Module 3

Question 1

Blood and tissue parasites

Answer 1

• protozoa: amoebas, nematodes and cestodes
• sporozoa
• free-living amoeba
• hemoflagellates

Question 2

Blood and tissue parasites (general characteristics)

Answer 2

• arthropod vector (blood parasites)
• mammals serve as definitive or intermediate host (tissue parasites)
• transmitted via ingestion

Question 3

Sporozoa

Answer 3

• 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)

Question 4

Schizogony (Plasmodium)

Answer 4

• 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

Question 5

Plasmodium life cycle stages

Answer 5

Gametocyte –> exflagellation –> sporocyst –> sporozoite –> proboscis –> cryptozoites –> merozoites –> rings –> trophozoites –> Schizont

Question 6

Identification of Plasmodium species

Answer 6

observe differences in size and distribution of the ring forms, size and shape of the gametocytes, and appearance or the infected erythrocytes

Question 7

ID of Plasmodium falciparum

Answer 7

• 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

Question 8

Plasmodium falciparum (pathology)

Answer 8

• 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

Question 9

ID of Plasmodium vivax

Answer 9

• 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

Question 10

Plasmodium vivax (pathology)

Answer 10

• 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

Question 11

ID of Plasmodium malariae

Answer 11

• 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”

Question 12

Plasmodium malariae (pathology)

Answer 12

• 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

Question 13

ID of Plasmodium ovale

Answer 13

• 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

Question 14

Plasmodium ovale (pathology)

Answer 14

• 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

Question 15

Preparation of specimen for malarial examination

Answer 15

• 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

Question 16

Specific assays for malarial confirmation

Answer 16

• indirect fluorescent antibody (IFA)
• enzymes immunoassays
• species-specific PCR

Question 17

ID of Babesia

Answer 17

• ring forms are tiny
• four segments are formed during schizogony
• segments align across from each other in shape of a Maltese cross

Question 18

Babesia (pathology)

Answer 18

• 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

Question 19

ID of Toxoplasma gondii

Answer 19

• 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

Question 20

Toxoplasma gondii life cycle

Answer 20

oocysts in cat feces –> tachyzoites –> invasive tachyzoites –> tissue cyst –> bradyzoite –> cat reinfection

Question 21

Toxoplasma gondii (pathology)

Answer 21

• 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

Question 22

Diagnosis (Toxoplasma)

Answer 22

• diagnosis made by demonstrating parasitic forms in blood, body fluids and/or tissue biopsies
• molecular assays and serology

Question 23

ID of Pneumocystis carinii

Answer 23

• 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

Question 24

Pneumocystis carinii (pathology)

Answer 24

• 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

Question 25

Hemoflagellates

Answer 25

Trypanosoma

Leishmania

Question 26

Hemoflagellates (general characteristics)

Answer 26

• vectors include flies
• reproduce via binary fission (no sexual forms)
• 4 stage life cycle

Question 27

Hemoflagellates life cycle

Answer 27

• motile, circulating trypoastigotes
• aflagellar amastigotes characteristic
• promastigote
• epimastigote

Question 28

Trypanosomes

Answer 28

• 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

Question 29

Trypanosomes (diagnosis)

Answer 29

• 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

Question 30

Trypanosoma brucei gambiense

Answer 30

• 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

Question 31

Trypanosoma brucei rhodesiense

Answer 31

• diagnostic forms are spindle-shaped flagellates that are indistinguishable from T. gambiense
• difference is large number of circulating forms

Question 32

Trypanosoma brucei (pathology)

Answer 32

• 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

Question 33

Trypanosoma cruzi

Answer 33

• diagnostic forms are spindle-shaped and are shorter than T. brucei
• have distinctive “C” form
• intracellular amastigotes occur in tissues

Question 34

Trypanosoma cruzi (pathology)

Answer 34

• 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

Question 35

ID of Leishmania

Answer 35

• 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

Question 36

Leishmania donovani (pathology)

Answer 36

• 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

Question 37

Lieshmania (cutaneous) pathology

Answer 37

• identical to L. donovani
• lesions are confined to the skin
• diagnosis is made by finding amastigotes in stained smears from base of ulcers