Comparative evaluation of microscopy and polymerase chain reaction (PCR) for the diagnosis in suspected malaria patients of Nepal.

Microscopy has been the most common technique for the diagnosis of malaria in Nepal. This study was undertaken at CDM, TU, Kathmandu, and Department of Clinical Tropical Medicine, Mahidol University, Bangkok to compare the efficiency of microscopy and PCR for malaria diagnosis in Nepalese context. During July-August 2007, blood samples were collected in glass slides and on filter papers from suspected malaria cases of Kanchanpur, Jhapa and Morang Districts. Sample transportation and storage was done using standard protocol. Microscopy was done at the heath posts in the district in Nepal while Nested PCR using previously standardized primers was carried out at Mahidol University. Among 824 malaria suspected cases, 19.2% (157) were laboratory confirmed as malaria cases (P. vivax 10.9%, P. falciparium 7.7% and 0.4% were of mixed infection) by microscopy. The parasite count range was detected as 320-25020 parasites/microl. Among total 132 samples (114 microscopic positive, 18 negative) were processed for nested PCR. Among microscopic positive samples with increase of the parasitaemia/microl of the blood, the rate of detection by PCR (75.4%) was increased though the PCR failed to detect 2 cases having the parasitaemia 5000-15000/microl of blood however 4 microscopic negative cases were detected as P. vivax infection. Among the microscopy positive samples for P. falciparum, 3 were found P. vivax and 2 were found as mixed infection of Pv and Pf and 6 P. vivax were found positive for P. falciparum by PCR. Two microscopy positive samples for mixed infection were found be positive for one Pv and one Pf by PCR. PCR could be good tool in confirming the clinically strongly suspected but microscopically negative malaria cases and advanced molecular epidemiological studies, although its use in routine diagnosis may not be feasible.