Module 3 Flashcards
Blood and tissue parasites
- protozoa: amoebas, nematodes and cestodes
- sporozoa
- free-living amoeba
- hemoflagellates
Blood and tissue parasites (general characteristics)
- arthropod vector (blood parasites)
- mammals serve as definitive or intermediate host (tissue parasites)
- transmitted via ingestion
Sporozoa
- Plasmodium species, Babesia species
- malaria life cycle includes schizogony (asexual cycle) and sporogony (sexual cycle) which take place in Anopheles mosquito
- babesia life cycle includes ticks (intermediate host) which are infected by taking blood of infected mammals or transovarial (females transmit infective forms to progeny)
Schizogony (Plasmodium)
- asexual cycle which takes place in human or animal host
- sporozoites are injected into skin during mosquito bite
- enter bloodstream and invade liver cells
- replicates into multiple cryptic merozoites which are released into bloodstream as merozoites that invade RBC’s
- ring forms (trophozoites) develop within RBC’s
- trophozoites develop into schizonts (multi-nucleated forms)
- upon rupture of RBC, merozoites are released to invade other RBC’s
- some merozoites develop into micro (male) and macro (female) gametocytes
- gametocytes initiate sexual phase in mosquito stomach
- micro fertilizes macro to a zygote, which becomes an oocyst
- sporozoites develop in the oocyst and can be injected into next mammal
Plasmodium life cycle stages
Gametocyte –> exflagellation –> sporocyst –> sporozoite –> proboscis –> cryptozoites –> merozoites –> rings –> trophozoites –> Schizont
Identification of Plasmodium species
observe differences in size and distribution of the ring forms, size and shape of the gametocytes, and appearance or the infected erythrocytes
ID of Plasmodium falciparum
- ring forms are small (< 1/4 of cell)
- RBC’s are not enlarged
- Schuffner’s dots do not appear
- multiple ring forms may be seen
- no schizonts seen
- presence of banana-shaped gametocytes
- high percentage of infected RBC’s
Plasmodium falciparum (pathology)
- congestion of parenchyma and hypertrophy of cells in spleen and liver
- desposition of brown-black malarial pigment in Kupffer cells
- Hemoglobin casts in renal tubule cells (seen by dark red-black urine)
- vascular congestion of brain and capillary plugging by infected RBC’s
- febrile paroxysms every other day
- malignant tertian
- splenomegaly and anemia
- cerebral malaria (seizures, coma, etc.)
- progress of symptoms may be rapid
ID of Plasmodium vivax
- infected RBC’s are enlarged and pale
- Schuffner’s dots are present
- Schizonts have > 13 segments
- rings forms are small
- trophozoite cytoplasm is flowing and ameboid
- malarial pigment is finely granular
- gametocytes have a single large nucleus with compact chromatin
Plasmodium vivax (pathology)
- splenomegaly
- phagocytes have finely divided brown-black malarial pigment (hemozoin) - may be seen in Kupffer cells during cryptozoic stage
- malarial pigment must be distinguished from Hb deposits seen in hemochromatosis (stain blue with Prussian blue)
- fever spikes 48 hours apart
- benign tertian
ID of Plasmodium malariae
- infected RBC’s are not enlarged and normochromogenic with no granules
- Schizonts have < 13 granules (8-9)
- cytoplasm in trophozoites is compact
- segments arrant in a rosette and clumps of brown malarial pigment is seen in the “hoff”
Plasmodium malariae (pathology)
- mild splenomegaly
- malarial pigment is coarse and granular
- older kids have tendency to develop nephrotic syndrome
- fever spikes occur every 3rd day
- less anemia than with other species
ID of Plasmodium ovale
- infected RBC’s are enlarged, pale and contain Schuffner’s dots
- oval shape of RBC’s**
- < 13 segments that are finely granular
- brown-staining malarial pigment present
Plasmodium ovale (pathology)
- splenomegaly is often seen
- phagocytosis of malarial pigment by macrophages
- malarial pigment in cytoplasm in cryptozoic stage
- fever spikes every other day (tertian malaria)
- symptoms are usually mild
Preparation of specimen for malarial examination
- thin and thick Giemsa-stained blood smears
- level of parisitemia can be determined
- ID based on background morphological changes in the infected RBC, and in appearance of trophozoites, schizonts and gametocytes
Specific assays for malarial confirmation
- indirect fluorescent antibody (IFA)
- enzymes immunoassays
- species-specific PCR
ID of Babesia
- ring forms are tiny
- four segments are formed during schizogony
- segments align across from each other in shape of a Maltese cross
Babesia (pathology)
- fatal pathology is related to hypoxia and shock
- acute renal tubular necrosis
- jaundice
- hemorrhagic manifestations (DIC)
- symptoms often mimic the flu
- symptoms usually subside in one week
ID of Toxoplasma gondii
- tachyzoites measure 2-4 x 6-8 microns and are bow-shaped
