Malaria Flashcards

Question

Thick and thin films

Answer 1

Should be prepared in all cases where possible Thin films: conventional ‘wedge’ blood films Thick films: thicker and should be about 1 cm in diameter All films should be prepared, stained and examined without delay due to morphological changes that occur over time Common stains used:Romanowsky, Leishman’s, May Grunwald/Giemsa Thick films are not fixed Proper drying is essential prior to examination

Answer 2

Advantages ‘Gold standard’ in malaria diagnosis Cheap Can be used for species identification and quantification Disadvantages Parasites can be missed, especially at low levels of infestation Requires some degree of experience Can be time consuming Requires a microscope (not much use in non-lab settings)

Answer 3

Knowledge of geographical distribution may give a clue: P. Vivax: Widest distribution extending through the tropics, subtropics and temperate zones P. Falciparum: Generally confined to tropics P. Malariae: Sporadic distribution P. Ovale: Mainly Central West Africa & some South Pacific Islands Both the sexual and asexual forms have certain characteristics which enable species identification Earliest forms of trophozoites in the blood cannot be differentiated but identification of the species becomes possible as they get older

Answer 4

Maurer’s clefts appear as irregular red/mauve dots inside red cells infected with P. falciparum. Schüffner’s dots are multiple, small, brick-red dots inside red cells infected with P. vivax or P. ovale.

Answer 5

Cycles of development in the blood last 36-48 hours - liver stage lasts for 8-10 days - Liver schizont contains 40,000 merozoites - Mature erythrocytic schizont contains 16-30 merozoites- rarely seen unless patient is gravely ill - Red blood cells of all ages are invaded - More than 40% of erythrocytes may be invaded -Most common and severe form of malaria - Typical incubation period for P. falciparum is 7–14 days, while P. vivax and P. ovale 12–17 days and P. malariae 18–40 days.

Answer 6

Often only ring forms No increase in red cell size Marginal forms (accole) Fine cytoplasm in young rings Maurer’s clefts in late ring forms Dark brown or black pigment Often higher parasitaemia Ring forms with 2 or more chromatin dots (not specific) Often multiple parasites per cell (not specific) Giemsa-stained thin films of P. falciparum infection (high power).: Characteristic thin, delicate rings (note the double chromatin dot—headphone appearance—in the infected red cell at the top and the accolé form in the infected red cell at the bottom); note the multiply infected red cell; P. falciparum trophozoites are rarely seen in peripheral blood—older, ring forms are referred to as the trophozoites, which tend to have more dense cytoplasm than in younger rings; mature schizont containing merozoites; crescent-shaped gametocyte.

Answer 7

Cycles of development in the blood last 48 hours All stages are often seen in peripheral blood Fewer merozoites are seen in liver and erythrocytic stages (e.g. 12-24 merozoites in the erythrocytic stage) Parasitaemia is much lower than with P. falciparum Dormant hypnozoites may be formed Reticulocytes are preferentially invaded

Answer 8

Cells may reach twice normal size Fine cytoplasm in young rings Amoeboid forms Schuffner’s dots Golden brown pigment Schizonts with average of merozoites (up to 24) Gametocytes difficult to differentiate Giemsa-stained thin films of P. vivax infection. High-power field showing large rings with heavy chromatin dots but faintly stained cytoplasm; (b) medium-power field showing one ring form and three large, amoeboid trophozoites; (c) high-power field with mature schizont containing merozoites virtually filling the red cell; (d) gametocyte filling the entire red cell, which is enlarged. e) Large trophozoites...

Answer 9

Also has a 48 hour erythrocytic stage 8-12 merozoites are seen in erythrocytic schizonts More restricted in distribution Hypnozoites occur in this species also Reticulocytes are preferentially invaded

Answer 10

Thicker cytoplasm of ring forms Trophozoites compact and rounded with fine, brown grains of pigment Cells increase in size but less than P. Vivax Schuffner’s dots Schizonts with 6-12 merozoites Oval red cells with fimbriated edge Gametocytes difficult to differentiate Giemsa-stained thin films of P. ovale infection (high power). a) Ring form with heavy chromatin dot and thick, deep-staining cytoplasm; (b) ring forms and a developing trophozoite; (c) Schizont containing merozoites with large nuclei; (d) gametocyte.

Answer 11

Has an erythrocytic cycle of 72 hours Has a low prevalence Liver and erythrocytic schizonts produce fewer merozoites than other species ( 6-12 merozoites in erythrocytic schizonts) so parasitaemias are generally low P. malariae infects older red blood cells preferentially

Answer 12

Cytoplasm noticeably thicker in ring forms ‘Band’ appearance Dark brown/black pigment No red cell enlargement Rarely see granules Parasites often scanty and difficult to find Schizonts with 8-10 merozoites arranged in ‘daisyhead’ formation Mature gametocytes fill the red cell Giemsa-stained thin films of P. malariae infection (high power). Ring form with heavy chromatin dot and thick, deep-staining cytoplasm; (b) band form trophozoite; (c) mature schizont with fewer merozoites than P. falciparum or P. vivax, central clump of pigment; (d) gametocyte.

Answer 13

Can be found in Southeast Asia Morphology similar to P. malariae Higher parasitaemia Can be fatal

Answer 14

(a) Ring forms; (b) ring form and a developing, band form trophozoite; (c) mature schizont (note the pigment has concentrated into a single mass); (d) spherical gametocyte. Giemsa-stained thin films of P. knowlesi infection (high power). Ring forms; (b) ring form and a developing, band form trophozoite; ( c) mature schizont (note the pigment has concentrated into a single mass); ( d) spherical gametocyte.

Answer 15

Laboratory results entered into the hospital computer system so that medical staff can view them All positive malaria screens are phoned to the requesting doctor and haematology medic on-call Positive malaria screeb: A patient report form is then filled in and sent to the School of Tropical Medicine. A copy of this also goes to Public Health England. (Procedures vary between hospitals)

Malaria Flashcards

(40 cards)