Abstract. Cultivated Plasmodium falciparum gametocytes reach maturity in vitro in approximately 14-16 days, during which they pass through five morphologically distinct developmental stages. Purification of the earlier developmental stages has not been previously reported. We have modified the standard discontinuous Percoll gradient method for the separation of stage IV and V gametocytes to obtain enriched preparations of those and the earlier P. falciparum gametocyte stages. In contrast to the stages II, III, and IV, the mature stage V gametocytes from our gradient readily transformed into gametes. Such preparations may be useful in research studies on the mechanisms that underlie gametocytogenesis.Several previously reported techniques for the purification of mature Plasmodium falciparum gametocytes exploit the differences in sedimentation rates and buoyant densities of uninfected erythrocytes and erythrocytes infected with the various stages of the parasite. 1,2 The major limitation of these techniques is their inability to maintain physiologic osmolality throughout the purification procedure and avoid cell damage. 3 Percoll, a colloidal solution of polyvinylpyrrolidone-coated silica particles, can be used to overcome this problem of osmotically induced cell damage because of its low osmolality, 10 mOsm at 1.13 g/ml. 4 A Percoll step gradient centrifugation method has been successfully used to obtain highly purified preparations of viable mature P. falciparum and P. yoelii gametocytes. 5 The addition of fresh erythrocytes to P. falciparum cultures leads to loss of synchrony. 6,7 Synchrony can be restored by the addition of DNA inhibitors during gametocytogenesis. 8 However, inhibitors such as mitomycin C and chloroquine are toxic to stages I and II gametocytes. Mature gametocytes that have been synchronized by the addition of mitomycin C cannot be used immediately for research studies and membrane feeds because gametogenesis is inhibited for 24-48 hr after removal of the drug. 8 To avoid this transient drug toxicity, Ponnudurai and others synchronized gametocytes in an automated culture system by using gelatin flotation and N-acetyl glucosamine treatment. 9 Despite the fact that methods for synchronization and purification of the mature sexual stages of P. falciparum cultures have been separately described, these two techniques have not been combined to obtain purified fractions of the early gametocyte stages. This is a crucial requirement for research because the events that regulate gametocytogenesis are still in question. Our ability to study the early sexual stages, soon after morphologic differentiation, may provide insight into this intriguing aspect of cell cycle regulation. We have modified the Percoll step gradient technique to obtain enriched fractions of almost all the stages of P. falciparum gametocytes from in vitro culture. MATERIALS AND METHODS Culture of gametocytes.Plasmodium falciparum strain NF54 was cultured in vitro according to the Ifediba and Vandeberg 10 modification of the Trager and ...

Eight genotypes of hepatitis B virus (A-H) and subgenotypes have been recognized worldwide. However, there is limited information on prevalent genotypes in many countries in Africa. This study was undertaken to determine the hepatitis B virus (HBV) genotypes in Kenya. Seropositive HBV blood samples from a blood donor setting were used in the study. HBV genotypes were determined in 52 nucleic acid-positive samples using specific primer in a nested PCR and sequencing employed in the HBV genotyping. This study shows presence of HBV variants with genotypes A (88%), E (8%) and D (4%). In conclusion, we found that HBV genotype A is the most predominant genotype in Kenya with both subgenotype A1 and A2 present. Genotype D and E are also present in our population. This demonstrates that there could be a high genetic diversity of HBV in Kenya.

Pedram (2020) Forecasting vegetation condition for drought early warning systems in pastoral communities in Kenya. Remote Sensing of Environment, 248. a111886 1-10.

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