- have red-blue nucleus and pale blue-gray cytoplasm
- cysts measure 5-25 microns in diameter and are engorged with tiny bradyzoites
- no kinetoplast (differentiates it from amistigotes)
- intermediate host: birds, mice, humans
- final host: cat
Toxoplasma gondii life cycle
oocysts in cat feces –> tachyzoites –> invasive tachyzoites –> tissue cyst –> bradyzoite –> cat reinfection
Toxoplasma gondii (pathology)
- proliferating tachyzoites cause cell death, necrosis and intense PMN response to all involved organs (CNS, lungs, heart)
- meningoencephalitis, interstitial pneumonitis and focal myocarditis
- hydrocephalus is common
- cysts containing bradyzoites may be seen in brain and other organs following and immune response
- severe febrile illness with pneumonia, liver dysfunction and myocarditis in infants and kids
Diagnosis (Toxoplasma)
- diagnosis made by demonstrating parasitic forms in blood, body fluids and/or tissue biopsies
- molecular assays and serology
ID of Pneumocystis carinii
- cysts measuring up to 7 microns demonstrated in silver-stained preparations
- up to 8 nuclei may be seen with Giemsa or methylene blue stains
- opportunistic pathogen
Pneumocystis carinii (pathology)
- causes pneumonia in ICP’s
- aveolar spaces fill with foamy, vacuolated, amorphous exudate
- interstitial plasma cell pneumonia
- difficulty breathing, dyspnea, nonproductive cough, fever
- progressive respiratory compromise often leads to death
Hemoflagellates
Trypanosoma
Leishmania
Hemoflagellates (general characteristics)
- vectors include flies
- reproduce via binary fission (no sexual forms)
- 4 stage life cycle
Hemoflagellates life cycle
- motile, circulating trypoastigotes
- aflagellar amastigotes characteristic
- promastigote
- epimastigote
Trypanosomes
- most commonly infect humans
- African trypanosomiasis = sleeping sickness is caused by Trypanosoma brucei with vector tse tse fly
- Chaga’s disease (South American) is caused by Trypanosoma cruzi with vector reduviid bug
- long and fishlike, rounded on one end, pointed on the other
- has posterior kinetoplast (dark-staining dot) and flagellum
- has a centrally located nucleus
Trypanosomes (diagnosis)
- African: only seen in trypanosomal form in blood and lymph nodes early in infection and in CNS in chronic infection
- South American: circulating trypanosomal form and intracellular form seen
Trypanosoma brucei gambiense
- diagnostic forms are spindle-shaped flagellates with posterior kinetoplast and undulating membrane and anterior flagellum
- circulating forms are few in number
- only trypomastigote stage occurs in humans
Trypanosoma brucei rhodesiense
- diagnostic forms are spindle-shaped flagellates that are indistinguishable from T. gambiense
- difference is large number of circulating forms
Trypanosoma brucei (pathology)
- intense subcutaneous inflammation
- lymphadenopathy and splenomegaly with infiltrate of lymphs, plasma cells and macrophages
- presence of Mott cells
- invade CNS causing leptomeningitis extending into the perivascular Virchow Robbins spaces
- intermittent long cycles of fever in stage 1
- slowly-progressive neurologic manifestations in stage 2
Trypanosoma cruzi
- diagnostic forms are spindle-shaped and are shorter than T. brucei
- have distinctive “C” form
- intracellular amastigotes occur in tissues
Trypanosoma cruzi (pathology)
- erythematous subcutaneous swelling (chagoma) develops at site of bug bite
- trypomastigotes invade host cells and assume an amastigote
- formation of cysts packed with amastigotes
- varying degrees of muscle fiber degeneration with surrounding acute and chronic myocarditis
- swelling of tissue around one eye at site of entry
- fever, malaise, anorexia and edema
- cardiac arythmias and cardiac failure in chronic infections
ID of Leishmania
- dissemiated disease (kala azar) or remain in skin/mucous membrane (tropical sore)
- intermediate host: sandflies (Phelotomus and Lutzomyia)
- mammalian hosts: rodents, canines
- humans are accidental hosts
- organisms are small and oval
- have rod-shaped kinetoplasts perpendicular to nucleus and an anterior parabasal body giving rise to an inactive flagellum
- invade visceral organs
Leishmania donovani (pathology)
- hepatomegaly, splenomegaly and lymphadenopathy
- phagocytic cells in these organs are full of leishmania
- immune complexes, mesangial proliferation and amyloid deposit in kidneys and can lead to renal failure
- spiking fever, chills and malarial symptoms in acute cases
- abdominal discomfort in chronic cases
- normo, normo anemia and leukopenia
- hypergammagglobulinemia, circulating immune complexes and rheumatoid factors lead to secondary complications
- gray pigmentation of skin
Lieshmania (cutaneous) pathology
- identical to L. donovani
- lesions are confined to the skin
- diagnosis is made by finding amastigotes in stained smears from base of ulcers