocutaneous leishmaniasis
--trans: phlebotomine sandflies
--reservoir: forest rodents, domestic dogs, humans
--incubation: weeks to months
--pathogenicity: sandfly bites reservoir animal, ingests promastigote-->multiplies and invades buccal cavity of sandfly-->sandfly infects next host providing blood meal-->parasites are opsonized via alternative complement pathway-->phagocytosed by macrophages-->parasite transforms to amastigote w/o flaggellae-->multiply and rupture macrophage-->gradual dissemination to every organ via macrophages
--different species-->different immune responses
--cutaneous only response-->parasite held in check
--overresponse of immune system can form antibody complexes-->glomerulonephritis
--S/Sx: papules that itch, ulcerate (painlessly) then heal, initial lymphadenopathy
--papule = oriental sore, chiclero ulcer (tropica in Asia, Africa or mexicana in Latin America), Click here for a photograph of a skin lesion
--This is a very disturbing picture of a young man who is anergic to leishmania.
--Dx: organisms in biopsy or aspiration specimens
--KALA AZAR aka visceral leishmaniasis: semi-epidemic as each non-immune generation appears, caused by L. donovani, 90% mortality without treatment.
--incubation: 3-12 months, fever for 2-8 weeks then passes and may return
--pathogenicity: organisms seed liver and spleen
S/Sx: lymphadeonpathy, diarrhea, malabsorption, gray skin discoloration in light-skinned patients, anemia, thrombocytopenia, agranulocytosis

PLASMODIUM spp. (sporozoan) MALARIA
--sp that infect humans include: P. faciparun (predominant), vivax, ovale, malariae
--there are many other species
--over 120 million clinical cases and over 1 million deaths per year worldwide
--endemic in 91 countries and present in 8 more in Africa, South & Southeast Asia, Central America and northern South America
--80% of cases occur in tropical Africa
--trans: female anopheles mosquito feeds on person with malaria then on uninfected person
--trans: hosts are mammals, birds & reptiles
--some genera cause malaria in lizards and are carried by Diptera (sand flies)
--pathogenesis: bite-->organism in blood-->infects hepatocytes and RBC's
--gametocytes formed in RBC's
--Dx: ID infecting species via blood, giemsa stain, IgM response at first then marked IgG.
--S/Sx: spenomegaly, hepatomegaly, anemia, malarial paroxysm (when mreozoites release from ruptured RBC's) incl: malaise, chills, fever, polyuria, rapid pulse, headache, nausea--> fever falls, profuse sweating 2-3 hours. One paroxysm every 48 hours or so with all but P. malaria, which cycles at 72 hours.
--Dx: forms gamonts in erythrocytes, merogony occurs in erythrocytes and in other tissues, hemozoin is present
--in certain regions the parasites are resistant chloroquine

--trans: ingestion of eggs, domestic cat feces have eggs, also in raw meat and water
--trans: placenta to fetus if mother has 1st exposure while preg
--part of TORCH panel, can result in abortion, stillbirth, malformation, chorioretinitis, mental retardation
--S/Sx: asymptomatic except in immunocompromised pts-->invades CNS-->encephalitis or flu-like sx

--sexual and asexual reprod in small intestine of single host
--trans: oocysts spread via fecal-oral
--highly resistant to chlorine (look out swimming pools and hot tubs!!)
--rarely asymptomatic
--outbreaks can occur in day cares & institutional settings (whole cities when water contaminated)
--causes up to 4% of acute diarrhea cases in children
--incubation: 1-2 weeks
--S/Sx: explosive watery diarrhea wtih pain for 5-11 days
--Dx: O&Px3
--immunocompromised-->can be lethal

--lives in RBC's
--trans: ticks
--loc: New England islands
--S/Sx: fatigue, arthritis, fever, hemolytic anemia



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