BackgroundThe genetic diversity of Plasmodium falciparum has been extensively studied in various parts of the world. However, limited data are available from Pakistan. This study aimed to establish molecular characterization of P. falciparum field isolates in Pakistan measured with two highly polymorphic genetic markers, i.e. the merozoite surface protein 1 (msp-1)and 2 (msp-2).MethodsBetween October 2005 and October 2007, 244 blood samples from patients with symptomatic blood-slide confirmed P. falciparum mono-infections attending the Aga Khan University Hospital, Karachi, or its collection units located in Sindh and Baluchistan provinces, Pakistan were collected. The genetic diversity of P. falciparum was analysed by length polymorphism following gel electrophoresis of DNA products from nested polymerase chain reactions (PCR) targeting block 2 of msp-1 and block 3 of msp-2, including their respective allelic families KI, MAD 20, RO33, and FC27, 3D7/IC.ResultsA total of 238/244 (98%) patients had a positive PCR outcome in at least one genetic marker; the remaining six were excluded from analysis. A majority of patients had monoclonal infections. Only 56/231 (24%) and 51/236 (22%) carried multiple P. falciparum genotypes in msp-1 and msp-2, respectively. The estimated total number of genotypes was 25 msp-1 (12 KI; 8 MAD20; 5 RO33) and 33 msp-2 (14 FC27; 19 3D7/IC).ConclusionsThis is the first report on molecular characterization of P. falciparum field isolates in Pakistan with regards to multiplicity of infection. The genetic diversity and allelic distribution found in this study is similar to previous reports from India and Southeast Asian countries with low malaria endemicity.

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The practical advantages of sampling and storing blood on filter paper for analyses of human and pathogen genes highlight the need for reliable, sensitive, and cost-effective DNA extraction methods. We describe a new Tris-EDTA (TE) buffer-based method for extraction of DNA from blood dried on filter paper. The method was evaluated against the commonly used methanol and Chelex methods, regarding polymerase chain reaction detection of Plasmodium falciparum parasites from samples stored for 1-2 years. The sensitivity of detection was dependent on the parasite density and type of filter paper. For 3MM Whatman filter paper, the sensitivity was 100%, 73%, and 93% for the TE, methanol, and Chelex methods, respectively. For the longer stored 903 Schleicher & Schuell filter paper, the sensitivity was 93%, 73%, and 0%, respectively. This rapid, simple, and inexpensive extraction method generated superior results from archived specimens compared with the two standard methods and may represent a useful tool in molecular epidemiologic studies.