Comparative Studies of Different Diagnostic Techniques of Malaria used in Sudan

Abstract

In the Sudan where 90% of malaria infections are due to Plasmodium falciparum, the accuracy of diagnosis at the out patients level is becoming increasingly important. The need for better and rapid malaria diagnosis is evident due to the problems of drug resistance and use of alternative, costly antimalarial drugs. This study was carried out in Khartoum, with the objectives for assessing the staining methodologies of malaria diagnosis, comparing their accuracy and also minimizing the use of antimalanial drugs to (true) malaria cases. Samples were taken from 1000 patients (407 males and 593 females) from different laboratories in Khartoum area during the period of October 1995 to October 1996. Five thick blood films were obtained from each patient and brought to (the National Health Laboratories for standard staining and tested for malaria by using 3% Giemsa stained thick smears (3% GTS), 10% Giemsa stained thick smears (10%GTS), complete Field's Stain A&B, and Field's Stain (A) alone. The sensitivity, specificity and degree of concordance of these tests were compared to the findings of 3% Giemsa stained thick smears, the gold standard applied in our laboratory. The sensitivity of 10% GTS was 99.1 % (120/121), and the specificity was 97.5% (868/879), and the degree of concordance between these two methods was 98.8% (988/1000). The sensitivity of Field's Stain A&B was 96.3% (98/107), the specificity was 96.3% (860/893), with a degree of concordance between these two methods (Field's Stain A&B and Field's Stain A alone) of 94.8% (948/1000). The sensitivity of fields Stain (A) alone was 71% (71/100), the specificity was 94.4% (840/900), and the degree of concordance was 91.1 % (911/1000). At the same time the results of the routine blood examination of the field laboratories were compared with the reference results. From the standard results (3%GTS) it was found that 131 (13%) were positive for malaria parasites, and out of them only 5(3.8%) were P.vivax and the rest 126 (96.2%) were P. falciparum. which is the predominant species in Sudan. The results obtained from the routine examination in the field laboratories were 297(29.7%) positive for malaria parasites where results were recorded as positives or negatives, without taking into consideration the parasite species or density. One hundred and twenty five samples were collected from patients attending the out patient clinic in the field laboratories and tested for malaria by microscopy of 3% Giemsa stained thick smears (3% GTS), the Immunochromatography test (lCT), and the polymerase chain reaction (PCR) technique. Twenty samples (16%) were malaria positive by microscopy with parasitaemias ranging from 90 to 40000 parasites peril blood (mean 2528.18+0.45-p/ul blood). Twenty-one samples (16.7%) were malaria positive by the ICT test. Infection due to P. vivax was present only in one case (4.75%), and all the rest (95.25%) were due to P. jalciparum. Out of a total of the 125 samples tested for malaria parasites, the PCR technique did not miss a single sample that was identified positive by microscopy; all the 20 samples gave PCR products. Infections due to p. falciparum were present in 14 cases (70%) and to P. vivax alone in 2 cases (10%). Four patients (20%) were found to be simultaneously infected with p. falciparum and P. vivax. The four patients diagnosed by PCR as infected with P. falciparum and P. vivax as mixed species, were found by microscopy as infected with p. falciparum only. To limit antimalarial treatment to true malaria attacks, differential diagnosis was studied in 1000 symptomatic patients with malaria like symptoms that were refered to the eight laboratories included in the study. In this study the effect of age as a factor for acquisition of immunity against malaria infection was confirmed and the parasite positive rate and density of infection decreased significantly with age (p<0.0). History of fever and raised body temperature were found to be good predictors for malaria infection. Eighty-seven percent of the infected individuals had a history of fever that significantly exceed 78% of the uninfected individuals (p<0.01). The results showed that fever of more than one week duration was very unlikely to be caused by malaria (chi-square test for trend, p=0.013). The study clearly demonstrated that fever, headache and history of previous treatment with anti-malarial are the most common clinical symptoms and signs associated with falciparum malaria infection. Given the presenting symptoms of malaria, their duration and severity, in Khartoum State, it is suggest that diagnosis of malaria should be based on laboratory diagnosis and that appropriate steps should be taken to provide health facilities with well trained and competent microscopist even in the most remote areas of the province. Further studies in this field, specially regarding the species specification of malaria parasites are needed, as the frequency of infections with other species is not well documented. Close monitoring of the existing laboratories is essential to control their performance and quality control of the laboratories.