Browsing by Author "Kimani, Francis T."

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    PublicationOpen Access
    Mapping of DBLα Sequence Tags of Field Isolates from Two Malaria Endemic Sites in Kenya
    (Journal of Natural Sciences Research, 2015) Makokha, Francis W.; Bull, Peter C.; Kimani, Francis T.; Hungu, Charity; Shaviya, Nathan; Magoma, Gabriel; Ahmed, Sabah O.
    Plasmodium falciparum Erythrocyte Membrane Protein 1 (PfEMP1) found on the surface of infected erythrocytes (IEs) mediate antigenic variation during P. falciparum infection enabling the parasite evade host immune responses and prolong infection. These molecules mediate binding of IEs to host endothelial cells and uninfected erythrocytes. Cytoadhesion of IE to host cells leads to sequestration in tissues and PfEMP1 is thought to play an important role in parasite virulence. Here we analysed 1725 sequence tags sampled from the DBLa region of PfEMP1 encoding “var” genes from 27 patients in two different geographical regions in Kenya, Mbita in Western Kenya and Twiga on the Kenyan coast. The objective of this study was to construct a network to assess the extent of shared position specific polymorphic blocks (PSPBs) in sequences isolated from genomic DNA of field isolates from the two malaria endemic sites in Kenya. Sequences from Mbita study site and those from Tiwi largely clustered into separate giant networks with only a limited number of sequences from the two sites linking to each other. This observation suggests that the parasite populations from the two endemic sites could be genetically varied and that PfEMP1 sequencing could be a useful tool of understanding the genetics of parasite populations. Thus the network approach of studying relationships between DBLα sequences is a useful tool of uncovering the genetic structure of parasite populations circulating in different malaria endemic regions.
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    PublicationOpen Access
    PfEMP1 DBLα Sequence Tags in Genomic DNA of P. falciparum Field Isolates from Two Malaria Endemic Sites in Kenya
    (Journal of Natural Sciences Research, 2015) Makokha, Francis W.; Omar, Sabah A.; Kimani, Francis T.; Magoma, Gabriel; Udu, Rahma
    Background Malaria caused by Plasmodium falciparum remains a major cause of childhood morbidity and mortality in sub- Saharan Africa. PfEMP1 protein, coded for by a family of about sixty variant var genes, is a parasite protein found on infected erythrocyte membrane. PfEMP1 protein mediates cytoadherence of infected erythrocytes on endothelial cells which may lead to severe symptoms of malaria. Although PCR amplification of the whole gene is difficult due to high variability, primers targeting the DBLα domain have been designed and used to study pfemp1 genes. This objective of this study was to establish the distribution of DBLα sequence tags in isolates of Plasmodium falciparum from two malaria endemic sites in Kenya. Methods DNA extracted from field isolates collected from Mbita (Western Kenya) and Tiwi (Coastal region) was used to isolate and amplify DBLα domain sequence tags of pfemp1 by PCR. PCR products were sequenced by 454 next generation sequencing. After assembly, the translated protein sequences (GenBank KP085750-KP087726) were then aligned in Mega 5.2 and classified into cys/PoLV groups based on the number of cysteine residues and the motifs at PoLV1 and PoLV2 within the sequence tag. Six sequence groups were found in sequences from both endemic sites. Group 4 sequences were the most prevalent (57.35% and 57.07% in isolates from Mbita and Tiwi respectively) in the isolates from both sites. Sequence tags from Tiwi had a higher proportion of cys2 (group 1 and 2) than sequences from Mbita although individual group 2 sequence tags were slightly higher in Mbita tags. Similarly the proportion of groups 5 and 6 sequence tags was higher in sequence tags from Tiwi than those from Mbita. Conclusion In conclusion, the frequency of the different cyc/PoLV groups of DBLα sequence tags at both endemic sites follow almost similar pattern with group four sequence tags being the majority among the sequence tags isolated from patient isolates from both study sites. However, in the absence of expression data, the impact of this genomic distribution pattern on malaria pathology remains unknown. Key Words: Malaria, PfEMP1, cys/PoLV, DBLα, var, Sequence tags
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    PublicationOpen Access
    Prevalence of Plasmodium falciparum chloroquine resistant gene markers, pfcrt-76 and pfmdr1-86, eight years after cessation of chloroquine use in Mwea, Kenya
    (Sabah Ahmed Omar et al., 2007-08-08) Sabah Ahmed, Omar; Makokha, Francis W.; Mohammed, Fat’hia Abdo; Kimani, Francis T.
    The prevalence of T76 and Y86 Plasmodium falciparum molecular markers for chloroquine (CQ) resistance in the Pfcrt and Pfmdr1 genes were investigated by PCR-RFLP and dot blot analysis in samples (50 for Pfcrt and 51 for Pfmdr1) collected in May 2005, eight years after chloroquine (CQ) cessation. Results: Our findings show that 94% of field isolates from this site still harbor T76 mutation in Pfcrt while 6% have the wild type allele K76 [T test, P=0.04058 (1997 versus 2005)]. Dot blot analysis revealed that most of the isolates had MET polymorphism at position 74, 75 and 76 wild type allele of the Pfcrt gene. When Pfmdr1-86 was analyzed by dot blot, 6% of the isolates had wild type allele N86, 73% had mutant allele Y86, and 21% had both N and Y [T test, P=0.04058 (1997 versus 2005)]). Conclusions: Dot blot hybridization was found to be more sensitive and specific than PCR-RFLP. The study showed a moderate reversal to sensitivity by the P. falciparum population in the study site compared to the situation before CQ cessation