Demonstration of the Parasite• asexual forms of the parasite - peripheral-blood smears.• negative blood smear- repeat smears .• stains- Giemsa at pH 7.2 is preferred; Wrights, Fields, or Leishmans stain .• Both thin and thick smears .• The level of parasitemia is expressed as the number of parasitized erythrocytes per 1000 RBCs.• advantage of concentrating the parasites (by 40- to 100-fold and thus increasing diagnostic sensitivity.
• Both parasites and WBCs are counted, and the number of parasites per unit volume is calculated from the total leukocyte count. This figure is converted to the number of parasitized erythrocytes per microliter.• A minimum of 200 WBCs should be counted under oil immersion. .• 100–200 fields should be examined• In high-transmission areas, the presence of up to 10,000 parasites/L of blood may be tolerated without symptoms or signs in partially immune individuals. Thus the detection of malaria parasites is sensitive but only poorly specific in identifying malaria as the cause of illness.
Method Advantage DisadvantageThick Sensitive Requires (0.001% experienceSmear parasitemia); (artifacts may be species specific; misinterpreted as inexpensive low-level parasitemia); underestimates true countThin Rapid; species Insensitive specific; (<0.05%Smear inexpensive; in parasitemia); severe malaria, uneven provides distribution of P. prognostic vivax, as enlarged
Immunochromatographic TestPfHRP2 dipstick orcard test Robust and relatively inexpensive; rapid; Detects only Plasmodium sensitivity similar to falciparum; remains or slightly lower than positive for weeks that of thick films after infectionf; does (~0.001% not quantitate P. parasitemia) falciparum parasitemialasmodium LDH dipstick Rapid; sensitivity similar difficult preparationor card test to or slightly lower than may miss low-level that of thick films for P. parasitemia with P. vivax, falciparum (~0.001% P. ovale, and P. malariae parasitemia) and does not speciate these organisms; does not quantitate P. falciparumMicrotube concentration Sensitivity similar or Does not speciate ormethods with acridine superior to that of thick quantitate; requiresorange staining films (~0.001% fluorescence microscopy parasitemia); ideal for
Rapid Malaria Test• Blood• +buffer[hemolysing agent+ sp. Ab –labeled- coll. Gold• Ag *Ab complex – Migrate up the test strip to be captured by predeposited capture Ab. Sp. Againist the Ag & againist the labeled Ab(control)• pLDH-100-200 p/mcL• PfHRP2- >40 p/mcL
• Malaria cannot be diagnosed clinically with accuracy, but treatment should be started on clinical grounds if the laboratory confirmation is likely to be delayed. In areas of the world where malaria is endemic and transmission is high, low-level asymptomatic parasitemia is common in otherwise- healthy people. Thus malaria may not be the cause of a fever, although in this context the presence of >10,000 parasites/L (–0.2% parasitemia) does indicate that malaria is the cause. Antibody and polymerase chain reaction tests have no role in the diagnosis of malaria.
• Asexual parasites/200 WBCs x 40 = parasite count/L (assumes a WBC count of 8000/μL).• cGametocytemia may persist for days or weeks after clearance of asexual parasites. Gametocytemia without asexual parasitemia does not indicate active infection.• dParasitized RBCs (%) x hematocrit x 1256 = parasite count/L
; in general, patients with >105 parasites/L are at increased risk of dying, a poor prognosis - predominance of more mature P. falciparum parasites (i.e., >20% of parasites with visible pigment) in the peripheral blood film or by the presence of phagocytosed malarial pigment in >5% of neutrophils. In P. falciparum infections, gametocytemia peaks 1 week after the peak of asexual parasites. Because the mature gametocytes of P. falciparum are not affected by most antimalarial drugs, their persistence does not constitute evidence of drug resistance.
• Phagocytosed malarial pigment seen inside monocytes or polymorphonuclear leukocytes -clue to recent infection . After the clearance of the parasites, this intraphagocytic malarial pigment is often evident for several days in the peripheral blood or for longer in bone marrow aspirates or smears of fluid expressed after intradermal puncture. Staining of parasites with the fluorescent dye acridine orange allows more rapid diagnosis of malaria (but not speciation of the infection) in patients with low-level parasitemia.
• Normochromic, normocytic anemia• . The leukocyte count is generally normal, or rised• slight monocytosis, lymphopenia, and eosinopenia, with reactive lymphocytosis and eosinophilia in the weeks after the acute infection.• The erythrocyte sedimentation rate, plasma viscosity, and levels of C-reactive protein and other acute-phase proteins are high.• The platelet count is usually reduced to ~105/L• . Severe infections may be accompanied by prolonged prothrombin and partial thromboplastin times and by more severe thrombocytopenia. Levels of antithrombin III are reduced even in mild infection.
electrolytes, blood urea nitrogen (BUN), and creatinine are usually normal.severe malaria may - metabolic acidosis, hypoglycemia, low sodium, bicarbonate, calcium, phosphate, and albumin together with elevations in lactate, BUN, creatinine, urate, muscle and liver enzymes, and conjugated and unconjugated bilirubin.Hypergammaglobulinemia is usual in immune and semi- immune subjects. Urinalysis generally gives normal results. In adults and children with cerebral malaria, the mean opening pressure at lumbar puncture is ~160 mm of cerebrospinal fluid (CSF); usually the CSF is normal or has a slightly elevated total protein level [<1.0 g/L ] and cell count (<20/L)