Field evaluation of a rapid diagnostic test (Parascreen™) for malaria diagnosis in the Peruvian Amazon

Malaria Journal RFeiseealrdch evaluation of a rapid diagnostic test (Parascreen) for malaria diagnosis in the Peruvian Amazon Jorge Bendezu Angel Rosas Tanilu Grande Hugo Rodriguez Alejandro Llanos-Cuentas Jorge Escobedo Dionicia Gamboa Background: The rapid diagnostic tests for malaria (RDT) constitute a fast and opportune alternative for noncomplicated malaria diagnosis in areas where microscopy is not available. The objective of this study was to validate a RDT named Parascreen under field conditions in Iquitos, department of Loreto, Peru. Parascreen is a RDT that detects the histidine-rich protein 2 (HRP2) antigen from Plasmodium falciparum and lactate deshydrogenase from all Plasmodium species. Methods: Parascreen was compared with microscopy performed by experts (EM) and polymerase chain reaction (PCR) using the following indicators: sensitivity (Se), specificity (Sp), positive (PV+) and negative predictive values (PV-), positive (LR+) and negative likehood ratio (LR-). Conclusions: The study results indicate that Parascreen is not a valid and acceptable test for malaria diagnosis under the field conditions found in the Peruvian Amazon. The relative proportion of Plasmodium species, in addition to the genetic characteristics of the parasites in the area, must be considered before applying any RDT, especially after the finding of P. falciparum malaria parasites lacking pfhrp2 gene in this region. - Background Malaria affects people in more than 108 countries around the world, with nearly 243 million estimated cases and nearly 863 thousands of deaths reported in the last year [1]. Despite a reduction of the incidence by up to 40% during the last four years in Peru, malaria due to Plasmodium falciparum and Plasmodium vivax remains an important public health problem, especially in the Amazon region where more than 70% of the cases of the country are reported [2]. * Correspondence: 1 Instituto de Medicina Tropical "Alexander Von Humboldt", Universidad Peruana Cayetano Heredia, AP 4314, Lima 100, Peru Full list of author information is available at the end of the article In malaria patients, a prompt and accurate diagnosis is the key for effective disease management, in order to reduce the probability of complications and mortality. The two diagnostic approaches currently in use, clinical diagnosis and microscopy, do not allow a satisfactory diagnosis of malaria. Clinical diagnosis, the most widely used, is unreliable because the symptoms of malaria are non-specific [3,4]. Diagnosis by microscopy, the established method for laboratory confirmation of malaria, presents technical and personnel requirements that often cannot be achieved [4-8], particularly in many areas of the Amazon region, far away from the main cities, where the population is widely dispersed and few health centres exist. Because of the reasons mentioned above and with the appearance of severe vivax malaria cases in different countries around the world in the last years [9], it is imperative to have a rapid and appropriate diagnosis method for malaria in Peru. Rapid diagnostic tests for malaria (RDT) offer a good alternative with the advantage that it is an easy and rapid method, which requires minimum training [6,7,10-12]. The evaluation of different RDTs in many places in the last decade has demonstrated high sensitivity and specificity, compared with expert microscopy diagnosis as gold standard [3,6,8,10,11,13-15]. However, it was also observed that the same RDT used in different places showed different results, which is probably related to different conditions found in these places (temperature, humidity, characteristics of the malaria parasites, etc.). This is one of the reasons why initiatives like the WHO/ TDR/FIND malaria RDT product testing programme, evaluating different RDTs under standardized conditions; could guide the malaria programmes in different countries to select the best RDT for a specific region [16]. Furthermore, the recent finding of P. falciparum field isolates lacking expression of the pfhrp2 gene in the Peruvian Amazon region should also be taken into account to choose the proper RDT for this region [17]. For more sensitive malaria detection, several polymerase chain reaction (PCR) assays have also been developed, and are mainly used in epidemiological studies [18]. The major advantage of this approach is the capability to detect malaria parasites in patients with low levels of parasitaemia, (five or less parasites per L of blood), including sub-patent malaria infections, which can be detected with 100% of sensitivity and specificity. However, the difficulty in acquiring and maintaining the required technical skills is the main disadvantage of this technique [7,8,14]. Parascreen is a RDT that has been assessed in different studies in Asian and African countries [19-21], where the test performed well under field conditions. In the present study Parascreen was evaluated in different communities around Iquitos, department of Loreto, Peru, and compared its performance with expert microscopy and PCR. Patients with history of fever with or without chills, sweating and headache (clinical symptoms suspicious of malaria), and with no history of anti-malarial treatment during the last two weeks, were enrolled through a passive malaria case detection in six health facilities around Iquitos (Department of Loreto) in the Peruvian Amazon, between October and December 2006. The minimum required sample size for this study was determined to be 96 confirmed malaria cases and 96 non-malaria cases, assuming a sensitivity and specificity at 90% with a precision of 6%, at a 95% confidence interval. Blood samples for thick and thin blood films, for the Parascreen test and for PCR (collected on filter paper, 3 MM), were collected by finger-prick. Diagnosis procedures, including microscopy, Parascreen and PCR, were carried out by different staff blinded to each other result. This procedure was carried out in the six health centres, located in rural areas, using standard protocols according to the Peruvian national guidelines [22]. Thick smears prepared with a finger-prick sample were stained with 10% Giemsa and examined using a microscope with a 100 oil immersion objective. The parasite density was expressed as the number of parasites/l of blood, by using an average number of leucocytes per microlitre of blood of 6,000 (according to the Peruvian national guidelines) for the calculations (number of counted parasites, multiplied by 6,000, divided by the number of counted leucocytes, by counting a total of 200 and 500 leucocytes if the number of parasites per microscope field is > 10 and < 10, respectively) [22]. The results were recorded together with clinical and epidemiological data from each patient. For the quality control, 10% of the slides were examined by a second expert microscopist at the reference laboratory (Centro de Salud San Juan) in Iquitos. Parascreen(Zephyr Biomedical Sy (...truncated)